Report of the 2004 ICES Working Group on Nephrops Stocks

Abstract

The Working Group on Nephrops Stocks [WGNEPH] met in Lisbon, Portugal, from 28 March–1 April 2004 to:
a) assess the status of Nephrops stocks in the Bay of Biscay (FUs 23-24) and around the Iberian Pensinsula
(FUs 25, 26-27, 28-29, 30 and 31), utilising new data where available, revising catch options only where
necessary;
b) evaluate the extent to which official landings statistics reflect the true levels of landings in Nephrops
fisheries, considering the implications for assessments and advice;
c) revise, where appropriate, Nephrops landings statistics for Subarea IV, Division VIa and Subarea VII in
the light of new information on reporting levels;
d) update the assessments and catch options of Nephrops for the Management Areas mentioned under c) as
appropriate;
e) continue the Working Group’s investigations on the application of medium-term catch projections to
Nephrops;
f) continue the Working Group’s investigations on the applicability of alternative assessment techniques,
focusing particularly on CSA and any outcomes of the 2003 meeting of the Study Group on Age-length
Structured Assessment Models;
g) investigate the implications for assessment and data collection of differences in selection patterns by
different fleets apparently targeting the same stock;
h) provide specific information on possible deficiencies in the 2004 assessments including, at least, any
major inadequacies in the data on catches, effort or discards; any major inadequacies in research vessel
surveys data, and any major difficulties in model formulation, including inadequacies in available
software. The consequences of these deficiencies for the assessment of the status of the stocks and for the
projection should be clarified;
i) advise ACFM on a future allocation, preferably from 2005 and onwards, of functional units to regionallybased
fisheries assessment groups. Prepare the databases for transfer to these regionally-based fisheries
assessment groups.

Full text

ICES Advisory Committee on Fishery Management
ICES CM 2004/ACFM:19
Report of the
Working Group on Nephrops Stocks
28–01 April 2004
Lisbon, Portugal
This report is not to be quoted without prior consultation with the General Secretary. The document is a report of an Expert
Group under the auspices of the International Council for the Exploration of the Sea and does not necessarily represent the
views of the Council.
WGNEPH Report 2004 1

International Council for the Exploration of the Sea
Conseil International pour l’Exploration de la Mer
Palægade 2–4 DK–1261 Copenhagen K Denmark
Telephone + 45 33 15 42 25 · Telefax +45 33 93 42 15
www.ices.dk · info@ices.dk
WGNEPH Report 2004
2

Contents
1 TERMS OF REFERENCE......................................................................................................................................... 1
2 PARTICIPANTS........................................................................................................................................................ 1
3 METHODS EMPLOYED IN THE ASSESSMENT OF NEPHROPS STOCKS ...................................................... 2
3.1 Analysis of trends in fishery data.................................................................................................................... 2
3.2 Analytical assessments.................................................................................................................................... 2
3.3 Fishery independent data ................................................................................................................................ 3
3.4 Judging the status of a stock ........................................................................................................................... 3
4 INPUT DATA AND BIOLOGICAL PARAMETERS USED IN NEPHROPS ASSESSMENTS............................ 4
4.1 Fishery data..................................................................................................................................................... 4
4.2 Length composition sampling......................................................................................................................... 4
4.3 Biological input parameters ............................................................................................................................ 4
5 ASSESSMENTS AND MANAGEMENT POSSIBILITIES FOR NEPHROPS ....................................................... 6
5.1 General introduction ....................................................................................................................................... 6
5.1.1 Functional Units, Management Areas and TAC Areas........................................................................ 6
5.1.2 Assessments......................................................................................................................................... 6
5.1.3 Management considerations, provision of catch options..................................................................... 6
5.1.4 Section layout ...................................................................................................................................... 7
5.2 Management Area N..................................................................................................................................... 18
5.2.1 Bay of Biscay (FUs 23-24)................................................................................................................ 18
5.2.2 Summary for Management Area N.................................................................................................... 24
5.3 Management Area O..................................................................................................................................... 67
5.3.1 North Galicia (FU 25)........................................................................................................................ 67
5.3.2 Cantabrian Sea (FU 31) ..................................................................................................................... 70
5.3.3 Summary for Management Area O.................................................................................................... 71
5.4 Management Area Q................................................................................................................................... 129
5.4.1 West Galicia (FU 26) and North Portugal (FU 27).......................................................................... 129
5.4.2 South-West and South Portugal (FUs 28-29) .................................................................................. 132
5.4.3 Gulf of Cádiz (FU 30)...................................................................................................................... 135
5.4.4 Summary for Management Area Q.................................................................................................. 137
6 REPORTING LEVELS FOR LANDINGS........................................................................................................... 267
6.1 Data on reporting levels .............................................................................................................................. 267
6.2 Implications of reporting levels for analytical stock assessments...............................................................267
6.3 Implications for advice................................................................................................................................ 268
6.3.1 Utility of underwater TV survey data .............................................................................................. 268
6.4 Conclusions................................................................................................................................................. 269
7 APPLICATION OF MEDIUM-TERM CATCH PROJECTIONS TO NEPHROPS............................................. 271
7.1 Introduction................................................................................................................................................. 271
7.2 ‘CP’ model implementation ........................................................................................................................ 271
7.3 Conclusions................................................................................................................................................. 271
8 APPLICABILITY OF ALTERNATIVE ASSESSMENT METHODS TO NEPHROPS STOCKS ..................... 274
8.1 Introduction................................................................................................................................................. 274
8.2 Length-based approaches............................................................................................................................ 274
8.2.1 A size-transition matrix approach to the assessment of Firth of Forth Nephrops ............................ 274
8.2.2 Developing a Bayesian, length based model for Metanephrops challengeri................................... 275
8.3 Catch Survey Analysis................................................................................................................................ 276
8.4 Conclusions................................................................................................................................................. 276
9 IMPLICATIONS OF DIFFERING SELECTION PATTERNS FOR DATA COLLECTION AND ASSESSMENT
................................................................................................................................................................................ 281
9.1 Introduction................................................................................................................................................. 281
9.2 Celtic Sea FUs 20-22 .................................................................................................................................. 281
9.3
9.4
9.5
9.6
WGNEPH Report 2004 3
Porcupine Bank FU 16................................................................................................................................ 282
Botney Gut-Silver Pit area (FU 5) .............................................................................................................. 282
North Minch (FU 11) and South Minch (FU 12)........................................................................................ 283
Kattegat (FU 4) and Skagerrak (FU 3)........................................................................................................ 284

9.7 ................................................................................................ 284 General conclusions and recommendations
10 ASSESSMENT DEFICIENCIES FOR NEPHROPS STOCKS
10.1
............................................................................. 291
Generic assessment problems for Nephrops stocks .................................................................................... 291
10.1.1 Age determination ........................................................................................................................... 291
10.1.2 Sampling levels for catch, landings and discards ............................................................................ 291
10.1.3 Quality of landings and effort statistics ........................................................................................... 292
10.1.4 Validity of information on biological parameters............................................................................ 292
10.1.5 Sedentary nature, the potential for spatial targeting of fishing effort, and spatial differences in fleet
selection patterns .......................................................................................................................... 293
10.1.6 Seasonal and diurnal differences in availability and their consequences for assessment models.... 294
10.1.7 Methodological/software limitations
Stock-specific assessment problems
............................................................................................... 294
........................................................................................................... 294 10.2
11 .............................................. 296 ALLOCATION OF NEPHROPS FUS TO AREA-BASED ASSESSMENT WGS
12 WORKING DOCUMENTS AND PRESENTATIONS
12.1
12.2
12.3
12.4
12.5
12.6
12.7
12.8
12.9
12.10
........................................................................................ 298
STECF Recovery Plans for Southern Hake and Norway Lobster in IXa and VIIIc ................................... 298
Major developments in data collection and related issues, and their impact on Nephrops-work................ 298
Nephrops and the ICES-FAO Working Group on Fishing Technology and Fish Behaviour ..................... 299
Use of underwater TV survey data in formulating management advice for Nephrops stocks .................... 300
New underwater TV survey data................................................................................................................. 300
Review of Nephrops stock assessment in the western Irish Sea ................................................................. 300
New data on Nephrops to the north of Ireland............................................................................................ 300
Spatial patterns of Nephrops exploitation
Sexual maturity in male Nephrops
Length-based assessment methods
................................................................................................... 300
.............................................................................................................. 301
.............................................................................................................. 301
13 ....................................................................................................................................... 302 RECOMMENDATIONS
14 REFERENCES....................................................................................................................................................... 304
APPENDIX 1 - Using Underwater Television and Harvest Ratios to Provide Nephrops TAC Advice – A Scottish
Example................................................................................................................................................ 306
APPENDIX 2 - New Survey Information on Scottish Nephrops Stocks........................................................................ 314
APPENDIX 3 - Preliminary Results of the Joint MI-DARDNI UWTV Survey on the Western Irish Sea Nephrops
Grounds ................................................................................................................................................. 318
APPENDIX 4 - A Review of Western Irish Sea Nephrops Assessment (FU 15)........................................................... 333
APPENDIX 5 - Observations on Nephrops Norvegicus catches from grounds to the North of Ireland (ICES SubArea
VIa). ..................................................................................................................................................... 343
APPENDIX 6 - Sexual Maturity of Male Nephrops Norvegicus (L.) in the Irish Sea.................................................... 363
APPENDIX 7 - Developing A Length-Based Population Model for Bay of Plenty Scampi (Metanephrops Challengeri)
............................................................................................................................................................ 374
APPENDIX 8 - More Thoughts On A Length-Based Approach To The Assessment Of Firth Of Forth Nephrops:
Incorporation Of Auxiliary Data ........................................................................................................... 407
WGNEPH Report 2004
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APPENDIX 9 - Meeting on Data Collection on Nephrops Lisbon, April 2 2004 .......................................................... 422

1 Terms of Reference
The Working Group on Nephrops Stocks [WGNEPH] met in Lisbon, Portugal, from 28 March–1 April 2004 to:
a) assess the status of Nephrops stocks in the Bay of Biscay (FUs 23-24) and around the Iberian Pensinsula
(FUs 25, 26-27, 28-29, 30 and 31), utilising new data where available, revising catch options only where
necessary;
b) evaluate the extent to which official landings statistics reflect the true levels of landings in Nephrops
fisheries, considering the implications for assessments and advice;
c) revise, where appropriate, Nephrops landings statistics for Subarea IV, Division VIa and Subarea VII in
the light of new information on reporting levels;
d) update the assessments and catch options of Nephrops for the Management Areas mentioned under c) as
appropriate;
e) continue the Working Group’s investigations on the application of medium-term catch projections to
Nephrops;
f) continue the Working Group’s investigations on the applicability of alternative assessment techniques,
focusing particularly on CSA and any outcomes of the 2003 meeting of the Study Group on Age-length
Structured Assessment Models;
g) investigate the implications for assessment and data collection of differences in selection patterns by
different fleets apparently targeting the same stock;
h) provide specific information on possible deficiencies in the 2004 assessments including, at least, any
major inadequacies in the data on catches, effort or discards; any major inadequacies in research vessel
surveys data, and any major difficulties in model formulation, including inadequacies in available
software. The consequences of these deficiencies for the assessment of the status of the stocks and for the
projection should be clarified;
i) advise ACFM on a future allocation, preferably from 2005 and onwards, of functional units to regionally-
based fisheries assessment groups. Prepare the databases for transfer to these regionally-based fisheries
assessment groups.
2 Participants
The following scientists attended the meeting of the WG:
Bo Sølgaard Andersen Charlottenlund, Denmark
Mike Bell (Chair) Lowestoft, UK, England
Richard Briggs Belfast, UK, Northern Ireland
Martin Cryer Auckland, New Zealand
Helen Dobby Aberdeen, UK, Scotland
Jon Elson Lowestoft, UK, England
Celso Fariña La Coruña, Spain
Juan Gil Cádiz, Spain
Isabel González Herraiz Palma, Spain
Francisco Leotte Lisbon, Portugal
Colm Lordan Dublin, Ireland
Graham Norman Bergen, Norway
Frank Redant Oostende, Belgium
Cristina Silva Lisbon, Portugal
Catherine Talidec Lorient, France
Ian Tuck Aberdeen, UK, Scotland
Stein Tveite Flödevigen, Norway
Mats Ulmestrand Lysekil, Sweden
Adrian Weetman Aberdeen, UK, Scotland
WGNEPH Report 2004 1

In addition, written contributions were received from:
Nick Bailey Aberdeen, UK, Scotland
Alain Biseau Lorient, France
Jennifer Doyle Galway, Ireland
Emmet Jackson Dun Laoghaire, Ireland
Nuala McQuaid Belfast, UK, Northern Ireland
Conor Nolan Dun Laoghaire, Ireland
3 Methods employed in the assessment of Nephrops stocks
The assessment methods employed by the WG were mainly based on:
1. the analysis of long-term trends in fishery data (landings, effort, CPUE, LPUE, mean sizes of Nephrops in catches
and/or landings, etc.);
2. the results of the age-based VPA, applied to ‘age’ groups obtained by slicing the length compositions of the
removals;
3. short-term predictions and yield per recruit analyses based on the output of the VPA.
The following review summarises the main methods, dealing first with the most basic approaches.
3.1 Analysis of trends in fishery data
The examination of trends in fishery data remains an important element of Nephrops assessments, especially for stocks
with few biological or sampling data. For most stocks, available information now extends over many years. Thus,
attention should be paid to the broad, overall trends rather than to small fluctuations in the most recent years.
Long-term trend plots are provided for landings, effort, CPUE and/or LPUE, and mean size in catches and/or
landings. For many stocks, CPUEs and LPUEs are also given for size classes below and above a certain ‘cut-value’
(usually 35 mm carapace length, CL), corresponding to the size that is almost always retained by fishermen for landing,
regardless of how liberal discarding may be. This approach was introduced several years ago (ICES, 1995a), and has the
advantage that it produces CPUEs and LPUEs for the larger size classes which can be regarded as indices of relative
abundance, and CPUEs for the smaller size classes which can be regarded as indices of recruitment.
3.2 Analytical assessments
Length based assessments
The WG has moved away from using Length Cohort Analysis (LCA) as an assessment tool in cases where the
steady-state assumptions are not met or where there is already a satisfactory age based assessment. LCA gives no
information on recruitment over-fishing, and where this occurs, can give rise to severely misleading conclusions about
stock status with respect to growth over-fishing (see e.g. ICES, 1999a).
Age based assessments
In the absence of routine methods of direct age determination in Nephrops, age compositions of removals were
inferred from length compositions by means of ‘slicing’. This procedure, introduced at the 1991 WG, uses von
Bertalanffy growth parameters to determine length boundaries between age classes. All animals in length classes
between boundaries are assigned deterministically to the same age class. The method is implemented in the L2AGE
programme which automatically generates the VPA input files. The programme was modified in 1992 to accommodate
the two-stage growth pattern of female Nephrops (ICES, 1992a) and again in 2001 to separate ‘true’ as opposed to
‘nominal’ age classes (ICES, 2001a). The age classes are ‘true’ to the extent that the first slicing boundary, i.e. lower
length boundary for ‘age’ 0, is the length at age zero rather than the lowest length in the data. This ensures
comparability of ‘age’ classes across stocks.
Age based assessments were performed by means of the Lowestoft VPA suite (Darby & Flatman, 1994).
Commercial effort data and/or survey data were used to apply Extended Survivors Analysis (XSA) to all stocks for
which there was a sufficiently long series of age composition data. The assessment procedures followed the
standardisation guidelines drawn up by the 2001 WG (Section 3.3 of ICES, 2001a).
WGNEPH Report 2004
2

In striving to produce the highest possible quality of assessments, full use was made of the XSA tuning
diagnostics. The main elements in quality evaluation and interpretation were: (a) examination of retrospective biases in
recruitment and biomass estimates; (b) standard errors of catchability estimates; (c) size and pattern of log catchability
residuals; (d) the relative contributions of data and shrinkage to population estimates; and (e) retrospective VPA plots
of recruitment, SSB and Fbar.
Short-term term predictions and yield per recruit analyses
Short-term predictions of yield and biomass have been an important component of the advice offered by the WG
in 2002 and 2003 for southern stocks (Management Areas N, O and Q). The MFDP (Multi Fleet Deterministic
Projection) software was used again at this WG meeting to assist in the formulation of short-term management options
for these stocks. Where appropriate, the distinction was made between fishing mortality due to human consumption
(i.e. landings) and that due to discarding. Short-term projections are not generally performed as a matter of routine for
other stocks, given that advice is given principally on a Precautionary rather than an Analytical basis. Given uncertainty
about stock-recruitment relationships for Nephrops, medium-term projections are problematic. However, medium-term
projections were considered for stocks in Management Area N (see Section 5.2), and the topic is further considered in
Section 7.
The MFYPR (Multi Fleet Yield Per Recruit) software was used to perform yield per recruit analyses for all stocks
for which an age based assessment was performed, making the same distinctions between landings and discards where
appropriate.
3.3 Fishery independent data
Since they were introduced in the early 1990s, underwater TV surveys have become an increasingly useful tool in the
assessment of Nephrops stocks - firstly as a means to obtain fishery independent estimates of stock size and biomass,
and secondly as a means to validate the estimates of total stock biomass (TB) and recruitment given by the analytical
assessments.
For some stocks, where landing statistics are believed to be unreliable or where sampling levels were inadequate
for a standard analytical approach, they have even become the only means for assessing the state of exploitation of the
stock and for making predictions on its fisheries potential. TV surveys were not, however, undertaken for any of the
stocks assessed in Sections 5.2-5.4 of this report, but relevant information was presented for a number of other stocks
(see Section 12).
3.4 Judging the status of a stock
As before, it was decided that most attention should be paid to the male component of the stock since (a) in most cases, this
was perceived as the most vulnerable component, and (b) most assessments suggested that F on the females is generally low,
and that the female stock is not over-exploited.
For stocks where the VPA appeared to perform well, this was used to give some idea of the trends in the
stock, together with the trends in fishery-related data (usually CPUEs and/or LPUEs), and – whenever available – the
results of fishery independent surveys. For stocks where sufficient data were not available to run a VPA, or where the
results of the VPA were considered as ‘suspicious’, the judgement of the status of the stock was mostly based on the
trends in fishery-dependent indices (particularly CPUEs, LPUEs and mean size in catches and/or landings).
Because of the differences between FUs in biological features and quality of the data available, no attempt was
made to use the same pieces of information as a basis for the judgement for all stocks. Each one was dealt with on the
merits of the assessments applied.
WGNEPH Report 2004 3

4 Input data and biological parameters used in Nephrops assessments
4.1 Fishery data
Updated information on landings and effort was provided for all southern FUs considered by the WG (FUs 23-24, 25,
26-27, 28-29, 30 and 31). Where available, landings and effort data, together with CPUEs and LPUEs for the last 10
years, are given on both a quarterly and an annual basis.
With the advent of TAC management, and increased fishing effort by finfish vessels switching to Nephrops, there
are indications that the quality of landing statistics has fallen. Unreported landings are believed to have occurred in
recent years, some of which are thought to be substantial. With some exceptions, estimates of these unreported landings
were not available, and so could not be incorporated into the assessments. The main concern is that the proportion of
unreported landings might be increasing over time (there is some evidence of this for at least one FU). This could result
in the WG under-estimating the current levels of exploitation. Increases in unreported landings could also bias the
length composition samples if particular market categories are more affected than others, and could influence VPA
estimated trends in fishing mortality, total stock biomass and recruitment. The implications of misreporting for
assessments and advice were discussed during the meeting (see Section 6).
4.2 Length composition sampling
For each FU, a summary table is provided with details on the sampling levels for catches, landings and discards. These
are given by quarter for the last two years, and annually for the last 10 years.
For most stocks, sampling levels are assumed to be sufficiently high – with respect to both sampling frequency
and sample size – to produce reliable annual length frequency distributions of the removals (i.e. landings plus dead
discards). For many stocks, however, there is little statistical evidence that the reliability requirements are actually being
achieved. In 1996, the Nephrops Study Group comprehensively reviewed the sampling procedures used by different
countries (ICES, 1996a). The SG, however, did not prescribe minimum sampling requirements, acknowledging instead
that some of the observed differences in sampling intensity relate to particular features of the stocks and fisheries.
EC Regulation 1639/2001, relating to National Data Gathering Programmes, contains extensive provisions for the
collection of fishery data. As noted in ICES (2002a), it is hoped that this will lead to additional sampling schemes for
Nephrops catches, landings and discards being set up, particularly for those stocks where sampling has been very low or
even at zero levels in the past years. The Regulation specifies appropriate sampling levels for Nephrops in each FU.
4.3 Biological input parameters
Biological input parameter (Table 4.1 and relevant tables under Section 5) were reviewed by the Nephrops Study Group
in 2000 (ICES, 2000b) and again in 2001 WG (ICES, 2001a). No new data were reported at this year’s WG.
The continuous need for the WG to rely upon biological parameters estimated several years ago is a consequence
of the relatively low level of biological research on Nephrops in more recent years. Here too, the upcoming National
Data Gathering Programmes could provide a basis for collecting such data, since EC Regulation 1639/2001 also
specifies the obligation for regular updates of biological parameters, such as growth and sexual maturity.
WGNEPH Report 2004
4

Management
Area
Functional
Units
Functional Unit(s)
Group interval
LCA
Group interval
Slicing
Discard survival
KLinf M
a and b from
L-W relationship
W = a * L exp b
KLinf
Transition
length
M
a and b from
L-W relationship
W = a * L exp b
N 23-24 Bay of Biscay na 1 0.30 0.140 76 0.3 0.00039 3.180 0.140 76 25 0.3 0.00081 2.970
0.110 56 0.2 0.00081 2.970
O 25 North Galicia na 1 na 0.160 70 0.2 0.00043 3.160 0.160 70 28 0.2 0.00043 3.160
0.080 60 0.2 0.00043 3.160
31 Cantabrian Sea
Q 26-27 West Galicia and na 1 na 0.150 80 0.2 0.00043 3.160 0.150 80 26 0.2 0.00043 3.160
North Portugal 0.100 65 0.2 0.00043 3.160
28-29 SW and S Portugal na 1 na 0.200 70 0.3 0.00028 3.222 0.200 70 30 0.3 0.00056 3.029
0.065 65 0.2 0.00056 3.029
30 Gulf of Cadiz 2 na na 0.160 60 0.2 0.00043 3.160 0.160 60 28 0.2 0.00043 3.160
0.090 58 0.2 0.00043 3.160
na = not applicable
Table 4.1. - Input parameters used in analytical assessments of male and female Nephrops . For some Functional Units, growth and natural
mortality parameters are given for immature females (above) and mature females (below). New or modified inputs sho
No analytical assessments done at W G
Males FemalesBoth sexes
WGNEPH Report 2004 5

WGNEPH Report 2004
6
In line with ACFM’s directions, the WG offers recommendations for all assessed stocks, which are based on collective
discussions, made in the light of the quality of the input data, the parameter values and the assessment results, together
with any other considerations relevant to the FU in question.
For southern stocks (Bay of Biscay, FUs 23-24, and Iberian Peninsula, FUs 25, 26-27, 28-29, 30 and 31), the
updated assessments confirm that there is serious cause for concern. Last year’s WG report presented evidence of
declining trends in biomass and recruitment across these stocks, and this picture has been strongly reinforced by the
results of this year’s assessments. Short-term stock projections indicate that strong management action would be
required to halt or reverse these trends of decline (see Sections 5.2, 5.3 and 5.4).
5.1.3 Management considerations, provision of catch options
5 Assessments and management possibilities for Nephrops
5.1 General introduction
5.1.1 Functional Units, Management Areas and TAC Areas
Functional Units and Management Areas
The Functional Units (FUs) are defined by the groupings of ICES statistical rectangles given in Table 5.1.2 and
illustrated in Figures 5.1.1, 5.1.2 and 5.1.3. The Functional Unit is the level at which the WG collects fishery data
(quantities landed and discarded, fishing effort, CPUEs and LPUEs, etc.) and length distributions, and at which it
performs analytical assessments.
Table 5.1.3 summarises the types of assessment that were carried out for the different FUs, and gives some idea of the
general ‘quality’ of these assessments and the state of exploitation of the stocks in terms of Fbar, Fmax and F01-03. To
allow easy comparison, a similar table with the results of the 2003 assessments is also included (Table 5.1.4).
Most assessments were conducted on males and females separately, and these frequently gave rather different
results. The reasons for adopting this approach have been discussed before (ICES, 1991a) and are based on the greater
availability and associated vulnerability of males in many of the stocks, and on the desirability of accommodating
different growth and natural mortality rates for the two sexes. However, in 2003 for the first time some assessments for
males and females combined were attempted. A Working Document was presented to the 2003 WG demonstrating that
for stocks in Management Area N combined assessments provided essentially the same information as the sum of
separate sex assessments (ICES, 2003a). The WG concluded that combined assessments are applicable in circumstances
where it can be established that there is no loss of management information. Accordingly, an assessment for males and
females combined was adopted for stocks in Management Area N.
5.1.2 Assessments
Functional Units are aggregated into Management Areas (MA) (Table 5.1.1), the level at which the WG
recommends management should take place. In the case of some northern stocks, TACs are set for large areas which
encompass several MAs (e.g. North Sea), leading to actual and potential problems of management (see ICES, 2001a).
TAC areas
Both the WG and ACFM have repeatedly pointed out that TACs based on the present large areas defined by ICES
boundaries are not satisfactory. They do not allow for a type of management which takes account of the different levels
of exploitation in different FUs. The WG wishes to reiterate its view that Nephrops are more appropriately managed at a
smaller scale and recommends that the Management Areas described be adopted, or that specific management strategies
be developed, aiming at the control of fishing effort on a much smaller geographical scale than is the case in the
existing quota-based system.
Outstanding examples of actual and potential problems inherent to the current system are the North Sea (where
difficulties will continue to arise if the recommended catch option for MA G – which includes the Fladen Ground –
continues to be aggregated with those for other areas into a single TAC), and Sub-Area VII (where the TAC covers a
large area which offers no opportunity to effectively manage each FU or even each MA according to their individual
states of exploitation).

Concern also remains on the possible impact of effort transfers from the increasingly restricted finfish fisheries to
the more lucrative Nephrops fisheries. For most Nephrops FUs this would in the long-term be detrimental.
Summaries of the past advice given by the WG and by ACFM are given in Tables 5.1.5-7 for each TAC area. The
proposed and agreed TACs in these tables are taken from the relevant reports of the WG and of ACFM respectively; the
landing figures from this year’s WG report (see MA summary tables at the ends of Sections 5.2 to 5.4). With respect to
these tables it is worth noting that:
(a) before 1995, management advice was given on an annual basis for all stocks (in 1991 for the year 1992, etc.);
(b) from 1995 onwards, advice has been given every two years for most stocks (in 1995 for the years 1996 and 1997,
etc.);
(c) in 2001, advice for southern stocks (Management Areas N, O and Q) was given for 2002 only, with new advice for
2003 being given after a special WG meeting in 2002;
(d) past advice was based on the landings and effort data as they were available to the WG at the time, since when,
many data series have been improved and revised, thus adding to the apparent discrepancy between proposed
TACs and actual (read ‘revised’) landings.
5.1.4 Section layout
The stock assessment section (Sections 5.2 to 5.4) have been organised to list MAs, and then FUs contained within each
MA, according to ICES Subareas and Divisions. Tables and figures appear at the end of each MA section.
For each FU, there are sections covering the following:
(a) Description of the fisheries.
(b) Trends in landings, effort, CPUE and/or LPUE, mean sizes in catches and/or landings.
(c) Data and biological inputs for analytical assessments.
(d) General comments on quality of data and inputs.
(e) Type of assessments carried out and why.
(f) Age based assessments (VPA) (if any).
(g) Y/R analysis based on outputs of VPA (if any).
(h) Short-term predictions based on outputs of VPA (if any).
(i) Fishery independent data (if any).
(j) Comments on quality of assessments.
(k) Management considerations.
Summaries of the management considerations for the MA as a whole are given at the end of each MA section,
together with tables summarising the recent history (1993-2002) of the landings by FU and by country.
References to ‘standard’ tables and graphs are listed at the beginning of each section or sub-section, but in the text
they are restricted to an absolute minimum (in an attempt to improve the flow of the text).
With respect to the fishery related statistics, it is worth reminding that, for several years now, the WG has
consistently made the distinction between catches and landings, and between catches per unit effort or CPUEs (which
include the discards) and landings per unit effort or LPUEs.
WGNEPH Report 2004 7

A Va 1 Ice land
B Vb (n on EC) 2 Fa e r oe I sla nd s
C Vla 11 North Minch
12 So ut h Min ch
13 Clyd e
D Vb (EC) + Vlb None
E llla 3 Skagerrak
4 Kattegat
F lVa, rect. 44-48 E6-E7 + 44E8 9 Moray Firth
10 Noup
G l Va, W e st of 2° E excl . M A F 7 Fla de n
H l Vb,c, Ea st of 1 ° E ex cl. rec t. 43F5-F7 5 Botney Gu t
33 Off Horn Reef
I lVb,c, West of 1 ° E 6 Farn Deeps
8 Firth of Forth
J Vlla, North of 53° N 14 Irish Sea East
15 Irish Sea West
K Vlld,e None
L Vllb,c,j,k 16 Porcupine Bank
17 Aran Grounds
18 Ireland NW coa st
19 Irelan d SW a nd SE coas t
M Vllf,g,h, excl. rect. 31E1 32E1-E2 + 20+21+22 Celtic Sea
Vlla, South of 53° N
N Vllla,b 23+24 Bay of Biscay
O V l llc 25 Nort h Galicia
31 Cantabrian Sea
P Vllld,e None
Q lXa 26 West Galicia
27 Nort h Portu g al
28+29 South-West and South Portugal
30 Gulf of Cadiz
R lXb + X None
S lVa, East of 2° E + rect. 43F5-F7 32 Norwegian Deep
Table 5.1.1. - Description of Management Areas, together with their Working Group labels
and the Functional Units contained within them.
ICES description
WG
label
Functional Units (FUs) or groupings thereof
when treated as one in assessments
WGNEPH Report 2004
8

WGNEPH Repo
1 Iceland South coast Va 55-56 C6-D0; 55-56 D2-D4
2 Faeroe Islands Vb 55E3
3 Skagerrak IIIa 47G0-G1; 46F9-G1; 45F8-G1;
44F7-G0; 43F8-F9
4 Katteg at IIIa 44G1-G2 ; 42 -43G0 -G2; 41G1-G2
5 Botney Gut - Silver Pit IVb,c 36-37 F1-F4; 35F2-F3
6 Farn Deeps IVb 38-40 E8-E9; 37E9
7 Fladen Ground IVa 44-49 E9-F1; 45-46E8
8 Firth of Forth IVb 40-41E7; 41E6
9 Moray Firth IVa 44-45 E6-E7; 44E8
10 Noup IVa 47E6
11 North Minch VIa 44-46 E3-E4
12 South Minch VIa 41-43 E2-E4
13 Clyde VIa 39-40 E4-E5
14 Irish Sea East VIIa 35-38E6; 38E5
15 Irish Sea West VIIa 36E3; 35-37 E4-E5; 38E4
16 Porcupine Bank VIIc,k 31-36 D5-D6; 32-35 D7-D8
17 Aran Grounds VIIb 34-35 D9-E0
18 Ireland NW coast VIIb 37D9-E1; 36D9
19 Ireland SW and SE coast VIIg,j 31-33 D9-E0; 31E1; 32E1-E2; 33E2-E3
20 NW Labadie, Baltimore and Galley VIIg,j )
21 Jo nes and Cockburn VIIg,h,j ) 28-30 E1; 28-31 E2; 30-32 E3; 31 E4
22 Smalls VIIg )
23 Bay of Biscay North VIIIa 22-24 E6-E7; 23-24E5
24 Bay of Biscay South VIIIb 20-21 E7-E8; 19E8
25 North Galicia VIIIc 15E0-E1; 16E1
26 West Galicia IXa 13-14 E0-E1
27 North Portugal (N of Cape Espichel) IXa 6-12E0; 9-12E1
28 S out h-W est Port ugal (A lentejo) IXa 3-5 E 0-E 1
29 So ut h Port ugal (Algarv e) IXa 2E0-E2
30 Gulf of Cadiz IXa 2-3 E2-E3
31 Cantabrian Sea VIIIc 16E4-E7
32 Norwegian Deep lVa 44-52 F2-F6; 43F5-F7
33 Off Horn Reef lVb 39-41E4; 39-41E5
Table 5.1.2. - Nephrops Functional Units and descriptions by statistical rectangles.
FU no. Na me Stat ist ical r ec tangle s
ICES
area
rt 2004 9

WGNEPH Report 2004
10
Mal Fem Mal Fem Y/R Mal Fem Mal Fem Mal Fem Mal Fem Mal Fem
N 23-24 – – – – – –
O 25 x x x – – – ++ + – – – 0.50 0.13 0.77 5.25
31
Q 26-27 x x x – – – ++ + – – – 0.70 0.31 0.33 0.87
28-29 x x x – – – ++ + – – – 0.53 0.24 0.72 5.67
30 ––––++–––0.610.13––0.543.51
LCA = Length based assessment ; VPA = age based assessment ; TV survey = underwater television survey ; Mal = males ; Fem = females
X = new assessment performed ; P = assessment not repeated, results of previous assessment used ; ++ = acceptable quality ; + = questionable quality ; nr = not reported
Figures in brackets are from assessments of questionable quality ; Mean F from VPA is for 2001-2003
Table 5.1.3. - Summary of Nephrops assessments carried out by the WG in 2004.
MA FU
Analytical assessments performed Quality of assessments Major ouputs of assessments
LCA VPA TV
survey
F multiplier Fmax
None Sexes combined ++ 0.48 0.62
VPA TV
survey
Mean F from LCA Fbar from VPA
X
None
None
None
None
LCA
No analytical assessments performed
Mal Fem Mal Fem Y/R Mal Fem Mal Fem Mal Fem Mal Fem Mal Fem
N23-24 – – – – –
O 25 X X X – – – ++ + – – – 0.420.140.76>1.50
31
Q 26-27 X X X – – – ++ + – – – 0.58 0.26 0.34 0.94
28-29 X X X – – – ++ + – – – 0.530.240.61>1.50
30
LCA = Length based assessment ; VPA = age based assessment ; TV survey = underwater television survey ; Mal = males ; Fem = females
X = new assessment performed ; P = assessment not repeated, results of previous assessment used ; ++ = acceptable quality ; + = questionable quality ; nr = not reported
Figures in brackets are from assessments of questionable quality ; Mean F from VPA is for 2000-2002
Mean F from LCA
Table 5.1.4. - Summary of Nephrops assessments carried out by the WG in 2003.
MA FU
Analytical assessments performed Quality of assessments Major ouputs of assessments
LCA VPA TV
survey
Fbar from VPA F multiplier Fmax
None Sexes combined ++ 0.55 0.58
LCA VPA TV
survey
No analytical assessments performed
None
No analytical assessments performed
None
None

WGNEPH Report 2004 11
Kind of advice given
WG
proposal
(t) (*)
ACFM
proposal
(t)
Agreed
TAC
(t)
Reported
landings
(t) (**)
% taken
vs. WG
proposal
% taken
vs. agreed
TAC
ion pattern likely to improve - set TAC at max. over 1985-89 6675 ~ 6800 6800 5728 86 84
quo advice - TAC adjusted to include landings taken outside FUs 6885 6800 6800 5158 75 76
ort at 1989-91 level - set TAC accordingly 5575 6800 6800 4119 74 61
quo effort and TAC (5575) 6800 6800 4467 80 66
quo effort and TAC (5575) 6800 6800 4133 74 61
he year 1996 (5575) 6800 6800 3640 65 54
of decreasing trend in male and female recruitment
rease to 70 or 80 mm recommended
effort - adjust TAC accordingly (no figure proposed)
he year 1998 4200 5500 3238 na 59
iation of stock less pessimistic than in 1997 assessment
of decreasing trend in male stock biomass
rease to 70 or 80 mm recommended - no TAC proposed
ably decrease fishing pressure to allow stock to recover
r-exploitation
ment options given 2200 3000
ment options given 3300
ment options given
tion chosen.
urrent TAC to stop decline in stock biomass 1650 or
SQ (***) 4200 4000 3753
ata series must be regarded as provisional.
by the WG and by ACFM, agreed TACs, reported landings and percentages of TACs taken, by Management Area
(as defined by ICES) - Data for TAC area VIIIa,b.
gures in brackets are not explicitly mentioned in the W G reports, but follow from the recommended catch options.
4200 4440
3266
3717
227/na 94
na 594200 5500
1750 or
1450 (***) 2000 3200
3105 na 70
212-256 116
MA or
TAC area FUs Year
1992 Exploitat
1993 Status
1994 Keep eff
1995 Status
1996 Status
1997 As for t
Evidence
Mesh inc
Constrain
1999 As for t
Apprec
Evidence
Mesh inc
Consider
from ove
2003 Manage
2004 Manage
2005 Manage
(***) Depending on type of management ac
2001 Revise c
(**) Landings for the most recent year in the d
TAC area VIIIa,b = MA N
FUs 23 & 24
(single advice for comb. FUs)
Table 5.1.5. - Summary of TACs proposed
(as defined by the WG) and by TAC area
(*) All figures rounded to the nearest 5 t ; Fi
2000
1998
2002

MA or
TAC area FUs Year Kind of advice given
WG
proposal
(t) (*)
ACFM
proposal
(t)
Agreed
TAC
(t)
Reported
landings
(t) (**)
% taken
vs. WG
proposal
% taken
vs. agreed
TAC
FU 25: Keep effort constant - set TAC at level of 1984-90 landings
FU 31: Keep effort constant - set TAC at level of 1988-90 landings
FU 25: Status quo advice - adjust TAC to match revised landings
FU 31: Status quo advice - adjust TAC to match revised landings
1994 All FUs: Keep effort at current levels - status quo TAC 570 510 1000 393 69 39
1995 All FUs: Keep effort at current levels - status quo TAC 570 510 1000 367 64 37
All FUs: Keep effort at current levels - status quo TAC
Expl. pattern of Nephrops largely defined by TACs for other species
1997 As for the year 1996 510 1000 317 na 32
All FUs: Keep effort at current levels - status quo TAC
1998 175
area VIIIc = MA O
FUs 25 & 31
1993 570
1992 510 510 800
1000 3381996 510
Table 5.1.6. - Summary of TACs proposed by the WG and by ACFM, agreed TACs, reported landings and percentages of TACs taken, by Management Area
(as defined by the WG) and by TAC area (as defined by ICES) - Data for TAC area VIIIc.
510 1000 365 64
522 102 65
37
na 18
na 34
510 1000
Expl. pattern of Nephrops largely defined by TACs for other species
1999 As for the year 1998 510 1000 172 na 17
All FUs: Keep effort at current levels - status quo TAC
Expl. pattern of Nephrops largely defined by TACs for other species
2001 As for the year 2000 (510) 510 720 174 34 24
FU 25: Severe decline in TSB & recruitment - Drastically reduce F
FU 31: Decline in landings - Reduce F
2003 Management options given 0 180 0
2004 Maximum possible reduction in fishing mortality 0 0
2005 Maximum possible reduction in fishing mortality 0
TAC
(**) Landings for the most recent year in the data series must be regarded as provisional.
2000 (510) 510 800 14
(*) All figures rounded to the nearest 5 t ; Figures in brackets are not explicitly mentioned in the WG reports, but follow from the recommended catch options.
115 23
169 ∞472002 00360
WGNEPH Report 2004
12

MA or
TAC area FUs Year Kind of advice given
WG
proposal
(t) (*)
ACFM
proposal
(t)
Agreed
TAC
(t)
Reported
landings
(t) (**)
% taken
vs. WG
proposal
% taken
vs. agreed
TAC
FU 26: Provisional TAC corresponding to level of 1989-91 landings
FU 27: Insuff. data - provisional TAC corresponding to 1990 landings
FUs 28 & 29: Recent landings unreliable - set TAC at 1984-85 level
FU 30: Insuff. data - provisional TAC at max. historic landings
FU 26: Status quo advice - status quo TAC
FU 27: Adjust TAC to match improved landing figures
FUs 28 & 29: Adjust TAC to match improved landing figures
FU 30: Status quo TAC
FU 26: Keep effort constant - adjust TAC to level of 1991-92 landings
FU 27: Status quo advice - adjust TAC to level of 1987-92 landings
FU 28 & 29: Assessment improved - no reason to revise TAC
FU 30: Status quo TAC
1995 All FUs: Status quo advice - status quo TAC (1390) 1300 2500 916 66 37
FU 26: Status quo advice - status quo TAC
FU 27: Insuff. data - no advice given
FUs 28 & 29: Reduce F - avoid effort increases - no TAC proposed
FU 30: Insuff. data - no advice given
MA as a whole: No reason to revise TAC proposed by ACFM
1997 As for the year 1996 1300 1300 2500 668 51 27
FUs 26 & 27: No particular advice given
Expl. pattern of Nephrops largely defined by TACs for other species
FUs 28 & 29: Strong evidence of decreases in TSB and recruitment
Drastically reduce overall fishing pressure - no TAC proposed
20
1998 500
TAC area IXa = MA Q
FUs 26 to 30
32
1996 1300
na
2500 512 39
1993
2500 792
2500
1300
1390
595
1335
103 54
1300 57
1315 1300 2500 1349
Table 5.1.7. - Summary of TACs proposed by the WG and by ACFM, agreed TACs, reported landings and percentages of TACs taken, by Management Area
(as defined by the WG) and by TAC area (as defined by ICES) - Data for TAC area IXa.
1300 2500 1059 79 42
1994
24
1992
FU 30: Insuff. data - no advice given
1999 As for the year 1998 500 2000 581 na 29
(*) All figures rounded to the nearest 5 t ; Figures in brackets are not explicitly mentioned in the WG reports, but follow from the recommended catch options.
(**) Landings for the most recent year in the data series must be regarded as (highly) provisional.
WGNEPH Report 2004 13

MA or
TAC area FUs Year Kind of advice given
WG
proposal
(t) (*)
ACFM
proposal
(t)
Agreed
TAC
(t)
Reported
landings
(t) (**)
% taken
vs. WG
proposal
% taken
vs. agreed
TAC
FUs 26 & 27: No particular advice given
Expl. pattern of Nephrops largely defined by TACs for other species
FUs 28 & 29: Strong evidence of decreases in TSB and recruitment
Drastically reduce overall fishing pressure, either by effort reduction,
mesh size increase or establishment of closed area
FU 30: Insuff. data - no advice given
MA as a whole: Maintain TAC at 500 t
2001 As for the year 2000 500 500 1200 582 116 49
FUs 26 & 27: Significantly reduce F
FUs 28 & 29: TSB and recruitment at very low levels - Significantly
reduce F
FU 30: Insuff. data - no advice given
MA as a whole: Reduce F to lowest possible level
2003 Management options given 50 600 0
2004 Reduce F to the lowest possible level 50 50 600
2005 Reduce F to the lowest possible level 50
(**) Landings for the most recent year in the data series must be regarded as (highly) provisional.
448 90 302000 500 500 1500
693
Table 5.1.7. - (continued).
FUs 26 to 30
∞87
(*) All figures rounded to the nearest 5 t ; Figures in brackets are not explicitly mentioned in the W G reports, but follow from the recommended catch options.
2002 0 170 800
TAC area IXa =
MA Q
WGNEPH Report 2004
14

WGNEPH Report 2004 15
Figure 5.1.1. - Nephrops Management Areas and Functional Units in ICES Division IIIa and Subarea IV (letters and
figures refer to the Management Areas and Functional Units given in Tables 5.1.1 and 5.1.2).
-4.00 -2.00 0.00 2.00 4.00 6.00 8.00 10.00 12.00 14.00
51.00
52.00
53.00
54.00
55.00
56.00
57.00
58.00
59.00
60.00
61.00
62.00
G
F
I
H
10 732
3
33
S
5
8
9
6
4
E

WGNEPH Report 2004
16
Figure 5.1.2 – Nephrops Management Areas and Functional Units in ICES Sub-areas V, VI and VII (letters and figures
refer to the Management Areas and Functional Units are given in Tables 5.1.1 and 5.1.2).
24° 23° 22° 21° 20° 19° 18° 17° 16° 15° 14° 13° 12° 11° 10° 9° 8° 7° 6° 5° 4° 3° 2°
48°
49°
50°
51°
52°
53°
54°
55°
56°
57°
58°
59°
60°
61°
62°
63°
64°
65°
1A
DC
16
L
B
11
12
13
15 14
20-22
19
17
18
J
M
K
2

rt 2004 17
-18.00 -16.00 -14.00 -12.00 -10.00 -8.00 -6.00 -4.00 -2.00 0.00
36.00
37.00
38.00
39.00
40.00
41.00
42.00
43.00
44.00
45.00
46.00
47.00
48.00
P
R
O
N
23
24
31
25
26
27
28
29 30
Q
Figure 5.1.3. - Nephrops Management Areas and Functional Units in ICES Sub-areas VIII, IX and X (letters and figures
refer to the Management Areas and Functional Units given in Tables 5.1.1 and 5.1.2).
WGNEPH Repo

5.2 Management Area N
ICES description VIIIa,b
Functional Units Bay of Biscay North (FU 23)
Bay of Biscay South (FU 24)
The statistical rectangles comprised in this Management Area and its constituent Functional Units are shown in Figure
5.1.3.
5.2.1 Bay of Biscay (FUs 23-24)
Description of the fisheries
France
Almost all fishing for Nephrops in FUs 23-24 is by French trawlers. The general features of the French Nephrops
fishery were updated in the 2003 WG report (ICES, 2003a).
Trends in landings, effort, LPUE and mean size
Table 5.2.1 Landings by country, 1994-2003
Table 5.2.2 Effort and LPUEs French fleet, 1994-2003
Table 5.2.3 LPUEs of Le Guilvinec District and other ports, 1987-2003
Table 5.2.4a Mean sizes of Nephrops in catches and landings, French data, 1994-2003
Table 5.2.4b Mean sizes of Nephrops in catches and discards for years with a discards sampling program, French
data, 1987-2003
Figure 5.2.1 Long-term trends in landings, effort, LPUE and mean size, French data
Figure 5.2.2 Landings by sex + Quarterly plots of effort and LPUEs by sex, 1994-2003
Figure 5.2.3 Length frequency distributions of landings by sex, 2000-2003
Landings, effort and LPUE
Nearly all the landings from FUs 23-24 are taken by French trawlers. Small landings are reported by Belgium from
rectangles inside the FUs, and by Spain from rectangles outside the FUs but inside the MA (see Section 5.2.2).
Throughout the late 1960s and early 1970s, the landings by French trawlers from FUs 23-24 steadily increased, to
a peak value of around 7100 t in 1973 and 1974, then fell to 4700 t in 1978. During the 1980s and early 1990s, landings
fluctuated, typically between 4500 and 6100 t, but since the mid-1990s they have shown an overall downward trend. In
1998, they fell to around 3200 t, and they remained at this record low level in the following two years (Figure 5.2.1). In
2001, the landings slightly increased again to around 3700 t, a recovery to the level of 1997. Generally speaking, males
predominate in the landings, but since 1997 the proportion of females in the landings has shown a slight increase,
reaching nearly 40 % of the total (Figure 5.2.2).
The logbook regulation is not particularly well enforced in the Bay of Biscay. Very few skippers regularly fill in
their logbooks (in 2003, for example, skippers of 209 out of a total of 266 Nephrops trawlers had filled in their logbook
for at least one trip, and 108 for between one and fifty trips). Only 16 % of the 2003 auction sales could be linked to
logbook data.
Up to 1998, the majority of the vessels were not compelled to keep logbooks, and fishing forms were established
by agents of the IFREMER statistical services. Since 1999, when logbooks became compulsory for all vessels > 10 m,
no further effort data have been collected by IFREMER, the consequence being a severe degradation in the quality of
the effort data.
Estimates of Nephrops directed effort are based on information on the landings composition and the number of
hours fished per voyage (Table 5.2.2). Voyages are considered to be Nephrops directed when > 10 % of their revenue is
accounted for by Nephrops (or > 10 % of the weight landed if the revenue is not recorded). Since most of the vessels
involved in this fishery do not comply with the EU logbook regulations, the number of hours trawling per voyage was
obtained as explained below:
• Up to 1998 from enquiries amongst fishermen.
• From 1999 onwards, the limited effort data available from the logbooks were raised to the whole fleet, using the
ratio of total landings over recorded logbooks landings.
WGNEPH Report 2004
18

The overall LPUEs and estimated effort figures are likely to be biased, since many vessels fill in their log-books
very irregularly or not at all. In view of the ongoing deterioration of the quality of the logbook data, an attempt was
made this year to define a better effort index.
The fleet which was chosen to calculate the effort index was that of the Le Guilvinec District, which groups four
ports specialised in Nephrops trawling. The reference period considered was the 2nd quarter. This is the period of
maximum availability of Nephrops, and the period during which all boats target Nephrops, as opposed to the autumn
and winter period, when a (variable) proportion of the fleet prefers to target finfish for part of their trips. In the area
covered by the Le Guilvinec fleets, fishing trips typically are daily, hence the number of sales is equal to the number of
trips. The number of sales are available from the auction halls database. Fishing hours per trip vary seasonally: from 9
hours from April to October, to 6 hours in the other months. The overall effort index was then obtained by summing
monthly products of fishing time by number of sales. The Le Guilvinec District effort series thus obtained is consistent
with the data available before 1999, and was used to calculate LPUEs with landings data from the auction halls (Table
5.2.3).
The LPUEs for the other ports in the Bay of Biscay, equally restricted to the second quarter, are also presented
(Table 5.2.3). For the reasons explained above, this data series however should be considered as less reliable. It was not
possible to ‘re-construct’ the series using the approach that was applied to the Le Guilvinec ports, because trip and sales
numbers did not correspond in the case of the other ports. Besides, the duration of the trips can vary and not all effort
within a trip is directed towards Nephrops.
Effort indices (landings/LPUE) for the French Nephrops trawlers are available since 1983 (Figure 5.2.1). Between
1983 and 1990, total Nephrops directed effort remained fairly stable. The apparent increase in effort in 1991 and 1992
can be attributed to improvements in the recording system. Since then, and up to 2000, effort dropped. It then levelled
off again until 2003. The decrease in effort in the mid- and late 1990s can be explained by (a) the decrease in the
number of fishing vessels, following the decommissioning scheme implemented by the EU (400 vessels in 1978, 300 in
1987, and 230 in 2000), and (b) a change in fishing practices, with a tendency to direct effort to finfish in the season of
low Nephrops availability.
The LPUEs of the Bay of Biscay Nephrops fleet as a whole have been fairly stable, fluctuating around a long-term
average of 8.6 kg/hour (Figure 5.2.1) until 2000. Three higher values (> 10 kg/hour) have been observed since then. The
two LPUE series computed for the second quarter (Le Guilvinec and other ports) show a peak in 2001, then decrease.
Increases in gear efficiency which are known to have occurred mostly in the late 1990s (twin trawls, rockhoppers, GPS)
are still not taken into account in the calculation of the LPUEs.
The LPUEs for both males and females are usually higher in the 2nd and 3rd quarters (Figure 5.2.2).
Mean size
Mean sizes for males and females in the landings are presented for total catch and landings, i.e. all size categories
combined (Table 5.2.4a), and for ‘small’ (< 35 mm) and ‘large’ (> 35 mm) Nephrops separately (Figure 5.2.1). Length
distributions of discards were obtained in 1987, 1991 and 1999, and are being collected again since June 2002. For
these years, the mean lengths of the discards are shown in Table 5.2.4b. The length frequency distributions of the
landings for both males and females from 2000 to 2003 are presented in Figure 5.2.3.
The mean sizes of ‘small’ male and female Nephrops in the landings show an overall increase, from 31.0 mm to
32.4 mm for males, and from 28.7 mm to 29.8 mm for females (Figure 5.2.1).
The mean sizes of ‘large’ Nephrops in the landings were fairly stable until 1996. This was followed by a period
with lower values in the late 1990s and early 2000s, and a slight recovery in 2003, particularly for males.
Mean sizes of discards show increases between 1987 and 1991 (1.4 mm and 1.1 mm for males and females
respectively), which may be related to the mesh size increase from 50 mm to 55 mm in 1990. Then a smaller increase
was observed from 1991 to 1998 (1.0 mm and 0.9 mm for males and females respectively). Finally, between 1998 and
2003, the changes were very small (increases of 0.2 mm and 0.7 mm for males and females respectively).
Data and biological inputs for analytical assessments
Table 5.2.5 Sampling data and input parameters
Length compositions of the French landings have been sampled since 1984, but for reasons of lack of confidence in the
older data sets, the data for 1984-86 were omitted from the assessments. Discard data are available for 1987, 1991 and
1998 only, and the numbers discarded at length for the other years in the reference period were derived from these. The
derivation method was revised for this WG, and is now based on the total numbers landed for the two sexes combined,
instead of by sex. Derivations were performed in the following way:
•
•
•
the estimates for 1987-90 from the data collected during the 1987 discard sampling programme;
those for 1991-96 from the 1991 sampling programme; and
those for 1997, 1999-2003 from the 1998 sampling programme.
WGNEPH Report 2004 19

Data processing is in progress to raise the discard samples collected since June 2002 to the whole fleet and to
derive new estimates for the discards in 2002 and 2003, but the methodology has not been settled yet, particularly the
choice of the best raising factor.
All biological parameters used in this year’s assessment (growth parameters, length-weight relationships, natural
mortality rates, discard survival rates, etc.) were the same as the ones used previously (see e.g. ICES, 2003a).
In previous years, the tuning data were estimates of Nephrops directed effort based on information on the landings
composition and the number of hours fished per voyage, averaged on an annual basis. However, since the effort data
recorded in the logbooks were too scanty to be considered as representative of the effort by the whole fleet, the effort
figures thus obtained must be considered as rough estimates of nominal effort.
In this year’s assessment, an attempt was made to improve the tuning data series. As explained above, this was
done (a) by choosing another reference fleet (the Le Guilvinec district) and another reference period (the 2nd quarter,
which is much more indicative of the true directedness of the fleet towards Nephrops), and (b) by adding a second
tuning fleet, covering the other ports of the Bay of Biscay, with selected Nephrops directed voyages also in the second
quarter. For those two fleets, age compositions were obtained by using the ratios of fleet landings over quarter 2
landings.
General comments on quality of data and inputs
Table 5.2.6 Assessment deficiencies in 2004
Issues that may generally cause problems for assessment of Nephrops are highlighted in Section 10. Assessment
deficiencies specific to FUs 23-24 are summarised in Table 5.2.6.
Length frequency data for the landings are available on a monthly basis (see also Table 5.2.5). Discards however,
could not be sampled every year because of insufficient technical and financial resources. Since the estimates from the
new discard program were not yet available at this WG, discards were derived from the available data as explained
above. Applying discard data from ‘sampled’ to ‘non-sampled’ years bears the risk of inconsistency between the
different data sets:
•
•
Males discarded in 1998 were of almost the same length range as those discarded in 1991, but they were much
more numerous.
Females discarded in 1998 were generally larger than those discarded in 1991 (a change caused by the market-
driven increase in minimum landing size, which only affected the females because of the differences in growth
between males and females), and they were also more numerous.
Although the effort series used this year is considered to be better than the one used before, it still fails to take into
account changes in gear efficiency and hence may not fully reflect the real changes in fishing effort.
Type of assessments carried out and why
In 2003, a comparison was made between the summed results of the assessments for males and females separately, and
the results of a ‘combined sexes’ assessment. Since this exercise gave very similar results (ICES, 2003a), it was decided
to run a single VPA on males and females combined, using the Lowestoft VPA package. The same approach was taken
this year. In order to give more basis for management advice, short-term catch predictions were also made.
Age based assessments (XSA)
The male and female length distributions for the years 1987-2003 were each split into 9 ‘age’ groups (the last one being
a plus-group), using the L2AGE slicing programme. The catches-at-age for the two sexes were then summed to a
combined input file for XSA. Catch weights-at-age were averages weighted by numbers-at-age for each sex.
Males and females combined
Table 5.2.7 XSA settings males & females combined
Table 5.2.8 Output VPA: Fs-at-age
Table 5.2.9 Output VPA: Long-term trends in landings, Fbar, TB and recruitment
Table 5.2.14 Full listing of VPA input and output data tables
Table 5.2.15 Full listing of XSA diagnostic output
Figure 5.2.4 VPA diagnostics: Log catchability residuals, Le Guilvinec District fleet
Figure 5.2.5 VPA diagnostics: Log catchability residuals, ‘other’ ports fleet
Figure 5.2.6 VPA diagnostics: Retrospective analyses
Figure 5.2.7 Output VPA: Long-term trends in landings, Fbar, TB and recruitment
Figure 5.2.8 Output VPA: Plots of Fbar vs. Effort
Figure 5.2.9 Comparison between WG 2003 and WG 2004 assessments
WGNEPH Report 2004
20

The log-catchability residuals of the Le Guilvinec fleet are quite high from 1987 to 1990 for ages 1 and 2 (Figure 5.2.4).
This can be explained by the limited number of samples available to estimate the discards in 1987 and to derive those
for the years 1988 to 1990. From 1991 onwards, the residuals are lower, but they show some small year effects.
The log-catchability residuals for the ‘Other ports’ fleets (i.e. all Bay of Biscay ports, other than the Le Guilvinec
ones) are also quite high from 1987 to 1990 for ages 1 and 2 (Figure 5.2.5) and this for the same reasons. From 1991
onwards, the residuals are lower, but again they show some small year effects.
The two tuning fleets give very similar estimates of survivors and have the same weight in the F-at-age estimates.
The retrospective analysis shows a noisy pattern, but there does not appear to be a systematic bias in the estimates
of recruitment, Fbar and SSB (Figure 5.2.6). In recent years, recruitment and SSB were strongly under-estimated, but in
2002 they appear to have been overestimated. Fbar has been overestimated since 2001.
Total stock biomass (TB) steadily decreased from 19 103 t in 1987, to 14 103 t in 1999. Since then, there has been
an increase to just under 17 103 t in 2001-2003 (Figure 5.2.7), but the stock is still at a lower biomass level compared to
the beginning of the time series. Since the estimates of TB may be sensitive to the poor estimates of recruitment, it was
also decided to plot the TB for the fully recruited ages. The age range was consistent with that chosen to calculate Fbar
(ages 2-5). This data series shows a very similar pattern.
Recruitment shows a decreasing trend from 1987 (921 million) to 1998 (474 million), and a peak in 2000 (682
million). Since then, recruitment decreased again to a value of 525 million in 2002. The 2003 value of 452 million was
considered uncertain and for the purposes of stock projection was replaced by the geometric mean over the years 1990
to 2001 (609 million). Since discards were not sampled every year and discard data were obtained by extrapolating
‘sampled’ to ‘non-sampled’ years, the recruitment figures for the last three years may be unreliable.
Fbar has fluctuated mainly between 0.6 and 0.7 from 1987 to 1993 (Figure 5.2.7), after which it remained fairly
stable at around 0.6 for five years. Since 1998, a decreasing trend is observed. The average Fbar across the reference
period (1987-2003) is 0.56. The regression of Fbar on effort is significant (r = 0.80, p < 0.01) (Figure 5.2.8).
Compared to last year, this year’s assessment shows a slightly different picture (Figure 5.2.9): biomass appears to
be higher in recent years, but recruitment shows a decrease since 2000. The apparent change in biomass estimates can
be explained by the new tuning series used this year. Nevertheless, the stock is still at a lower level compared to the
beginning of the reference period, with total stock biomass and recruitment at about 88 % of the levels in the early
1990s.
Yield and biomass per recruit
Table 5.2.10 Long-term Y/R and SSB/R based on outputs of VPA: males and females combined
Figure 5.2.10 Long-term Y/R and SSB/R based on outputs of VPA: males and females combined
Y/R analyses were made for landings and discards separately, assuming the current exploitation pattern. Results
of equilibrium landings Y/R and SSB/R are given in Table 5.2.10 and Figure 5.2.10. In the Y/R curve for landings only,
Fmax (at Fbar = 0.24) is estimated to be at 62 % of the reference F. Under the current exploitation pattern, the predicted
long-term gains upon a reduction of F to Fmax would be about 6 %. F0.1 is at 39 % of the reference F.
Short term predictions
Table 5.2.11 Males & females combined : Short-term predictions of landings and biomass, status quo F in 2003
Figure 5.2.11 Males & females combined : Short-term predictions of landings and biomass, status quo F in 2003
Figure 5.2.12 Stock numbers sources used in predictions and their relative (%) contributions to landings and TB (by
weight)
The exploitation patterns for the projection are based on the unscaled average Fs-at-age in the years 2001-2003
(F2-5 = 0.48, i.e. slightly higher than the 2003 F of 0.45). These were then split into landings and discard F, based on the
average discard ratios at age in 2001-2003. The geometric mean for 1990-2001 (GM90-01) was used for age 1 from 2003
onwards (609 million). Stock number at age 2 in 2004 (442 million) was derived from GM90-01, reduced by the total
mortality at age 1 in 2003. Mean weights-at-age for discards and landings were taken as the averages for 2001-2003.
Table 5.2.11 and Figure 5.2.11 give the short-term yield and SSB forecasts. Assuming status quo F, landings
are predicted to increase slightly from 3742 t in 2003 to about 4000 t in 2004, and to stay at this level in 2005. SSB is
expected to stay at the same level in 2004, and to increase slightly in 2005 (16500 t). This would be somewhat higher
than the long-term average of the time series (15600 t). The year classes for which GM90-01 recruitment was assumed,
would contribute 40 % to the landings in 2005, and 63 % to the TB in 2006 (Figure 5.2.12). This shows the strong
impact of the assumptions about recruitment on the results of the short-term prediction. If recruitment is in fact
declining, then the assumption is somewhat over-optimistic.
The predicted landings for 2004 (4000 t) are higher than the 2961 t French quota for FUs 23-24. The assumption
that a TAC will constrain exploitation only holds if the measures taken to reduce fishing effort are effectively
implemented. A reduction in F by 27 % from the status quo level is required to comply with the proposed TAC for
2004. If this was achieved, then at status quo F in 2005 (i.e. with F at the 2000-2003 level), biomass would be expected
to increase in 2005.
WGNEPH Report 2004 21

Changes in selection pattern
Figure 5.2.13 Males & females combined : Short-term predictions of landings and biomass with or without changes in
selection pattern
Another Y/R analysis was performed using constant fishing effort but with progressive improvement of the selection
pattern. In this alternative approach, an F multiplier is applied to one particular age class (mFa), thus assuming that (a)
all younger ages are not fished at all (F multiplier 0), and (b) all older age classes are exploited at status quo F levels (F
multiplier 1). For example, a mFa of 0.8 applied to age 3 means that the selection pattern was improved such that the
catch at age 3 is reduced by 20 %, whilst there is no catch at age 1 and age 2. The software to run this type of Y/R
analysis (YRMFMD) was developed in IFREMER by A. Biseau.
As can be seen from Figure 5.2.13, larger long-term gains can be obtained by changing the fishing pattern than by
reducing F. Y/R starts to increase by 23 % when all of age 1 and 20 % of age 2 are spared, to a maximum of 48 % when
all of ages 1 to 3 are spared.
Medium term projections
Figure 5.2.14 Males & females combined : Medium-term projections for status quo F, with or without an improved
selection pattern from 2005 onwards
Figure 5.2.15 Males & females combined : Medium-term projections for constant landings of 3500 t for 2004
onwards, with or without an improved selection pattern from 2005 onwards
Figure 5.2.16 Males & females combined : Medium-term projections for constant landings of 3700 t for 2004
onwards, with or without an improved selection pattern from 2005 onwards
Figure 5.2.17 Males & females combined : Medium-term projections summarised for various scenarios
Using the same input data as for the short-term predictions and internal standard errors on the stock numbers-at-age as
given by the XSA tuning diagnostics (see Table 5.2.15), a medium-term prediction was carried out, assuming a random
recruitment from 2004 onwards, chosen from the values estimated for the period 1990-2001.
The software (developed by Bertignac and Biseau, see ICES, 2003a) allows a modification of the fishing pattern
by means of F-multipliers for each age.
Since selectivity experiments in the Bay of Biscay show that a 50 % escapement of under-sized Nephrops could
easily be achieved, simulations using F-multipliers of 0.5 for ages 1 and 2 (mostly undersized Nephrops) were tested.
In total, nine scenarios were considered, with the following features:
Scenario Features
S1 Status quo F, with constant recruitment
S2 Status quo F, with recruitment sampled randomly from 1990-2001 values
S3 Status quo F, with recruitment sampled randomly from 1990-2001 values and improved fishing
pattern from 2005 onwards
S4 Constant landings at 3500 t from 2005 onwards, with recruitment sampled randomly from 1990-2001
values
S5 Constant landings at 3500 t from 2004 onwards, with recruitment sampled randomly from 1990-2001
values
S6 Constant landings at 3500 t from 2004 onwards, with recruitment sampled randomly from 1990-2001
values and improved fishing pattern from 2005 onwards
S7 Constant landings at 3700 t from 2005 onwards, with recruitment sampled randomly from 1990-2001
values
S8 Constant landings at 3700 t from 2004 onwards, with recruitment sampled randomly from 1990-2001
values
S9 Constant landings at 3700 t from 2004 onwards, with recruitment sampled randomly from 1990-2001
values and improved fishing pattern from 2005 onwards
WGNEPH Report 2004
22

Three pairs of scenarios are highlighted below and in Figures 5.2.14-16, showing projections based on either status quo
F, constant landings of 3500 t or constant landings of 3700 t, contrasted between two patterns of selectivity:
a) the same fishing pattern as in 2003; and
b) an improvement in the fishing pattern (50 % escapement of ages 1 and 2) from 2005 onwards.
A comparison between these and all other scenarios is shown in Figure 5.2.17.
1. Scenarios of status quo F (S2 and S3) (Figure 5.2.14).
If the fishing pattern would stay the same, then we would expect SSB to stabilize at around 16500 t, and landings to
stabilize at around 4000 t (scenario S2).
With an improved fishing pattern, a slight increase in SSB would be expected in 2007 (+ 5 %), exceeding 18000 t
in 2008, and landings would be stable around 4000 t until 2006, then slightly increase up to 4600 t (scenario S3).
2. Scenarios of constant landings of 3500 t (S5 and S6) (Figure 5.2.15).
It should be noted that landings of 3500 t in 2004 could not be achieved without a reduction in F by 16 %.
If the fishing pattern would stay the same, then we would expect an annual 5-7 % increase SSB to above 18000 t
in 2006 (scenario S5).
With an improved fishing pattern, SSB would be expected to increase at a greater rate after 2007 (7-9 %),
exceeding 18000 t in 2006 (scenario S6).
2. Scenarios of constant landings of 3700 t (S8 and S9) (Figure 5.2.16).
It should be noted that landings of 3700 t in 2004 could not be achieved without a reduction in F by 10 %.
If the fishing pattern would stay the same, then we would expect an annual 4-5 % increase in SSB to above
18000 t in 2007 (one year later than with constant landings of 3500 t) (scenario S8).
With an improved fishing pattern, SSB would be expected to increase at a greater rate after 2007 (6-7 %),
exceeding 18000 t in 2007 (scenario S9).
Note that for the scenarios with constant landings, fishing mortality needs to be reduced every year to provide the same
landings year after year with an increasing stock.
General comments
Figure 5.2.18 Simulation of annual increase in gear efficiency - Males and females combined
The XSA assessment for FUs 23-24 is tuned using commercial Nephrops directed LPUE data. It should be noted that
LPUEs for this stock are computed from nominal and not from actual effort data. As already stated, vessel and gear
efficiency have increased over the reference period (increased use of twin trawls, rockhoppers and GPS) leading to
changes in catchability. An attempt to quantify these increases in efficiency is underway. In the absence of hard figures
that quantify the changes in efficiency, extra assessments were performed, using tuning files that account for a 2 % and
a 4 % annual increase in efficiency. Under these assumptions, the recent increases in TB and recruitment which were
seen in the other assessments, do not appear. This means that the current assessments should be considered as being
optimistic, with the observed increase in LPUE being interpreted by XSA as an increase in abundance rather than as an
increase in gear efficiency.
Management considerations
1. The combined sexes VPA shows some increase in biomass in recent years, but overall stock biomass remains close to
the levels seen in the mid 1990s. It is estimated to be currently 13 % less than at the beginning of the time series (1987).
2. The effort data used in the assessment do not take into account likely increases in catching efficiency associated with
the introduction of new gears and equipment in this fishery in the late 1990s. The assessment is therefore likely to be
over-optimistic.
3. Owing to uncertainty about the stock-recruitment relationship, precautionary reference points have not yet been defined
for this stock. The only available reference points are Fmax and F0.1 calculated with reference to landings only, which
correspond to reductions in F of 38 % and 61 % respectively, under the current exploitation pattern.
WGNEPH Report 2004 23

4. Short-term forecasts indicate that no increase in stock biomass can be expected if the current fishing mortality and
the current exploitation pattern are maintained. Landings are predicted to stabilise at around 4000 t. However, the
contribution of the assumed recruitment is around 40 %. Furthermore, GM90-01 recruitment used for the short term
predictions (609 million), is somewhat higher than the last recruitment estimated by the XSA (452 million in 2003).
5. Improvement of the exploitation pattern would improve the state of the stock. Any selective device or changes in
the fishing tactics that are able to prevent or strongly decrease the catch of small Nephrops should be encouraged.
At status quo F, an improvement of the fishing pattern which would reduce catches of undersized Nephrops by
50 %, would lead to a slight increase in SSB (5 % each year, i.e. to above 18000 t in 2008).
6. Together with the increased willingness to consider the introduction of selective grids, fishermen seem ready to
settle for new management rules in the Nephrops fishery, based on licences. One of the aims (at least the most
immediate) is to prevent increases in the number of vessels targeting Nephrops in the Bay of Biscay. In this respect,
it should be noted that, even though some new vessels could enter in the fishery in the near future (2006), more
than 12 Nephrops trawlers will be decommissioned in Brittany in 2004.
7. Any improvement in the quality of the recruitment estimates will provide better predictions (short and medium
term). Therefore, it is essential that the new French discard sampling programme (which started in June 2002) be
continued.
5.2.2 Summary for Management Area N
Table 5.2.12 Landings by FU and from Other rectangles, 1994-2003
Table 5.2.13 Landings by country, 1994-2003
MA N includes two FUs, Bay of Biscay North (FU 23) and Bay of Biscay South (FU 24). Nephrops landings from other
rectangles within MA N but outside FUs 23 and 24 are almost negligible. Therefore, the management considerations for FUs
23 and 24 can be extended to the MA as a whole.
The WG is particularly concerned about the overshoot of the Subarea VIIIa,b TAC in 2003, with landings exceeding the
agreed TAC by roughly 740 t. Managers and policy makers should be aware that setting TACs to protect a stock from
over-exploitation or to stop declines is of little or no use if these TACs are not adequately implemented.
WGNEPH Report 2004
24

Belgium
FUs 23-24 FU 23 FU 24
0 37 21 371 4092
0 40 73 380 4453
04034844118
2 34 50 147 3599
2 33 00 565 3867
2 28 73 337 3212
0 28 48 221 3069
1 34 21 309 3731
2 33 23 356 3681
1 33 99 343 3743
(1) working group estimates
* pro vi sional
'000 hrs kg/ hr
562 7. 3
533 8. 4
439 9. 4
418 8. 6
406 9. 5
372 8. 6
329 9. 3
336 11 .1
332 11 .1
344 10 .9
* pro vi sional
2003*
2002
1994
1999
2000
1995
1996
1997
1998
2001
Ye ar
Table 5.2.1. - Bay of Biscay (FUs 23- 24): Landings (tonn es) by country, 1994-2003.
Table 5.2.2. - Bay of Biscay (FUs 23- 24): estimated total effort (‘000 hour s trawling) and
LPUE (kg /hour trawling). All figures for 1994 -200 3.
Ye ar T o tal
1994
1995
2002
France (1 )
1998
1999
2000
1996
1997
2003*
2001
Estimated
effo rt
Estimated
LPUE
WGNEPH Report 2004 25

Yea r Quarter 2 Quarter 2
kg /h r k g/ hr kg/hr
11.6 13.8 9.2
12.3 16.5 9.8
9.9 13.0 8.7
9.0 11.3 9.6
7.7 9.8 9.1
9.1 11.1 8.9
8.5 11.0 8.4
7.9 10.3 8.0
8.8 9.7 9.1
9.5 12.0 11.4
8.8 11.8 10.4
8.9 12.7 14.3
9.0 11.9 10.5
9.7 10.8 9.8
11.0 16.7 14.3
11.5 14.2 12.8
10.4 13.4 12.0
2003*
1998
1999
2002
2000
2001
Table 5.2.3. - Bay of Biscay (FUs 23- 24): LPUEs (kg/hour fishing) of Le Guilvinec District
and othe r ports, 1987- 2003 .
Ye ar
LPUE
of Le
Guilvinec
District
LPUE
of Le
Guilvine c
Dis tr ict
1990
LPUE
of othe r
ports
1987
1988
1989
* pro visio na l
1991
1992
1993
1994
1995
1996
1997
WGNEPH Report 2004
26

Mal es Fe males Males Femal es
27.7 25.5 31.0 2 8. 7
27.9 25.8 31.0 2 8. 8
28.0 26.1 31.4 2 9. 4
26.4 26.1 29.5 2 8. 8
27.7 26.4 31.8 2 9. 9
27.8 26.9 31.9 2 9. 9
27.5 26.6 31.5 2 9. 7
27.1 26.6 30.5 2 9. 5
27.0 25.6 30.6 2 8. 3
27.5 26.0 32.4 2 9. 8
* pro vi sional
** catches estimated with discards derived from
1987 , 1991, 1998 and 20 03 samp li ng progra mmes
Mal es Fe males Males Femal es
21.1 20.6 25.7 2 3. 0
22.5 21.7 27.7 2 5. 4
23.5 22.6 27.7 2 6. 4
23.7 23.3 27.5 2 6. 0
1987
1991
1998
2003
Ye ar Discards Catches
Table 5.2.4b. - Bay of Biscay (FUs 23-24): Mean sizes (mm CL) of male and fe male
Ne phrop s in French catches and landings, fo r years with discards sampling programmes.
1996
Catches** Landings
1994
1995
Ye ar
1997
1998
1999
2000
2002
2001
2003*
Table 5.2.4a. - Bay of Biscay (FUs 23-24): Mean sizes (mm CL) of male and fe male
Ne phrop s in French catches and landings, 1994- 2003 .
WGNEPH Report 2004 27

FU MA
FLEET GEAR
Qt r 1 Q tr 2 Qtr 3 Q tr 4 Qtr 1 Q tr 2 Qtr 3 Qtr 4
Catch 76 106 92 97 79
Landings 68 95 79 87 57 52 64 56 46 74
Discards 8 11 13 10 249
Year 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994
Catch 371 324
Landings 329 218 229 182 158 252 227 206 174 167
Discards 42 72
Value
0.30 Gueguen and Charuau, 1975
0.140 aft er Conan and Moriz ur, 1 979 ; plus unpublished data
76 "
0.3 Morizur, 19 82
0.00039 Conan, 1978
3.180 "
0.140 aft er Conan and Moriz ur, 1 979 ; plus unpublished data
76 "
0.3 Morizur, 19 82
25 Morizur, 1982
0.110 aft er Conan and Moriz ur, 1 979 ; plus unpublished data
56 "
0.2 based on Morizur, 1982 ; as suming lower rate f or mature females
0.00081 Conan, 1978
2.970 "
Table 5.2.5. - Bay of Biscay (FUs 23- 24): Input data and parameters.
Length/ wei gh t - b
Source
Mean
no. per
sample
Mean
no. per
sample
Growth - K
Growth - L(inf)
N atural m ortality - M
Length/ wei gh t - a
Growth - L(inf)
N atural m ortality - M
S ize at ma turit y
Mature Growth
Length/ wei gh t - b
FEMALES
Immature Growth
Growth - K
Growth - K
Growth - L(inf)
N atural m ortality - M
Length/ wei gh t - a
I NPUT PARAMET ERS
Paramet er
Dis card Survival
MALES
Number of samples Number of samples
N umber of sa mple s
2003 2002
23 + 24
Fran ce
N
Trawl
WGNEPH Report 2004
28

WGNEPH Report 2004 29
Table 5.2.6. – Bay of Biscay (FUs 23-24): Assessment deficiencies 2004.
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
XSA 2
Tuning data 2 Two fleets selected for tuning:
- Specialised Nephrops trawling fleet (Le Guilvinec District), and
- Other ports’ fleets (all Bay of Biscay, exclusive of Le Guilvinec fleets)
both for a restricted period (quarter 2, i.e. the season during which directedness towards Nephrops
is highest).
New approach is considered to provide better estimates of Nephrops directed effort than the one
used in previous assessments.
CSA N/A
Fishery independent
methods
N/A
Assessment
method
LCA N/A
Definition 1 The FU 23 stock is located in an area called “La Grande Vasière”, and the FU 24 stock in a smaller
muddy area off the Gironde estuary.
Stock
Structure 3 New investigation are in progress in Ifremer on the spatial and temporal variations in Nephrops
size.
Fishery Defi ed, nition (Mix
targeted, multifleet)
1 Nephrops are targeted only by French vessels. This fishery has a major impact on the northern
stock of hake, because the Nephrops fishing grounds are on a hake nursery. Hake discards are very
important. By-catches of other species are much smaller.
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

WGNEPH Report 2004
Table 5.2.6. – Bay of Biscay (FUs 23-24): Assessment deficiencies 2004 (continued).
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Catch N/A
Landings 1 Landings data are provided by the French auction halls database.
Discards 3 Discard data are available for 1987, 1991 and 1998 only, and the discards-at-length for the other
years are derived from these. Discard data are being collected again on a much more regular basis
since June 2002.
Effort 2-3 Total effort: Logbook regulation not particularly well enforced in the Bay of Biscay. Estimates of
total effort obtained by selecting directed trips (voyages with > 10 % of Nephrops) and raising the
figure thus obtained to total fleet level by means of the ratio total landings / landings from
logbooks. Logbooks data cannot be considered as a representative sample of the whole fleet.
Effort index available for the fleets pertaining to the Le Guilvinec District, based on data for
quarter 2.
Catch
statistics
LPUE 2 Three series available:
- Total fleet (from estimated total effort).
- Fleets in Le Guilvinec District, quarter 2.
- Other ports (all Bay of Biscay ports, exclusive of Le Guilvinec fleets).
Catch 3 Available since June 2002 but data not fully processed yet.
Landings 1 Collected on a monthly basis by commercial category.
Sampling
levels
Discards 3 Discard data are available for 1987, 1991 and 1998 only. New data are being collected on a much
more regular basis since June 2002.
...continued overleaf
CPUE N/A
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.
30

WGNEPH Report 2004 31
Table 5.2.6. – Bay of Biscay (FUs 23-24): Assessment deficiencies 2004 (continued).
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Age and growth 3 In the absence of routine methods of direct age determination in Nephrops, the age compositions of
the removals were inferred from the length compositions by means of ‘slicing’. This procedure was
introduced at the 1991 WG. The von Bertalanffy growth parameters used are adapted from Conan
& Morizur (1979).
Maturity 3 Data after Morizur (1982). Not revised since then.
Natural mortality 3 Derived from Morizur (1982) for males and immature females.
Lower value assumed for mature females.
Discard Mortality 2 Estimated in 1975 as 0.7. Not revised since then.
Escape Mortality N/A
Biological
parameters
Length/weight
coefficients
2 Not revised since 1978.
Fishing surveys Survey data available but not used for assessment purposes. France conducts an annual trawl
survey in the area in November-December, but Nephrops catch rates are highly variable. Never-
theless, this survey correctly picked up the high recruitment in 2000.
Larval surveys N/A
Availability
of research
survey data
TV survey N/A
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

rt 2004
N Males and Females combined
Justification
Table 5.2.7. - Bay of Biscay (FUs 23-24) : XSA settings used in the assessment - Males and Females combined.
Available range
SSB and F estimates better than with Plus group at 6 as used before
Available range
WGNEPH Repo
32
23-24 MA
First year Last year
1987 2003
Last age Plus group
9 Yes - 9+
First year Last year
1987 2003
Years used Ages used
1987-2003 1-8
1987-2003 1-8
No
1
6
Yes/No Type
Yes Tricubic over 20 years
Yes/No If Yes: Min. SE for Mean F
Yes 1.5
If Yes: Year range If Yes: Age range
1999-2003 4-8
Yes/No
Yes
0.3
No (32 iterations)
First age for normal catchability independent analysis
XSA Settings
First age at which q is considered independent of age
Prior fleet weighting?
Choices
Did tuning converge after 30 iterations or less ?
Population shrinkage
Minimum Log SE for terminal population estimates
Taper time weighting
applied ?
Fleets used
Tuning range
(2) Other ports Q2
(1) Le Guilvinec Q2
F shrinkage
Age range
Year range
FU

WGNEPH Repo
Age
1
2
3
4
5
6
7
8
+ gr
Tab
rt 2004 33
2003
0.02
0.29
0.48
0.50
0.51
0.45
0.40
0.48
0.48
1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002
0.03 0. 04 0.03 0.03 0.02 0.03 0.02 0.02 0.02 0.02 0.02 0.02 0.01 0.01 0.01 0.02
0.60 0.71 0.60 0.4 4 0.34 0.4 5 0.4 1 0.32 0.3 4 0.28 0.4 2 0.3 6 0.29 0.2 6 0.2 9 0.33
0.74 0.76 0.56 0.5 2 0.58 0.7 7 0.7 0 0.61 0.6 7 0.60 0.7 2 0.6 4 0.55 0.5 4 0.5 9 0.62
0.66 0.76 0.55 0.7 3 0.67 0.7 9 0.8 2 0.65 0.6 5 0.71 0.6 8 0.6 2 0.61 0.5 9 0.6 4 0.53
0.52 0.58 0.51 0.6 7 0.61 0.7 3 0.8 2 0.52 0.6 0 0.62 0.4 5 0.5 7 0.57 0.5 4 0.6 1 0.40
0.45 0.44 0.53 0.7 8 0.62 0.5 6 0.8 6 0.43 0.5 4 0.48 0.3 5 0.5 7 0.43 0.4 1 0.5 7 0.33
0.49 0.43 0.55 0.7 4 0.71 0.5 1 0.8 3 0.60 0.5 1 0.53 0.2 3 0.5 9 0.45 0.3 5 0.4 4 0.24
0.54 0. 61 0.64 0.63 0.71 0.96 0.95 0.54 0.63 0.43 0.28 0.51 0.41 0.39 0.54 0.27
p0.54 0. 61 0.64 0.63 0.71 0.96 0.95 0.54 0.63 0.43 0.28 0.51 0.41 0.39 0.54 0.27
le 5.2.8. - Ba y of Bis cay (FUs 23 -24): V PA Fs-at-ag e males an d f emales comb in ed .
'000 tonnes tonnes tonnes
1987 921 19343 17501 6634 0.38 0.63
1988 769 19226 17687 7211 0.41 0.70
1989 733 17892 16426 5857 0.36 0.56
1990 730 17995 16534 5875 0.36 0.59
1991 748 18381 16885 5603 0.33 0.55
1992 664 18983 17654 6789 0.38 0.68
1993 614 16785 15557 6120 0.39 0.69
1994 585 16273 15102 4834 0.32 0.52
1995 595 16489 15299 5213 0.34 0.56
1996 578 16193 15036 4822 0.32 0.55
1997 508 15080 14065 4856 0.35 0.57
1998 474 14944 13996 4882 0.35 0.55
1999 557 14112 12999 4033 0.31 0.51
2000 682 15079 13714 3918 0.29 0.48
le 5.2.9. - Bay of Biscay (FUs 23-24): VPA output males and females combined.
Recruits
Age 1
Total
Biomass SSB Removals
Year Yi el d/S S B Fbar
2- 5
2001 636 16626 15353 4788 0.31 0.53
2002 525 16762 15713 4831 0.31 0.47
2003 452 16853 15948 4706 0.30 0.45
Average 01-03 0.48
Tab

WGNEPH Report 2004
MFYPR version 2a
Run: CR1
Time and date: 11:44 31/03/2004
Yield per results
Total Landings Discards
FMult Fbar CatchNos Landing Yield Fbar CatchNos D
0.0000 0.0000 0.0000 0.0000 0.0000 0.0000
0.1000 0.0389 0.0904 0.0033 0.0095 0.0233
0.2000 0.0778 0.1519 0.0052 0.0189 0.0452
0.3000 0.1167 0.1948 0.0062 0.0284 0.0659
0.4000 0.1555 0.2252 0.0068 0.0379 0.0854
0.5000 0.1944 0.2469 0.0070 0.0473 0.1038
0.6000 0.2333 0.2623 0.0071 0.0568 0.1213
0.7000 0.2722 0.2732 0.0071 0.0663 0.1379
0.8000 0.3111 0.2807 0.0070 0.0757 0.1537
0.9000 0.3500 0.2857 0.0068 0.0852 0.1687
1.0000 0.3889 0.2887 0.0067 0.0947 0.1830
1.1000 0.4277 0.2902 0.0065 0.1041 0.1967
1.2000 0.4666 0.2906 0.0063 0.1136 0.2098
1.3000 0.5055 0.2900 0.0061 0.1231 0.2223
1.4000 0.5444 0.2888 0.0060 0.1325 0.2343
1.5000 0.5833 0.2871 0.0058 0.1420 0.2458
1.6000 0.6222 0.2849 0.0056 0.1515 0.2568
1.7000 0.6611 0.2824 0.0054 0.1609 0.2673
1.8000 0.6999 0.2797 0.0053 0.1704 0.2775
1.9000 0.7388 0.2768 0.0051 0.1799 0.2873
2.0000 0.7777 0.2737 0.0050 0.1893 0.2967
Reference point F multiplier Absolute F
Fleet1 Landings Fbar(2-5) 1.0000 0.3889
FMax 0.6164 0.2397
F0.1 0.3853 0.1498
F35%SPR 0.5861 0.2279
iscard Yield Total Yield StockNos Biomass SpwnNosJan SSBJan SpwnNosSpwn SSBSpwn
0.0000 0.0000 4.3491 0.1193 3.8491 0.1173 3.8491 0.1173
0.0002 0.0035 3.8970 0.0941 3.3970 0.0921 3.3970 0.0921
0.0005 0.0057 3.5664 0.0767 3.0664 0.0747 3.0664 0.0747
0.0007 0.0069 3.3152 0.0642 2.8152 0.0622 2.8152 0.0622
0.0009 0.0077 3.1186 0.0549 2.6186 0.0529 2.6186 0.0529
0.0010 0.0080 2.9610 0.0478 2.4610 0.0458 2.4610 0.0458
0.0012 0.0083 2.8321 0.0424 2.3321 0.0404 2.3321 0.0404
0.0013 0.0084 2.7250 0.0380 2.2250 0.0360 2.2250 0.0360
0.0015 0.0085 2.6346 0.0346 2.1346 0.0326 2.1346 0.0326
0.0016 0.0084 2.5574 0.0317 2.0574 0.0297 2.0574 0.0297
0.0017 0.0084 2.4907 0.0294 1.9907 0.0274 1.9907 0.0274
0.0018 0.0083 2.4325 0.0274 1.9325 0.0254 1.9325 0.0254
0.0020 0.0083 2.3812 0.0258 1.8812 0.0238 1.8812 0.0238
0.0021 0.0082 2.3357 0.0244 1.8357 0.0224 1.8357 0.0224
0.0021 0.0081 2.2951 0.0232 1.7951 0.0212 1.7951 0.0212
0.0022 0.0080 2.2585 0.0222 1.7585 0.0202 1.7585 0.0202
0.0023 0.0079 2.2254 0.0212 1.7254 0.0192 1.7254 0.0192
0.0024 0.0078 2.1953 0.0204 1.6953 0.0184 1.6953 0.0184
0.0025 0.0078 2.1678 0.0197 1.6678 0.0177 1.6678 0.0177
0.0025 0.0076 2.1425 0.0191 1.6425 0.0171 1.6425 0.0171
0.0026 0.0076 2.1191 0.0185 1.6191 0.0165 1.6191 0.0165
Table 5.2.10. - Bay of Biscay (FUs 23-24): Long-term yield per recruit analysis of males and females combined.
34

WGNEPH Report 2004 35
MFDP version 1a
Run: CR1
Time and date: 11:26 31/03/2004
Fbar age range (Total) : 2-5
Fbar ag e range Fleet 1 : 2- 5
2004
Total La ndi ngs Discards
Biomass SSB FMult FBar Yield FBar Yield Total Yield
17606 16388 1.0000 0.3889 4004 0.0947 1024 5028
2005 200
6
Total La ndi ngs Discards
Bio mas s SSB FMult FBar Landing Yield FBar Discard Yield Total Yield Bioma ss SSB
17686 16468 0.0000 0.0000 0 0.0000 0 0 24294 23076
. 16468 0.1000 0.0389 492 0.0095 123 615 23495 22276
. 16468 0.2000 0.0778 960 0.0189 242 1202 22733 21514
. 16468 0.3000 0.1167 1405 0.0284 357 1762 22006 20788
. 16468 0.4000 0.1555 1830 0.0379 467 2297 21314 20095
. 16468 0.5000 0.1944 2234 0.0473 574 2808 20653 19435
. 16468 0.6000 0.2333 2619 0.0568 677 3296 20023 18805
. 16468 0.7000 0.2722 2986 0.0663 776 3762 19422 18204
. 16468 0.8000 0.3111 3336 0.0757 871 4207 18848 17630
. 16468 0.9000 0.3500 3669 0.0852 964 4633 18301 17083
. 16468 1.0000 0.3889 3987 0.0947 1053 5040 17779 16561
. 16468 1.1000 0.4277 4290 0.1041 1139 5429 17281 16062
. 16468 1.2000 0.4666 4578 0.1136 1223 5801 16805 15587
. 16468 1.3000 0.5055 4853 0.1231 1303 6156 16351 15132
. 16468 1.4000 0.5444 5116 0.1325 1381 6497 15917 14699
. 16468 1.5000 0.5833 5366 0.1420 1456 6822 15503 14284
. 16468 1.6000 0.6222 5604 0.1515 1528 7132 15107 13889
. 16468 1.7000 0.6611 5832 0.1609 1599 7431 14729 13511
. 16468 1.8000 0.6999 6049 0.1704 1666 7715 14368 13150
. 16468 1.9000 0.7388 6257 0.1799 1732 7989 14023 12804
. 16468 2.0000 0.7777 6454 0.1893 1796 8250 13693 12475
Table 5.2.11. - bay of Biscay (FU 23-24): Short-term predictions of landings and biomass of males and females
combined. Status qu o F in 2004.

WGNEPH Report 2004
36
FU 23 FU 24 FU s 23-24
** Other Total
3721 371 0 27 4119
4073 380 0 14 4467
4034 84 0 15 4133
3450 147 2 41 3640
3300 565 2 40 3907
2873 337 2 26 3238
2848 221 0 36 3105
3421 309 1 22 3753
3323 356 2 36 3717
3399 343 1 49 3792
Belgium France(1) Spain Total
0409227
4119
0445314
4467
0411815
4133
2359741
3640
2386540
3907
2321026
3238
0306936
3105
1373022
3753
2367936
3717
1374249
3792
(1) Working group estimates
* pro vi sional
2003*
Table 5.2.12. - Management Area N (VIIIa,b): Total Nephrops landing s (tonnes) by
Function al Unit plus Other rectangles, 1994- 2003.
Table 5.2.13. - Management Area N (VIIIa,b): Total Nephrops landings (tonnes ) by country ,
1994-2003.
Year
1994
1995
1996
1997
1998
2001
1996
1997
1998
1999
2003*
2000
1999
2000
2001
Year
2002
* pro vi sional
** c o untries reporti ng o nl y aggr eg ate d landings f or F Us 23- 2 4
1994
1995
2002

WGNEPH Report 2004 37
R un title : bay of bisca y M+F W G 200 4 t 0=0 9+
At 16/0 3/200 4 12 :02
Tabl e 1 C atch nu mbers at age Numb ers*1 0** -3
YEAR 198719881989199019911992199319941995
AGE
1 25573 28369 20440 15895 10216 14817 12754 9110 7988
2 2 59 86 4 29 53 70 21 79 67 1 64 43 1 133 52 3 17 37 81 1436 52 1 07 11 3 107 8 27
3 127252 129866 96257 82787 102945 1383 82 120553 99389 107835
4 4227 4 4 84 77 3 78 00 51 19 3 46 71 2 5 54 03 5 21 75 44 11 7 43 9 04
5 1291 8 1 53 84 1 31 77 19 55 8 17 02 5 1 96 11 1 99 10 12 97 4 17 0 60
6452851706298833473186818818243356222
7190821453141365428072646397521302469
8 936 1068 1463 154 8 1 32 4 12 93 19 17 100 3 9 32
+gp 149315282948151416112042275617781497
0 T OT ALN UM 4 7674 5 52 7377 39 9490 3 4891 4 3 2348 2 41 4794 36 5872 2 8194 9 2 957 33
T ON SLAN D 6 634 72 11 58 57 587 5 5 603 6789 6120 483 4 52 13
S OPC OF % 10 1 1 00 101 10 0 10 0 98 1 00 9 8 99
YEAR 19961997199819992000200120022003
AGE
180049773767060366458805193037766
2 93154 127062 99003 77413 82164 111944 115574 85186
3 9442 9 1161 48 8 99 11 74 29 8 73 44 8 9 59 22 11 89 23 87 99 7
4 4488 2 4 37 07 3 96 88 35 99 7 35 00 6 3 78 79 3 85 94 41 95 2
5 1731 5 1 23 98 1 53 53 15 46 3 13 78 6 1 55 50 1 08 41 17 16 9
661964619729453925291654541006199
727871606386226652306290014002654
8 101 9 7 60 19 14 126 6 1 19 2 18 24 9 53 154 9
+gp 137 6 805 25 50 1 621 147 0 16 36 9 93 2 278
0 T OT ALN UM 2 6916 1 31 6878 26 7245 2 2015 0 2 2112 1 28 2251 30 0679 2 5275 0
T ON SLAN D 4 822 48 56 48 82 403 3 3 918 4788 4831 470 6
S OPC OF % 99 1 01 101 101 10 1 99 1 02 99
Tabl e 2 C atch we ights a t age (k g)
YEAR 198719881989199019911992199319941995
AGE
1 0 . 00 4 0 . 0 04 0.0 04 0. 00 4 0 . 00 4 0.0 04 0. 0 04 0. 00 4 0. 0 04
2 0 . 00 8 0 . 0 08 0.0 08 0. 00 8 0 . 00 9 0.0 09 0. 0 09 0. 00 9 0. 0 09
3 0 . 01 6 0 . 0 17 0.0 16 0. 01 7 0 . 01 6 0.0 17 0. 0 16 0. 01 7 0. 0 17
4 0 . 02 8 0 . 0 27 0.0 28 0. 02 8 0 . 02 7 0.0 26 0. 0 25 0. 02 7 0. 0 26
5 0 . 04 2 0.04 0.039 0. 0 4 0.04 0 .0 38 0. 0 33 0. 03 8 0. 0 36
6 0 . 05 8 0 . 0 53 0.0 52 0. 05 2 0 . 05 1 0.0 51 0. 0 43 0. 04 7 0. 0 48
7 0.069 0.061 0.063 0.06 6 0.064 0.062 0.05 0.058 0.062
8 0 . 07 9 0 . 0 64 0.0 69 0. 07 2 0 . 07 3 0.06 0.059 0. 06 6 0 .0 76
+gp 0.0 9 0 .087 0.084 0. 072 0 .078 0 .081 0.078 0.08 1 0.0 93
0 S OP COFAC 1. 013 4 0. 9995 1 .00 77 0. 996 2 0.9 992 0. 98 16 1. 0011 0 .9 842 0. 99 24
YEAR 19961997199819992000200120022003
AGE
1 0 . 00 4 0 . 0 04 0.0 04 0. 00 4 0 . 00 4 0.0 04 0. 0 04 0. 00 4
2 0 . 00 9 0 . 0 09 0.0 09 0. 00 9 0 . 00 9 0.0 09 0. 0 09 0. 00 9
3 0 . 01 7 0 . 0 16 0.0 16 0. 01 6 0 . 01 6 0.0 17 0. 0 16 0. 01 7
4 0 . 02 7 0 . 0 24 0.0 27 0. 02 7 0 . 02 6 0.0 26 0. 0 26 0. 02 6
5 0 . 03 5 0 . 0 31 0.0 38 0. 03 6 0 . 03 6 0.0 34 0. 0 36 0. 03 6
6 0 . 04 3 0 . 0 39 0.0 46 0. 04 5 0 . 04 2 0.0 41 0. 0 46 0. 05 1
7 0 . 05 3 0 . 0 48 0.0 48 0. 04 8 0.05 0. 05 0. 0 54 0. 05 9
8 0 . 06 4 0 . 0 52 0.0 58 0. 05 3 0 . 05 9 0.0 53 0. 0 53 0. 06 4
+gp 0.07 9 0.0 66 0.0 68 0. 061 0 .072 0 .074 0 .07 0 .07
0 S OP COFAC 0. 987 7 1. 0067 1 .01 27 1. 014 7 1.0 149 0. 99 44 1. 0152 0 .9 941
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables.
...continued overleaf

WGNEPH Report 2004
38
1996
0.3
0.2 5
0.2 5
0.2 5
0.2 5
0.2 5
0.2 5
0.2 5
0.2 5
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables (continued).
T able 3 Stoc k we ight s at age (k g)
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994 1995
AG E
1 0.004 0.004 0.004 0.004 0.004 0.0 04 0. 004 0.004 0.004
2 0.008 0.008 0.008 0.008 0.009 0.0 09 0. 009 0.009 0.009
3 0.016 0.017 0.016 0.017 0.016 0.0 17 0. 016 0.017 0.017
4 0.028 0.027 0.028 0.028 0.027 0.0 26 0. 025 0.027 0.026
5 0.042 0.0 4 0.039 0.04 0.04 0.038 0.033 0.038 0.036
6 0.058 0.053 0.052 0.052 0.051 0.0 51 0. 043 0.047 0.048
7 0.069 0.061 0.063 0.066 0.064 0.0 62 0.05 0.058 0.062
8 0.079 0.064 0.069 0.072 0.073 0.06 0.059 0. 066 0.076
+gp 0.09 0.087 0.084 0.072 0.078 0.081 0. 078 0.081 0.093
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003
AG E
1 0.004 0.004 0.004 0.004 0.004 0.004 0.004 0.004
2 0.009 0.009 0.009 0.009 0.009 0.009 0.009 0.009
3 0.017 0.016 0.016 0.016 0.016 0.017 0.016 0.017
4 0.027 0.024 0.027 0.027 0.026 0.026 0.026 0.026
5 0.035 0.031 0.038 0.036 0.036 0.034 0.036 0.036
6 0.043 0.039 0.046 0.045 0.042 0.041 0.046 0.051
7 0.053 0.048 0.048 0.048 0.05 0.05 0.054 0.059
8 0.064 0.052 0.058 0.053 0.059 0.053 0.053 0.064
+gp 0.079 0.066 0.068 0.061 0.072 0.074 0.07 0.07
T able 4 Natu ral M orta lity (M ) at age
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994 1995
AG E
10.30.30.30.30.30.30.30.30.3
2 0. 25 0.2 5 0 .25 0 .2 5 0.2 5 0 .2 5 0.2 5 0 .25 0 .2 5
3 0. 25 0.2 5 0 .25 0 .2 5 0.2 5 0 .2 5 0.2 5 0 .25 0 .2 5
4 0. 25 0.2 5 0 .25 0 .2 5 0.2 5 0 .2 5 0.2 5 0 .25 0 .2 5
5 0. 25 0.2 5 0 .25 0 .2 5 0.2 5 0 .2 5 0.2 5 0 .25 0 .2 5
6 0. 25 0.2 5 0 .25 0 .2 5 0.2 5 0 .2 5 0.2 5 0 .25 0 .2 5
7 0. 25 0.2 5 0 .25 0 .2 5 0.2 5 0 .2 5 0.2 5 0 .25 0 .2 5
8 0. 25 0.2 5 0 .25 0 .2 5 0.2 5 0 .2 5 0.2 5 0 .25 0 .2 5
+g p 0. 25 0. 25 0 .25 0.2 5 0.2 5 0.2 5 0.2 5 0 .25 0 .25
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003
AG E
10.30.30.30.30.30.30.30.3
20.25 0.250.250.250.250.250.250.25
30.25 0.250.250.250.250.250.250.25
40.25 0.250.250.250.250.250.250.25
50.25 0.250.250.250.250.250.250.25
60.25 0.250.250.250.250.250.250.25
70.25 0.250.250.250.250.250.250.25
80.25 0.250.250.250.250.250.250.25
+g p 0. 25 0. 25 0 .25 0.2 5 0.2 5 0.2 5 0.2 5 0 .25
...continued overleaf

WGNEPH Report 2004 39
Ta ble 5 Prop ortio n matur e at ag e
YEAR 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
10.50.50.50.50.50.50.50.50.50.5
21 111111111
31 111111111
41 111111111
51 111111111
61 111111111
71 111111111
81 111111111
+gp 1 111111111
YEAR 1996 1997 1998 1999 2000 2001 2002 2003
AGE
10.50.50.50.50.50.50.50.5
21 1111111
31 1111111
41 1111111
51 1111111
61 1111111
71 1111111
81 1111111
+gp 1 1111111
Ta ble 6 Prop ortion of M bef ore Spawning
YEAR 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
10 000000000
20 000000000
30 000000000
40 000000000
50 000000000
60 000000000
70 000000000
80 000000000
+gp 0 000000000
YEAR 1996 1997 1998 1999 2000 2001 2002 2003
AGE
10 0000000
20 0000000
30 0000000
40 0000000
50 0000000
60 0000000
70 0000000
80 0000000
+gp 0 0000000
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables (continued).
...continued overleaf

WGNEPH Report 2004
40
1995
0
0
0
0
0
0
0
0
0
1995
0157
3381
6671
0. 64 8
6001
5386
5067
6287
6287
5633
BAR 01-03
0186
3055
5651
5564
5071
4489
359 1
4289
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables (continued).
T able 7 Prop ortio n of F be fore Spa wning
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994
AG E
10 0000000
20 0000000
30 0000000
40 0000000
50 0000000
60 0000000
70 0000000
80 0000000
+gp 0 0000000
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003
AG E
10 0000000
20 0000000
30 0000000
40 0000000
50 0000000
60 0000000
70 0000000
80 0000000
+gp 0 0000000
T able 8 Fish ing m ort ality (F ) a t ag e
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994
AG E
1 0.0328 0.0438 0.0329 0.0256 0.016 0.0263 0.0244 0.0182 0.
2 0.6035 0.7073 0.6029 0.438 0.3382 0.4479 0.4148 0.3196 0.
3 0.7379 0.7586 0.5628 0.5167 0.5832 0.7669 0.6997 0.6102 0.
4 0 .6 6 27 0 .7 6 3 4 0.5 5 2 2 0. 72 5 6 0. 67 3 5 0. 79 2 1 0 . 817 0. 6 46 5
5 0.5227 0.5786 0.5106 0.6728 0.6074 0.73 0. 8152 0.5166 0.
6 0.4539 0.4351 0.5307 0.7789 0.6182 0.5616 0.8577 0.4341 0.
7 0.4931 0.4299 0.5539 0.7373 0.7131 0.5063 0.8301 0.6049 0.
8 0.5366 0.6128 0.6358 0.6317 0.708 0.9554 0.9491 0.5435 0.
+gp 0.5366 0.6128 0.6358 0.6317 0.708 0.9554 0.9491 0.5 435 0.
0 FBAR 2- 5 0.6317 0.702 0.5571 0.5883 0.5506 0.6842 0.6867 0.5232 0.
T able 8 Fish ing m ort ality (F ) a t ag e
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003 F
AG E
1 0.0162 0.0226 0.019 0.0127 0.0111 0. 0148 0.0208 0.0201 0.
2 0.2786 0.4178 0.3641 0.2939 0.2597 0.2927 0.3312 0.2926 0.
3 0.6022 0.7222 0.6371 0.5504 0.5382 0.5878 0.6232 0.4842 0.
4 0.7072 0.6752 0.6248 0.6126 0.587 0.6389 0.5333 0.4971 0.
5 0.6193 0.4537 0.571 0.5695 0.5372 0. 6078 0.3985 0.5149 0.
6 0.4836 0.3478 0.5686 0.4266 0.4112 0.5684 0.3329 0.4455 0.
7 0 .5 2 83 0. 2 3 2 0.5 9 1 4 0. 44 5 2 0. 34 5 4 0. 44 3 1 0 . 23 6 0 . 3 98 1 0 .
8 0.4301 0.2794 0.5098 0.4148 0.3887 0.5433 0.2683 0.4753 0.
+gp 0.4301 0.2794 0.5098 0.4148 0.3887 0.5433 0.2683 0.4753
0 FBAR 2- 5 0.5518 0.5672 0.5493 0. 5066 0.4805 0.5318 0.4715 0.4472
...continued overleaf

rt 2004 41
963 244545 290581 259802 221211 246301 247790
342 90914 105801 121356 124679 101084 101358
585 38687 37376 48339 57490 39975 40060
782 17105 16406 19541 22496 17010 17071
945 9179 7545 9159 9748 7607 7717
194 4932 4590 4641 4791 3351 3462
117 4361 4740 6740 5511
416 1546123 1456115 1302513 774364
...continued overleaf
T able 9 Rela tive F at a ge
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994 1995
AG E
1 0.0519 0.0624 0.0591 0.0435 0.029 0.0384 0.0356 0.0349 0.0279
2 0.9554 1.0076 1.0821 0.7446 0.6143 0.6546 0.6041 0.6109 0.6002
3 1 .1 6 81 1 .0 8 0 7 1. 0 1 0 2 0 . 87 8 3 1. 05 9 2 1. 12 0 8 1 . 01 9 1 . 1 66 2 1 .1 84 2
4 1.0491 1.0875 0.9912 1.2335 1.2232 1.1577 1.1897 1.2356 1.1503
5 0.8274 0.8242 0.9165 1.1436 1.1032 1.0669 1.1871 0.9873 1.0653
6 0.7185 0.6198 0.9526 1.324 1.1229 0.8207 1.2491 0.8297 0.9562
7 0 .7 8 05 0 .6 1 2 5 0. 9 9 4 2 1 . 25 3 2 1. 29 5 2 0. 73 9 9 1. 2 08 9 1. 15 6 0 .8 99 5
8 0.8495 0.87 3 1.1411 1.0738 1. 2859 1.3963 1. 3821 1.0388 1.1161
+gp 0.8495 0.873 1.1411 1.0738 1.2859 1.3963 1.3821 1.0388 1.1161
0 REF MEAN 0.6317 0.702 0.5571 0.5883 0.5506 0. 6842 0.6867 0.5232 0.5633
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003 MEAN 01-03
AG E
1 0.0294 0.0399 0.0346 0.025 0.023 0.0278 0. 0442 0.0451 0.039
2 0.5049 0.7365 0.6629 0.5801 0.5404 0.5503 0.7023 0.6542 0.6356
3 1.0913 1.2733 1.1599 1.0864 1.1201 1.1054 1.3216 1.0827 1.1699
4 1 .2 8 16 1 .1 9 0 4 1.1 3 7 6 1. 20 9 2 1. 22 1 5 1. 20 1 4 1 . 131 1. 1 11 6 1.14 8
5 1.1223 0.7998 1.0395 1.1242 1.118 1.143 0. 8451 1.1515 1.0465
6 0.8764 0.6131 1.0352 0.842 0.8557 1.0689 0.706 0.9962 0.9237
7 0.9575 0.4089 1.0768 0.8787 0.7189 0.8333 0.5005 0.8901 0.7413
8 0 .7 7 94 0 .4 9 2 6 0. 9 2 8 2 0 . 81 8 9 0. 80 8 8 1. 02 1 6 0 . 56 9 1 . 0 62 7 0 .8 84 4
+g p 0.7 794 0 .49 26 0.9 28 2 0 .81 89 0. 80 88 1. 021 6 0. 569 1 .0 627
0 REF MEAN 0.5518 0.5672 0.5493 0. 5066 0.4805 0.5318 0.4715 0.4 472
T able 10 Sto ck nu mbe r at a ge ( start of ye ar ) N umb er s*10 **-3
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994 1995
AG E
1 920764 769332 732820 730198 748136 664316 613711 585481 595292
2 649842 660108 545518 525294 527263 545439 479384 443671 425894
3 276296 276768 253430 232495 263989 292799 271427 246573 251004
4 988 56 1 02880 100941 112425 108008 114746 105910 105000 104320
5 359 58 39683 37342 45255 42379 42894 40472 36439 42841
6 140 63 16605 17329 17453 17985 17980 16099 13949 16929
7 5554 6956 8369 7938 6238 7548 7986 5318 7038
8 2554 2642 3524 3746 2958 2381 3543 2712 2262
+gp 4018 3722 6990 3607 3537 3678 4985 4738 3578
0 TOTAL 2007906 1878696 1706263 1678411 1720493 1691782 1543517 1443880 1449158
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003 2004 GM8703 AM8703
AG E
1 578426 507546 473908 556549 682381 636438 524521 452366 0 643870 653020
2 434127 421620 367588 344478 407107 499962 464556 380567 328439 477101 485153
3 236529 255890 216226 198908 199
4 100319 100876 96787 89051 89
5 425 00 38520 39991 40354 37
6 183 09 17818 19058 17596 17
7 7694 8791 9801 8406 8
8 3302 3533 5429 4225 4
+gp 4409 3711 7141 5349 5
0 TOTAL 1425614 1358305 1235930 1264914 1452
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables (continued).
WGNEPH Repo

Table 11 Spawning stock number at ag e (spawning ti me) Numbers *10**-3
YEAR 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 460382 384666 366410 365099 374068 332158 306855 292741 297646 289213
2 649842 660108 545518 525294 527263 545439 479384 443671 425894 434127
3 276296 276768 253430 232495 263989 292799 271427 246573 251004 236529
4 98856 102880 100941 112425 108008 114746 105910 105000 104320 100319
5 35958 39683 37342 45255 42379 42894 40472 36439 42841 42500
6 14063 16605 17329 17453 17985 17980 16099 13949 16929 18309
7 5554 6956 8369 7938 6238 7548 7986 5318 7038 7694
8 2554 2642 3524 3746 2958 2381 3543 2712 2262 3302
+gp 4018 3722 6990 3607 3537 36 78 4985 4738 3578 4409
YEAR 1996 1997 1998 1999 2000 2001 2002 2003
AGE
1 289213 253773 236954 278275 341190 318219 262260 226183
2 434127 421620 367588 344478 407107 499962 464556 380567
3 236529 255890 216226 198908 199963 244545 290581 259802
4 100319 100876 96787 89051 89342 90914 105801 121356
5 42500 38520 39991 40354 37585 38687 37376 48339
6 18309 17818 19058 17596 17782 17105 16406 19541
7 7694 8791 9801 8406 8945 9179 7545 9159
8 3302 3533 5429 4225 4194 4932 4590 4641
+gp 4409 3711 7141 5349 5117 43 61 4740 6740
Ta ble 12 Stock biomass at ag e (star t of ye ar) Tonnes
YEAR 1987 1988 1989 1990 1991 1992 1993 1994 1995
AGE
1 3683 3077 2931 2921 2993 2657 2455 2342 2381
2 5199 5281 4364 4202 4745 4909 4314 3993 3833
3 4421 4705 4055 3952 4224 4978 4343 4192 4267
4 2768 2778 2826 3148 2916 2983 2648 2835 2712
5 1510 1587 1456 1810 1695 1630 1336 1385 1542
6 816 880 901 908 917 917 692 656 813
7 383 424 527 524 399 468 399 308 436
8 202 169 243 270 216 143 209 179 172
+gp 362 324 587 260 276 298 389 384 333
0 TOTALBIO 19343 19226 17892 17995 18381 18983 16785 16 273 16489
YEAR 1996 1997 1998 1999 2000 2001 2002 2003
AGE
1 2314 2030 1896 2226 2730 2546 2098 1809
2 3907 3795 3308 3100 3664 4500 4181 3425
3 4021 4094 3460 3183 3199 4157 4649 4417
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables (continued).
4 2709 2421 2613 2404 2323 2364 2751 3155
5 1487 1194 1520 1453 1353 1315 1346 1740
6 787 695 877 792 747 701 755 997
7 408 422 470 403 447 459 407 540
8 211 184 315 224 247 261 243 297
+gp 348 245 486 326 368 323 332 472
0 TOTALBIO 16193 15080 14944 14112 15079 16626 16762 16 853
...continued overleaf
WGNEPH Report 2004
42

Table 13 Spawning stock biomass at age (spawning time) Tonnes
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994 1995
AG E
1 1842 1539 1466 1460 1496 1329 1227 1171 1191
2 5199 5281 4364 4202 4745 4909 4314 3993 3833
3 4421 4705 4055 3952 4224 4978 4343 4192 4267
4 2768 2778 2826 3148 2916 2983 2648 2835 2712
5 1510 1587 1456 1810 1695 1630 1336 1385 1542
6 816 880 901 908 917 917 692 656 813
7 383 424 527 524 399 468 399 308 436
8 202 169 243 270 216 143 209 179 172
+gp 362 324 587 260 276 298 389 384 333
0 TOTSPBIO 17501 17687 16426 16534 16885 17654 15557 15102 15299
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003
AG E
1 1157 1015 948 1113 1365 1273 1049 905
2 3907 3795 3308 3100 3664 4500 4181 3425
3 4021 4094 3460 3183 3199 4157 4649 4417
4 2709 2421 2613 2404 2323 2364 2751 3155
5 1487 1194 1520 1453 1353 1315 1346 1740
6 787 695 877 792 747 701 755 997
7 408 422 470 403 447 459 407 540
8 211 184 315 224 247 261 243 297
+gp 348 245 486 326 368 323 332 472
0 TOTSPBIO 15036 14065 13996 12999 13714 15353 15713 15948
T able 14 Sto ck bio mas s a t age with SOP ( sta rt of year ) Ton nes
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994 1995
AG E
1 3732 3076 2954 2910 2990 2608 2458 2305 2363
2 5268 5278 4398 4186 4742 4818 4319 3930 3804
3 4480 4703 4086 3937 4221 4886 4348 4126 4235
4 2805 2777 2848 3136 2914 2928 2651 2790 2692
5 1530 1587 1468 1803 1694 1600 1337 1363 1531
6 827 880 908 904 917 900 693 645 806
7 388 424 531 522 399 459 400 304 433
8 204 169 245 269 216 140 209 176 171
+gp 366 324 592 259 276 292 389 378 330
0 TOTALBIO 19602 1921 7 18029 17926 18367 18633 1 6804 16017 16364
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003
AG E
1 2285 2044 1920 2259 2770 2532 2130 1799
2 3859 3820 3350 3146 3718 4475 4245 3405
3 3972 4122 3504 3229 3247 4134 4720 4391
4 2675 2437 2647 2440 2357 2351 2793 3137
5 1469 1202 1539 1474 1373 1308 1366 1730
6 778 700 888 803 758 697 766 991
7 403 425 476 409 454 456 414 537
8 209 185 319 227 251 260 247 295
+gp 344 247 492 331 374 321 337 469
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables (continued).
rt 2004 43
303 16533 17017 167530 TOTALBIO 15994 1518 0 15134 14319 15
...continued overleaf
WGNEPH Repo

Table 15 Spawning stock biomass with SOP (s pawning time) Tonnes
YEAR 19 87 1988 1989 1990 1991 1992 1993 1994 1995
AG E
1 1866 1538 1477 1455 1495 1304 1229 1153 1182
2 5268 5278 4398 4186 4742 4818 4319 3930 3804
3 4480 4703 4086 3937 4221 4886 4348 4126 4235
4 2805 2777 2848 3136 2914 2928 2651 2790 2692
5 1530 1587 1468 1803 1694 1600 1337 1363 1531
6 827 880 908 904 917 900 693 645 806
7 388 424 531 522 399 459 400 304 433
8 204 169 245 269 216 140 209 176 171
+gp 366 324 592 259 276 292 389 378 330
0 TOTSPBIO 17736 17679 16552 16471 16872 17329 15575 14864 15182
YEAR 19 96 1997 1998 1999 2000 2001 2002 2003
AG E
1 1143 1022 960 1129 1385 1266 1065 899
2 3859 3820 3350 3146 3718 4475 4245 3405
3 3972 4122 3504 3229 3247 4134 4720 4391
4 2675 2437 2647 2440 2357 2351 2793 3137
5 1469 1202 1539 1474 1373 1308 1366 1730
6 778 700 888 803 758 697 766 991
7 403 425 476 409 454 456 414 537
8 209 185 319 227 251 260 247 295
+gp 344 247 492 331 374 321 337 469
0 TOTSPBIO 14851 14158 14175 13190 13918 15268 15952 15853
Table 5.2.14. - Bay of Biscay (FUs 23-24): VPA input and output tables (continued).
T able 16 Su mma ry (wit hout S OP corre ction )
RECRU ITS TOTALBIO TOTSPBIO REMOVALS LANDI NGS YIELD/SSB FBAR 2- 5
Age 1
1987 920764 19343 17501 6634 5397 0.379 0.6317
1988 769332 19226 17687 7211 5875 0.4077 0.702
1989 732820 17892 16426 5857 5149 0.3565 0.5571
1990 730198 17995 16534 5875 4972 0.3553 0.5883
1991 748136 18381 16885 5603 4754 0.3318 0.5506
1992 664316 18983 17654 6789 5681 0.3845 0.6842
1993 613711 16785 15557 6120 5109 0.3934 0.6867
1994 585481 16273 15102 4834 4092 0.3201 0.5232
1995 595292 16489 15299 5213 4452 0.3407 0.5633
1996 578426 16193 15036 4822 4118 0.3207 0.5518
1997 507546 15080 14065 4856 3598 0.3453 0.5672
1998 473908 14944 13996 4882 3865 0.3488 0.5493
1999 556549 14112 12999 4033 3209 0.3103 0.5066
2000 682381 15079 13714 3918 3069 0.2857 0.4805
2001 636438 16626 15353 4788 3730 0.3119 0.5318
2002 524521 16762 15713 4831 3679 0.3074 0.4715
2003 452366 16853 15948 4706 3742 0.2951 0.4472
Arith.
Mean 633658 16883 15616 5351 0.3408 0. 5643
0 Units (Thous and
s
(T onnes) (Tonnes) (Tonnes)
T able 17 Su mma ry (wit h SOP cor recti on)
RECRU ITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB SOPCOFAC FBAR 2- 5
Age 1
1987 920764 19602 17736 6634 0.374 1.0134 0.6317
1988 769332 19217 17679 7211 0.4079 0.9995 0.702
1989 732820 18029 16552 5857 0.3538 1.0077 0.5571
1990 730198 17926 16471 5875 0.3567 0.9962 0.5883
1991 748136 18367 16872 5603 0.3321 0.9992 0.5506
1992 664316 18633 17329 6789 0.3918 0.9816 0.6842
1993 613711 16804 15575 6120 0.3929 1.0011 0.6867
1994 585481 16017 14864 4834 0.3252 0.9842 0.5232
1995 595292 16364 15182 5213 0.3434 0.9924 0.5633
1996 578426 15994 14851 4822 0.3247 0.9877 0.5518
1997 507546 15180 14158 4856 0.343 1.0067 0.5672
1998 473908 15134 14175 4882 0.3444 1.0127 0.5493
1999 556549 14319 13190 4033 0.3058 1.0147 0.5066
2000 682381 15303 13918 3918 0.2815 1.0149 0.4805
2001 636438 16533 15268 4788 0.3136 0.9944 0.5318
2002 524521 17017 15952 4831 0.3028 1.0152 0.4715
2003 452366 16753 15853 4706 0.2968 0.9941 0.4472
Arith.
M ea n 633 65 8 1 68 94 1 5625 5 351 .34 06 .56 43
0 Units (Thous and
s
(T onnes) (Tonnes) (Tonnes)
WGNEPH Report 2004
44

rt 2004 45
2003
3 0.019 0.013 0.011 0.015 0.021 0.02
8 0.364 0.294 0.26 0.293 0.331 0.293
2 0.637 0.55 0.538 0.588 0.623 0.484
5 0.625 0.613 0.587 0.639 0.533 0.497
4 0.571 0.57 0.537 0.608 0.398 0.515
8 0.569 0.427 0.411 0.568 0.333 0.445
2 0.591 0.445 0.345 0.443 0.236 0.398
9 0.51 0.415 0.389 0.543 0.268 0.475
Lowest
16/0 3/
Extende
bay of b
CPUE d
Catch d
Flee
oft VPA Version 3.1
2004 12: 00
d Survivo rs Analysis
iscay M+F WG 2004 t0=0 9+
ata from file TUNEFF.DAT
ata for 17 years. 1987 to 2003. Ages 1 to 9.
t Fir
s
Last First Last Alpha Beta
year year age age
QGV Q2 1987 2003 1 8 0.25 0.5
TOT-QGV Q2 1987 2003 1 8 0.25 0.5
ries weights :
red time weighting applie d
er = 3 over 20 years
ility analysis :
hability independent of stock size for all ages
hability independent of age for ages >= 6
al population estimation :
ivor esti mates shrunk towards the m ean F
e final 5 years or the 5 oldest ages.
of the mean to which the estimates are shrunk = 1.500
mum standard error for population
ates derived from each fleet = .300
weighting n ot applied
converged after 32 iterations
sion wei ght s
0.751 0.82 0.877 0.921 0.954 0.976 0.99 0.997 1
mor talit ies
e 199419951996199719981999200020012002
e 5.2.15. - Bay of Biscay (FUs 23-24): XSA tuning diagnostics.
FLEET
FLEET
Time se
Tape
Pow
Catchab
Catc
Catc
Termin
Surv
of th
S.E.
Mini
estim
Pr ior
Tuning
Re gre s
1
Fish ing
Ag
1 0.018 0.016 0.016 0.02
2 0.32 0.338 0.279 0.41
3 0.61 0.667 0.602 0.72
4 0.646 0.648 0.707 0.67
5 0.517 0.6 0.619 0.45
6 0.434 0.539 0.484 0.34
7 0.605 0.507 0.528 0.23
8 0.544 0.629 0.43 0.27
Tabl
...continued overleaf
WGNEPH Repo

...continued overleaf
XSA population numbers (Thousands)
AGE
YEAR 12345678
1994 585000 444000 247000 10 50 00 3 640 0 1390 0 5 32 0 2 710
1995 595000 426000 251000 10 40 00 4 280 0 1690 0 7 04 0 2 260
1996 578000 434000 237000 10 00 00 4 250 0 1830 0 7 69 0 3 300
1997 508000 422000 256000 10 10 00 3 850 0 1780 0 8 79 0 3 530
199 8 474 000 36 80 00 2160 00 9 68 00 4 0000 1910 0 9 80 0 5430
199 9 557 000 34 40 00 1990 00 8 91 00 4 0400 1760 0 8 41 0 4220
200 0 682 000 40 70 00 2000 00 8 93 00 3 7600 1780 0 8 95 0 4190
200 1 636 000 50 00 00 2450 00 9 09 00 3 8700 1710 0 9 18 0 4930
2002 525000 465000 291000 10 60 00 3 740 0 1640 0 7 55 0 4 590
2003 452000 381000 260000 12 10 00 4 830 0 1950 0 9 16 0 4 640
Estimated population abundance at 1st Jan 2004
0 328000 221000 125000 57500 22500 9750 4790
Taper weighted geometric mean of the VPA populations:
5 84 000 44 00 00 24 40 00 10 20 00 4 040 0 1740 0 8 00 0 3 720
Standard error of the weighted Log(VPA populations) :
0.1 607 0.15 39 0. 12 36 0. 09 45 0.080 9 0.083 5 0 .163 7 0.2721
Log catch ability residu als.
Fleet : FLEET QGV Q2
Age 1987 1988 19 89 1990 1991 199 2 1 993 1994 1995
1 1.16 1.55 1.23 0.93 -0.4 -0.0 7 -0.3 6 -0.09 -0.18
2 0.49 0.68 0.49 -0.04 -0.37 -0.12 -0.19 -0.24 -0.24
3 0.1 0.34 -0.15 -0.44 -0.38 -0.21 -0.28 -0.08 -0.17
4 - 0. 05 0.17 -0.3 -0 . 15 -0 .2 3 - 0. 2 -0. 19 -0. 12 - 0. 38
5 -0 .2 - 0. 09 - 0. 21 -0 . 14 -0 .2 5 - 0.1 -0.0 1 -0.39 -0.3
6 -0.23 -0 .2 0. 08 0. 2 -0 .2 6 -0 .2 1 0.3 4 -0. 32 - 0. 23
7 -0.05 - 0.17 0. 14 0 .14 -0 .15 -0 .44 0.3 2 -0. 07 - 0. 25
8 -0.03 0. 22 0.16 0. 07 -0 .1 5 -0 .0 8 0. 35 -0.03 - 0.12
Age 1996 1997 19 98 1999 2000 200 1 2 002 2003
1 -0.03 0. 05 - 0. 04 -0 . 21 -0 .4 9 0 .01 0 . 2 0.04
2 -0.34 0. 19 0.11 0. 11 -0 .0 6 0 .1 3 0 . 3 -0. 04
3 -0.13 0. 24 0.08 0. 14 -0 .0 3 0 .2 9 0.3 7 -0. 14
4 0.05 0.16 0.03 0 .17 0.09 0.48 -0.01 -0.06
5 0.12 -0.06 0.04 0.16 0.12 0.54 -0.09 0.06
6 0.05 - 0. 16 0.16 -0 .04 0 0 .62 -0 . 2 -0. 01
7 0.19 - 0. 46 0.24 0. 11 - 0. 3 0.31 -0.5 1 -0.02
8 0.12 - 0. 14 0.18 0. 01 -0 .0 3 0 .3 8 -0. 14 0.14
Mean log catchability and stan dard error of ages with catchability
in de pen de nt of ye ar cla ss str eng t h an d cons ta nt w.r .t. ti me
Age 12345678
Mean Log q -13. 2301 - 9. 5792 - 8.8765 -8. 58 68 -8. 560 7 - 8. 634 - 8.63 4 -8. 634
S.E(Log q) 0.4171 0.2427 0.2367 0.2202 0.2351 0.2621 0.3034 0.1855
Table 5.2.15. - Bay of Biscay (FUs 23-24): XSA tuning diagnostics (continued).
WGNEPH Report 2004
46

rt 2004 47
me.
No Pts Reg s.e Mean Q
8 17 0.36 -13.96
1 17 0.24 -10.31
6 17 0.22 -9.61
0 1 7 2.3 5 -9. 3 2
2 17 0.23 -9.29
3 17 0.13 -9.37
3 17 0.25 -9.43
1 17 0.18 -9.32
Regr
Ages
Age
Fle et
Age
Age
Mean
in de
Mean
S.E (L
Regression stati stics :
Ages with q independent of year class strength and constant w.r.t. ti
Age Slope t-value Intercept RSquare
1 0.77 0.341 13.81 0.1
2 0.85 0.325 10.72 0.3
3 0.75 0.466 10.31 0.2
4 10.76 - 1.303 -12.22
5 1.01 -0.008 9.29 0.1
6 0.52 1.06 9.56 0.3
7 0.85 0.339 9.36 0.3
8 0.97 0.171 9.28 0.7
Ta
ession statistics :
with q independent of year class strength and constant w.r.t. time.
Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
1 0.67 0 .612 1 3.25 0.26 17 0.29 -13.23
2 0.86 0 .327 1 0.06 0.35 17 0.22 -9.58
3 1.03 -0.053 8.76 0.2 17 0.26 -8.88
4 - 2. 24 -2 .503 18. 13 0 .06 1 7 0 .41 -8.5 9
5 1 0 .004 8.57 0.11 17 0 .25 -8.56
6 0.6 0.684 9.08 0.23 17 0.16 -8.63
7 0.69 0 .798 8.79 0.4 17 0 .2 1 -8 . 7
80.781.561 8.50.83 170.13-8.58
: FLEET TOT-QGV Q 2
1 987 1988 1989 1990 199 1 199 2 1 99 3 1994 1995
1 1.29 1.09 1.26 0.88 -0.19 0.01 -0.59 -0.07 0.05
2 0.61 0.22 0.52 -0.09 -0.16 -0.04 -0.41 -0.22 -0.01
3 0.22 -0.12 -0.13 -0.49 -0.18 -0.13 -0.5 -0.06 0.07
4 0.07 - 0. 29 - 0. 27 -0.2 -0 .0 2 -0 .1 2 -0. 4 2 - 0.1 -0.15
5 -0.07 - 0.55 - 0.18 - 0.19 -0.04 -0.0 2 -0. 2 4 -0. 37 - 0. 06
6 -0.11 -0.66 0.11 0.15 -0.05 -0.14 0.12 -0.3 0.01
7 0.07 - 0. 63 0.16 0. 09 0 .0 5 -0 .3 7 0.0 9 -0. 05 - 0. 02
8 0.09 - 0.24 0. 19 0 .02 0.06 0 0.13 -0.01 0. 11
1 996 1997 1998 1999 200 0 200 1 2 00 2 2003
1 0.15 0.29 0.14 -0.53 -0.55 -0.23 0.27 -0.08
2 -0.15 0. 43 0.29 -0.2 -0 .1 2 -0 .1 2 0. 3 7 -0. 16
30.060.480.26-0.17-0.090.050.44-0.26
4 0. 24 0 .4 0. 21 - 0 . 15 0 .0 3 0 .2 3 0. 0 5 -0. 18
5 0.31 0.19 0.22 -0.15 0.06 0.3 -0.03 -0.06
60.230.080.34-0.36-0.060.37-0.13-0.13
7 0.38 - 0. 22 0.41 -0.2 -0 .3 7 0 .0 7 -0. 4 4 -0. 13
8 0.31 0.1 0.36 -0.31 -0.09 0.14 -0.07 0.02
log catchabilit y and standard error of ages with catchabili ty
pendent of year class str eng t h an d con s tant w.r.t. ti me
Age 12345678
Log q -13. 9 642 -1 0. 31 33 - 9.6106 -9. 32 09 -9. 294 8 -9.3681 -9.368 1 -9.3 681
og q) 0.4516 0.27 0.28 33 0.2 25 0 .214 7 0 .242 4 0 .287 2 0. 1873
ble 5.2.15. - Bay of Biscay (FUs 23-24): XSA tuning diagnostics (continued).
...continued overleaf
WGNEPH Repo

...continued overleaf
Terminal year survivor an d F summaries :
Age 1 Cat chabi li ty consta nt w.r .t. tim e and de pe nd en t on ag e
Year cl ass = 2002
Fleet Estim ated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
FLEET QGV Q2 3429480.4340010.5160.019
FLEET TOT-QGV Q2 3045060.470010.440.022
F shrinkage mean 421469 1.5 0.044 0.016
Wei ghte d pr edi c tion :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
328439 0.31 0.06 3 0.181 0.02
Age 2 Cat chabi li ty consta nt w.r .t. tim e and de pe nd en t on ag e
Year cl ass = 2001
Fleet Estim ated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
FLEET QGV Q2 229696 0.247 0.111 0.45 2 0.503 0.283
FLEET T OT-QGV Q2 213214 0.253 0.191 0.76 2 0.479 0.302
F shrinkage mean 206317 1.5 0.018 0.311
Wei ghte d pr edi c tion :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
221211 0. 18 0.08 5 0.452 0.29 3
Age 3 Cat chabi li ty consta nt w.r .t. tim e and de pe nd en t on ag e
Year cl ass = 2000
Fleet Estim ated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
FLEET QGV Q2 129638 0.193 0.142 0.73 3 0.498 0.469
FLEET T OT-QGV Q2 120822 0.196 0.211 1.07 3 0.486 0.496
F sh rin k ag e me an 95749 1 .5 0. 01 6 0.59 4
Wei ghte d pr edi c tion :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
124679 0.14 0.1 7 0.76 0.484
Age 4 Cat chabi li ty consta nt w.r .t. tim e and de pe nd en t on ag e
Year cl ass = 1999
Fleet Estim ated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
FL EE T QG V Q2 60 198 0 .174 0. 14 0. 8 4 0. 49 6 0.47 9
F LEET TOT -QGV Q2 55 316 0 .176 0.1 72 0 .98 4 0.48 9 0. 512
F sh rin k ag e me an 44432 1 .5 0. 01 5 0.60 6
Wei ghte d pr edi c tion :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
57490 0. 12 0 .1 9 0.783 0. 49 7
Table 5.2.15. - Bay of Biscay (FUs 23-24): XSA tuning diagnostics (continued).
WGNEPH Report 2004
48

rt 2004 49
F
3 0.39 8
for age) 6
N Scaled Estima ted
Weights F
3 8 0.487 0.458
3 8 0.501 0.49 3
0.012 0.473
F
3 0.47 5
Age
Year
Fleet
FLEE
F LEE
F sh
Wei g
Survi
at en
Age
Year
Fleet
FLEE
FLEE
F sh
Wei g
Survi
at en
Age
Year
Fleet
FLEE
FLEE
F sh
Wei g
Survivors Int Ext N Var
at end of year s.e s.e Ratio
4791 0. 11 0.06 15 0.5 1
Age 8 Catchabili ty constant w.r.t. time and age (fixed at the value
Year cl ass = 1995
Fleet Estim ated Int Ext Var
Survivors s.e s.e Ratio
FLEET QGV Q2 2353 0.152 0.142 0.9
F LEE T T OT-Q GV Q 2 2 148 0. 15 0 .109 0 .7
F shrinkage mean 2263 1.5
Wei ghte d pr edi c tion :
Survivors Int Ext N Var
at end of year s.e s.e Ratio
2247 0. 11 0.08 17 0.7 8
Ta
5 Cat cha bi li ty con stant w.r.t. tim e an d de pe nd en t on ag e
cl as s = 1998
Estimated Int Ext Var N Scaled Estima ted
Survivors s.e s.e Ratio Weights F
T QGV Q2 23550 0.164 0.059 0.36 5 0.495 0.497
T T OT- QGV Q 2 21525 0 .165 0. 06 0 .37 5 0.49 1 0. 533
rin k age me an 21 033 1 .5 0.01 5 0.543
hte d pr edi c tion :
vors Int Ext N Var F
d of year s.e s.e Ratio
22496 0. 12 0.04 11 0.3 45 0. 51 5
6 Cat cha bi li ty con stant w.r.t. tim e an d de pe nd en t on ag e
cl as s = 1997
Estimated Int Ext Var N Scaled Estima ted
Survivors s.e s.e Ratio Weights F
T QGV Q2 10186 0.157 0.082 0.52 6 0.495 0.43
T TOT -QGV Q2 9341 0.158 0.057 0.36 6 0.493 0.461
rinkage mean 9215 1.5 0.013 0.466
hte d pr edi c tion :
vors Int Ext N Var F
d of year s.e s.e Ratio
9748 0. 11 0.05 13 0.4 22 0. 44 5
7 Catchability constant w.r.t. time and age (fixed at the value for age) 6
cl as s = 1996
Estimated Int Ext Var N Scaled Estima ted
Survivors s.e s.e Ratio Weights F
T QGV Q2 4992 0.156 0.098 0.63 7 0.485 0.385
T TOT-QGV Q2 4611 0.155 0.07 0.45 7 0.50 3 0.411
rinkage mean 4540 1.5 0.012 0.416
hte d pr edi c tion :
ble 5.2.15. - Bay of Biscay (FUs 23-24): XSA tuning diagnostics (continued).
WGNEPH Repo

WGNEPH Report 2004
-term trends in landings, effort, LPUEs and mean sizes of Nephrops .
2005
Effort - French Nephrops trawlers
0
100
200
300
400
500
600
700
800
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Effort ('000 hours)
2005
Mean sizes (mean sizes of catches estimated )
22
26
30
34
38
42
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Mean size (mm carapace length)
Catch Mal < 35 mm CL
Catch Fem < 35
Landings Mal < 35
Landings Fem < 35
Landings Mal > 35
Landings Fem > 35
Figure 5.2.1. - Bay of Biscay (FUs 23-24): Long
Landings - France
0
1000
2000
3000
4000
5000
6000
7000
8000
1960 1965 1970 1975 1980 1985 1990 1995 2000
Landings (tonnes)
LPUE - French Nephrops trawlers
0
2
4
6
8
10
12
14
16
18
1960 1965 1970 1975 1980 1985 1990 1995 2000
LPUE (kg/hour)
total
Le Guilvinec District
all ports Guilvinec District excluded
50

WGNEPH Report 2004 51
Figure 5.2.2. - Bay of Biscay (FU
0
1
2
3
4
5
6
7
1994 1995 1996 1997 1998 1999 2000
LPUE (kg/hour)
Qtr 2 Qt
s 23-24): Landings, effort and LPUEs by quarter and sex from French Nephrops trawlers.
LPUE - Females
0
1
2
3
4
5
6
7
8
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
LPUE (kg/hour)
Qtr 2 Qtr 4 Annual
2000 2001 2002 2003
Total
Qtr 1 Qtr 3
Females
Qtr 1 Qtr 3
Qtr 1 Qtr 3
Landings
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
1994 1995 1996 1997 1998 1999
Landings (tonnes)
Males
LPUE - Males
8
2001 2002 2003
r 4 Annual
Effort
0
50
100
150
200
250
300
350
400
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Quarterly effort ('000 hours)
0
100
200
300
400
500
600
Annual effort ('000 hours)
Qtr 4 TotalQtr 2

Figure 5. 2. 3. - Ba y of Bi scay (FUs 23 -24): L en gt h-f requen cy d is t ributions (in '000) o f N ephro ps landed
in 2000-2003. Males and females shown separately.
Male landings
0
2000
4000
6000
8000
100 00
120 00
140 00
15 20 25 30 35 40 45 50 55 60
Size (mm CL)
Number landed ('000
)
2000
2001
2002
2003
Female landings
0
2000
4000
6000
8000
100 00
120 00
140 00
15 20 25 30 35 40 45 50 55 60
Size (mm CL)
Number landed ('000
)
200 0
200 1
200 2
200 3
WGNEPH Report 2004
52

WGNEPH Repo
Figur e 5.2.4 . - Bay of Biscay (FU s 23-24) VPA diagnostics males and females combined :
Log catchability residu als for Le Gu ilvinec District Fleet Quar ter 2.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1987 1992 1997 2002
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1987 1992 1997 2002
6 7 8
rt 2004 53

Figur e 5.2.5 . - Bay of Biscay (FU s 23-24) VPA diagnostics males and females combined :
Log catchability residua ls for all ports fleet (Le Guilvine c excluded ) Qua rter 2.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1987 1992 1997 2002
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1987 1992 1997 2002
6 7 8
WGNEPH Report 2004
54

rt 2004 55
4): VPA diagnostics males an d females
spective analysis.
Fbar 2- 5
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
1980 1985 19 90
Fbar
1995 2000 2005
Recruitment
0
100000
200000
300000
400000
500000
600000
700000
800000
900000
1000000
1980 1985 199 0 19 95 2 00 0 20 05
Recruits (millions
Spawning Stock Biomass
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1980 198 5 1 99 0 1 995 2 000 20 05
SSB (tonnes
)
Figure 5.2.6. - Bay of Biscay (FU 23-2
combined : Retro
WGNEPH Repo

WGNEPH Report 2004
females combined : Trends in Landin
g
s, Fbar, Total Stock Biomass and Recruitment.
Fishing Mortality Fbar 2-5
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1980 1985 1990 1995 2000 2005
Fbar
Recruitment (age 1)
0
200
400
600
800
1000
1980 1985 1990 1995 2000 2005
Recruits (millions)
56
tonnes
Fi
g
ure 5.2.7. - Ba
y
of Bisca
y
(
FU 23-24
)
: Output VPA males and
Removals and Landings
0
1000
2000
3000
4000
5000
6000
7000
8000
1980 1985 1990 1995 2000
removals
landings
Total Stock Biomass
0
5000
10000
15000
20000
25000
1980 1985 1990 1995 2000 2005
TB (tonnes) all ages
all ages
ages 2-5 only

WGNEPH Repo
R = 0.799
Males and Females combined
Figur e 5.2.8. - Bay of Biscay (FU s 23 -24): E ffo rt and Fbar , and relationship
between them, for males and fem ales c ombined.
0
200
400
600
800
1980 19 85 1990 19 95 20 00 2005
Effort ('000 hours)
0.0 0
0.2 0
0.4 0
0.6 0
0.8 0
1.0 0
1.2 0
Fbar
Effor t Fbar
0.0 0
0.2 0
0.4 0
0.6 0
0.8 0
1.0 0
1.2 0
0 100 200 300 400 500 600 700 800
Effort ('000 hours)
Fbar
rt 2004 57

WGNEPH Report 2004
parison of 2003 and 2004 output VPA males and females combined
Fishing Mortality Fbar 2-5
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1980 1985 1990 1995 2000 2005
Fbar
2004 WG
2003 WG
Recruitment (age 1)
0
200
400
600
800
1000
1980 1985 1990 1995 2000 2005
Recruits (millions)
2004 WG
2003 WG
2005
58
tonnes
Fi
g
ure 5.2.9. - Ba
y
of Bisca
y
(
FU 23-24
)
: Com
Removals and Landings
0
1000
2000
3000
4000
5000
6000
7000
8000
1980 1985 1990 1995 2000
removals
landings
Total Stock Biomass
0
5000
10000
15000
20000
25000
1980 1985 1990 1995 2000
TB (tonnes) all ages
2004 WG
2003 WG

WGNEPH Report 2004 59
Figure 5.16.11. - Bay of Biscay (FU 23-24): Short-term predictions of relative changes in landings and
SSB over two years, based on output of VPA with status quo F in the intermediate year.
Males and Females combined
20
40
60
80
100
F multiplier Absolute FbarReference point
Fleet1 Landin
g
s Fbar
(
2-5
)
1.0000 0.388
9
0.3853 0.1498
FMax
Figure 5 .16 .1 0. - Bay of Biscay (FUs 23 -24): Y/ R an al ysi s base d on output VPA:
Relative changes in long-term Y/R and long-term SSB/R upon relative changes in effort.
Males and females combined.
0.6164 0.2397
F0.1
Males and Females combined
-50
-40
-30
-20
-10
0
10
20
30
40
50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
% Cha ng e in Effort
% C hange in Y/R and SSB/ R
SSB/R long-term Landings Y/R long- term
-100
-80
-60
-40
-20
0
-100 -80 -60 -40 -20 0 20 40 60 80 100
% change in effort
% change in landings or SSB
Landings in 2005 vs 2004 SSB in 2006 vs 2004

WGNEPH Report 2004
Figure 5. 2. 12 Bay of Biscay males and females combined
Stock numbers of recruits and their source for recent year classes used in
predictions, and the relative (%) contributi
Year-class 2000 2001 2002 2003
Stock No. (thousands) 636438 524521 609152 609152
of 1 year-olds
Source XSA XSA GM 90-01 GM 90-01
Status Quo F:
% in 2004 landings 29.9 29.3 6.3 0.0
% in 2005 17.1 23.6 33.7 6.3
% in 2004 TB 18.4 20.9 22.6 13.8
% in 2005 TB 11.1 14.4 23.9 22.5
% in 2006 TB 6.8 8.7 16.4 23.8
GM : geometric mean recruitment
Bay of Biscay males and females c
a ) 2005 landings
ons to landings and TB (by weight) of these year classes
2004
609152
GM 90-01
-
0.0
-
13.8
22.4
ombined : Year-class % contribution to
b ) 2006 T B
2000
XSA 2001
XSA
2002
GM 90-01
2003
GM 90-01
2004
GM 90-01
2000
XSA
2001
XSA
2002
GM 90-01
2003
GM 90-01
2004
GM 90-01
60

(a) Relative changes in long-term Y/R upon relative changes in overall F (fishing effort)
assuming a constant selection pattern
(b) Relative changes in long-term Y/R for various fishing patterns
assuming a constant overall F (fishing effort)
-100
-80
-60
-40
-20
0
20
40
60
-100 -80 -60 -40 -20 0 20 40 60 80 100
% Change in F
% Change in Y/R
0
20
40
60
Figure 5.2.13. - Bay of Biscay (FUs 23-24): Relative changes in Y/R upon (a) changes in fishing effort
and constant selection pattern, and (b) changes in selection pattern and constant effort.
-100
-80
-60
-40
-20
1 * 00%
1 * 60%
2 * 20%
2 * 80%
3 * 40%
3 * 100%
4 * 60%
5 * 20%
5 * 80%
6 * 40%
6 * 100%
7 * 60%
8 * 20%
8 * 80%
9 * 40%
9 * 100%
First age caught * % decrease in F at age
% Change in Y/R
improvement in fishing pattern
(selectivity/tactic)
WGNEPH Report 2004 61

WGNEPH Report 2004
62
0
1000
2003 2004
25%
50%
75%
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2003 2004 2005
F-multiplier
25%
50%
75%
Status quo F with random R (within 1 990-2001)
SSB
2005 2006 2007 2008 2009 2010 2011 2012 2013
25%
50%
75%
Landings
2005 2006 2007 2008 2009 2010 2011 2012 2013
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
2003 2004
SSB (tonnes)
2000
3000
4000
5000
tonnes
Relative F
2006 2007 2008 2009 2010 2011 2012 2013
Figure 5.2.14. - Bay of Biscay: Medium-term projections based on a scenario of status quo F and random recruitment within range of 1990-2001 values. Left-
hand column: S2 - no improvement in fishing pattern. Right-hand column: S3 - improved fishing pattern from 2005 onwards.
Status quo F with random R (within 1 990-2001)
50% spared at ages 1 and 2 in 2005 onwards
SSB
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
SSB (tonnes)
25%
50%
75%
Landings
0
1000
2000
3000
4000
5000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
tonnes
25%
50%
75%
Relative F
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2003 2004 2005 2006 2007 200 8 2009 2010 2011 2012 2013
F-multiplier
25%
50%
75%

WGNEPH Report 2004 63
Constant landings of 3500 t for 2004 onw ards
SSB
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
SSB (tonnes)
25%
50%
75%
Landings
0
1000
2000
3000
4000
5000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
tonnes
25%
50%
75%
Relative F
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
F-multiplier
25%
50%
75%
Constant landings of 3500 t for 2004 onw ards
50% spared at ages 1 and 2 in 2005 onwards
SSB
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
SSB (tonnes)
25%
50%
75%
Landings
0
1000
2000
3000
4000
5000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
tonnes
25%
50%
75%
Relative F
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
F-multiplier
25%
50%
75%
Figure 5.2.15. - Bay of Biscay: Medium-term projections based on a scenario of constant landings of 3500 t for 2004 onwards and random recruitment within
range of 1990-2001 values. Left-hand column: S5 - no improvement in fishing pattern. Right-hand column: S6 - improved fishing pattern from 2005 onwards.

WGNEPH Report 2004
64
0
1000
2003 2004 200
50%
75%
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2003 2004 2005
F-multiplier
25%
50%
75%
Constant landings of 3700 t for 2004 onw ards
SSB
5 2006 2007 2008 2009 2010 2011 2012 2013
25%
50%
75%
Landings
5 2006 2007 2008 2009 2010 2011 2012 2013
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
2003 2004 200
SSB (tonnes)
2000
3000
4000
5000
tonnes
25%
Relative F
2006 2007 2008 2009 2010 2011 2012 2013
Figure 5.2.16. - Bay of Biscay: Medium-term projections based on a scenario of constant landings of 3700 t for 2004 onwards and random recruitment within
range of 1990-2001 values. Left-hand column: S8 - no improvement in fishing pattern. Right-hand column: S9 - improved fishing pattern from 2005 onwards.
Constant landings of 3700 t for 2004 onw ards
50% spared at ages 1 and 2 in 2005 onwards
SSB
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
SSB (tonnes)
25%
50%
75%
Landings
0
1000
2000
3000
4000
5000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
tonnes
25%
50%
75%
Relative F
0
0.2
0.4
0.6
0.8
1
1.2
1.4
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
25%
50%
75%

SSB
0
5000
10000
15000
20000
25000
30000
35000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
SSB (tonnes)
S1
S2
S3
S4
S5
S6
S7
S8
S9
Landings
0
1000
2000
3000
4000
5000
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
tonnes
S1
S2
S3
S4
S5
S6
S7
S8
S9
Figure 5.2.17. - Bay of Biscay: Comparison of medium-term projection
scenarios S1-S9 (see text).
Relative F
0
0.2
0.4
0.6
0.8
1
1.2
2003 2004 2005 2006 2007 2008 2009 2010 2011 2012 2013
F-multiplier
S1
S2
S3
S4
S5
S6
S7
S8
S9
WGNEPH Report 2004 65

WGNEPH Report 2004
66
Figure 5.2.18. - Bay of Bisc
0
5000
10000
15000
20000
25000
1987 1992
TB (tonnes)
WG 2004
2%
4%
ay (FUs 23-24): Results of assessments assuming 2% or 4% annual gains in efficiency of fishing operations compared with the
standard WG 2004 assessment.
ning Stock Biomass
92 1997 2002
Fbar 2-5
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1987 1992 1997 2002
Fbar
WG 2004
2%
4%
Recruitment (age 1)
0
200000
400000
600000
800000
1000000
1987 1992 1997 2002
Recruits ('000)
WG 2004
2%
4%
Total Stock Biomass
1997 2002
Spaw
0
4000
8000
12000
16000
20000
1987 19
SSB (tonnes)
WG 2004
2%
4%

5.3 Management Area O
ICES description VIIIc
Functional Units North Galicia (FU 25)
Cantabrian Sea (FU 31)
The statistical rectangles comprised in this Management Area and its constituent Functional Units are shown in Figure
5.1.3.
5.3.1 North Galicia (FU 25)
Description of the fisheries
Spain
Since the decline of the main target species (southern hake) in the area, the bottom fisheries in the North and Northwest
Spain have targeted a variety of species, including hake, anglerfish, megrim, horse mackerel, mackerel. At present, the
trawl fleet comprises three components: baca bottom trawl, great vertical opening bottom trawl and bottom pair trawl,
each targeting a different species. Only the baca bottom trawl, using a codend mesh size of 65 mm, catches Nephrops.
An update of the description of these fisheries was given in STECF (2002) and SGMOS (2003).
Trends in landings, effort, CPUE, LPUE and mean size
Table 5.3.1 Landings by country, 1994-2003
Table 5.3.2 Effort and CPUEs Spanish fleet, 1994-2003
Table 5.3.3 Mean sizes of Nephrops in landings, Spanish data, 1994-2003
Figure 5.3.1 Long-term trends in landings, effort, CPUE and mean size
Figure 5.3.2 Landings by sex + Quarterly plots of effort and CPUEs by sex, 1994-2003
Landings, effort, CPUE, LPUE and mean size
Landings were reported only by Spain. The long-term series of the landings shows various phases, but the overall trend
is clearly downward (Figure 5.3.1). Landings declined from the peak values in 1975 and 1978 of about 700 t, fluctuated
around 425 t during 1979-92 before a further decline to between 210 t and 280 t in 1993-97. More recently, the landings
have continued to decline. There was slight increase to 143 t in 2002, although the fishery was virtually closed during
November and December, owing to an oil spill off Spain’s NW coast. Landings were 89 t in 2003 (Table 5.3.1), but the
fishery remained practically closed from January to April 2003, and during the rest of the year the monthly landings
were slightly below 2002 levels.
Fishing effort data are available for the A Coruña trawler fleet (Figure 5.3.1), which accounts for most of the
Nephrops landings from FU 25. The overall trend in effort is decreasing, with current effort being approximately half
the level in 1995. The long time series of effort shows a marked decrease between 1976 and 1987, then effort remained
quite stable (fluctuating around 5000 days fishing) until 1993. Since then, fishing effort decreased from 1999 onwards
(Table 5.3.2). Effort in this fishery is directed primarily at a set of demersal and bottom species, with Nephrops being a
by-catch and making only a small contribution to overall fishery landings.
LPUE shows an overall decreasing trend (Table 5.3.2 and Figure 5.3.1). After a period with quite variable LPUE
between 1975 and 1991, values gradually dropped from 13.5 kg/day * average BHP/100 in 1992 to 3.9 kg/day *
average BHP/100 in 2000. LPUE increased slightly after this, but by 2003 had declined to 5.2 kg/day * average
BHP/100.
Fishing effort generally shows no seasonal pattern (Figure 5.3.2), although as described above, fishing effort in the
latter part of 2002 and the first part of 2003 was reduced. Male and female LPUE peak in the second and third quarter.
Mean size
The long-term data series of mean sizes in the landings shows fluctuations about a trend of increase in both males and
females (Figure 5.3.1). Since 2001 the increase in mean size of male and female (42.5 mm and 39.1 mm respectively in
2003) coincides with an increase in mesh size (Table 5.3.3 and Figure 5.3.1).
Trawl survey abundance indices
Table 5.3.4 Nephrops abundance indices from trawl surveys, 1994-2003
WGNEPH Report 2004 67

Table 5.3.4 gives the abundance indices of Nephrops off North Galicia, derived from the autumn bottom trawl surveys
carried out to estimate hake recruitment and to collect information on the relative abundance of demersal species. Data
for 2003 are not available. In general, these results show a higher degree of variability between years than the
commercial LPUEs. The table also gives an indication of the relatively low density of Nephrops in this FU compared
with more northerly Nephrops stocks.
Data and biological inputs for analytical assessments
Table 5.3.5 Sampling data and input parameters
Annual length compositions of the landings are available since 1980 for the A Coruña trawl fleet. For analytical
assessment, the data series 1984-2003 was used. These data were raised to the total landings from FU 25. Nephrops
discards are negligible in this fishery (estimates for 1994, 1997 and 1999 ranged from 0.4 to 2.4 % by weight of the
catches).
There is no new biological information on growth, maturity, length-weight coefficients and natural mortality
applicable to this FU, and the input parameters (Table 5.3.5) are the same as the ones used in previous assessments
(ICES, 2003a).
General comments on quality of data and inputs
Table 5.3.6 Assessment deficiencies in 2004
Issues that may generally cause problems for assessment of Nephrops are highlighted in Section 10. Assessment
deficiencies specific to FUs 23-24 are summarised in Table 5.3.6.
The monthly sampling programme of the landings from this FU is considered to be at a sufficient level of intensity
to produce reliable LFDs of the landings. Fishery statistics and fishing effort data are believed to be reliable, although
during the period 1998-2001 the quality of the data deteriorated.
Type of assessments carried out and why
The long data series were considered to be adequate for an age-based assessment. The XSA assessment was considered
acceptable in terms of trends.
Age based assessments (VPA)
Males
Table 5.3.7 XSA settings males
Table 5.3.9 Output VPA males: Fs-at-age
Table 5.3.11 Output VPA males: Long-term trends in landings, Fbar, TB and recruitment
Table 5.3.23 Full listing of VPA input and output data tables
Table 5.3.25 Full listing of XSA diagnostic output
Figure 5.3.3 VPA diagnostics males: Log catchability residuals
Figure 5.3.5 VPA diagnostics males: Retrospective analyses
Figure 5.3.7 Output VPA males: Long-term trends in landings, Fbar , TB and recruitment
Figure 5.3.9 Output VPA males: Plots of Fbar vs. effort
A single fleet assessment was carried out using Spanish length composition and effort data for 1984-2003. The
Lowestoft VPA program was used on ‘age’ groups generated by slicing the length distributions with the L2AGE
program. The slicing procedure generated 9 ‘age’ groups and ‘age’ 10+ was adopted as the plus group. The first age for
the VPA was age 2. The XSA tuning options are summarised in Table 5.3.7. The log catchability residuals from the
final run (Figure 5.3.3) are noisy for age 2, and ages 3-5 show some year effects. The large residuals probably result
from the fishery being not primarily directed at Nephrops.
Retrospective analyses are ‘noisy’, but show fairly consistent stock trends over recent years (Figure 5.3.5). The
convergence in the recruitment is less evident than in SSB and Fbar. Similar results were obtained in the previous
assessment (ICES, 2003a). Different shrinkage strengths for the mean F were tried, and no great differences were found.
A final weight of 0.5 was adopted.
The trends in the estimates of yield, Fbar, total stock biomass (TB) and recruitment are plotted in Figure 5.3.7. Fbar
was high in 1984-85, 1989, 1992-93 and 1995, but has decreased since then to 0.4 in 2003. TB has declined almost
continuously since the beginning of the time series, and particularly from 1991 onwards. The current estimate is at the
lowest observed level. Recruitment was high in the first period of the time series (1984-86) and in 1989-90. Since then
the recruitment has dramatically fallen and recent estimates are exceptionally low.
WGNEPH Report 2004
68

The correlation between Fbar and effort is significant (r = 0.69, p < 0.01) (Figure 5.3.9), indicating that the VPA
has accounted for the pattern of exploitation over the years.
Females
Table 5.3.8 XSA settings females
Table 5.3.10 Output VPA females: Fs-at-age
Table 5.3.12 Output VPA females: Long-term trends in landings, Fbar, TB and recruitment
Table 5.3.24 Full listing of VPA input and output data tables
Table 5.3.26 Full listing of XSA diagnostic output
Figure 5.3.4 VPA diagnostics females: Log catchability residuals
Figure 5.3.6 VPA diagnostics females: Retrospective analyses
Figure 5.3.8 Output VPA females: Long-term trends in landings, Fbar, TB and recruitment
Figure 5.3.9 Output VPA females: Plots of Fbar vs. effort
The slicing procedure generated 10 ‘age’ groups (with the age 11+ a plus-group). The first age for the VPA was age 2.
The XSA settings are shown in Table 5.3.8. The log catchability residuals were quite noisy (Figure 5.3.4), particularly
for ‘age’ classes 2 to 4, and showed some evidence of year effects.
Retrospective analysis for females shows an overall lower convergence in Fbar, SSB and recruitment than for males
(Figure 5.3.6). A value of 0.5 shrinkage weights for the mean F was adopted for the final analysis.
Trends in the estimates of yield, Fbar, TB and recruitment are plotted in Figure 5.3.8. Fbar has been quite stable
throughout the time series, around a value of 0.2. TB has continuously declined since the beginning of the series. As
with the males, recruitment has continuously decreased through the time series. Recent recruitment estimates are
exceptionally low and represent less than 2% of the 1984 recruitment. The correlation coefficient between Fbar and
effort is significant (r = 0.49, p < 0.05) (Figure 5.3.9).
Y/R analysis based on outputs of VPA
Table 5.3.13 Long-term Y/R and SSB/R based on outputs of VPA: males
Table 5.3.14 Long-term Y/R and SSB/R based on outputs of VPA: females
Figure 5.3.10 Long-term Y/R and SSB/R based on outputs of VPA: males and females
The results of Y/R analysis (based on the outputs of VPA) indicate that for males current F is far above Fmax, but the
Y/R curve is very flat-topped and negligible gains in yield are predicted upon a reduction of F to Fmax (Table 5.3.13 and
Figure 5.3.10). For females, current F appears to be below Fma x (Table 5.3.14 and Figure 5.3.10).
Short-term predictions
Table 5.3.15 Males: Short-term predictions of landings and biomass, with status quo F in 2004
Table 5.3.16 Females: Short-term predictions of landings and biomass, with status quo F in 2004
Figure 5.3.11 Males and females: Short-term predictions of relative changes in landings and SSB over two years,
based on the output of VPA
Short term predictions were made using the MFDP package, for a single trawl fleet with no discards, using as
recruitment input for 2004-2006 the arithmetic mean of the last three years (2001-2003).
At status quo F, the prediction for males gives a decline in TB in 2006 of 30% relative to 2004. Even with zero F
in 2005, no increase in biomass is expected in 2006 (Table 5.3.15 and Figure 5.3.11). The predictions for females
indicate that status quo F would result in a 31% decrease in TB in 2006 relative to the biomass in 2004, and no
increases in TB would be expected even with zero F (Table 5.3.16 and Figure 5.3.11). These results are similar to those
obtained in the previous assessment (ICES, 2003a) and support the conclusion that stock biomass is critically low.
Management considerations
The overall trend shown in landings of Nephrops from the North Galicia FU 25 is of a strong decline. Landings have
dramatically decreased since 1992, in comparison with the early 1980s, and are now less than a quarter of this previous
level.
The assessment for FU 25 indicates that stock biomass and recruitment are at very low levels. Recent estimates of
recruits are less than 10% of the estimates in the early 1980s. XSA indicates drastic reductions in stock biomass and
recruitment since 1993.
The short-term predictions suggest that at current levels of fishing mortality the stock biomass will continue
decreasing (30% for males and females in 2006 relative to 2004). Even drastic reductions (80%) in fishing mortality
would not have significant short-term effects on the current trend of declining biomass.
WGNEPH Report 2004 69

5.3.2 Cantabrian Sea (FU 31)
Description of the fisheries
Spain
The description of these fisheries was updated and reported in STECF (2002) and SGMOS (2003). Mackerel and horse
mackerel contribute 80 % of the landed species by the baca bottom trawl fleet in the Cantabrian Sea, while hake and
Nephrops together represent only 1% of their total landings. Other trawl fleet components operating in the Cantabrian Sea
(great vertical opening trawl and pair trawl) do not impact on Nephrops.
Trends in landings, effort, LPUE and mean size
Table 5.3.17 Landings by country, 1994-2003
Table 5.3.18 Effort and LPUEs Spanish fleet, 1994-2003
Table 5.3.19 Mean sizes of Nephrops in catches, Spanish data, 1994-2003
Figure 5.3.12 Long-term trends in landings, effort, CPUE and mean size
Landings, effort and LPUE
Nephrops landings from FU 31 are reported only by Spain (Table 5.3.17). Landings data are available for the period
1983-2003 (Figure 5.3.12). Up to the mid-1990s, landings fluctuated between 90 and 177 t. The highest landings were
recorded in 1989 and 1990. Since 1996, however, landings have declined sharply, falling to 22 t in 2003, the lowest in
the time series. The effects of the recent change to 65 mm mesh size in the codend and a reduction in effort by bottom
trawlers fishing Nephrops are still to be quantified.
Fishing effort data include two bottom trawl fleets operating in the Cantabrian Sea (Avilés and Santander). The
available time series of effort shows a period of relative stability from the early 1980s to the beginning of the 1990s.
However, since 1992, effort shows a marked downward trend (Figure 5.3.12) interrupted by a brief period of stability
during the late 1990s. Fishing effort has continued to decline since 1999 (Table 5.3.18), and current effort is less than
half the 1999 value. The opportunistic use of other gears (great vertical opening, pair trawl) by these fleets makes a
strong contribution to effort reduction.
The LPUE data series show large fluctuations. In spite of the severe drop in both landings and effort, the LPUE
has remained stable at intermediate levels (Table 5.3.18 and Figure 5.3.12). This may suggest that the stock has
remained relatively stable, while fluctuations in effort and landings have been related to factors other than the state of
the Nephrops stock.
Mean size
Time series of mean sizes for male and female are available from 1988 to 2003 (Figure 5.3.12). Overall, mean size in
the landings show a long-term trend of increase in males, although since 1999 mean size seems to have remained stable
around 47 mm CL, and there is evidence of a dip in 2002. Mean size for females also shows a general increase through
the time series, but shows a sharp dip in 2002 (from 42.6 mm in 2001 to 38.1 mm in 2002), increasing again in 2003 to
40.6 mm (Table 5.3.19 and Figure 5.3.12).
Trawl survey abundance indices
Table 5.3.20 Nephrops abundance indices from trawl surveys, 1994-2003
Table 5.3.20 shows the abundance indices of Nephrops on the Cantabrian shelf, as derived from autumn bottom trawl
surveys carried out to estimate hake recruitment. The figure for 2003 is not available. The low average catch rates of
Nephrops for the Cantabrian shelf as a whole are explained by the fact that the spatial distribution of Nephrops is
restricted to two relatively small grounds (viz. off Cape Peñas and Basque Country) within the much larger area that
was surveyed.
Data and biological inputs for analytical assessments
In view of the very low levels of landings and fishing effort, an assessment of this FU was not performed. The last
assessment for this stock was conducted in 2002 (ICES, 2002a).
WGNEPH Report 2004
70

WGNEPH Report 2004 71
Management considerations
No new assessment was performed for FU 31. Given the low levels of landings and fishing effort in 2002 and 2003, the
WG considers that management considerations formulated in previous years (ICES, 2002a) remain an appropriate basis
for the management of this FU.
5.3.3 Summary for Management Area O
Table 5.3.21 Landings by FU and from Other rectangles, 1994-2003
Table 5.3.22 Landings by country, 1994-2003
MA O includes two FUs (North Galicia, FU 25 and Cantabrian Sea, FU 31). Landings from both FUs have declined
dramatically in recent years. XSA assessments of FU 25, and the very low levels of landings from FU 31, confirm the
results of previous assessments (ICES, 2002a, 2003a) indicating the collapsed status of the both stocks.
The agreed Nephrops TAC for division VIIIc (MA O) in 2004 is 180 t. In spite of the drastic reduction in TACs
from 720 t in 2001, landings in recent years 1998-2003 were below the TAC for 2003, and therefore the TAC is not
restrictive. At current fishing mortality, the Nephrops stocks in MA O will at best remain at very low levels.
ICES advice for 2002 -2004 was for a zero TAC. Based on the most recent assessments of the stocks and the very
unfavourable short term predictions, the WG has no basis on which to suggest any other catch option. It is relevant to
point out that in order to achieve this outcome, all fishing activity which imposes mortality on Nephrops would have to
be stopped.
A recovery plan for the southern hake and Iberian Nephrops fisheries has been prepared (SGMOS, 2003),
involving closures in areas of higher Nephrops abundance and effort reduction over a 5 to 10 year period.
Recommendations have been made to the EU, but the recovery plan is yet to be implemented. Given the present status
of Nephrops stocks in MA O, the implementation of an effort reduction scheme such as proposed for southern hake and
Nephrops in this recovery plan (SGMOS, 2003) is of the utmost urgency.

WGNEPH Report 2004
72
Spain Total
245 245
273 273
209 209
219 219
103 103
124 124
81 81
147 147
143 143
89 89
* provisional
Effort LPUE
5216 9.3
5538 8.4
4911 7.6
4850 7.9
4560 na
4147 6.0
4325 3.9
4262 7.3
3240 7.9
2693 5.2
* provisional na = not available
Males Females
36.6 34.7
37.1 35.8
37.0 34.7
36.5 35.1
39.4 37.5
37.3 36.8
38.0 36.7
37.4 35.8
39.0 37.1
42.5 39.1
* provisional
2002
2002
1995
1999
1996
1997
1998
Table 5.3.3. - North Galicia (FU 25): Mean sizes (mm CL) of male and female Nephrops in
Spanish landings, 1994-2003.
Table 5.3.2. - North Galicia (FU 25): Effort (days fishing) and LPUE (kg/day * BHP/100) of
Spanish “bacas”, home port A Coruña, 1994-2003.
Year Catches
1994
2000
2001
2003*
2003*
1994
1995
1996
1997
1998
1999
2000
1996
1997
2001
1998
1999
Year
1994
1995
2003*
Year
2002
2000
2001
Table 5.3.1. - North Galicia (FU 25): Landings (tonnes) by country, 1994-2003.

WGNEPH Repo
Kg / 30 min haul No. / 30 min haul
MSC SE MSC SE
0.15 0.06 4.4 1.9
0.43 0.09 15.0 3.3
0.30 0.08 11.1 3.3
0.06 0.01 1.4 0.3
0.06 0.02 1.5 0.5
0.08 0.02 2.3 0.7
0.05 0.01 1.2 0.3
0.09 0.03 2.1 0.6
0.06 0.02 1.7 0.4
na na
na = not available
2002
1995
2001
2003
Year
1997
1998
1999
2000
1994
1996
Table 5.3.4. - North Galicia (FU 25): Mean stratified catches (MSC) and standard errors
(SE) of Nephrops in bottom trawl surveys off North Galicia, 1994-2003.
rt 2004 73

FU MA
FLEET GEAR
Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Qtr 4
Catch
Landings 2 9 13 11 136 9 4 0 15 111
Discards
Year 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994
Catch
Landings 35 28 51 68 69 70 72 68 101 99
Discards
Value
na
0.160
70
0.2
0.00043
3.160
0.160
70
0.2
28
0.080
60
0.2
0.00043
3.160
25
A Coruña
O
Trawl
Fariña (1984)
"
Fariña (1996)
ICES (1994a)
"
Assumed from Morizur (1982)
"
ICES (1994a)
"
"
ICES (1994a)
"
"
Fariña (1984)
Number of samples Number of samples
Number of samples
2003 2002
Mean
no. per
sample
INPUT PARAMETERS
Parameter
Discard Survival
MALES
Not aplicable - few discards (< 1 % on average)
Growth - K
Growth - L(inf)
Natural mortality - M
Length/weight - a
Size at maturity
Mature Growth
Length/weight - b
FEMALES
Immature Growth
Growth - K
Table 5.3.5. - North Galicia (FU 25): Input data and parameters.
Length/weight - b
Source
Mean
no. per
sample
Growth - K
Growth - L(inf)
Natural mortality - M
Length/weight - a
Growth - L(inf)
Natural mortality - M
WGNEPH Report 2004
74

WGNEPH Report 2004 75
Table 5.3.6. – North Galicia (FU 25): Assessment deficiencies 2004.
A 2
CSA N/A
N/A
LCA N/A
ure 1
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
XS
Tuning data 3 The tuned fleet is not Nephrops directed. High log catchability residuals in
several ages.
Fishery independent
methods
Assessment
method
Definition 1 The stock is widely distributed. There are other stocks in adjacent areas
(FU 26 West Galicia), but limits are well defined basing on the operating
trawl fleets.
Stock
Struct
Fish nition (Mix
targeted, multifleet)
1 Nephrops is a by catch of the bottom mixed fishery. Only the baca trawl
component fish Nephrops.
ery Defi ed,
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

WGNEPH Report 2004
Table 5.3.6. – North Galicia (FU 25): Assessment deficiencies 2004 (continued).
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Catch N/A
Landings 1 Landings data are extracted from the sale sheets. The accuracy of these
data is considered high, except for 1998-2001, when the information
sources failed.
Discards rates are very low, due to the high value of the species.
Effort 2 The fishing effort correspond to the total bottom trawl fleet, that fish for a
set of demersal and bottom species depending on marked forces.
Catch
statistics
LPUE 2 Depends on accounting of fishing effort on bottom fishery and not
exclusively on Nephrops.
Catch
Landings 1 The length frequency distributions of Nephrops were obtained by
sampling commercial landings at port. The monthly sampling programme
of the landings from this FU is considered to be at a sufficient level of
intensity.
Sampling
levels
Discards N/A
Discards 1
CPUE N/A
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.
76

77
WGNEPH Report 2004
Table 5.3.6. – North Galicia (FU 25): Assessment deficiencies 2004 (continued).
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Age and growth 2 Age compositions of removals were inferred by slicing the length
compositions.
Maturity 1 Female maturity data were obtained from an annual biological cycle.
Annual variability was not investigated. In the male assessment 100%
maturity is assumed. The sensitivity of the assessment to this approach has
not been investigated
Natural mortality 2 No experimental data on M have been made. There are not known
predators on Nephrops in the area, nor drastic temporal changes in the
environmental and habitat conditions. A standard value of M (0.2) for
males and females was adopted, in similar way to others Nephrops stocks.
Discard Mortality N/A
Escape Mortality N/A
Biological
parameters
Length/weight
coefficients
1 Length/weight relationship significant and derived from biological
sampling.
Fishing surveys 3 Data on Nephrops in surveys are collected as associated information.
Surveys are undertaken outside of the main season for Nephrops. Survey
design is not directed to estimate the Nephrops abundance.
Larval surveys N/A
Availability
of research
survey data
TV survey N/A
Availability
of other
information
Species composition 1 Programme for monitoring the species composition of the trawl fleet
continued as a rule. Database is updated annually.
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

WGNEPH Report 2004
25 MA O Males
FU
Age range
XSA Setting
Year range
Fleets used
Tuning ra
(3)
Prior fleet
Table 5.3.7. - North Galicia (FU 25): XSA settings used in the assessment - Males.
(1) A Co
(2)
78
Taper time
applied ?
Did tuning
Population
F shrinkage
First age at
Minimum
First age fo
First year Last year
1984 2003
Last age Plus group
9 Yes - 10+
First year Last year
1986 2003
Years used Ages used
1986-2003 2-9
No
2
4
Yes/No Type
Yes Tricubic over 20 years
Yes/No If Yes: Min. SE for Mean F
Yes 0.5
If Yes: Year range If Yes: Age range
1999-2003 6-10
Yes/No
Yes
0.3
Yes (17 iterations)
s
weighting
nge
converge after 30 iterations or less ?
weighting? Not relevant
shrinkage
Chosen from several trials
Default option
Default option
Default option
Chosen from several trials
Available data
which q is considered independent of age
in numbers
Available data
ruña fleet
Through examination of regression statistics and residuals
Through examination of catchability at age
Log SE for terminal population estimates
Choices Justification
r normal catchability independent analysis
Plus-group chosen such that proportion in catches was > 0.5 % but < 3.0 %
No individuals in age 1

25 MA O Females
First year Last year
1984 2003
Last age Plus group
10 Yes - 11+
First year Last year
1986 2003
Years used Ages used
1986-2003 2-10
No
2
6
Yes/No Type
Yes Tricubic over 20 years
Yes/No If Yes: Min. SE for Mean F
Yes 0.5
If Yes: Year range If Yes: Age range
1999-2003 7-11
Yes/No
Yes
0.3
No
Settings
imum Log SE for terminal population estimates
Choices Justification
rst age for normal catchability independent analysis
Plus-group chosen such that proportion in catches was > 0.5 % but < 3.0 %
)
No individuals in age 1
able 5.3.8. - North Galicia (FU 25): XSA settings used in the assessment - Females.
Available data
rst age at which q is considered independent of age
in numbers
Available data
) A Coruña fleet
Through examination of regression statistics and residuals
Through examination of catchability at age
Default option
Default option
Default option
Default option
Default option
tuning converge after 30 iterations or less ?
ior fleet weighting? Not relevant
pulation shrinkage
shrinkage
)
time weighting
eets used
ning range
ge range
ear range
FU
XSA
Min
Fi
(2
T
Fi
(1
Did
Pr
Po
F
(3
Taper
applied ?
Fl
Tu
A
Y
WGNEPH Report 2004 79

80
Age 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.02 0.030.030.020.010.000.000.010.010.050.020.010.020.010.000.010.000.010.010.01
3 0.45 0.340.190.180.260
4 0.87 0.660.570.420.850
5 0.86 0.800.660.551.020
6 1.14 1.390.590.870.861
7 1.61 1.440.870.850.601
8 0.77 2.701.460.860.351
9 1.06 1.410.820.680.711
+ grp 1.06 1.410.820.680.711
Age 1984 1985 1986 1987 1988 19
2 0.03 0.060.040.020.000
3 0.11 0.180.110.100.030
4 0.16 0.190.110.120.110
5 0.20 0.160.160.180.180
6 0.18 0.150.170.250.160
7 0.11 0.140.190.230.160
8 0.09 0.200.120.200.150
9 0.21 0.150.170.160.110
10 0.16 0.16 0.17 0.20 0.18 0.2
+ grp 0.16 0.160.170.200.180
Table 5.3.9. - North Galicia (FU 25): VPA Fs-at-age males.
Table 5.3.10. - North Galicia (FU 25): VPA
.050.100.450.300.130.250.250.220.390.080.140.070.210.340.15
.480.420.650.950.670.620.720.640.950.340.480.290.640.690.39
.950.530.771.051.050.841.080.910.990.620.600.350.590.570.42
.430.620.801.331.341.051.280.870.670.690.570.300.610.530.42
.820.830.670.851.090.851.021.230.530.550.490.250.320.470.38
.111.240.400.880.900.900.471.390.800.460.440.300.480.660.44
.120.760.650.930.900.750.800.850.600.600.500.390.500.490.41
.120.760.650.930.900.750.800.850.600.600.500.390.500.490.41
89 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
.000.010.020.000.010.020.020.020.010.000.010.010.030.030.01
.000.040.190.050.040.080.070.090.090.020.030.020.070.040.03
.020.070.240.180.040.110.130.140.200.050.070.030.090.090.05
.100.120.240.280.130.160.190.200.280.070.100.060.130.160.09
.250.180.220.290.260.250.290.220.340.150.210.130.130.170.13
.290.260.290.290.280.270.310.180.290.170.220.110.140.130.15
.380.250.310.330.250.220.310.200.300.190.220.110.130.160.20
.260.320.260.280.210.180.430.220.270.200.310.140.210.200.21
8 0.26 0.25 0.27 0.23 0.22 0.28 0.17 0.20 0.19 0.17 0.12 0.14 0.16 0.16
.280.260.250.270.230.220.280.170.200.190.170.120.140.160.16
Fs-at-age females.
WGNEPH Report 2004

WGNEPH Report 2004 81
.55
.54
.30
56
.40
.15
.17
.20
.15
.21
.26
.19
.20
.19
.28
.13
.16
.09
.12
.14
.12
Table 5.3.11. - North Galicia (FU 25): VPA output males.
ar
7
ar
8
'000 tonnes tonnes tonnes
1984 12609 985 985 371 0.38 1.12
1985 12128 832 832 302 0.36 1.07
1986 11197 778 778 219 0.28 0.68
1987 7005 784 784 225 0.29 0.67
1988 7262 794 794 323 0.41 0.84
1989 10303 686 686 221 0.32 1.17
1990 12230 682 682 140 0.21 0.60
1991 7837 754 754 272 0.36 0.72
1992 6196 654 654 286 0.44 1.04
1993 6179 480 480 183 0.38 1.04
1994 5629 450 450 153 0.34 0.84
1995 4860 422 422 158 0.37 1.03
1996 3321 355 355 128 0.36 0.91
1997 3115 301 301 125 0.42 0.79
1998 4167 261 261 58 0.22 0
1999 4023 296 296 71 0.24 0
2000 3646 325 325 54 0.17 0
2001 1717 336 336 109 0.32 0.54
2002 432 286 286 106 0.37 0.
2003 123 196 196 57 0.29 0
Average 01-03 0.50
'000 tonnes tonnes tonnes
1984 12829 1401 1247 144 0.12 0
1985 10800 1365 1236 175 0.14 0
1986 9726 1247 1140 145 0.13 0.15
1987 10998 1354 1222 186 0.15 0
1988 10535 1207 1070 121 0.11 0
1989 10300 1067 1067 155 0.15 0
1990 9290 1123 1012 140 0.14 0.18
1991 7967 1027 923 180 0.20 0
1992 6465 850 766 141 0.18 0.27
1993 6827 757 675 91 0.13 0
1994 5349 702 638 93 0.15 0
1995 4748 674 617 115 0.19 0.24
1996 4143 603 553 80 0.14 0
1997 4114 542 492 94 0.19 0
1998 3771 480 431 45 0.10 0
1999 2291 456 428 53 0.12 0
2000 1567 378 359 27 0.08 0
2001 891 349 339 38 0.11 0
2002 263 293 291 37 0.13 0
2003 160 256 254 32 0.13 0
Average 01-03 0.13
Recruits
Age 2
Total
Biomass SSB Catch
Year Yield/SSB Fb
4-
Table 5.3.12. - North Galicia (FU 25): VPA output females.
Recruits
Age 2
Total
Biomass SSB Catch
Year Fb
4-
Yield/SSB

rt 2004
Table 5.3.13. - North Galicia (FU 25): Long-term yield per recruit analysis of males.
MFYPR version 2a
Run: 1
Time and date: 18:38 28/03/04
Yield per results
FMult Fbar CatchNos
Y
ield Sto
0.0000 0.0000 0.0000 0.0000 5
0.1000 0.0402 0.1248 0.0108 4
0.2000 0.0804 0.2151 0.0169 4
0.3000 0.1206 0.2833 0.0205 4
0.4000 0.1607 0.3366 0.0225 3
0.5000 0.2009 0.3794 0.0236 3
0.6000 0.2411 0.4145 0.0242 3
0.7000 0.2813 0.4438 0.0245 3
0.8000 0.3215 0.4686 0.0245 3
0.9000 0.3617 0.4899 0.0244 3
1.0000 0.4019 0.5084 0.0242 2
1.1000 0.4420 0.5246 0.0240 2
1.2000 0.4822 0.5390 0.0238 2
1.3000 0.5224 0.5517 0.0235 2
1.4000 0.5626 0.5632 0.0233 2
1.5000 0.6028 0.5735 0.0230 2
1.6000 0.6430 0.5828 0.0228 2
1.7000 0.6831 0.5914 0.0226 2
1.8000 0.7233 0.5992 0.0224 2
1.9000 0.7635 0.6064 0.0222 2
2.0000 0.8037 0.6131 0.0220 2
Reference point F multiplier
A
bsolute F
Fbar(4-7) 1.0000 0.4019
FMax 0.7668 0.3081
F0.1 0.4105 0.1649
F35%SPR 0.5823 0.2340
ckNos Biomass SpwnNosJan SSBJan SpwnNosSpwn SSBSpwn
.5167 0.4270 5.5167 0.4270 5.5167 0.4270
.8949 0.3334 4.8949 0.3334 4.8949 0.3334
.4462 0.2697 4.4462 0.2697 4.4462 0.2697
.1078 0.2244 4.1078 0.2244 4.1078 0.2244
.8437 0.1910 3.8437 0.1910 3.8437 0.1910
.6321 0.1658 3.6321 0.1658 3.6321 0.1658
.4590 0.1464 3.4590 0.1464 3.4590 0.1464
.3148 0.1310 3.3148 0.1310 3.3148 0.1310
.1929 0.1187 3.1929 0.1187 3.1929 0.1187
.0886 0.1087 3.0886 0.1087 3.0886 0.1087
.9983 0.1005 2.9983 0.1005 2.9983 0.1005
.9195 0.0937 2.9195 0.0937 2.9195 0.0937
.8500 0.0879 2.8500 0.0879 2.8500 0.0879
.7883 0.0830 2.7883 0.0830 2.7883 0.0830
.7331 0.0788 2.7331 0.0788 2.7331 0.0788
.6836 0.0751 2.6836 0.0751 2.6836 0.0751
.6387 0.0720 2.6387 0.0720 2.6387 0.0720
.5980 0.0692 2.5980 0.0692 2.5980 0.0692
.5608 0.0667 2.5608 0.0667 2.5608 0.0667
.5266 0.0645 2.5266 0.0645 2.5266 0.0645
.4952 0.0626 2.4952 0.0626 2.4952 0.0626
WGNEPH Repo
82

WGNEPH Report 2004 83
MFYPR version 2a
Run: 1
Time and date: 18:42 28/03/04
Yield per results
FMult Fbar CatchNos
Y
ield
0.0000 0.0000 0.0000 0.0000
0.1000 0.0124 0.0456 0.0020
0.2000 0.0248 0.0855 0.0037
0.3000 0.0372 0.1207 0.0051
0.4000 0.0496 0.1520 0.0062
0.5000 0.0619 0.1801 0.0072
0.6000 0.0743 0.2054 0.0080
0.7000 0.0867 0.2284 0.0087
0.8000 0.0991 0.2493 0.0093
0.9000 0.1115 0.2685 0.0098
1.0000 0.1239 0.2862 0.0102
1.1000 0.1363 0.3025 0.0106
1.2000 0.1487 0.3176 0.0109
1.3000 0.1610 0.3317 0.0112
1.4000 0.1734 0.3449 0.0115
1.5000 0.1858 0.3573 0.0117
1.6000 0.1982 0.3688 0.0119
1.7000 0.2106 0.3797 0.0120
1.8000 0.2230 0.3900 0.0122
1.9000 0.2354 0.3998 0.0123
2.0000 0.2478 0.4090 0.0124
Reference point F multiplier
StockNos Biomass SpwnNosJan SSBJan SpwnNosSpwn SSBSpwn
5.5167 0.1968 4.5167 0.1858 4.5167 0.1858
5.2894 0.1818 4.2894 0.1708 4.2894 0.1708
5.0907 0.1691 4.0907 0.1581 4.0907 0.1581
4.9155 0.1580 3.9155 0.1470 3.9155 0.1470
4.7597 0.1484 3.7597 0.1374 3.7597 0.1374
4.6201 0.1400 3.6201 0.1290 3.6201 0.1290
4.4943 0.1326 3.4943 0.1216 3.4943 0.1216
4.3802 0.1260 3.3802 0.1150 3.3802 0.1150
4.2762 0.1201 3.2762 0.1091 3.2762 0.1091
4.1809 0.1148 3.1809 0.1038 3.1809 0.1038
4.0933 0.1100 3.0933 0.0990 3.0933 0.0990
4.0123 0.1057 3.0123 0.0947 3.0123 0.0947
3.9372 0.1018 2.9372 0.0908 2.9372 0.0908
3.8674 0.0983 2.8674 0.0873 2.8674 0.0873
3.8022 0.0950 2.8022 0.0840 2.8022 0.0840
3.7411 0.0920 2.7411 0.0810 2.7411 0.0810
3.6838 0.0892 2.6838 0.0782 2.6838 0.0782
3.6299 0.0867 2.6299 0.0757 2.6299 0.0757
3.5790 0.0843 2.5790 0.0733 2.5790 0.0733
3.5309 0.0821 2.5309 0.0711 2.5309 0.0711
3.4854 0.0801 2.4854 0.0691 2.4854 0.0691
A
bsolute F
Fbar(4-8) 1.0000 0.1239
FMax 5.2462 0.6499
F0.1 1.4041 0.1739
F35%SPR 2.2206 0.2751
Table 5.3.14. - North Galicia (FU 25): Long-term yield per recruit analysis of females.

WGNEPH Report 2004
84
MFDP version 1a
Run: 1
Table 5.3.15. - North Galicia (FU 25): Short-term predictions of landings and biomass of males.
Status quo F in 2004.
North Galicia Males
Time and date: 18:22 28/03/04
Fbar age range: 4-7
2004
Biomass SSB FMult FBar Landings
149 149 1.0000 0.4019 41
2005 2006
Biomass SSB FMult FBar Landings Biomass SSB
121 121 0.0000 0.0000 0 139 139
. 121 0.1000 0.0402 4 135 135
. 121 0.2000 0.0804 7 131 131
. 121 0.3000 0.1206 10 128 128
. 121 0.4000 0.1607 13 124 124
. 121 0.5000 0.2009 17 121 121
. 121 0.6000 0.2411 19 117 117
. 121 0.7000 0.2813 22 114 114
. 121 0.8000 0.3215 25 111 111
. 121 0.9000 0.3617 28 108 108
. 121 1.0000 0.4019 30 105 105
. 121 1.1000 0.4420 33 102 102
. 121 1.2000 0.4822 35 100 100
. 121 1.3000 0.5224 38 97 97
. 121 1.4000 0.5626 40 95 95
. 121 1.5000 0.6028 42 92 92
. 121 1.6000 0.6430 44 90 90
. 121 1.7000 0.6831 46 88 88
. 121 1.8000 0.7233 48 86 86
. 121 1.9000 0.7635 50 83 83
. 121 2.0000 0.8037 52 81 81

MF
N
Ti
F
DP version 1a
Run: 1
orth Galicia FemaleINDEX FILE
me and date: 18:35 28/03/04
bar age range: 4-8
2004
Biomass SSB FMult FBar Landings
208 203 1.0000 0.1239 25
2005 2006
Biomass SSB FMult FBar Landing Yield Biomass SSB
172 168 0.0000 0.0000 0 165 160
. 168 0.1000 0.0124 2 163 158
. 168 0.2000 0.0248 4 161 156
. 168 0.3000 0.0372 7 158 154
. 168 0.4000 0.0496 9 156 152
. 168 0.5000 0.0619 11 154 149
. 168 0.6000 0.0743 13 152 147
. 168 0.7000 0.0867 15 150 145
. 168 0.8000 0.0991 17 148 143
. 168 0.9000 0.1115 19 146 141
. 168 1.0000 0.1239 21 144 139
. 168 1.1000 0.1363 23 142 137
. 168 1.2000 0.1487 25 140 135
. 168 1.3000 0.1610 27 138 134
. 168 1.4000 0.1734 28 137 132
. 168 1.5000 0.1858 30 135 130
. 168 1.6000 0.1982 32 133 128
. 168 1.7000 0.2106 34 131 126
. 168 1.8000 0.2230 36 129 125
. 168 1.9000 0.2354 37 128 123
. 168 2.0000 0.2478 39 126 121
Table 5.3.16. - North Galicia (FU 25): Short-term predictions of landings and biomass of
females. Status quo F in 2004.
WGNEPH Report 2004 85

WGNEPH Report 2004
86
Trawl Trap
146 2 148
90494
120 9 129
97198
69372
46248
33134
26 <1 26
25126
21122
* provisional
7505 3.4 21.3
4608 3.0 15.2
3809 3.8 17.1
4049 5.0 17.2
3845 4.5 16.8
4232 2.1 10.2
3367 1.8 11
2031 2.9 12.4
1871 1.3 12.1
1787 2.0 12.2
* provisional
Table 5.3.17. - Cantabrian Sea (FU 31): Landings (tonnes) by country, 1994-2003.
Table 5.3.18. - Cantabrian Sea (FU 31): Effort (fishing days) and LPUE (kg/day * BHP/100
and kg/fishing days) of Spanish trawlers, home port Avilés and Santander respectively,
1994-2003.
Spain TotalYear
1994
1995
1996
1997
1998
1999
2000
2001
2003*
Year
2002
1999
2000
2001
2003*
2002
1995
1996
1997
1998
1994
Total
Effort
LPUE
Avilés
LPUE
Santander

WGNEPH Report 2004 87
Males Females
46.6 42.0
44.6 41.5
45.6 41.8
43.2 40.5
46.2 41.5
47.8 42.7
47.5 42.4
47.3 42.6
45.6 38.1
47.5 40.6
* provisional
Kg / 30 min haul Nos. / 30 min haul
MSC SE MSC SE
0.13 0.06 2.6 1.1
0.08 0.03 1.2 0.5
0.12 0.05 2.0 0.9
0.05 0.02 0.8 0.3
0.05 0.02 1.2 0.6
0.03 0.01 0.6 0.2
0.08 0.04 1.7 1.0
0.05 0.03 1.2 0.9
0.03 0.02 0.6 0.4
na na
Table 5.3.19. - Cantabrian Sea (FU 31): Mean sizes (mm CL) of male and female
Nephrops in Spanish landings, 1994-2003.
Table 5.3.20. - Cantabrian Sea (FU 31): Mean stratified catches (MSC) and standard errors
(SE) of Nephrops in bottom trawl surveys in the Cantabrian Sea, 1994-2003.
2003*
Year
1996
1997
1998
1999
2000
2001
1994
2003
1994
1995
1996
1997
1998
1999
2000
2001
Catches
2002
Year
2002
1995
na = not available

WGNEPH Report 2004
88
209 129 0 338
219 98 0 317
103 72 0 175
124 48 0 172
81 34 0 115
147 26 0 173
143 26 0 169
89 22 0 111
* provisional
Spain Total
393 393
367 367
Table 5.3.22 - Management Area O (VIIIc): Total Nephrops landings (tonnes) by count
1994-2003.
1996
1997
1998
1999
1995
2000
2001
2003*
Year
2002
1994
FU 25 FU 31 Other Total
245 148 0 393
273 94 0 367
338 338
317 317
175 175
172 172
115 115
173 173
169 169
111 111
* provisional
2002
Table 5.3.21 - Management Area O (VIIIc): Total Nephrops landings (tonnes) by Functional
Unit plus Other rectangles, 1994-2003.
ry,
Year
1994
1995
1996
2001
2003*
1997
1998
1999
2000

Run title
At 25/
Table
YEAR
AGE
+g
0 TOTA
TONSLA
SO
Table
YEAR
AGE
+g
0 TOTA
TONSLA
SO
Table
YEAR
AGE
+gp
0 SOPC
Table
YEAR
AGE
+gp
0 SOPC
Table 5
: North Galicia MalesINDEX FILE
03/2004 11:14
1 Catch numbers at age Numbers*10**-3
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
2 242 272 289 121 42 1 10 93 28 262
3 3942 2656 1544 1306 1159 278 710 3277 1503 573
4 4121 2707 2318 2013 3172 1224 1424 2697 2895 1687
5 1447 1335 1155 1034 2040 1187 676 1197 1581 978
6 597 651 400 583 670 717 281 431 622 515
7 345 176 103 232 156 336 104 131 165 122
8 105 66 35 35 42 103 38 22 66 60
95555 2 4115522 62223
p 3321121937431810 7 3
LNUM 10886 7938 5857 5348 7328 3943 3283 7863 6888 4223
ND 371 302 219 225 323 221 140 272 286 183
PCOF % 929999999999999999100
1 Catch numbers at age Numbers*10**-3
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
276625634 720 614 5 1
3 964 920 701 784 166 409 212 510 360 44
4 1507 1428 1231 1432 386 658 553 1066 888 238
5 826 956 665 712 340 350 257 596 422 252
6 279 370 232 179 171 142 91 231 248 155
785788257655534588593
830202715252518366242
9 18 9 15 3 5 13 12 17 19 18
p 18 831 5 6 816105137
LNUM 3802 3851 3038 3221 1170 1680 1199 2538 2140 878
ND 153 158 128 125 58 71 54 109 106 57
PCOF % 9898999999991001009999
2 Catch weights at age (kg)
1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
2 0.012 0.012 0.012 0.012 0.013 0.014 0.012 0.012 0.012 0.009
3 0.022 0.021 0.021 0.021 0.023 0.024 0.023 0.021 0.022 0.022
4 0.034 0.035 0.035 0.036 0.036 0.036 0.035 0.035 0.035 0.035
5 0.053 0.052 0.052 0.052 0.053 0.053 0.052 0.052 0.052 0.052
6 0.072 0.072 0.071 0.072 0.071 0.072 0.071 0.071 0.072 0.072
7 0.093 0.092 0.091 0.092 0.092 0.092 0.091 0.091 0.091 0.092
8 0.109 0.112 0.11 0.11 0.111 0.113 0.114 0.11 0.114 0.114
9 0.135 0.13 0.128 0.136 0.132 0.13 0.131 0.128 0.133 0.131
0.1487 0.2072 0.1662 0.1764 0.2079 0.1811 0.2054 0.1886 0.1731 0.145
OFAC 0.9158 0.9897 0.9914 0.9945 0.9931 0.9923 0.9879 0.9923 0.9921 0.9976
2 Catch weights at age (kg)
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.012 0.013 0.012 0.012 0.013 0.013 0.013 0.013 0.012 0.014
3 0.021 0.022 0.022 0.022 0.022 0.022 0.023 0.022 0.023 0.023
4 0.036 0.036 0.035 0.035 0.036 0.035 0.035 0.035 0.035 0.037
5 0.052 0.052 0.052 0.052 0.053 0.052 0.052 0.052 0.053 0.053
6 0.072 0.072 0.072 0.071 0.072 0.072 0.072 0.071 0.073 0.073
7 0.092 0.09 0.092 0.092 0.093 0.094 0.094 0.093 0.093 0.092
8 0.113 0.112 0.112 0.109 0.111 0.11 0.112 0.113 0.112 0.112
9 0.133 0.131 0.131 0.135 0.131 0.134 0.135 0.131 0.132 0.132
0.1828 0.1857 0.2081 0.2284 0.2011 0.1511 0.1806 0.1691 0.1932 0.2027
OFAC 0.985 0.9827 0.9897 0.9919 0.9909 0.9913 1.0017 0.9956 0.9896 0.9909
.3.23. - North Galicia (FU 25): VPA input and output tables for males.
...continued overleaf
WGNEPH Report 2004 89

WGNEPH Report 2004
90
Table 3 Stock weights at age (kg)
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.012 0.012 0.012 0.012 0.013 0.014 0.012 0.012 0.012 0.009
Table 5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).
3 0.022 0.021 0.021 0.021 0.023 0.024 0.023 0.021 0.022 0.022
4 0.034 0.035 0.035 0.036 0.036 0.036 0.035 0.035 0.035 0.035
5 0.053 0.052 0.052 0.052 0.053 0.053 0.052 0.052 0.052 0.052
6 0.072 0.072 0.071 0.072 0.071 0.072 0.071 0.071 0.072 0.072
7 0.093 0.092 0.091 0.092 0.092 0.092 0.091 0.091 0.091 0.092
8 0.109 0.112 0.11 0.11 0.111 0.113 0.114 0. 11 0.114 0.114
9 0.135 0.13 0.128 0.136 0.132 0.13 0.131 0.128 0.133 0.131
+gp 0.1487 0.2072 0.1662 0.1764 0.2079 0.1811 0.2054 0.1886 0.1731 0.145
Table 3 Stock weights at age (kg)
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.012 0.013 0.012 0.012 0.013 0.013 0.013 0.013 0.012 0.014
3 0.021 0.022 0.022 0.022 0.022 0.022 0.023 0.022 0.023 0.023
4 0.036 0.036 0.035 0.035 0.036 0.035 0.035 0.035 0.035 0.037
5 0.052 0.052 0.052 0.052 0.053 0.052 0.052 0.052 0.053 0.053
6 0.072 0.072 0.072 0.071 0.072 0.072 0.072 0.071 0.073 0.073
7 0.092 0.09 0.092 0.092 0.093 0.094 0.094 0.093 0.093 0.092
8 0.113 0.112 0.112 0.109 0.111 0.11 0.112 0.113 0.112 0.112
9 0.133 0.131 0.131 0.135 0.131 0.134 0.135 0.131 0.132 0.132
+gp 0.1828 0.1857 0.2081 0.2284 0.2011 0.1511 0.1806 0.1691 0.1932 0.2027
Table 4 Natural Mortality (M) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
Table 4 Natural Mortality (M) at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
...continued overleaf

Table 5 Proportion mature at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
21111111111
31111111111
41111111111
51111111111
61111111111
71111111111
81111111111
91111111111
+gp 1111111111
Table 5 Proportion mature at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
21111111111
31111111111
41111111111
51111111111
61111111111
71111111111
81111111111
91111111111
+gp 1111111111
Table 6 Proportion of M before Spawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
+gp 0000000000
Table 6 Proportion of M before Spawning
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
+gp 0000000000
Table 5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004 91

Table 7 Proportion of F bef ore Spawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
+gp 0000000000
Table 7 Proportion of F bef ore Spawning
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
+gp 0000000000
Table 8 Fishing mortality (F) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.0215 0.0251 0.0289 0.0193 0.0064 0.0001 0.0009 0.0132 0.005 0.048
3 0.4542 0.3431 0.1938 0.1769 0.2582 0.0533 0.0976 0.4494 0.3043 0.134
4 0.8713 0.6581 0.5736 0.4165 0.8528 0.4784 0.4205 0.6459 0.9475 0.6687
5 0.8618 0.7986 0.6641 0.548 1.0202 0.9546 0.5346 0.7688 1.0495 1.0546
6 1.1364 1.3913 0.5933 0.871 0.8619 1.4338 0.6214 0.7987 1.3258 1.3408
7 1.6061 1.4379 0.8721 0.8495 0.6048 1.8241 0.828 0.6709 0.8479 1.0865
8 0.7742 2.695 1.4614 0.8621 0.3508 1.1149 1.2436 0.4005 0.8841 0.8961
9 1.0622 1.4143 0.8238 0.6782 0.7083 1.1164 0.7564 0.6534 0.9344 0.9022
+gp 1.0622 1.4143 0.8238 0.6782 0.7083 1.1164 0.7564 0.6534 0.9344 0.9022
0 FBAR 4- 7 1.1189 1.0715 0.6758 0.6713 0.835 1.1727 0.6011 0.7211 1.0427 1.0377
Table 8 Fishing mortality (F) at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 FBAR 01-03
AGE
2 0.015 0.0142 0.0187 0.012 0.002 0.0056 0.0019 0.009 0.0129 0.0063 0.0094
3 0.2495 0.2535 0.2198 0.3923 0.0755 0.1424 0.0742 0.2095 0.3359 0.1483 0.2312
4 0.6174 0.7192 0.6375 0.9516 0.3406 0.4781 0.2916 0.6411 0.6856 0.3889 0.5719
5 0.8416 1.0848 0.913 0.994 0.6185 0.5975 0.3459 0.59 0.5691 0.418 0.5257
6 1.0542 1.2835 0.8658 0.6749 0.6923 0.573 0.2992 0.6056 0.5254 0.4203 0.5171
7 0.8483 1.0203 1.2292 0.5345 0.5542 0.4932 0.2541 0.3152 0.4709 0.3802 0.3888
8 0.9007 0.466 1.3938 0.7982 0.4636 0.4387 0.2967 0.4774 0.6648 0.4415 0.5279
9 0.7472 0.7978 0.85 0.5991 0.5952 0.5009 0.3902 0.5044 0.4946 0.4129 0.4706
+gp 0.7472 0.7978 0.85 0.5991 0.5952 0.5009 0.3902 0.5044 0.4946 0.4129
0 FBAR 4- 7 0.8404 1.027 0.9114 0. 7888 0.5514 0.5355 0.2977 0.538 0.5627 0.4019
Table 5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004
92

Table 9 Relative F at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.0192 0.0234 0.0428 0.0288 0.0076 0.0001 0.0015 0.0184 0.0048 0.0463
3 0.4059 0.3203 0.2868 0.2635 0.3093 0.0455 0.1624 0.6232 0.2918 0.1292
4 0.7787 0.6142 0.8489 0.6205 1.0214 0.408 0.6995 0.8957 0.9087 0.6445
5 0.7702 0.7454 0.9827 0.8164 1.2219 0.814 0.8894 1.0662 1.0066 1.0163
6 1.0156 1.2985 0.8779 1.2976 1.0323 1.2226 1.0337 1.1077 1.2715 1.2922
7 1.4355 1.342 1.2905 1.2655 0.7244 1.5555 1.3774 0.9304 0.8132 1.047
8 0.692 2.5153 2.1626 1.2843 0.4202 0.9507 2.0688 0.5554 0.8479 0.8636
9 0.9493 1.32 1.2191 1.0104 0.8484 0.952 1.2584 0.9062 0.8961 0.8694
+gp 0.9493 1.32 1.2191 1.0104 0.8484 0.952 1.2584 0.9062 0.8961 0.8694
0 REFMEAN 1.1189 1.0715 0.6758 0.6713 0.835 1.1727 0.6011 0.7211 1.0427 1.0377
Table 9 Relative F at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 MEAN 01-03
AGE
2 0.0178 0.0138 0.0205 0.0153 0.0036 0.0104 0.0065 0.0167 0.0229 0.0156 0.0184
3 0.2969 0.2468 0.2412 0.4974 0.1369 0.2658 0.2492 0.3895 0.5969 0.369 0.4518
4 0.7347 0.7003 0.6995 1.2064 0.6176 0.8929 0.9794 1.1917 1.2183 0.9678 1.126
5 1.0015 1.0563 1.0018 1.2603 1.1217 1.1159 1.1619 1.0967 1.0113 1.0401 1.0494
6 1.2545 1.2498 0.9499 0.8556 1.2555 1.0701 1.005 1.1257 0.9336 1.046 1.0351
7 1.0094 0.9935 1.3487 0.6777 1.0051 0.9211 0.8537 0.5859 0.8368 0.9461 0.7896
8 1.0718 0.4538 1.5294 1.0119 0.8407 0.8193 0.9967 0.8874 1.1814 1.0987 1.0558
9 0.8891 0.7769 0.9326 0.7596 1.0794 0.9354 1.3107 0.9375 0.879 1.0275 0.948
+gp 0.8891 0.7769 0.9326 0.7596 1.0794 0.9354 1.3107 0.9375 0.879 1.0275
0 REFMEAN 0.8404 1.027 0.9114 0.7888 0.5514 0.5355 0.2977 0.538 0.5627 0.4019
Table 10 Stock number at age (start of year) Numbers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 12609 12128 11197 7005 7262 10303 12230 7837 6196 6179
3 11935 10104 9684 8906 5626 5908 8435 10004 6332 5048
4 7830 6204 5870 6532 6110 3558 4586 6264 5226 3824
5 2769 2682 2631 2708 3526 2132 1805 2466 2688 1659
6 972 958 988 1109 1282 1041 672 866 936 771
7 477 255 195 447 380 443 203 296 319 203
8 214 78 50 67 156 170 59 73 124 112
9 92 81 4 9 23 90 46 14 40 42
+gp 542923438069372312 6
0 TOTAL 36952 32520 30641 26826 24445 23713 28072 27842 21873 17844
Table 10 Stock number at age (start of year) Numbers*10**-3
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 GM8403 AM8403
AGE
2 5629 4860 3321 3115 4167 4023 3646 1717 432 123 0 5988 6857
3 4822 4540 3923 2669 2520 3405 3275 2979 1393 349 100 5448 6117
4 3615 3076 2885 2578 1476 1913 2418 2490 1978 815 246 3838 4247
5 1604 1596 1227 1248 815 860 971 1479 1074 816 452 1777 1937
6 473 566 442 403 378 360 387 562 671 498 440 673 731
7 165 135 128 152 168 155 166 235 251 325 268 229 251
8 56 58 40 31 73 79 77 105 140 128 182 80 90
9 37 19 30 8 11 38 42 47 54 59 68 28 37
+gp 371658131522542814412097
0 TOTAL 16439 14867 12054 10217 9623 10854 11036 9643 6137 3233 1853
Table 5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004 93

Table 11 Spawning stock number at age (spawning time) Numbers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 12609 12128 11197 7005 7262 10303 12230 7837 6196 6179
3 11935 10104 9684 8906 5626 5908 8435 10004 6332 5048
4 7830 6204 5870 6532 6110 3558 4586 6264 5226 3824
5 2769 2682 2631 2708 3526 2132 1805 2466 2688 1659
6 972 958 988 1109 1282 1041 672 866 936 771
7 477 255 195 447 380 443 203 296 319 203
8 214 78 50 67 156 170 59 73 124 112
9 92 81 4 9 23 90 46 14 40 42
+gp 542923438069372312 6
Table 11 Spawning stock number at age (spawning time) Numbers*10**-3
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 5629 4860 3321 3115 4167 4023 3646 1717 432 123
3 4822 4540 3923 2669 2520 3405 3275 2979 1393 349
4 3615 3076 2885 2578 1476 1913 2418 2490 1978 815
5 1604 1596 1227 1248 815 860 971 1479 1074 816
6 473 566 442 403 378 360 387 562 671 498
7 165 135 128 152 168 155 166 235 251 325
856584031737977105140128
9 37 19 30 8 11 38 42 47 54 59
+gp 3716581315225428144120
Table 12 Stock biomass at age (start of year) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 151 146 134 84 94 144 147 94 74 56
3 263 212 203 187 129 142 194 210 139 111
4 266 217 205 235 220 128 161 219 183 134
5 147 139 137 141 187 113 94 128 140 86
670697080917548616755
744231841354118272919
8239571719781413
91211113126255
+gp 864817128421
0 TOTALBIO 985 832 778 784 794 686 682 754 654 480
Table 12 Stock biomass at age (start of year) Tonnes
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
26863403754524722 5 2
3 101 100 86 59 55 75 75 66 32 8
4 130 111 101 90 53 67 85 87 69 30
583836465434550775743
634413229272628404936
715121214161516222330
86643899121614
95241156678
+gp 7 312 3 3 310 52824
0 TOTALBIO 450 422 355 301 261 296 325 336 286 196
Table 5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004
94

Table 13 Spawning stock biomass at age (spawning time) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 151 146 134 84 94 144 147 94 74 56
3 263 212 203 187 129 142 194 210 139 111
4 266 217 205 235 220 128 161 219 183 134
5 147 139 137 141 187 113 94 128 140 86
670697080917548616755
744231841354118272919
8239571719781413
91211113126255
+gp 864817128421
0 TOTSPBIO 985 832 778 784 794 686 682 754 654 480
Table 13 Spawning stock biomass at age (spawning time) Tonnes
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
26863403754524722 5 2
3 101 100 86 59 55 75 75 66 32 8
4 130 111 101 90 53 67 85 87 69 30
583836465434550775743
634413229272628404936
715121214161516222330
86643899121614
95241156678
+gp 7 312 3 3 310 52824
0 TOTSPBIO 450 422 355 301 261 296 325 336 286 196
Table 14 Stock biomass at age with SOP (start of year) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 139 144 133 84 94 143 145 93 74 55
3 240 210 202 186 128 141 192 208 138 111
4 244 215 204 234 218 127 159 218 181 134
5 134 138 136 140 186 112 93 127 139 86
664687079907447616755
741231841354018272919
8219571719781413
91110113126255
+gp 764817127421
0 TOTALBIO 902 824 771 780 788 681 673 748 649 479
Table 14 Stock biomass at age with SOP (start of year) Tonnes
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
26762393754524722 5 2
3 100 98 85 58 55 74 75 65 32 8
4 128 109 100 90 53 66 85 87 69 30
582826364434451775643
634403128272628404836
715121214151416222330
86643899121614
95241156678
+gp 7 312 3 3 310 52724
0 TOTALBIO 443 414 351 299 259 294 326 335 283 194
Table 5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004 95

T
YEA
AGE
+gp
0 TOTS
T
YEA
AGE
+gp
0 TOTS
Table
able 15 Spawning stock biomass with SOP (spawning tim e) Tonnes
R 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
2 139 144 133 84 94 143 145 93 74 55
3 240 210 202 186 128 141 192 208 138 111
4 244 215 204 234 218 127 159 218 181 134
5 134 138 136 140 186 112 93 127 139 86
664687079907447616755
741231841354018272919
8 21 9 5 7 17 19 7 8 14 13
91110 1 1 312 6 2 5 5
7 6 4 8 17 12 7 4 2 1
PBIO 902 824 771 780 788 681 673 748 649 479
able 15 Spawning stock biomass with SOP (spawning tim e) Tonnes
R 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
26762393754524722 5 2
3 100 98 85 58 55 74 75 65 32 8
4 128 109 100 90 53 66 85 87 69 30
582826364434451775643
634403128272628404836
715121214151416222330
8 6 6 4 3 8 9 9121614
95241156678
7 3 12 3 3 3 10 5 27 24
PBIO 443 414 351 299 259 294 326 335 283 194
5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004
96

Table
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
Arith.
Mean
0 Units
16 Summary (without SOP correction)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB FBAR 4-7
Age 2
12609 985 985 371 0.3766 1.1189
12128 832 832 302 0.3629 1.0715
11197 778 778 219 0.2816 0.6758
7005 784 784 225 0.2869 0.6713
7262 794 794 323 0.407 0.835
10303 686 686 221 0.3221 1.1727
12230 682 682 140 0.2054 0.6011
7837 754 754 272 0.3607 0.7211
6196 654 654 286 0.4372 1.0427
6179 480 480 183 0.3812 1.0377
5629 450 450 153 0.3402 0.8404
4860 422 422 158 0.3747 1.027
3321 355 355 128 0.3606 0.9114
3115 301 301 125 0.415 0.7888
4167 261 261 58 0.2219 0.5514
4023 296 296 71 0.2395 0.5355
3646 325 325 54 0.166 0.2977
1717 336 336 109 0.324 0.538
432 286 286 106 0.3703 0.5627
123 196 196 57 0.2911 0.4019
6199 533 533 178 0.3262 0.7701
(Thousand
s
(Tonnes) (Tonnes) (Tonnes)
17 Summary (with SOP correction)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB SOPCOFAC FBAR 4-7
Age 2
12609 902 902 371 0.4113 0.9158 1.1189
12128 824 824 302 0.3667 0.9897 1.0715
11197 771 771 219 0.284 0.9914 0.6758
7005 780 780 225 0.2885 0.9945 0.6713
7262 788 788 323 0.4098 0.9931 0.835
10303 681 681 221 0.3246 0.9923 1.1727
12230 673 673 140 0.2079 0.9879 0.6011
7837 748 748 272 0.3635 0.9923 0.7211
6196 649 649 286 0.4406 0.9921 1.0427
6179 479 479 183 0.3821 0.9976 1.0377
5629 443 443 153 0.3454 0.985 0.8404
4860 414 414 158 0.3813 0.9827 1.027
3321 351 351 128 0.3644 0.9897 0.9114
3115 299 299 125 0.4184 0.9919 0.7888
4167 259 259 58 0.2239 0.9909 0.5514
4023 294 294 71 0.2416 0.9913 0.5355
3646 326 326 54 0.1657 1.0017 0.2977
1717 335 335 109 0.3254 0.9956 0.538
432 283 283 106 0.3742 0.9896 0.5627
123 194 194 57 0.2938 0.9909 0.4019
6199 525 525 178 .3307 .7701
(Thousand
Table
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
Arith.
Mean
0 Units
s
(Tonnes) (Tonnes) (Tonnes)
5.3.23. - North Galicia (FU 25): VPA input and output tables for males (continued).Table
WGNEPH Report 2004 97

Run t
At 25
T
YE
AG
+g
0 TO
TO
SO
T
YE
AG
+g
0 TO
TO
T
YE
AG
2 0.012 0.012 0.011 0.012 0.013 0 0.012 0.013 0.013 0.012
3 0.017 0.017 0.017 0.017 0.018 0.018 0.017 0.017 0.018 0.017
4 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.022 0.023 0.023
5 0.028 0.028 0.028 0.028 0.028 0.029 0.028 0.028 0.028 0.029
6 0.034 0.034 0.034 0.034 0.034 0.034 0.034 0.033 0.033 0.034
7 0.039 0.039 0.04 0.039 0.04 0.04 0.039 0.04 0.04 0.04
8 0.045 0.046 0.045 0.046 0.045 0.045 0.046 0.046 0.046 0.046
9 0.053 0.052 0.053 0.052 0.052 0.052 0.052 0.052 0.052 0.052
10 0.058 0.058 0.058 0.058 0.059 0.058 0.058 0.059 0.059 0.058
+gp 0.0752 0.0823 0.0817 0.0801 0.0796 0.0774 0.0773 0.0804 0.0713 0.0744
0 SOPCOFAC 0.8761 0.989 0.9867 0.9945 0.9948 0.996 0.9882 0.9917 0.9909 0.9826
Table 2 Catch weights at age (k g)
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.012 0.012 0.012 0.012 0.013 0.012 0.012 0.011 0.01 0.012
3 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.018 0.017 0.017
4 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.023
5 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028
6 0.034 0.034 0.033 0.034 0.034 0.034 0.034 0.033 0.034 0.034
7 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
8 0.046 0.046 0.046 0.046 0.046 0.046 0.046 0.046 0.046 0.046
9 0.052 0.052 0.052 0.052 0.052 0.052 0.052 0.052 0.052 0.052
10 0.058 0.059 0.058 0.059 0.058 0.058 0.059 0.059 0.059 0.058
+gp 0.0748 0.0725 0.0818 0.0812 0.0782 0.0793 0.0769 0.0762 0.0772 0.0848
Ta
itle : North Galicia FemaleIN DEX FILE
/03/2004 13:43
able 1 Catch numbers at age Numbers *10**-3
AR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
E
2 377 540 356 240 8 0 56 155 22 59
3 1153 1501 785 629 248 18 279 1185 267 166
4 1356 1455 662 623 537 124 410 1299 761 181
5 1187 900 856 745 668 369 574 1044 931 374
6 684 602 668 870 460 607 468 738 779 547
7 267 367 526 630 359 554 399 477 602 471
8 137 337 233 376 265 549 298 295 329 331
9 200 171 189 220 147 316 272 196 162 131
10 175 104 136 152 170 254 204 127 130 84
p 202 257 225 582 332 557 513 334 178 131
TALNUM 5739 6232 4635 5067 3194 3347 3473 5850 4159 2474
NSLAND 144 175 145 186 121 155 140 180 141 91
PCOF % 88 99 99 99 99 100 99 99 99 98
able 1 Catch numbers at age Numbers *10**-3
AR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
E
290916349 918 920 6 2
3 372 277 291 258 59 76 31 80 25 5
4 382 450 395 476 102 172 65 114 73 26
5 524 468 507 510 122 168 112 219 153 56
6 506 625 368 524 179 246 157 174 202 86
7 364 386 250 311 166 181 91 122 127 120
8 234 251 159 271 133 144 61 80 99 132
9 157 274 111 141 116 136 66 84 82 87
10 91 157 68 67 62 64 35 46 45 45
p 102 215 158 141 136 134 63 85 94 107
TALNUM 2822 3194 2368 2747 1082 1338 689 1022 904 665
NSLAND 93 115 80 94 45 53 27 38 37 32
SOPCOF % 9899999898999910010099
able 2 Catch weights at age (kg)
AR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
E
ble 5.3.24. - North Galicia (FU 25): VPA input and output tables for females.
...continued overleaf
WGNEPH Report 2004
98

WGNEPH Report 2004 99
Table 3 Stock weights at age ( kg)
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.012 0.012 0.011 0.012 0.013 0 0.012 0.013 0.013 0.012
3 0.017 0.017 0.017 0.017 0.018 0.018 0.017 0.017 0.018 0.017
4 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.022 0.023 0.023
5 0.028 0.028 0.028 0.028 0.028 0.029 0.028 0.028 0.028 0.029
6 0.034 0.034 0.034 0.034 0.034 0.034 0.034 0.033 0.033 0.034
7 0.039 0.039 0.04 0.039 0.04 0.04 0.039 0.04 0.04 0.04
8 0.045 0.046 0.045 0.046 0.045 0.045 0.046 0.046 0.046 0.046
9 0.053 0.052 0.053 0.052 0.052 0.052 0.052 0.052 0.052 0.052
10 0.058 0.058 0.058 0.058 0.059 0.058 0.058 0.059 0.059 0.058
+gp 0.0752 0.0823 0.0817 0.0801 0.0796 0.0774 0.0773 0.0804 0.0713 0.0744
Table 3 Stock weights at age ( kg)
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.012 0.012 0.012 0.012 0.013 0.012 0.012 0.011 0.01 0.012
3 0.017 0.017 0.017 0.017 0.017 0.017 0.017 0.018 0.017 0.017
4 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.023 0.023
5 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028
6 0.034 0.034 0.033 0.034 0.034 0.034 0.034 0.033 0.034 0.034
7 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04 0.04
8 0.046 0.046 0.046 0.046 0.046 0.046 0.046 0.046 0.046 0.046
9 0.052 0.052 0.052 0.052 0.052 0.052 0.052 0.052 0.052 0.052
10 0.058 0.059 0.058 0.059 0.058 0.058 0.059 0.059 0.059 0.058
+gp 0.0748 0.0725 0.0818 0.0812 0.0782 0.0793 0.0769 0.0762 0.0772 0.0848
Table 4 Natural Mortality (M) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
10 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
Table 4 Natural Mortality (M) at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
10 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
Table 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
...continued overleaf

WGNEPH Report 2004
100
Table 5 Proportion matur e at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
31111111111
41111111111
51111111111
61111111111
71111111111
81111111111
91111111111
101111111111
+gp 1111111111
Table 5 Proportion matur e at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
31111111111
41111111111
51111111111
61111111111
71111111111
81111111111
91111111111
101111111111
+gp 1111111111
Table 6 Proportion of M before Spawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
+gp 0000000000
Table 6 Proportion of M before Spawning
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
+gp 0000000000
Table 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
...continued overleaf

WGNEPH Report 2004 101
Table 7 Proportion of F befo re Spawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
+gp 0000000000
Table 7 Proportion of F befo re Spawning
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
+gp 0000000000
Table 8 Fishing mortality (F) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.033 0.0568 0.0412 0.0244 0.0009 0 0.0067 0.0217 0.0038 0.0096
3 0.1072 0.1782 0.1096 0.0954 0.0317 0.0023 0.0372 0.1904 0.0472 0.0355
4 0.1642 0.1916 0.111 0.1191 0.1102 0.0199 0.0666 0.243 0.1798 0.0409
5 0.1995 0.1561 0.1647 0.1761 0.1813 0.1029 0.1205 0.2408 0.2755 0.1257
6 0.1772 0.1469 0.1662 0.2512 0.1567 0.2491 0.1837 0.2243 0.2851 0.2586
7 0.1135 0.1358 0.1852 0.2337 0.1553 0.287 0.2579 0.2895 0.2882 0.2792
8 0.086 0.2044 0.1195 0.1956 0.1451 0.3767 0.2469 0.3086 0.3322 0.2538
9 0.2076 0.1471 0.1688 0.1586 0.1092 0.2586 0.3238 0.2553 0.2774 0.2122
10 0.1574 0.1587 0.1672 0.1993 0.1769 0.2775 0.2642 0.2461 0.2673 0.2257
+gp 0.1574 0.1587 0.1672 0.1993 0.1769 0.2775 0.2642 0.2461 0.2673 0.2257
0 FBAR 4- 8 0.1481 0.167 0.1493 0.1951 0.1497 0.2071 0.1751 0.2612 0.2722 0.1916
Table 8 Fishing mortality (F) at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 FBAR 01-03
AGE
2 0.0188 0.0214 0.0168 0.0133 0.0025 0.0086 0.0067 0.0253 0.0273 0.0118 0.0214
3 0.0771 0.074 0.0882 0.0894 0.0197 0.0278 0.0184 0.0719 0.0391 0.0284 0.0465
4 0.1069 0.1261 0.1434 0.2037 0.046 0.0737 0.0296 0.088 0.0862 0.0529 0.0757
5 0.1598 0.185 0.2047 0.2787 0.0731 0.0996 0.0629 0.1324 0.1635 0.0885 0.1281
6 0.2503 0.2911 0.2166 0.3376 0.1484 0.2078 0.1278 0.1312 0.1739 0.1304 0.1452
7 0.274 0.3075 0.1801 0.2878 0.1694 0.2199 0.1103 0.1385 0.1335 0.1478 0.1399
8 0.2179 0.309 0.2002 0.303 0.1909 0.2163 0.106 0.1329 0.1584 0.1998 0.1637
9 0.1835 0.4264 0.2182 0.2737 0.204 0.3059 0.1448 0.2089 0.1965 0.2052 0.2035
10 0.2236 0.283 0.1746 0.1964 0.185 0.1671 0.1188 0.1425 0.164 0.1562 0.1542
+gp 0.2236 0.283 0.1746 0.1964 0.185 0.1671 0. 1188 0.1425 0.164 0.1562
0 FBAR 4- 8 0.2018 0.2437 0.189 0.2822 0.1256 0.1635 0.0873 0.1246 0.1431 0.1239
Table 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
...continued overleaf

WGNEPH Report 2004
102
N 01-03
GM8403 AM8403
0 5579 6812
130 5265 6125
167 4562 5125
435 3695 4056
547 2747 2985
560 1913 2072
679 1325 1430
538 913 982
346 644 705
808
Table 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
Table 9 Relative F at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.2229 0.3404 0.2762 0.1252 0.0057 0 0.0384 0.083 0.0138 0.0499
3 0.7242 1.0674 0.7339 0.4891 0.2119 0.0112 0.2126 0.729 0.1736 0.1852
4 1.1086 1.1475 0.7435 0.6105 0.7362 0.096 0.3803 0.9303 0.6606 0.2133
5 1.3473 0.935 1.1027 0.9022 1.2108 0.4969 0.6878 0.9218 1.0123 0.6559
6 1.1969 0.8801 1.1132 1.287 1.0464 1.2027 1.0493 0.8587 1.0474 1.3494
7 0.7664 0.8134 1.2404 1.1978 1.0375 1.3858 1.4727 1.108 1.059 1.4571
8 0.5808 1.224 0.8002 1.0025 0.9692 1.8186 1.4099 1.1812 1.2207 1.3243
9 1.402 0.881 1.13 0.8127 0.729 1.2483 1.8488 0.9772 1.0191 1.1076
10 1.063 0.9506 1.1194 1.0211 1.1819 1.3399 1.5084 0.9422 0.9822 1.1781
+gp 1.063 0.9506 1.1194 1.0211 1.1819 1.3399 1.5084 0.9422 0.9822 1.1781
0 REFMEAN 0.1481 0.167 0.1493 0.1951 0.1497 0.2071 0.1751 0.2612 0.2722 0.1916
Table 9 Relative F at age
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 MEA
AGE
2 0.0933 0.0877 0.089 0.0472 0.0199 0.0528 0.0762 0.2027 0.1908 0.0952 0.1629
3 0.3823 0.3035 0.4667 0.317 0.1567 0.1698 0.2102 0.577 0.2735 0.2292 0.3599
4 0.5298 0.5175 0.7585 0.722 0.3664 0.4508 0.3394 0.706 0.6025 0.427 0.5785
5 0.7918 0.7589 1.083 0.9877 0.5822 0.6093 0.7202 1.0626 1.1426 0.7144 0.9732
6 1.2405 1.1944 1.1458 1.1964 1.1817 1.2711 1.4638 1.0533 1.2151 1.0526 1.107
7 1.3579 1.2615 0.953 1.0199 1.349 1.3453 1.263 1.1115 0.9331 1.1933 1.0793
8 1.0799 1.2678 1.0595 1.074 1.5207 1.3234 1.2135 1.0666 1.1067 1.6128 1.262
9 0.9094 1.7494 1.1547 0.9701 1.6248 1.8713 1.6579 1.677 1.3729 1.6568 1.5689
10 1.1082 1.1611 0.924 0.6961 1.4737 1.0222 1.3604 1.1438 1.1457 1.2606 1.1834
+gp 1.1082 1.1611 0.924 0.6961 1.4737 1.0222 1.3604 1.1438 1.1457 1.2606
0 REFMEAN 0.2018 0.2437 0.189 0.2822 0.1256 0.1635 0.0873 0.1246 0.1431 0.1239
Table 10 Stock number at age (start of year) Num bers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 12829 10800 9726 10998 10535 10300 9290 7967 6465 6827
3 12535 10162 8354 7641 8787 8618 8433 7555 6383 5273
4 9902 9219 6962 6130 5686 6970 7039 6652 5113 4985
5 7256 6880 6232 5101 4455 4170 5594 5392 4271 3497
6 4654 4866 4819 4328 3502 3043 3080 4060 3470 2655
7 2754 3191 3440 3341 2756 2452 1942 2098 2656 2136
8 1835 2013 2281 2340 2165 1932 1506 1228 1286 1630
9 1178 1378 1344 1657 1575 1533 1085 963 739 755
10 1330 784 974 929 1158 1156 969 643 611 458
+gp 1526 1927 1610 3541 2253 2523 2425 1681 831 715
0 TOTAL 55799 51222 45741 46005 42873 42696 41363 38239 31825 28931
Table 10 Stock number at age (start of year) Num bers*10**-3
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
AGE
2 5349 4748 4143 4114 3771 2291 1567 891 263 160
3 5536 4298 3805 3335 3323 3080 1860 1275 711 209
4 4167 4196 3268 2852 2497 2668 2452 1495 971 560
5 3918 3065 3028 2318 1905 1953 2029 1949 1121 729
6 2525 2734 2086 2021 1436 1450 1447 1560 1398 779
7 1678 1610 1673 1375 1180 1014 964 1043 1120 962
8 1323 1045 969 1144 844 816 666 707 743 802
9 1036 871 628 649 692 571 538 491 507 519
10 500 706 466 413 404 462 344 381 326 341
+gp 558 956 1083 868 886 956 618 702 682 813
0 TOTAL 26590 24229 21149 19090 16940 15260 12487 10493 7842 5876 4210
...continued overleaf

WGNEPH Report 2004 103
Table 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
Table 11 Spawning stock number at age (spawning time) Numbers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
3 12535 10162 8354 7641 8787 8618 8433 7555 6383 5273
4 9902 9219 6962 6130 5686 6970 7039 6652 5113 4985
5 7256 6880 6232 5101 4455 4170 5594 5392 4271 3497
6 4654 4866 4819 4328 3502 3043 3080 4060 3470 2655
7 2754 3191 3440 3341 2756 2452 1942 2098 2656 2136
8 1835 2013 2281 2340 2165 1932 1506 1228 1286 1630
9 1178 1378 1344 1657 1575 1533 1085 963 739 755
10 1330 784 974 929 1158 1156 969 643 611 458
+gp 1526 1927 1610 3541 2253 2523 2425 1681 831 715
Table 11 Spawning stock number at age (spawning time) Numbers*10**-3
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
3 5536 4298 3805 3335 3323 3080 1860 1275 711 209
4 4167 4196 3268 2852 2497 2668 2452 1495 971 560
5 3918 3065 3028 2318 1905 1953 2029 1949 1121 729
6 2525 2734 2086 2021 1436 1450 1447 1560 1398 779
7 1678 1610 1673 1375 1180 1014 964 1043 1120 962
8 1323 1045 969 1144 844 816 666 707 743 802
9 1036 871 628 649 692 571 538 491 507 519
10 500 706 466 413 404 462 344 381 326 341
+gp 558 956 1083 868 886 956 618 702 682 813
Table 12 Stock biomas s at age (start of year) T onnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 154 130 107 132 137 0 111 104 84 82
3 213 173 142 130 158 155 143 128 115 90
4 228 212 160 141 131 160 162 146 118 115
5 203 193 174 143 125 121 157 151 120 101
6 158 165 164 147 119 103 105 134 115 90
7 107 124 138 130 110 98 76 84 106 85
8 83 93 103 108 97 87 69 57 59 75
962727186828056503839
10 77 45 56 54 68 67 56 38 36 27
+gp 115 159 132 283 179 195 187 135 59 53
0 TOTALBIO 1401 1365 1247 1354 1207 1067 1123 1027 850 757
Table 12 Stock biomas s at age (start of year) T onnes
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
26457504949271910 3 2
3947365575652322312 4
496977566576156342213
5 110 86 85 65 53 55 57 55 31 20
686936969494949514826
767646755474139424538
861484553393831333437
954453334363028262627
10 29 42 27 24 23 27 20 22 19 20
+gp 42698970697648545369
0 TOTALBIO 702 674 603 542 480 456 378 349 293 256
...continued overleaf

WGNEPH Report 2004
104
Table 13 Spawning stock biomass at age (spawning time) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
115 90
118 115
120 101
115 90
106 85
59 75
03839
36 27
59 53
766 675
2002 2003
312 4
42213
31 20
14826
24538
33437
62627
19 20
45369
291 254
1992 1993
83 81
114 88
117 113
119 100
113 89
105 84
59 74
03839
36 26
59 52
842 744
2002 2003
3 2
312 4
42213
31 20
14826
24538
23437
52627
19 20
35368
293 255
Table 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
3 213 173 142 130 158 155 143 128
4 228 212 160 141 131 160 162 146
5 203 193 174 143 125 121 157 151
6 158 165 164 147 119 103 105 134
7 107 124 138 130 110 98 76 84
8 83 93 103 108 97 87 69 57
9627271868280565
10 77 45 56 54 68 67 56 38
+gp 115 159 132 283 179 195 187 135
0 TOTSPBIO 1247 1236 1140 1222 1070 1067 1012 923
Table 13 Spawning stock biomass at age (spawning time) Tonnes
YEAR 1994 1995 1996 1997 1998 1999 2000 2001
AGE
20000000000
3947365575652322
4969775665761563
5 110 86 85 65 53 55 57 55
6869369694949495
7676467554741394
8614845533938313
9544533343630282
10 29 42 27 24 23 27 20 22
+gp 426989706976485
0 TOTSPBIO 638 617 553 492 431 428 359 339
Table 14 Stock biomass at age with SOP (start of year) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991
AGE
2 135 128 106 131 136 0 110 103
3 187 171 140 129 157 155 142 127
4 200 210 158 140 130 160 160 145
5 178 191 172 142 124 120 155 150
6 139 164 162 146 118 103 103 133
7 94 123 136 130 110 98 75 83
8 72 92 101 107 97 87 68 56
9557170868179565
10 68 45 56 54 68 67 56 38
+gp 101 157 130 282 178 195 185 134
0 TOTALBIO 1227 1350 1230 1347 1201 1063 1110 1018
Table 14 Stock biomass at age with SOP (start of year) Tonnes
YEAR 1994 1995 1996 1997 1998 1999 2000 2001
AGE
26356494948271910
3937264565552312
4949574655660563
5 108 85 84 64 52 54 56 54
6859268684849495
7666466544640384
8604744523837303
9534532333529282
10 29 41 27 24 23 26 20 22
+gp 416887696875475
0 TOTALBIO 692 665 595 533 470 449 373 347
...continued overleaf

T
Y
+
0 T
T
Y
0 T
Ta
able 15 Spawning stock biomass with SOP (spawning tim e) Tonnes
EAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
3 187 171 140 129 157 155 142 127 114 88
4 200 210 158 140 130 160 160 145 117 113
5 178 191 172 142 124 120 155 150 119 100
6 139 164 162 146 118 103 103 133 113 89
7 94 123 136 130 110 98 75 83 105 84
8 72 92 101 107 97 87 68 56 59 74
955717086817956503839
10 68 45 56 54 68 67 56 38 36 26
gp 101 157 130 282 178 195 185 134 59 52
OTSPBIO 1092 1222 1125 1216 1064 1063 1000 916 759 664
able 15 Spawning stock biomass with SOP (spawning tim e) Tonnes
EAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
3937264565552312312 4
494957465566056342213
5 108 85 84 64 52 54 56 54 31 20
685926868484949514826
766646654464038424538
860474452383730323437
953453233352928252627
10 29 41 27 24 23 26 20 22 19 20
+gp 41688769687547535368
OTSPBIO 628 609 546 484 422 422 355 337 290 253
ble 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
...continued overleaf
WGNEPH Report 2004 105

WGNEPH Report 2004
106
Table 16 Summ ary (without SOP correction)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB FBAR 4-8
Age 2
1984 12829 1401 1247 144 0.1155 0.1481
1985 10800 1365 1236 175 0.1416 0.167
1986 9726 1247 1140 145 0.1272 0.1493
1987 10998 1354 1222 186 0.1522 0.1951
1988 10535 1207 1070 121 0.1131 0.1497
1989 10300 1067 1067 155 0.1453 0.2071
Table 5.3.24. - North Galicia (FU 25): VPA input and output tables for females (continued).
1990 9290 1123 1012 140 0.1384 0.1751
1991 7967 1027 923 180 0.195 0.2612
1992 6465 850 766 141 0.1841 0.2722
1993 6827 757 675 91 0.1347 0.1916
1994 5349 702 638 93 0.1458 0.2018
1995 4748 674 617 115 0.1864 0.2437
1996 4143 603 553 80 0.1446 0.189
1997 4114 542 492 94 0.191 0.2822
1998 3771 480 431 45 0.1044 0.1256
1999 2291 456 428 53 0.1238 0.1635
2000 1567 378 359 27 0.0752 0.0873
2001 891 349 339 38 0.1121 0.1246
2002 263 293 291 37 0.1273 0.1431
2003 160 256 254 32 0.1258 0.1239
Arith.
Mean 6152 807 738 105 0.1392 0.1801
0 Units (Thous and
s
(Tonnes) (Tonnes) (Tonnes)
Table 17 Summary (with SOP correction)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB SOPCOFAC FBAR 4-8
Age 2
1984 12829 1227 1092 144 0.1318 0. 8761 0.1481
1985 10800 1350 1222 175 0.1432 0.989 0.167
1986 9726 1230 1125 145 0.1289 0.9867 0.1493
1987 10998 1347 1216 186 0.153 0.9945 0.1951
1988 10535 1201 1064 121 0.1137 0. 9948 0.1497
1989 10300 1063 1063 155 0.1458 0.996 0.2071
1990 9290 1110 1000 140 0.14 0.9882 0.1751
1991 7967 1018 916 180 0.1966 0.9917 0.2612
1992 6465 842 759 141 0.1858 0.9909 0.2722
1993 6827 744 664 91 0.1371 0.9826 0.1916
1994 5349 692 628 93 0.148 0.9848 0.2018
1995 4748 665 609 115 0.1889 0.9865 0.2437
1996 4143 595 546 80 0.1464 0.9875 0.189
1997 4114 533 484 94 0.1942 0.9833 0.2822
1998 3771 470 422 45 0.1066 0.9796 0.1256
1999 2291 449 422 53 0.1256 0.9855 0.1635
2000 1567 373 355 27 0.0761 0.9876 0.0873
2001 891 347 337 38 0.1126 0.9951 0.1246
2002 263 293 290 37 0.1274 0.9994 0.1431
2003 160 255 253 32 0.1266 0.9933 0.1239
Arith.
Mean 6152 790 723 105 .1414 .1801
0 Units (Thous and
s
(Tonnes) (Tonnes) (Tonnes)

WGNEPH Report 2004 107
Lowestoft VPA Version 3.1
25/03/2004 11:03
Extended Survivors Analysis
North Galicia MalesINDEX FILE
CPUE data from file TUNEFF.DAT
Catch data for 20 years. 1984 to 2003. Ages 2 to 10.
Fleet Fir
s
Last First Last Alpha Beta
year year age age
FLEET 1 1986 2003 2901
Time series weights :
Tapered time weighting applied
Power = 3 over 20 years
Catchability analysis :
Catchability independent of stock size for all ages
Catchability independent of age for ages >= 4
Terminal population estimation :
Survivor estimates shrunk towards the mean F
of the final 5 years or the 5 oldest ages.
S.E. of the mean to which the estimates are shrunk = .500
Minimum standard error for population
estimates derived from each fleet = .300
Prior weighting not applied
Tuning converged after 17 iterations
Regression weights
0.751 0.82 0.877 0.921 0.954 0.976 0.99
Fishing mortalities
Age 1994 1995 1996 1997 1998 1999 2000
2 0.015 0.014 0.019 0.012 0.002 0.006 0.002
3 0.25 0.254 0.22 0.392 0.076 0.142 0.074
4 0.617 0.719 0.638 0.952 0.341 0.478 0.292
5 0.842 1.085 0.913 0.994 0.619 0.598 0.346
6 1.054 1.284 0.866 0.675 0.692 0.573 0.299
7 0.848 1.02 1.229 0.535 0.554 0.493 0.254
8 0.901 0.466 1.394 0.798 0.464 0.439 0.297
9 0.747 0.798 0.85 0.599 0.595 0.501 0.39
0.997 1 1
2001 2002 2003
0.009 0.013 0.006
0.21 0.336 0.148
0.641 0.686 0.389
0.59 0.569 0.418
0.606 0.525 0.42
0.315 0.471 0.38
0.477 0.665 0.442
0.504 0.495 0.413
Table 5.3.25. - North Galicia (FU 25): XSA tuning diagnostics for males.
...continued overleaf

XSA population numbers (Thousands)
AGE
YEAR 23456789
1994 5630 4820 3610 1600 473 165 56.2 37.4
1995 4860 4540 3080 1600 566 135 57.9 18.7
1996 3320 3920 2880 1230 442 128 39.8 29.7
1997 3110 2670 2580 1250 403 152 30.8 8.09
1998 4170 2520 1480 815 378 168 73 11.3
1999 4020 3410 1910 860 360 155 79 37.6
2000 3650 3280 2420 971 387 166 77.5 41.7
2001 1720 2980 2490 1480 562 235 105 47.2
2002 432 1390 1980 1070 671 251 140 53.5
2003 123 349 815 816 498 325 128 59.1
Estimated population abundance at 1st Jan 2004
0 100 246 452 440 268 182 67.7
Taper weighted geometric mean of the VPA populations:
2700 3060 2560 1310 538 202 78.5 30.3
Standard error of the weighted Log(VPA populations) :
1.2572 0.8351 0.5323 0.3976 0.3449 0.3522 0.4812 0.678
Log catchability residuals.
Fleet : FLEET 1
Age 1986 1987 1988 1989 1990 1991 1992 1993 1994
2 1.3 1.21 -0.24 -4.6 -2.51 0.39 -0.48 1.67 0.61
3 -0.05 0.15 0.22 -1.45 -1.04 0.64 0.36 -0.56 0.17
4 -0.1 -0.13 0.29 -0.38 -0.7 -0.12 0.37 -0.09 -0.04
5 0.05 0.15 0.46 0.3 -0.47 0.05 0.47 0.36 0.26
6 -0.06 0.61 0.3 0.7 -0.32 0.09 0.7 0.6 0.48
7 0.32 0.6 -0.05 0.93 -0.03 -0.08 0.25 0.4 0.26
8 0.83 0.57 -0.59 0.45 0.38 -0.56 0.29 0.22 0.32
9 0.45 0.42 0.2 0.43 -0.13 -0.03 0.36 0.22 0.16
Age 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.52 0.94 0.48 -1.5 0.03 -1.07 0.48 0.89 99.99
3 0.14 0.14 0.71 -1.15 -0.01 -0.72 0.37 0.97 0.07
Table 5.3.25. - North Galicia (FU 25): XSA tuning diagnostics for males (continued).
4 0.06 0.08 0.46 -0.76 0.08 -0.49 0.35 0.5 0.01
5 0.46 0.43 0.51 -0.17 0.29 -0.32 0.27 0.29 0.07
6 0.63 0.38 0.13 -0.07 0.25 -0.44 0.29 0.27 0.1
7 0.41 0.73 -0.1 -0.31 0.12 -0.63 -0.34 0.1 0.01
8 -0.4 0.85 0.28 -0.49 0 -0.42 0.07 0.44 0.07
9 0.13 0.32 0.17 -0.2 0.15 -0.14 0.13 0.24 0.02
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 23456789
Mean Log q -13.5519 -10.298 -9.1785 -9.1785 -9.1785 -9.1785 -9.1785 -9.1785
S.E(Log q) 1.283 0.6652 0.3947 0.3537 0.4083 0.3956 0.4273 0.2147
...continued overleaf
WGNEPH Report 2004
108

Regression statistics :
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
2 2.34 -1.217 20.76 0.08 17 2.94 -13.55
3 1.15 -0.532 10.64 0.55 18 0.79 -10.3
4 0.94 0.25 9.1 0.67 18 0.39 -9.18
5 0.8 1.16 8.62 0.77 18 0.22 -8.98
6 0.68 1.766 8.1 0.76 18 0.21 -8.95
7 1.01 -0.019 9.14 0.45 18 0.41 -9.12
81.12-0.4029.680.51 180.49 -9.1
9 0.95 0.645 8.78 0.94 18 0.17 -9.06
Terminal year survivor and F summaries :
Age 2 Catchability constant w.r.t. time and dependent on age
Year class = 2001
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 1000000
F shrinkage mean 100 0.5 1 0.006
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
100 0.5 0 1 0 0.006
Age 3 Catchability constant w.r.t. time and dependent on age
Year class = 2000
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 313 0.615 0.335 0.54 2 0.362 0.119
F shrinkage mean 215 0.5 0.638 0.168
Weighted prediction :
Table 5.3.25. - North Galicia (FU 25): XSA tuning diagnostics for males (continued).
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
246 0.39 0.26 3 0.657 0.148
Age 4 Catchability constant w.r.t. time and dependent on age
Year class = 1999
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 562 0.345 0.27 0.78 3 0.57 0.324
F shrinkage mean 339 0.5 0.43 0.491
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
452 0.29 0.25 4 0.871 0.389
...continued overleaf
WGNEPH Report 2004 109

A
Y
Fleet
F s
We
Sur
A
Y
Fleet
F s
We
Sur
A
Y
Fleet
F s
We
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
182 0.22 0.1 7 0.461 0.38
Age 8 Catchability constant w.r.t. time and age (fixed at the value for age) 4
Year class = 1995
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 70 0.216 0.097 0.45 7 0.686 0.428
F shrinkage mean 62 0.5 0.314 0.472
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
68 0.22 0.08 8 0.365 0.442
ge 5 Catchability constant w.r.t. time and age (fixed at the value for age) 4
ear class = 1998
Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 528 0.267 0.15 0.56 4 0.653 0.359
hrinkage mean 312 0.5 0.347 0.549
ighted prediction :
vivors Int Ext N Var F
at end of year s.e s.e Ratio
440 0.25 0.19 5 0.76 0.418
ge 6 Catchability constant w.r.t. time and age (fixed at the value for age) 4
ear class = 1997
Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 314 0.241 0.112 0.47 5 0.667 0.368
hrinkage mean 194 0.5 0.333 0.544
ighted prediction :
vivors Int Ext N Var F
at end of year s.e s.e Ratio
268 0.23 0.15 6 0.647 0.42
ge 7 Catchability constant w.r.t. time and age (fixed at the value for age) 4
ear class = 1996
Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 192 0.222 0.12 0.54 6 0.699 0.364
hrinkage mean 161 0.5 0.301 0.42
ighted prediction :
Table 5.3.25. - North Galicia (FU 25): XSA tuning diagnostics for males (continued).
...continued overleaf
WGNEPH Report 2004
110

A
Y
Fleet
FLEE
F s
We
Sur
ge 9 Catchability constant w.r.t. time and age (fixed at the value for age) 4
ear class = 1994
Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
T 1 32 0.193 0.11 0.57 8 0.762 0.413
hrinkage mean 32 0.5 0.238 0.413
ighted prediction :
vivors Int Ext N Var F
at end of year s.e s.e Ratio
32 0.19 0.09 9 0.473 0.413
Table 5.3.25. - North Galicia (FU 25): XSA tuning diagnostics for males (continued).
WGNEPH Report 2004 111

Low
Ex
CP
Catc
estoft VPA Version 3.1
25/03/2004 13:41
tended Survivors Analysis
North Galicia FemaleINDEX FILE
UE data from file TUNEFF.DAT
h data for 20 years. 1984 to 2003. Ages 2 to 11.
Fleet Fir
s
Last First Last Alpha Beta
year year age age
1 1986 2003 2 10 0 1
e series weights :
apered time weighting applied
Power = 3 over 20 years
hability analysis :
Catchability independent of stock size for all ages
Catchability independent of age for ages >= 6
rminal population estimation :
vivor estimates shrunk towards the mean F
the final 5 years or the 5 oldest ages.
S.E. of the mean to which the estimates are shrunk = .500
mum standard error for population
timates derived from each fleet = .300
ior weighting not applied
ng had not converged after 30 iterations
Table 5.3.26. - North Galicia (FU 25): XSA tuning diagnostics for females.
FLEET
Tim
T
Catc
Te
Sur
of
Mini
es
Pr
Tuni
Total absolute residual between iterations
29 and 30 = .00030
Final year F values
Age 2345678910
Iteration 29 0.0118 0.0284 0.0529 0.0885 0.1304 0.1479 0.1998 0.2053 0.1562
Iteration 30 0.0118 0.0284 0.0529 0.0885 0.1304 0.1478 0.1998 0.2052 0.1562
Regression weights
0.751 0.82 0.877 0.921 0.954 0.976 0.99 0.997 1 1
Fishing mortalities
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.019 0.021 0.017 0.013 0.002 0.009 0.007 0.025 0.027 0.012
3 0.077 0.074 0.088 0.089 0.02 0.028 0.018 0.072 0.039 0.028
4 0.107 0.126 0.143 0.204 0.046 0.074 0.03 0.088 0.086 0.053
5 0.16 0.185 0.205 0.279 0.073 0.1 0.063 0.132 0.164 0.088
6 0.25 0.291 0.217 0.338 0.148 0.208 0.128 0.131 0.174 0.13
7 0.274 0.307 0.18 0.288 0.169 0.22 0.11 0.138 0.134 0.148
8 0.218 0.309 0.2 0.303 0.191 0.216 0.106 0.133 0.158 0.2
9 0.184 0.426 0.218 0.274 0.204 0.306 0.145 0.209 0.196 0.205
10 0.224 0.283 0.175 0.196 0.185 0.167 0.119 0.143 0.164 0.156
...continued overleaf
WGNEPH Report 2004
112

XSA population numbers (Thousands)
AGE
YEAR 2345678910
1994 5350 5540 4170 3920 2530 1680 1320 1040 500
1995 4750 4300 4200 3070 2730 1610 1040 871 706
1996 4140 3810 3270 3030 2090 1670 969 628 466
1997 4110 3340 2850 2320 2020 1380 1140 649 413
1998 3770 3320 2500 1900 1440 1180 844 692 404
1999 2290 3080 2670 1950 1450 1010 816 571 462
2000 1570 1860 2450 2030 1450 964 666 538 344
2001 891 1270 1490 1950 1560 1040 707 491 381
2002 263 711 971 1120 1400 1120 743 507 326
2003 160 209 560 729 779 962 802 519 341
Estimated population abundance at 1st Jan 2004
0 130 167 435 547 560 679 538 346
Taper weighted geometric mean of the VPA populations:
2310 2570 2640 2350 1900 1410 995 688 471
Standard error of the weighted Log(VPA populations) :
1.3135 1.0575 0.7343 0.5714 0.4521 0.3577 0.3317 0.3216 0.3452
Log catchability residuals.
Fleet : FLEET 1
Age 1986 1987 1988 1989 1990 1991 1992 1993 1994
2 1.15 0.95 -2.68 99.99 -0.98 0.37 -1.28 -0.45 0.34
3 0.82 1 -0.44 -3.16 -0.56 1.23 -0.05 -0.45 0.45
4 0.18 0.54 0.15 -1.64 -0.63 0.83 0.63 -0.96 0.12
5 0.07 0.41 0.14 -0.5 -0.55 0.31 0.55 -0.35 0.01
6 -0.29 0.4 -0.37 0.02 -0.49 -0.12 0.22 0.01 0.1
7 -0.18 0.33 -0.38 0.16 -0.15 0.13 0.23 0.09 0.19
8 -0.61 0.15 -0.44 0.43 -0.19 0.19 0.38 -0.01 -0.04
9 -0.27 -0.06 -0.74 0.05 0.08 0 0.2 -0.19 -0.21
10 -0.28 0.17 -0.25 0.12 -0.12 -0.03 0.16 -0.13 -0.01
Age 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.41 0.33 0.07 -1.83 -0.04 -0.45 0.96 1.19 0.71
3 0.36 0.68 0.68 -1.05 -0.2 -0.7 0.75 0.24 -0.19
4 0.24 0.51 0.85 -0.85 0.13 -0.85 0.3 0.35 -0.17
5 0.11 0.35 0.65 -0.89 -0.08 -0.61 0.18 0.45 -0.08
6 0.2 0.05 0.48 -0.55 0.29 -0.27 -0.18 0.14 -0.04
7 0.26 -0.14 0.33 -0.42 0.35 -0.42 -0.13 -0.12 0.1
8 0.27 -0.03 0.37 -0.31 0.33 -0.46 -0.17 0.05 0.41
9 0.59 0.06 0.27 -0.24 0.67 -0.14 0.28 0.26 0.46
10 0.18 -0.16 -0.05 -0.32 0.08 -0.33 -0.1 0.09 0.15
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Table 5.3.26. - North Galicia (FU 25): XSA tuning diagnostics for females (continued).
Age 2345678910
Mean Log q -13.0484 -11.744 -11.0919 -10.5817 -10.2209 -10.2209 -10.2209 -10.2209 -10.2209
S.E(Log q) 0.9461 0.8152 0.6552 0.4654 0.29 0.2687 0.3032 0.3577 0.1801
...continued overleaf
WGNEPH Report 2004 113

Regression statistics :
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
2 1.66 -2.054 16.57 0.5 17 1.38 -13.05
3 1.04 -0.159 11.9 0.61 18 0.89 -11.74
4 1.05 -0.158 11.24 0.53 18 0.72 -11.09
5 0.97 0.129 10.49 0.62 18 0.47 -10.58
6 0.91 0.466 9.99 0.75 18 0.28 -10.22
7 0.83 0.903 9.71 0.73 18 0.22 -10.21
8 0.85 0.632 9.68 0.64 18 0.26 -10.17
9 1.71 -1.429 12.57 0.29 18 0.53 -10.07
10 0.91 0.633 9.9 0.83 18 0.16 -10.27
Terminal year survivor and F summaries :
Age 2 Catchability constant w.r.t. time and dependent on age
Year class = 2001
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 263 0.985 0 0 1 0.203 0.006
F shrinkage mean 108 0.5 0.797 0.014
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
130 0.45 0.79 2 1.776 0.012
Age 3 Catchability constant w.r.t. time and dependent on age
Year class = 2000
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 245 0.643 0.683 1.06 2 0.368 0.019
F shrinkage mean 133 0.5 0.632 0.035
Weighted prediction :
Survivors Int Ext N Var F
Table 5.3.26. - North Galicia (FU 25): XSA tuning diagnostics for females (continued).
at end of year s.e s.e Ratio
167 0.39 0.45 3 1.146 0.028
Age 4 Catchability constant w.r.t. time and dependent on age
Year class = 1999
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 531 0.468 0.308 0.66 3 0.513 0.044
F shrinkage mean 352 0.5 0.487 0.065
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
435 0.34 0.24 4 0.715 0.053
...continued overleaf
WGNEPH Report 2004
114

Age 5 Catchability constant w.r.t. time and dependent on age
Year class = 1998
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 606 0.338 0.203 0.6 4 0.655 0.08
F shrinkage mean 449 0.5 0.345 0.107
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
547 0.28 0.17 5 0.597 0.088
Age 6 Catchability constant w.r.t. time and dependent on age
Year class = 1997
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 591 0.226 0.138 0.61 5 0.799 0.124
F shrinkage mean 454 0.5 0.201 0.158
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
560 0.21 0.12 6 0.59 0.13
Age 7 Catchability constant w.r.t. time and age (fixed at the value for age) 6
Year class = 1996
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 686 0.182 0.169 0.93 6 0.852 0.147
F shrinkage mean 646 0.5 0.148 0.155
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
679 0.17 0.14 7 0.831 0.148
Table 5.3.26. - North Galicia (FU 25): XSA tuning diagnostics for females (continued).
Age 8 Catchability constant w.r.t. time and age (fixed at the value for age) 6
Year class = 1995
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 521 0.158 0.144 0.91 7 0.875 0.206
F shrinkage mean 679 0.5 0.125 0.162
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
538 0.15 0.13 8 0.853 0.2
...continued overleaf
WGNEPH Report 2004 115

Age 9 Catchability constant w.r.t. time and age (fixed at the value for age) 6
Year class = 1994
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 348 0.147 0.116 0.79 8 0.88 0.204
F shrinkage mean 332 0.5 0.12 0.213
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
346 0.14 0.1 9 0.714 0.205
Age 10 Catchability constant w.r.t. time and age (fixed at the value for age) 6
Year class = 1993
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
FLEET 1 239 0.136 0.123 0.91 9 0.896 0.156
F shrinkage mean 241 0.5 0.104 0.155
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
239 0.13 0.11 10 0.833 0.156
Table 5.3.26. - North Galicia (FU 25): XSA tuning diagnostics for females (continued).
WGNEPH Report 2004
116

WGNEPH Report 2004 117
Figure 5.3.1. - North G
alicia (FU 25): Long-term trends in landings, effort, LPUEs, and mean sizes of Nephrops .
Landings - Internation
0
200
400
600
800
1960 1965 1970 1975 1980 1985
Landings (tonnes)
al
1990 1995 2000 2005
Effort - Spanish 'bacas' from A Coruña
0
3000
6000
9000
12000
15000
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Effort (days fishing)
LPUE - Spanish 'baca
0
4
8
12
16
20
1960 1965 1970 1975 1980 1985
LPUE (kg / day * average BHP/100)
s' from A Coruña
1990 1995 2000 2005
Mean sizes - Spanish trawlers
26
30
34
38
42
46
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Mean size (mm carapace length)
Landings Mal
Landings Fem
International but
exclusively Spain

WGNEPH Report 2004
118
Figure 5.3.2. - North Galicia (FU 25): Landings, effort and LPUEs by quarter and sex from Spanish Nephrops trawlers.
LPUE - Females
0
3
6
9
12
15
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
LPUE (kg / trip * average BHP/100)
Qtr 2 Qtr 4 Annual
Landings
0
100
200
300
1994 1995 1996 1997 1998 1999
Landings (tonnes)
2000 2001 2002 2003
Total
LPUE - Males
0
3
6
9
12
15
1994 1995 1996 1997 1998 1999
LPUE (kg / trip * average BHP/100)
2000 2001 2002 2003
Qtr 4 Annual
Effort - A Coruña trawlers
0
3
6
9
12
15
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Quarterly effort ('000 trips
* average BHP/100)
0
10
20
30
40
Annual effort
Qtr 2 Qtr 4 Total
Qtr 1 Qtr 3
Females
Qtr 1 Qtr 3
Qtr 1 Qtr 3
Qtr 2
Males

Figure 5.3.3. - North Galicia (FU 25): VPA diagnostics males:
Log catchability residuals.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1985 1990 1995 2000 2005
2 3 4 5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1985 1990 1995 2000 2005
6 7 8 9
WGNEPH Report 2004 119

-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1985 1990 1995 2000 2005
2 3 4 5
1.0
1.5
2.0
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1985 1990 1995 2000 2005
678910
Figure 5.3.4. - North Galicia (FU 25): VPA diagnostics females:
Log catchability residuals.
WGNEPH Report 2004
120

Recruitment
0
5000
10000
15000
20000
1980 1985 1990 1995 2000 2005
Recruits (millions)
Spawning Stock Biomass
0
200
400
600
800
1000
1200
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 4-7
1.20
1.40
0.00
0.20
0.40
0.60
0.80
1.00
1980 1985 1990 1995 2000 2005
Fbar
Figure 5.3.5. - North Galicia (FU 25): VPA diagnostics males: Retrospective
analyses.
WGNEPH Report 2004 121

Recruitment
0
5000
10000
15000
20000
1980 1985 1990 1995 2000 2005
Recruits (millions)
Spawning Stock Biomass
0
200
400
600
800
1000
1200
1400
1600
1800
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 4-8
0.00
0.05
0.10
0.15
0.20
0.25
0.30
0.35
0.40
Fbar
1980 1985 1990 1995 2000 2005
Figure 5.3.6. - North Galicia (FU 25): VPA diagnostics females: Retrospective
analyses.
WGNEPH Report 2004
122

WGNEPH Report 2004 123
Fi
g
ure 5.3.7 - North Galicia
(
FU 25
)
: Output VPA males: Trends in Landin
g
s, Fbar, Total Stock Biomass and Recruitment.
Catches
0
100
200
300
400
1980 1985 1990
Catches (tonnes)
1995 2000 2005
Fishing Mortality Fbar 4-7
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1980 1985 1990 1995 2000 2005
Fbar
Recruitment (age 2)
0
3
6
9
12
15
18
1980 1985 1990 1995 2000 2005
Recruits (millions)
Total Stock Biomass
0
400
800
1200
1600
1980 1985 1990
TB (tonnes)
1995 2000 2005

WGNEPH Report 2004
124
Fi
g
ure 5.3.8. - North Galicia
(
FU 25
)
: Output VPA females: Trends in Landin
g
s, Fbar, Total Stock Biomass and Recruitment.
Catches
0
100
200
300
400
1980 1985 1990
Catches (tonnes)
1995 2000 2005
Fishing Mortality Fbar 4-8
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1980 1985 1990 1995 2000 2005
Fbar
Recruitment (age 2)
0
3
6
9
12
15
18
1980 1985 1990 1995 2000 2005
Recruits (millions)
Total Stock Biomass
0
400
800
1200
1600
1980 1985 1990
TB (tonnes)
1995 2000 2005

WGNEPH Report 2004 125
Males
Figure 5.3.9. - N
R = 0.693 R = 0.486
Females
orth Galicia (FU 25): Effort and Fbar, and relationship between them, for males and females.
0
1
2
3
4
5
6
7
8
9
10
1980 1985 1990
Effort ('000 days fishing)
1995 2000 2005
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Fbar
Fbar
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
3.5 4.0 4.5 5.0 5.5 6.0
Effort ('000 days fis
Fbar
6.5 7.0 7.5 8.0 8.5
hing)
0
1
2
3
4
5
6
7
8
9
10
1980 1985 1990 1995 2000 2005
Effort ('000 days fishing)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Fbar
Effort Fbar
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
3.5 4.0 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 8.5
Effort ('000 days fishing)
Fbar
Effort

F multiplier
A
bsolute FbarReference point
Fbar(4-7) 1.0000 0.4019
0.7668 0.3081
F0.1 0.4105 0.1649
FMax
Males
-50
-40
-30
-20
-10
0
10
20
30
40
50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
% Change in Effort
% Change in Y/R and SSB/R
SSB/R long-term Landings Y/R long-term
Females
-50
-40
-30
-20
-10
0
10
20
30
40
50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
% Change in Effort
% Change in Y/R and SSB/R
SSB/R long-term Landings Y/R long-term
Reference point F multiplier
A
bsolute Fbar
F0.1 1.4041 0.1739
Fbar(4-8) 1.0000 0.1239
FMax 5.2462 0.6499
Figure 5.3.10. - North Galicia (FU 25): Y/R analysis based on output VPA:
Relative changes in long-term Y/R and long-term SSB/R upon relative changes in effort.
Males and females shown separately.
WGNEPH Report 2004
126

Figure 5.3.11. - North Galicia (FU 25): Short-term predictions of relative changes in landings and SSB
over two years, based on output of VPA with status quo F in the intermediate year.
WGNEPH Report 2004 127
Males
-100
-80
-60
-40
-20
0
20
40
60
80
100
-100 -80 -60 -40 -20 0 20 40 60 80 100
% change in effort
% change in landings or SSB
Landings in 2005 vs 2003 SSB in 2006 vs 2004
Females
-100
-80
-60
-40
-20
0
20
40
60
80
100
-100 -80 -60 -40 -20 0 20 40 60 80 100
% change in effort
% change in landings or SSB
Landings in 2005 vs 2003 SSB in 2006 vs 2004

WGNEPH Report 2004
128
Figure 5.3.12. - Cantabrian Sea (FU 31): Long-term trends in landings, effort, CPUEs and/or LPUEs, and mean sizes of Nephrops .
Land
0
40
80
120
160
200
1960 1965 1970 1975 198
Landings (tonnes)
ings - International
0 1985 1990 1995 2000 2005
Effort - Spanish trawlers
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Effort (days fishing)
LPUE - Spanis
0
5
10
15
20
25
30
1960 1965 1970 1975 19
LPUE (kg / index)
h trawlers
80 1985 1990 1995 2000 2005
Mean sizes - Spanish trawlers
32
36
40
44
48
52
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Mean size (mm carapace length)
Landings Mal
Landings Fem
International but
exclusively Spain
Avilés
Santander

5.4 Management Area Q
ICES description IXa
Functional Units West Galicia (FU 26)
North Portugal (FU 27)
South-West Portugal - Alentejo (FU 28)
South Portugal - Algarve (FU 29)
Gulf of Cadiz (FU 30)
The statistical rectangles comprised in this Management Area and its constituent Functional Units are shown in Figure
5.1.3.
5.4.1 West Galicia (FU 26) and North Portugal (FU 27)
Description of the fisheries
Spain and Portugal
The description of bottom fisheries in the Northwest Spain was updated in STECF (2002) and SGMOS (2003). The
overall decline of some bottom target species (including hake and Nephrops) in recent years have influenced the fishing
strategies of the trawl fleet in terms of gears and target species. Nephrops is only caught by baca bottom trawl.
Consequently, the species composition of the landings from this fishery has changed.
Trends in landings, effort, LPUE, CPUE and mean sizes
Table 5.4.1 FUs 26 and 27 - Landings by country, 1994-2003
Table 5.4.2 FUs 26 and 27 - LPUEs Spanish fleet, 1994-2003
Table 5.4.3 FUs 26 and 27 - Mean sizes of Nephrops in landings, Spanish data, 1994-2003
Table 5.4.5 FU 27 - Effort and CPUEs Portuguese, 1994-2003
Table 5.4.6 FU 27 - Mean sizes of Nephrops in landings and surveys, Portuguese data, 1994-2003
Figure 5.4.1 FU 26 - Long-term trends in landings, effort, CPUE and mean size
Landings and effort statistics are reported by Spain. Minor quantities of landings are reported by Portugal. Catches by
the Spanish fleets are taken on the West Galicia (FU 26) and North Portugal (FU 27) fishing grounds. Nephrops
represents a minor proportion of the landings composition but is a very valuable species for the profitability of these
fleets.
Landings, effort and LPUE - Spain - FUs 26 and 27
Landings by the Spanish fleets are mostly from FU 26, together with smaller quantities taken from FU 27 (Table 5.4.1).
At recent low levels of landings, the difference between the quantities from the two FUs is reducing. Prior to 1996, no
distinction was made between the two FUs, and therefore they are considered together.
Two periods can be distinguished in the time series of landings available (1975-2003) (Figure 5.4.1). During 1975-
89, landings were more or less stable, between 600 and 800 t. From 1990 onwards there has been a marked downward
trend in landings. In 2002, the landings dropped to 83 t, and in 2003 the landings were at the lowest recorded level of
65 t. Part of the decrease in 2002 and 2003 landings is explained by the partial closure of the fishery on the West
Galicia grounds from November to December of 2002 and from January to April of 2003, due to an oil spill off Spain’s
NW coast.
The overall trend in total fishing effort (trips) is downward, with 2003 having approximately a half of the fishing
effort compared to the late 1980s. The reduction in effort was notably evident in the fleets of Marín since 1992, fishing
in both FUs 26 and 27, and Riveira fishing in FU 26 (Figure 5.4.1).
LPUE data are available for the fleets of Muros and Riveira (since 1984), Marín (since 1990) and Vigo (since
1995) (Figure 5.4.1). The general trend in the LPUEs is downward, with substantial decreases for the fleets of Marín
and Vigo since 1998. Given the substantial decrease in landings and the overall decrease in effort, the LPUEs remain at
low levels in recent years.
Landings, effort and CPUE - Portugal - FU 27
Table 5.4.1 shows the official landing figures for the years 1994-2003 and a breakdown of the landings by gear type
(trawl and artisanal). Total Portuguese landings from FU 27 have decreased since 1989, to a level of about 6 t in the last
three years.
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Numbers of trawlers pursuing this fishery have varied from 3 to 8 boats since 1992 (Table 5.4.5).
Mean size - Spanish data- Mostly FU 26
The mean sizes of both males and females in the Spanish landings have fluctuated widely, but without particular trend
(Figure 5.4.1). Mean sizes dropped to very low values in 1990, but have returned to much higher and relatively stable
values up to 2000. Mean sizes were 38.1 mm and 34.8 mm CL for males and females respectively in 2003.
Mean size - Portuguese data - FU 27
Mean sizes for males and females, derived from Portuguese port samples and demersal research surveys, are available
for 1985-98 and 1985-93 respectively (Table 5.4.6). There is no additional information for the most recent years.
Trawl survey abundance indices
Table 5.4.4 FU 26 - Nephrops abundance indices from trawl surveys, 1994-2003
Table 5.4.4 gives the abundance indices (mean stratified catches) of Nephrops off West Galicia, derived from data
collected during bottom trawl surveys carried out in autumn. The main objective of these surveys is the estimation of
hake recruitment, and catch rates of Nephrops are variable and low.
Data and biological inputs for analytical assessments
Table 5.4.7 Sampling data and input parameters
Annual length composition data are available for the Spanish landings for the period 1988-2003. Length composition
for the Portuguese landings are available solely for the period 1990-96. Since 1997 Spanish length composition data
were raised to total landings in FU 26 and 27. Nephrops discarding is minimal in these fisheries (primarily it is the soft
or crushed individuals that are rejected). Estimates of the quantities discarded (derived from data collected in 1994,
1997 and 1999) ranged from 0.1 to 3.4% by weight. The fishing effort for the Muros (1995-02) and Marín (1994-03)
trawl fleets were used for tuning.
Biological input parameters were unchanged to those used in previous assessments (ICES, 2003a).
General comments on quality of data and inputs
Table 5.4.8 Assessment deficiencies in 2004
Issues that may generally cause problems for assessment of Nephrops are highlighted in Section 10. Assessment
deficiencies specific to FU 26 are summarised in Table 5.4.8.
The Spanish landing statistics are considered reliable, and the sampling programme is assumed to be adequate for
the level of the landings. The length composition data available for the Portuguese landings are based on a very small
number of samples, which do not cover all months. However, the Portuguese landings from FU 27 are low. Fishing
effort is directed to a target species, and depending on the season, this may not be specifically Nephrops.
Age based assessments (VPA)
Males
Table 5.4.9 XSA settings males
Table 5.4.11 Output VPA males: Fs-at-age
Table 5.4.13 Output VPA males: Long-term trends in landings, Fbar, TB and recruitment
Table 5.4.47 Full listing of VPA input and output data tables
Table 5.4.49 Full listing of XSA diagnostic output
Figure 5.4.2 VPA diagnostics males: Log catchability residuals, Marín fleet
Figure 5.4.3 VPA diagnostics males: Log catchability residuals, Muros fleet
Figure 5.4.6 VPA diagnostics males: Retrospective analyses
Figure 5.4.8 Output VPA males: Long-term trends in landings, Fbar, TB and recruitment
Figure 5.4.10 Output VPA males: Plots of Fbar vs. effort
The assessment was carried out using Spanish length compositions for 1988-2003. Effort data for the Marín and Muros
fleets were used for tuning. The slicing procedure was used to separate 8 ‘age’ groups of which ‘age’ 8 was adopted as
the plus-group. The XSA tuning options for the final run are summarised in Table 5.4.9. The log catchability residuals
are high at all ages, but particularly at first ages for both tuning fleets (Figures 5.4.2-3).
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Retrospective analysis does not show any consistent bias pattern in Fbar, whereas there is a consistent
overestimation in recruitment and SSB. The retrospective results are quite similar to those obtained in the previous
assessment (ICES, 2003a). Different shrinkage weights for the mean F were tried and a value of 0.5 was adopted for
the final analysis, and applied over the last five years and on the five oldest ages.
The trends in the estimates of yield, Fbar, total stock biomass (TB) and recruitment are plotted in Figure 5.4.8. Fbar
estimates fluctuated widely between 0.5 and 1.2, but without overall trend. TB estimates were stable during 1988-92,
but declined markedly from this point onwards. The estimated recruitment also declined, from the peak in 1989 to very
low values in 1996 onwards. The assessment gives an extremely low recruitment estimate in 2001 onwards (Table
5.4.13.). Fbar did not correlate with effort (r = 0.40, p > 0.05) (Figure 5.4.10).
Females
Table 5.4.10 XSA settings females
Table 5.4.12 Output VPA females: Fs-at-age
Table 5.4.14 Output VPA females: Long-term trends in landings, Fbar, TB and recruitment
Table 5.4.48 Full listing of VPA input and output data tables
Table 5.4.50 Full listing of XSA diagnostic output
Figure 5.4.4 VPA diagnostics females: Log catchability residuals, Marín fleet
Figure 5.4.5 VPA diagnostics females: Log catchability residuals, Muros fleet
Figure 5.4.7 VPA diagnostics females: Retrospective analyses
Figure 5.4.9 Output VPA females: Long-term trends in landings, Fbar, TB and recruitment
Figure 5.4.10 Output VPA females: Plots of Fbar vs. effort
The slicing procedure separated 11 ‘age’ groups. ‘Age’ 11 was adopted as the plus-group. The XSA tuning options for
the final run are summarised in Table 5.4.10. Tuning was undertaken using data for both Marín and Muros fleets. High
log catchability residuals for the Marín fleet are observed in ages 1 and 2, with some year effects in the oldest ages
(Figure 5.4.4). Also, high values were noted at all ages for the Muros fleet, and positive values in ages 6 to 10 (Figure
5.4.5).
Retrospective analysis did not show a consistent bias in the estimation pattern of F and SSB, but recruitment is
consistently overestimated (Figure 5.4.7). Different shrinkage weights for the mean F were tried and a final value of 0.5
was adopted for the final analysis, and this was applied over the last five years and on the five oldest ages.
Trends in the estimates of yield, Fbar, total stock biomass (TB) and recruitment are plotted in Figure 5.4.9. Fbar
estimates are considerably lower than for males, and have fluctuated without trend between 0.2 and 0.6. Estimated TB
was stable up to 1994, but declined sharply in later years. Estimated recruitment has declined since 1989, remaining at
an extremely low level from 1996 onwards. The correlation between Fbar and effort is not significant (r = 0.11, p > 0.05)
(Figure 5.4.10). In general, the results of the trends from the assessment are similar to those obtained in the previous
year (ICES, 2003a).
Y/R analysis based on output of VPA
Table 5.4.15 Long-term Y/R and SSB/R based on outputs of VPA: males
Table 5.4.16 Long-term Y/R and SSB/R based on outputs of VPA: females
Figure 5.4.11 Long-term Y/R and SSB/R based on outputs of VPA: males and females
The long-term Y/R curves based on the VPA outputs indicate that the males are over-exploited, with current F well
above Fmax. The Y/R curve is very flat-topped in females.
Short-term predictions
Table 5.4.17 Males: Short-term predictions of landings and biomass, with status quo F in 2004
Table 5.4.18 Females: Short-term predictions of landings and biomass, with status quo F in 2004
Figure 5.4.12 Males and females: Short-term predictions of relative changes in landings and SSB over two years,
based on the output of VPA
Short-term predictions were performed using low values of recruitment (arithmetic mean for 2001-2003) for the years
2004-2006, according to the results suggested by the XSA for the last years of the time series, and applying the average
F-at-age for 2000-2002.
At status quo F, the short-term prediction results in a decrease of 30 % in male and 21% in female stock biomass
in 2006. Drastic reductions in F2005 (even > 90 %) will slightly increase male SSB in 2006 (about 7 %) but there would
be almost no change in female SSB compared to the 2003 level (Table 5.4.18, Figure 5.4.12).
WGNEPH Report 2004 131

Management considerations
Landings of Nephrops from FUs 26-27 have substantially declined since 1990.
The assessments for FUs 26-27 suggest that biomass and recruitment are at very low levels. XSA indicates a
drastic reduction in stock biomass and recruitment since 1995.
Short-term predictions indicate that at current levels of fishing mortality landings are expected to be very low in
2005 (Tables 5.4.17-18). A 50 % reduction in F, would result in a 28 % reduction in biomass. Severe reductions in F
would produce only small increase in the stock biomass in 2006 relative to 2004. Given the depleted status of the West
Galicia and North Portugal stocks, there are no reasons to change the 2003 ICES advice of zero TAC for these
Functional Units.
5.4.2 South-West and South Portugal (FUs 28-29)
Description of the fisheries
Portugal
The description and general characteristics of the fishery remain the same, yet there are some changes to the
information given in the previous WG reports (ICES, 1999a, 2001a), namely, estimates of fishing effort and landing
values. During 2003 there were 35 vessels licensed for the crustacean fishery, a number which has not changed for the
last 4 years. It should however be emphasised that despite the number of trawlers being the same, some vessels have
been replaced by new and more powerful ones. The crustacean trawlers’ overall lengths range from 23m to 35m and are
equipped with engines varying from 300 to 900 HP in power.
As stated in previous reports, the crustacean fleet targets deepwater shrimp and Nephrops, using a mesh size of
55 mm. Since the beginning of 2003, these vessels were also licensed for 70 mm, the legal mesh size for Nephrops. It is,
however, not clear that this mesh size is actually used.
The demersal fish trawlers catch deepwater shrimp and Nephrops as by-catch with a legal mesh size of 65 mm.
Fishing effort estimates for this mixed fishery have increased relatively to 2002 (measured in days during which
Nephrops was the main target species).
Trends in landings, effort, CPUE and mean size
Table 5.4.19 Landings by country, 1994-2003
Table 5.4.20 Effort and CPUEs Portuguese fleet, 1994-2003
Table 5.4.21 CPUEs in research trawl surveys, Portuguese data, 1994-2003
Table 5.4.22 Mean sizes of Nephrops in landings, Portuguese data, 1994-2003
Table 5.4.23 Mean sizes of Nephrops in research trawl surveys, 1994-2003
Figure 5.4.13 Long-term trends in landings, effort, CPUE and mean size, Portuguese data
Figure 5.4.14 Landings by sex and half yearly plots of effort and CPUEs by sex, 1994-2003
Figure 5.4.15 Mean sizes of Nephrops in Portuguese surveys, 1991-2003
Landings, effort and CPUE
Up to 1992 the estimated landings from FUs 28 and 29 have fluctuated between 450 and 530 t, with a long-term
average of about 480 t (Figure 5.4.13.). Between 1990 and 1996, the landings fell drastically, to an all time low of 132 t.
In 1999, landings increased again by approximately 40 %, remaining at this level in 2000 (~ 200 t). From 2000 to 2002,
landings have increased at a rate of almost 35 % in each year, reaching 360 t in 2002 and remained at the same level in
2003. The landings are, however, still below the levels observed in the 1980s. Males are the dominant component in all
landings with exception for 1995 and 1996 when total female landings exceeded male landings (Figure 5.4.14.). For the
last 3 years male to female sex-ratio has been close to 2:1.
Total fishing effort (fishing days), estimated from the CPUE obtained from the fishing logs of the trawler fleet,
decreased from a peak value in 1985 to much lower values in the early 1990s, and since 1999 fishing effort has
increased substantially (Figure 5.4.13). Very few fishing log records were available for the year 2001 and the figures
were therefore considered unreliable. The effort was estimated instead by the product of the number of fishing trips
targeting Nephrops and the average duration in days. For the year 2002, the effort was estimated as in the period before
and checked with the method used in 2001. It is important to state that this is an estimation of nominal effort and did not
take into consideration the changes in fleet composition or efficiency. In 2003 effort was estimated solely from the
CPUE obtained from the fishing logs of the crustacean trawl fleet. The estimated effort corresponds to 11 months as the
crustacean fishery was experimentally closed in January.
Since 1989, CPUE has declined considerably, from almost 120 kg/day in 1989 to a mean of about 50 kg/day in the
period 1995-2003 (Figure 5.4.13). This seems to be mostly the result of a decrease in male CPUE (Figure 5.4.14). The
CPUEs for females were more or less stable, with a peak in 1995. The highest CPUEs normally occur during the first
half of the year, but since 1997 this picture has become more variable. In 2001, male CPUE increased slightly and
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132

female CPUE decreased, whereas in 2002, only the female CPUE showed a little increase (Figure 5.4.14). In 2003, on
the other hand, both male and female CPUE have decreased by 7 % and 4.5 %, respectively.
Mean size
Mean carapace length (CL) data for males and females in the landings are available for 1984-2002 (Table 5.4.22 and
Figure 5.4.13), and from research survey catches since 1991 (Table 5.4.23 and Figure 5.4.15). The mean sizes of both
male and female Nephrops in the landings remained fairly stable until 1993, but have fluctuated since then. A slight
increase in mean size of males in the landings was observed in the period 1999-2002. The surveys also show some
evidence of this increase. In 2003 the observed mean CL for landed males has decreased slightly, whereas the mean CL
for females remained the same. The CL data obtained during the crustacean survey indicates that the mean CL has
decreased in both males and females.
Data and biological inputs for analytical assessments
Table 5.4.24 Sampling data and input parameters
Length distributions of the Portuguese trawl landings are obtained from samples taken once or twice a month at the
main landing ports. The sampling data are raised to the total landings by market category, vessel and month. It is
assumed that there are no discards. Excluding the year 2001 (see above), effort data were estimated from the fishing
logs provided by the trawlers reporting Nephrops catches (crustacean and finfish fleets).
Input parameters to the assessments were the same as those used in previous years (see e.g. ICES, 2003a). For
females, two growth curves were used, with the transition length set at 30 mm CL.
General comments on quality of data and inputs
Table 5.4.25 Assessment deficiencies in 2004
Issues that may generally cause problems for assessment of Nephrops are highlighted in Section 10. Assessment
deficiencies specific to FUs 28-29 are summarised in Table 5.4.25.
Since 1995, only the port of Vila Real de Santo António has been sampled for Nephrops, since almost all trawlers
targeting crustaceans land their catches in this port. Sampling frequency in 2003 was at the same level as in the years
before. The relatively small size of the samples may be a source of uncertainty, and may artificially increase the level of
variation in the estimated length compositions of the landings.
So far, it has been assumed that there are no discards in this fishery. A sampling programme, started at the end of
the year 2000 on board the crustacean fleet, will provide an estimate of the discards to be included in future
assessments.
The quality of data from the fishing logs must be improved in order to produce a more reliable estimate of effort.
Age based assessments (VPA)
A VPA was carried out on males and females separately, using the Portuguese length composition and effort data for
1984-2003.
The surveys performed in the period 1997-2003 were used in the tuning process. As the surveys were performed
with a smaller mesh size than the commercial fishery, this information should provide a better estimation of the
survivors of the first ages.
Males
Table 5.4.26 XSA settings males
Table 5.4.28 Output VPA males: Fs-at-age
Table 5.4.30 Output VPA males: Long-term trends in landings, Fbar, TB and recruitment
Table 5.4.51 Full listing of VPA input and output data tables
Table 5.4.53 Full listing of XSA diagnostic output
Figure 5.4.16 VPA diagnostics males: Log catchability residuals from trawl fleet data
Figure 5.4.17 VPA diagnostics males: Log catchability residuals from survey data
Figure 5.4.20 VPA diagnostics males: Retrospective analyses
Figure 5.4.22 Output VPA males: Long-term trends in landings, Fbar, TB and recruitment
Figure 5.4.24 Output VPA males: Plots of Fbar vs. effort
The slicing procedure separated landed numbers-at-age for ‘ages’ 1 to 8. The plus-group was set at ‘age’ 8. The
percentage of the removals at this age ranged from 0.2-3.8%, except for the years 2001 and 2002 when it reached 5%.
WGNEPH Report 2004 133

In 2003, this value slightly decreased to 4%. Landings at ‘age’ 1 were low or even zero and so this group was excluded
from the assessment.
Retrospective analysis (Figure 5.4.20) showed a consistent pattern of overestimation of F in the last year and a
consequent underestimation of the SSB. Recruitment does not seem to show any consistent bias. Different shrinkage
weights for the mean F were tried and a final value of 2.0, applied over the last three years and on the two oldest ages,
was adopted for the final analysis. The resulting F values were higher than those obtained with a stronger shrinkage, and
the estimated total stock biomass and recruitment were more conservative.
Data from the crustacean trawl fleet (1988-2003) and from crustacean trawl surveys (1997-2003) were used in the
tuning procedure. Due to the short time series of the surveys, the retrospective analysis was conducted using only the
trawl fleet data.
The XSA tuning options are summarised in Table 5.4.26.
Log catchability residuals are generally small, and whilst there are some year effects there are no overall trends
over time (Figure 5.4.16 and 5.4.17).
Estimated male total stock biomass (TB) and recruitment have decreased sharply since 1989 and 1992 respectively
(Figure 5.4.22). TB increased slightly from 1995. Recruitment was estimated at a low level, remaining constant since
1997. Fbar decreased from 1992 to 1997 but has increased since then. F2003 was estimated at 0.61, reaching a value
similar to those observed in 1994, approaching the highest value for the series. Fbar shows a significant correlation with
effort (r = 0.62, p < 0.05) (Figure 5.4.24).
Females
Table 5.4.27 XSA settings females
Table 5.4.29 Output VPA females: Fs-at-age
Table 5.4.31 Output VPA females: Long-term trends in landings, Fbar, TB and recruitment
Table 5.4.52 Full listing of VPA input and output data tables
Table 5.4.54 Full listing of XSA diagnostic output
Figure 5.4.18 VPA diagnostics females: Log catchability residuals from trawl fleet data
Figure 5.4.19 VPA diagnostics females: Log catchability residuals from survey data
Figure 5.4.21 VPA diagnostics females: Retrospective analyses
Figure 5.4.23 Output VPA females: Long-term trends in landings, Fbar, TB and recruitment
Figure 5.4.24 Output VPA females: Plots of Fbar vs. effort
The slicing procedure separated landed numbers-at-age for ‘ages’ 1 to 13. As landings at ‘age’ 1 were zero in some of
the years, this age was excluded from the assessment. The plus-group was set at ‘age’ 13. The percentage of the
removals at this age ranged from 0.1-2.0%, except in the period 2000-2003, when it was around 5%.
The log catchability residuals are generally small for the commercial fleet, but a little higher for the surveys, with
some year effects, but no overall trends over time (Figure 5.4.18 and 5.4.19).
Retrospective analysis (Figure 5.4.21) indicates that this assessment is poorly converged and unstable, but did not
show any consistent bias in the estimation of F, SSB and recruitment. As for the males, different shrinkage weights for
the mean F were tried and a final value of 2.0, applied over the last three years and on the five oldest ages, was adopted
for the final analysis. The XSA settings are shown in Table 5.4.27. Tuning was carried out in a similar way to that
performed for males.
Estimated total stock biomass of females shows a continuous declining trend in the period 1987-1996, stabilising
at a low current level. Similarly to male estimates female recruitment has remained constant since 1997, yet at lower
levels than in the period 1982-1992. Fbar was relatively stable from 1984 till 1994 (typically fluctuating between 0.20
and 0.40), but in 1995 a very high value (0.44) was recorded, which is associated with the high landings figure for the
females in that year (Figure 5.4.23). After a minimum value in 1997, Fbar values have returned to the pre-1995 levels,
increasing slightly in 2003 relatively to 2002. Fbar does not seem to be greatly influenced by changes in effort (r = 0.42,
p > 0.05). Contributing to this lack of correlation might be the high 1995 Fbar considered as an outlier (Figure 5.4.24).
Long-term Y/R analysis based on VPA outputs
Table 5.4.32 Long-term Y/R and SSB/R based on outputs of VPA: males
Table 5.4.33 Long-term Y/R and SSB/R based on outputs of VPA: females
Figure 5.4.25 Long-term Y/R and SSB/R based on outputs of VPA: males and females
The long-term Y/R curves indicate that the males are over-exploited, with current F well above Fmax.
Short-term predictions
Table 5.4.34 Males: Short-term predictions of landings and biomass, with status quo F in 2004.
Table 5.4.35 Females: Short-term predictions of landings and biomass, with status quo F in 2004.
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Figure 5.4.26 Males and females: Short-term predictions of relative changes in landings and SSB over two years,
based on the output of VPA.
Short-term predictions were performed using the MFDP package, for a single trawl fleet with no discards.
Predictions were performed using the geometric mean of the recruitment values for 1997-2003, which were
considered to be stable, yet at a low level. Taking into account the high Fbar estimated for 2003, the average Fs-at-age
for 2001-2003 were scaled for the last year.
At status quo F for males, the prediction shows a decline in total stock biomass in 2006 of 7 % relative to 2004
(Table 5.4.34 and Figure 5.4.26). Increases in SSB2006 relative to SSB2004 would be expected with reductions of F2005
greater than 30 %.
The projections for females imply that the status quo F in 2004-2005 will result in an 8 % decrease in SSB2006
relative to SSB2004 and only reductions in F greater than 50 % predict increases in the SSB2005 level (Table 5.4.35 and
Figure 5.4.26). The complete closure of the fishery will only result in a 9 % increase in female SSB2006.
Considering the males and females together, a decrease of 8 % in SSB2006 relative to SSB2004 would be expected at
current effort levels. To prevent an overall decrease in SSB, a 40% reduction in effort would be needed.
Fishery independent methods -Trawl surveys
Table 5.4.21. CPUEs in research trawl surveys, Portuguese data, 1991-2003
Over the past decade, several finfish and crustacean directed trawl surveys were carried out in FUs 28 and 29. Table
5.4.21 shows the average Nephrops CPUEs (in kg/hour trawling) from these surveys, which can be used as an overall
abundance index. The figures confirm the stabilisation of the total stock biomass at a low level.
Comments on quality of the assessments
As stated in previous WG reports (see e.g. ICES, 1999a), the growth parameters and the value of M are the main
sources of uncertainty in the assessment.
Management considerations
1. The stock assessment for FUs 28-29 suggests that stock biomass and recruitment remain at a very low level.
2. The increase in the estimated F in 2001-2003 may have been a result of the increased efficiency within the fleet as
well as of the redirected effort towards Nephrops.
3. Based on the combined output from male and female predictions using the F scaled to the most recent year, status
quo F would lead to a 8% reduction in SSB in 2006 relative to 2004 (7 % and 8 % for males and females,
respectively) and a 23 % decrease in landings in 2005 (22 % reduction in males and 6 % in females).
4. To maintain the combined biomass in 2006 at the 2004 level, a reduction of 40 % in F would be needed in 2005,
and a complete closure will only result in a 18 % increase in SSB.
5. There are no reasons to change the 2002 and 2003 ICES advice of zero TAC for these Functional Units. The WG
strongly recommends that urgent measures should be taken to reduce the present level of fishing mortality to the
lowest possible. These measures may be combined with other technical measures (closed seasons, closed areas,
etc.) aiming to rebuild the stock, as recommended in the recovery plan for the Southern Hake and Iberian Norway
Lobster proposal (SGMOS, 2003).
5.4.3 Gulf of Cádiz (FU 30)
Nephrops in the Gulf of Cádiz are caught in a mixed fishery prosecuted by the trawl fleet. Nephrops landings are clearly
seasonal with high values from April to September. The species represents 1.3% of the total trawl landings from the
area. The main Nephrops fishing grounds are located between 400 and 700 m depth.
Trends in landings, effort, CPUE/LPUE and mean sizes
Table 5.4.36 FU 30 - Landings by country, 1994-2003
Table 5.4.37 FU 30 - Effort and LPUE Spanish fleet, 1994-2002
Table 5.4.38 FU 30 - CPUE in Spanish research trawl surveys, 1993-2003
Table 5.4.39 FU 30 - Mean sizes of Nephrops in landings 2001-2003
Table 5.4.40 FU 30 - Mean sizes of Nephrops in surveys, 1993-2003
Figure 5.4.27 FU 30 - Long-term trends in landings, effort, LPUE and mean sizes
WGNEPH Report 2004 135

Figure 5.4.28 FU 30 - Mean size of Nephrops in surveys
Landings data for FU 30 are available for 1985-2003 (Figure 5.4.27). Up to 1993, the landings have fluctuated widely
around a long-term average of 215 t. Landings dropped to an absolute low of 49 t in 1996, but have since recovered to
129 t in 2000. Afterwards, landings increased and were 285 t in 2003 (Table 5.4.36). Practically all landings were
reported by Spain.
Total trawl fishing effort remained stabilised during 1994-2003 around an average of 32000 fishing days (Table
5.14.37). However, the effort targeting Nephrops increased in 2000, remained stable up to 2002 and increased again in
2003. This pattern seems to be due to the renewal of the trawl vessels, making it easier to access the more remote and
deeper fishing grounds. The estimate of the Nephrops directed effort in the Gulf of Cádiz has been based on the
definition of the landings from different fishing trips from its catch composition (Jiménez et al., 2004). Thus, to
estimate the target effort, only days fishing from the Nephrops and Nephrops-Parapenaeus longirostris fishing trips
were considered. However, from 1998 onwards the classification of the fishing trips deteriorated.
LPUE from vessels targeting Nephrops fluctuate without a clear trend since 1996, although previous values in
1994-95 were higher (Table 5.4.37). LPUE obtained from the whole trawl fleet show a relative increase during the last
three years. Table 5.4.38 gives the CPUE of Nephrops off the Gulf of Cádiz, collected during bottom trawl surveys
carried out in March and November. The series does not correspond to the main Nephrops season, because the main
objective of these surveys is the overall estimation of commercial fish abundance.
Male and female mean sizes in landings are available for 2001-2003 (Table 5.4.40). Mean sizes from surveys peak
in 1995 for both male and female (46.9 and 37.4 mm CL respectively), but are largely stable since 1997.
Data and biological inputs for analytical assessments
Table 5.4.41 Sampling data and input parameters
Length compositions of landings are only available for 2001, 2002 and 2003. Stock-specific biological data are lacking,
and biological inputs were adopted as a preliminary compromise between the observed data from surveys carried out in
the area, and biological information from other FUs (South Portugal and Galicia). L-infinity for males was taken as the
maximum Nephrops length in surveys and largest landing size of females was used as the female L-infinity.
General comments on quality of data and inputs
Table 5.4.42 Assessment deficiencies in 2004
Issues that may generally cause problems for assessment of Nephrops are highlighted in Section 10. Assessment
deficiencies specific to FU 30 are summarised in Table 5.4.42.
Length based assessments (LCA)
Table 5.4.43 LCA output males.
Table 5.4.44 LCA output females.
Figure 5.4.29 Output LCA: Relative changes in short-term and long-term Y/R and long term B/R upon relative
changes in effort.
The results of Y/R analysis indicate that for males current F is about 50% above Fmax, but the Y/R curve is very flat-
topped and small gains in yield are predicted upon a reduction of F to Fmax (Table 5.4.43 and Figure 5.4.29). For
females, current F appears to be below Fmax (Table 5.4.44 and Figure 5.4.29).
Comments on quality of the assessments
In view of the uncertainties about input parameters and given the poor sampling, the LCA assessment was considered as
preliminary. Furthermore, given recent increasing trends in landings and effort the steady state assumptions of the LCA
are questionable.
Management considerations
Landings from this FU have increased in line with fishing effort over recent years. However, there is some uncertainty
about the extent to which the recent stability of LPUE has been a result of increases in efficiency or could correspond to
the exploration of new fishing grounds not accessible at all to the older fleet. Assessment of this FU by LCA has been
attempted for the first time, but the results of this analysis are preliminary. At present, there is insufficient evidence that
current levels of landings could be sustained in the long-term.
WGNEPH Report 2004
136

5.4.4 Summary for Management Area Q
Table 5.4.45 Landings by FU and from Other rectangles, 1993-2002
Table 5.4.46 Landings by country, 1993-2002
MA Q includes five FUs (West Galicia, FU 26; North Portugal, FU 27; SW and S Portugal, FUs 28-29; and Gulf of
Cadiz, FU 30). Stock biomass and recruitment estimates from the age based assessments have seriously declined for
some FUs and remained at a very low level for others. The total landings in the northern FUs have decreased but a great
increase has been recorded in FUs 28-29 and 30 during the last two years. This corresponds to a sharp increase in F in
these FUs.
The WG strongly recommends that the Nephrops stocks in MA Q be monitored very closely and that they be re-
assessed in 2005. Considering the increased landings recorded in FUs 28-29 and FU 30, and the low levels of biomass
in recruitment in FUs 28-29, the WG also recommends that increased attention should be paid to collecting more and
detailed information on Nephrops stocks in FU 30, and to the links between the FUs 28-29 and FU 30 in terms of stocks
and fishing pressure.
Apart from a small allowance of 50 t for FU 30, ICES advice for MA O for 2003 was for a zero TAC. The
allowance of 50 t for FU 30 was based on the low level of landings observed in 1996, whereas the recent perception of
the fishery and current landings from this FU are well above the previous recommendation However, based on the
stock assessments and short-term predictions, which remain unfavourable for various stocks (FUs 26+27 and 28+29) in
this Management Area, the WG needs more evidence of sustainability in landings from FU 30 before suggesting any
other catch option.
WGNEPH Report 2004 137

FU 26
Trawl Creel Sub-total
426 na 14 8 22
501 na 9 1 10
264 50 17 0 17
359 68 6 0 6
295 42 8 0 8
194 48 6 0 6
102 21 9 0 9
105 21 6 0 6
59 24 4 0 4
39 26 7 0 7
* provisional na = not available
** Figures for 1994-95 include landings from FU 27
*** Landings for 1994-95 included under FU 26
Muros Riveira Marin Vigo
17.8 21.5 113.9 84.7
17.2 22.0 93.3 88.5
17.5 17.6 49.5 51.6
19.7 15.2 66.3 80.6
16.3 8.2 66.0 84.2
15.5 6.7 49.5 49.6
5.3 3.7 28.9 29.4
2.3 5.9 33.6 35.0
2.2 2.3 31.2 41.6
2.2 0.5 24.0 35.1
* provisional
LPUE (kg/trip)
132
132
72
87
433
345
248
448
511
331
Portugal
FU 27
Spain
***
FUs 26-27 combined
All countries
all gears
1994
1994
2003*
Year
2000
1995
1996
1997
1998
Table 5.4.1. - West Galicia (FU 26) and North Portugal (FU 27): Landings (tonnes) by
country, 1994-2003.
Table 5.4.2. - West Galicia (FU 26) and North Portugal (FU 27): LPUE (kg/trip) for Spanish
trawlers, home ports of Muros and Riveira (FU 26), and Marín and Vigo (FU 26+27), 1994-
2003.
Year Spain
**
2001
1995
1996
1997
1999
2002
2003*
1998
1999
2000
2001
2002
WGNEPH Report 2004
138

Males Females
36.0 34.4
33.4 32.2
32.1 31.4
36.7 35.6
38.4 37.8
37.8 38.3
34.8 32.2
30.3 28.4
36.6 35.3
38.1 34.8
* provisional
MSC SE MSC SE
0.06 0.02 1.5 0.6
0.28 0.16 10.5 6.6
0.08 0.05 4.2 2.5
0.05 0.02 1.1 0.3
0.13 0.09 1.8 1.2
0.18 0.06 4.3 1.5
0.08 0.04 1.5 0.7
0.31 0.15 8.3 3.7
0.02 0.01 0.4 0.2
na na
na = not available
Year
1997
1998
Table 5.4.3. - West Galicia (FU 26) and North Portugal (FU 27): Mean sizes (mm CL) of
male and female Nephrops in Spanish landings, 1994-2003.
Table 5.4.4. - West Galicia (FU 26): Mean stratified catches (MSC) and standard errors
(SE) of Nephrops in bottom trawl surveys off West Galicia, 1994-2003.
1999
2002
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
Nos. / 30 min haul
Year Landings
2000
2001
2003*
1994
1995
1996
Kg / 30 min haul
WGNEPH Report 2004 139

CPUE
t/boat
34.7
42.7
54.8
4na
4na
8na
8na
na na
na na
na na
* provisional na = not available
Males Females
35.1 32.9
2002
Table 5.4.6. - North Portugal (FU 27): Mean sizes (mm CL) of male and female Nephrops
in Portuguese landings, 1994-2003.
Table 5.4.5. - North Portugal (FU 27): Number of trawlers and CPUE (tonnes/boat) of
Portuguese trawlers, 1994-2003.
1995
1996
1997
1994
Year Landings
Year No. of
trawlers
2000
2001
2003*
1998
1999
1994
40.3 40.5
38.3 38.7
37.1 34.6
40.3 38.6
na na
na na
na na
na na
na na
na = not available
1997
1998
1995
1996
2001
2003
1999
2000
2002
WGNEPH Report 2004
140

WGNEPH Report 2004 141
108
1994
733
Table 5.4.7. - West Galicia and North Portugal (FUs 26-27): Input data and parameters.
Mean
no. per
sample
FU MA
FLEET GEAR
Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Qtr 4
Catch
Landings 10 7 15 14 83 14 14 15 12
Discards
Year 2003 2002 2001 2000 1999 1998 1997 1996 1995
Catch
Landings 46556564536461534
Discards
Value
na
0.150
80
0.2
0.00043
3.160
0.150
80
0.2
26
0.100
65
0.2
0.00043
3.160
26
Spain
Q
Trawl
Fariña (1984)
"
Fariña, unpublished
ICES (1991a)
"
"
"
Based on Fernandez et al. (1986)
Fernandez et al. (1986)
"
Based on Fernandez et al. (1986)
Fernandez et al. (1986)
"
Fariña (1984)
Number of samples Number of samples
Number of samples
2003 2002
INPUT PARAMETERS
Parameter
Discard Survival
MALES
Not applicable - few discards
Growth - K
Growth - L(inf)
Natural mortality - M
Length/weight - a
Natural mortality - M
Size at maturity
Mature Growth
Length/weight - b
FEMALES
Immature Growth
Growth - K
Length/weight - b
Source
Mean
no. per
sample
Growth - K
Growth - L(inf)
Natural mortality - M
Length/weight - a
Growth - L(inf)

Table 5.4.8. – West Galicia (FU 26): Assessment deficiencies 2004.
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
XSA 2
Tuning data 3 The tuned fleets are not Nephrops directed. High log catchability
residuals in all ages and for the two tuned fleets.
CSA N/A
Fishery independent
methods
N/A
Assessment
method
LCA N/A
Definition 1 There are other stock in adjacent areas FU 25 North Galicia and FU27
North Portugal. Limits between stocks are defined by fishing fleet
operations.
Stock
Structure 1 Juvenile fraction seems to be located in shallower waters
Fishery Definition (Mixed,
targeted, multifleet)
2 Nephrops is a by catch of the bottom mixed fishery. Only the baca trawl
component fish Nephrops.
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.
WGNEPH Report 2004
142

WGNEPH Report 2004 143
Table 5.4.8. – West Galicia (FU 26): Assessment deficiencies 2004 (continued).
CPUE N/A
Catch N/A
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Catch N/A
Landings 1 Landings data are extracted from the sale sheets. The accuracy of these
data is considered high.
Discards 1 Discards rates are very low, due to the high value of the species. Only
soft and damaged individuals are discarded.
Effort 2 The fishing effort correspond to the total bottom trawl fleet, that fish for
a set of demersal and bottom species depending on marked forces.
Catch
statistics
LPUE 2 Depends on accounting of fishing effort on bottom fishery and not
exclusively on Nephrops.
Landings 1 The length frequency distributions of Nephrops were obtained by
sampling commercial landings at port. The monthly sampling
programme of the landings from this FU is considered to be at a
sufficient level of intensity.
Sampling
levels
Discards N/A
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

WGNEPH Report 2004
144
Table 5.4.8. – West Galicia (FU 26): Assessment deficiencies 2004 (continued).
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Age and growth 2 Age compositions of removals were inferred by slicing the length
compositions.
Maturity 2 Female maturity data were derived from the adjacent stock of North
Galicia. In the male assessment 100% maturity is assumed. The
sensitivity of the assessment to this approach has not been investigated
Natural mortality 2 No experimental data on M have been made. There are not known
predators on Nephrops in the area, nor drastic temporal changes in the
environmental and habitat conditions. A standard value of M (0.2) for
males and females was adopted, in similar way as others Nephrops
stocks.
Discard Mortality N/A
Escape Mortality N/A
Biological
parameters
Length/weight
coefficients
1 Length/weight relationship derived from the adjacent stock of North
Galicia.
Fishing surveys 3 Data on Nephrops in surveys are collected as associated information.
Surveys are undertaken out of the main season for Nephrops. Survey
design is not directed to estimate the Nephrops abundance.
Larval surveys N/A
Availability
of research
survey data
TV survey N/A
Availability
of other
information
Species composition 1 Programme for monitoring the species composition of the trawl fleet
continued as a rule. Database collection is updated annually.
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

WGNEPH Report 2004 145
26-27 MA Q Males
Minimum
First age fo
(2) Muros
Table 5.4.9. - West Galicia and North Portugal (FUs 26-27): XSA settings used in the assessment - Males.
First age at
(1) Marín
Did tuning
Prior fleet
Population
F shrinkage
Taper tim
applied ?
Fleets used
Tuning ra
(3)
XSA Setting
Year rang
FU
Age range
First year Last year
1988 2003
Last age Plus group
7 Yes - 8+
First year Last year
1994 2003
Years used Ages used
1994-2003 1-7
1995-2003 2-7
No
1
3
Yes/No Type
Yes Tricubic over 20 years
Yes/No If Yes: Min. SE for Mean F
Yes 0.5
If Yes: Year range If Yes: Age range
1999-2003 4-8
Yes/No
Yes
0.3
Yes (20 iterations)
Log SE for terminal population estimates
Choices Justification
r normal catchability independent analysis
Plus-group chosen such that proportion in catches was > 0.5 % but < 3.0 %
Available data
which q is considered independent of age
in numbers
Available data
Through examination of regression statistics and residuals
Through examination of catchability at age
Default option
Default option
converge after 30 iterations or less ?
weighting?
shrinkage
e weighting
nge
s
e

WGNEPH Report 2004
146
26-27 MA Q Females
Age range
Year rang
(3)
Taper tim
applied ?
Fleets used
Tuning ra
Did tuning
Prior fleet
Population
F shrinkage
Table 5.4.10. - West Galicia and North Portugal (FUs 26-27): XSA settings used in the assessment - Females.
First age at
(1) Marín
Minimum
First age fo
(2) Muros
FU
XSA Setting
First year Last year
1988 2003
Last age Plus group
10 Yes - 11+
First year Last year
1994 2003
Years used Ages used
1994-2003 1-10
1995-2003 2-10
No
1
5
Yes/No Type
Yes Tricubic over 20 years
Yes/No If Yes: Min. SE for Mean F
Yes 0.5
If Yes: Year range If Yes: Age range
1999-2003 7-11
Yes/No
Yes
0.3
No (30 iterations)
e
e weighting
nge
converge after 30 iterations or less ?
weighting?
shrinkage
Default option
Default option
Available data
which q is considered independent of age
in numbers
Available data
Through examination of regression statistics and residuals
Through examination of catchability at age
Log SE for terminal population estimates
Choices Justification
r normal catchability independent analysis
Plus-group chosen such that proportion in catches was > 0.5 % but < 3.0 %
s

WGNEPH Report 2004 147
2002 2003
0.00 0.02
0.22 0.32
0.90 0.78
0.92 0.99
1.18 1.23
0.81 1.32
0.71 1.03
0.71 1.03
2002 2003
0.00 0.01
0.08 0.15
0.16 0.13
0.21 0.22
0.26 0.25
0.42 0.45
0.51 0.45
0.54 0.36
0.33 0.31
0.39 0.29
0.39 0.29
Table 5.4.11. - West Galicia and North Portugal (FUs 26-27): VPA Fs-at-age males.
Age 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
1 0.00 0.05 0.26 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.11
2 0.13 0.48 1.17 0.56 0.22 0.21 0.09 0.30 0.66 0.20 0.07 0.07 0.27 1.15
3 1.08 0.84 0.91 1.23 0.70 0.76 0.66 0.98 0.98 0.82 0.79 0.69 0.72 1.15
4 1.03 0.91 1.05 1.03 1.02 1.05 1.03 1.15 0.89 1.10 1.06 1.02 1.03 0.94
5 0.89 1.25 1.04 0.74 1.28 1.18 1.32 0.88 1.13 1.08 1.15 1.28 1.25 0.91
6 0.70 1.37 0.69 0.68 1.56 0.75 1.83 0.94 0.86 0.95 1.30 1.08 1.48 1.28
7 0.77 0.98 0.98 0.85 0.97 0.80 0.97 0.94 1.12 1.01 0.95 0.79 0.98 1.42
+ grp 0.77 0.98 0.98 0.85 0.97 0.80 0.97 0.94 1.12 1.01 0.95 0.79 0.98 1.42
Age 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001
1 0.00 0.05 0.17 0.01 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.02 0.05
2 0.09 0.37 0.48 0.25 0.10 0.09 0.07 0.15 0.34 0.08 0.03 0.02 0.18 0.55
3 0.33 0.36 0.25 0.32 0.20 0.20 0.14 0.40 0.26 0.26 0.19 0.16 0.19 0.29
4 0.48 0.43 0.21 0.31 0.32 0.27 0.28 0.50 0.29 0.48 0.40 0.43 0.39 0.29
5 0.57 0.43 0.22 0.44 0.30 0.37 0.34 0.45 0.29 0.47 0.56 0.65 0.35 0.26
6 0.52 0.44 0.18 0.39 0.26 0.40 0.37 0.28 0.27 0.38 0.60 0.74 0.35 0.27
7 0.55 0.28 0.25 0.39 0.28 0.47 0.39 0.25 0.22 0.34 0.55 0.84 0.45 0.22
8 0.46 0.33 0.27 0.30 0.21 0.54 0.54 0.25 0.23 0.35 0.61 0.86 0.37 0.20
9 0.44 0.82 0.21 0.27 0.34 0.53 0.45 0.53 0.27 0.41 0.51 1.15 0.27 0.25
10 0.51 0.46 0.23 0.36 0.28 0.46 0.43 0.42 0.47 0.55 0.57 0.61 0.32 0.26
+ grp 0.51 0.46 0.23 0.36 0.28 0.46 0.43 0.42 0.47 0.55 0.57 0.61 0.32 0.26
Table 5.4.12. - West Galicia and North Portugal (FUs 26-27): VPA Fs-at-age females.

WGNEPH Report 2004
148
1.09
1.07
0.52
0.62
1.04
1.00
0.90
0.92
0.53
0.92
0.99
1.17
0.75
0.66
0.78
0.68
0.70
0.48
0.38
0.23
0.36
0.26
0.37
0.34
0.36
0.26
0.38
0.49
0.61
0.35
0.26
0.35
0.31
0.31
Table 5.4.13. - West Galicia and North Portugal (FUs 26-27): VPA output males.
Fbar
3-5
Fbar
3-8
'000 tonnes tonnes tonnes
1988 25723 947 947 465 0.49
1989 35016 968 968 437 0.45
1990 24510 943 943 273 0.29
1991 14997 1026 1026 372 0.36
1992 13542 1012 1012 474 0.47
1993 14604 798 798 324 0.41
1994 12150 722 722 265 0.37
1995 10871 690 690 293 0.42
1996 5281 559 559 179 0.32
1997 3446 539 539 252 0.47
1998 2465 352 352 178 0.51
1999 2817 224 224 115 0.51
2000 3396 181 181 75 0.41
2001 1309 155 155 75 0.48
2002 685 113 113 48 0.42
2003 818 100 100 41 0.41
Average 01-03
'000 tonnes tonnes tonnes
1988 23161 1053 914 262 0.29
1989 30846 1023 869 271 0.31
1990 21433 1027 920 177 0.19
1991 15572 1057 979 231 0.24
1992 14358 1029 943 162 0.17
1993 12064 931 931 199 0.21
1994 11056 937 882 184 0.21
1995 8252 863 830 218 0.26
1996 3762 722 700 153 0.22
1997 2464 630 630 180 0.29
1998 2439 499 499 167 0.33
1999 3441 343 343 131 0.38
2000 3712 225 207 58 0.28
2001 2171 206 195 57 0.29
2002 843 182 177 39 0.22
2003 1548 155 147 31 0.21
Average 01-03
Recruits
Age 1
Total
Biomass SSB Catch
Year Yield/SSB
Table 5.4.14. - West Galicia and North Portugal (FUs 26-27): VPA output females.
Recruits
Age 1
Total
Biomass SSB Catch
Year Yield/SSB

MFYPR version 2a
Run: 1
Time and date: 19:20 28/03/04
Yield per results
FMult Fbar CatchNos
Y
ield StockNos Biomass SpwnNosJan SSBJan SpwnNosSpwn SSBSpwn
0.0000 0.0000 0.0000 0.0000 5.5167 0.4319 5.5167 0.4319 5.5167 0.4319
0.1000 0.0677 0.1940 0.0165 4.5511 0.2763 4.5511 0.2763 4.5511 0.2763
0.2000 0.1354 0.3086 0.0220 3.9820 0.1935 3.9820 0.1935 3.9820 0.1935
0.3000 0.2031 0.3846 0.0235 3.6057 0.1445 3.6057 0.1445 3.6057 0.1445
0.4000 0.2708 0.4390 0.0233 3.3375 0.1132 3.3375 0.1132 3.3375 0.1132
0.5000 0.3385 0.4800 0.0225 3.1360 0.0921 3.1360 0.0921 3.1360 0.0921
0.6000 0.4062 0.5122 0.0215 2.9786 0.0773 2.9786 0.0773 2.9786 0.0773
0.7000 0.4739 0.5382 0.0205 2.8518 0.0665 2.8518 0.0665 2.8518 0.0665
0.8000 0.5416 0.5598 0.0195 2.7471 0.0583 2.7471 0.0583 2.7471 0.0583
0.9000 0.6093 0.5780 0.0187 2.6591 0.0521 2.6591 0.0521 2.6591 0.0521
1.0000 0.6770 0.5936 0.0179 2.5839 0.0471 2.5839 0.0471 2.5839 0.0471
1.1000 0.7447 0.6072 0.0172 2.5187 0.0431 2.5187 0.0431 2.5187 0.0431
1.2000 0.8124 0.6192 0.0166 2.4616 0.0399 2.4616 0.0399 2.4616 0.0399
1.3000 0.8801 0.6298 0.0161 2.4111 0.0371 2.4111 0.0371 2.4111 0.0371
1.4000 0.9478 0.6394 0.0156 2.3660 0.0349 2.3660 0.0349 2.3660 0.0349
1.5000 1.0155 0.6480 0.0151 2.3255 0.0329 2.3255 0.0329 2.3255 0.0329
1.6000 1.0832 0.6558 0.0147 2.2888 0.0312 2.2888 0.0312 2.2888 0.0312
1.7000 1.1509 0.6630 0.0144 2.2555 0.0298 2.2555 0.0298 2.2555 0.0298
1.8000 1.2186 0.6695 0.0141 2.2249 0.0285 2.2249 0.0285 2.2249 0.0285
1.9000 1.2863 0.6756 0.0138 2.1969 0.0273 2.1969 0.0273 2.1969 0.0273
2.0000 1.3540 0.6812 0.0135 2.1710 0.0263 2.1710 0.0263 2.1710 0.0263
Reference point F multiplier
A
bsolute F
Fbar(3-5) 1.0000 0.6770
FMax 0.3297 0.2232
F0.1 0.2048 0.1386
F35%SPR 0.2833 0.1918
Table 5.4.15. - West Galicia & North Portugal (FUs 26-27): Long-term yield per recruit analysis of males.
WGNEPH Report 2004 149

WGNEPH Report 2004
150
MFYPR version 2a
Run: 1
Time and date: 19:22 28/03/04
Yield per results
FMult Fbar CatchNos
Y
ield StockNos Biomass SpwnNosJan SSBJan SpwnNosSpwn SSBSpwn
0.0000 0.0000 0.0000 0.0000 5.5167 0.2209 4.5167 0.2156 4.5167 0.2156
0.1000 0.0309 0.1037 0.0048 5.0002 0.1774 4.0002 0.1721 4.0002 0.1721
0.2000 0.0619 0.1825 0.0077 4.6080 0.1467 3.6080 0.1413 3.6080 0.1413
0.3000 0.0928 0.2446 0.0095 4.2993 0.1241 3.2993 0.1188 3.2993 0.1188
0.4000 0.1238 0.2949 0.0105 4.0496 0.1071 3.0496 0.1018 3.0496 0.1018
0.5000 0.1547 0.3367 0.0112 3.8428 0.0940 2.8428 0.0887 2.8428 0.0887
0.6000 0.1856 0.3719 0.0116 3.6684 0.0836 2.6684 0.0783 2.6684 0.0783
0.7000 0.2166 0.4021 0.0118 3.5190 0.0753 2.5190 0.0700 2.5190 0.0700
0.8000 0.2475 0.4284 0.0119 3.3893 0.0685 2.3893 0.0632 2.3893 0.0632
0.9000 0.2785 0.4515 0.0119 3.2754 0.0629 2.2754 0.0575 2.2754 0.0575
1.0000 0.3094 0.4720 0.0119 3.1745 0.0581 2.1745 0.0528 2.1745 0.0528
1.1000 0.3403 0.4904 0.0118 3.0842 0.0541 2.0842 0.0488 2.0842 0.0488
1.2000 0.3713 0.5070 0.0117 3.0030 0.0506 2.0030 0.0453 2.0030 0.0453
1.3000 0.4022 0.5220 0.0116 2.9293 0.0476 1.9293 0.0423 1.9293 0.0423
1.4000 0.4332 0.5357 0.0115 2.8622 0.0450 1.8622 0.0397 1.8622 0.0397
1.5000 0.4641 0.5484 0.0114 2.8007 0.0427 1.8007 0.0373 1.8007 0.0373
1.6000 0.4950 0.5600 0.0113 2.7442 0.0406 1.7442 0.0353 1.7442 0.0353
1.7000 0.5260 0.5707 0.0112 2.6920 0.0388 1.6920 0.0334 1.6920 0.0334
1.8000 0.5569 0.5807 0.0110 2.6435 0.0371 1.6435 0.0318 1.6435 0.0318
1.9000 0.5879 0.5900 0.0109 2.5985 0.0356 1.5985 0.0303 1.5985 0.0303
2.0000 0.6188 0.5987 0.0108 2.5566 0.0343 1.5566 0.0289 1.5566 0.0289
Reference point F multiplier
A
bsolute F
Fbar(3-8) 1.0000 0.3094
FMax 0.8720 0.2698
F0.1 0.4616 0.1428
F35%SPR 0.6317 0.1955
Table 5.4.16. - West Galicia & North Portugal (FUs 26-27): Long-term yield per recruit analysis of females.

MF
F
Ti
F
DP version 1a
Run: 1
U26+27 West GaliciaINDEX FILE
me and date: 19:11 28/03/04
bar age range: 3-5
2004
Biomass SSB FMult FBar Landings
73 73 1.0000 0.6770 30
2005 2006
Biomass SSB FMult FBar Landings Biomass SSB
58 58 0.0000 0.0000 0 82 82
. 58 0.1000 0.0677 3 78 78
. 58 0.2000 0.1354 6 74 74
. 58 0.3000 0.2031 9 71 71
. 58 0.4000 0.2708 11 67 67
. 58 0.5000 0.3385 14 64 64
. 58 0.6000 0.4062 16 61 61
. 58 0.7000 0.4739 18 58 58
. 58 0.8000 0.5416 20 55 55
. 58 0.9000 0.6093 22 53 53
. 58 1.0000 0.6770 24 51 51
. 58 1.1000 0.7447 25 48 48
. 58 1.2000 0.8124 27 46 46
. 58 1.3000 0.8801 28 44 44
. 58 1.4000 0.9478 30 43 43
. 58 1.5000 1.0155 31 41 41
. 58 1.6000 1.0832 32 39 39
. 58 1.7000 1.1509 33 38 38
. 58 1.8000 1.2186 34 36 36
. 58 1.9000 1.2863 35 35 35
. 58 2.0000 1.3540 36 34 34
Table 5.4.17. - West Galicia & North Portugal (FUs 26-27): Short-term predictions of landings
and biomass of males. Status quo F in 2004.
WGNEPH Report 2004 151

WGNEPH Report 2004
152
B
Table 5.4.18. - West Galicia & North Portugal (FUs 26-27): Short-term predictions of landings
and biomass of females. Status quo F in 2004.
MFDP version 1a
Run: 1
26+27 West Galicia FINDEX FILE
Time and date: 19:17 28/03/04
Fbar age range: 3-8
2004
Biomass SSB FMult FBar Landings
141 133 1.0000 0.3094 32
2005 2006
Biomass SSB FMult FBar Landing Yield Biomass SS
126 118 0.0000 0.0000 0 146 138
. 118 0.1000 0.0309 3 142 134
. 118 0.2000 0.0619 6 138 130
. 118 0.3000 0.0928 9 135 127
. 118 0.4000 0.1238 12 132 123
. 118 0.5000 0.1547 15 128 120
. 118 0.6000 0.1856 18 125 117
. 118 0.7000 0.2166 21 122 114
. 118 0.8000 0.2475 23 119 111
. 118 0.9000 0.2785 26 116 108
. 118 1.0000 0.3094 28 114 105
. 118 1.1000 0.3403 31 111 103
. 118 1.2000 0.3713 33 108 100
. 118 1.3000 0.4022 35 106 98
. 118 1.4000 0.4332 37 103 95
. 118 1.5000 0.4641 39 101 93
. 118 1.6000 0.4950 41 98 90
. 118 1.7000 0.5260 43 96 88
. 118 1.8000 0.5569 45 94 86
. 118 1.9000 0.5879 47 92 84
. 118 2.0000 0.6188 49 90 82

FUs 28-29
Spain
Trawl Artisanal Sub-total Trawl
237 0 237 na 237
272 1 273 na 273
128 4 132 na 132
134 2 136 na 136
159 2 161 na 161
206 5 211 na 211
197 4 201 na 201
269 2 271 na 271
358 1 359 na 359
327 35 362 na 362
* provisional na = not available
31 7.6 4183 57
30 9.1 4463 61
25 5.3 3451 38
25 5.5 2646 52
25 6.4 4404 36
29 7.3 3175 66
33 6.1 4344 46
33 8.2 5587 48
34 10.5 6646 54
35 9.3 6486 50
* provisional
2001
2000
1996
1997
2002
2003*
Year
2000
2001
1994
1995
1998
1999
CPUE
(t/boat)
Estimated
days
CPUE
(kg/day)
No. of
trawlers
1997
1996
1998
1999
2003*
2002
Table 5.4.19. - SW and S Portugal (FUs 28-29): Landings (tonnes) by country, 1994-2003.
Table 5.4.20. - SW and S Portugal (FUs 28-29): Effort and CPUE of Portuguese trawlers,
1994-2003.
1994
1995
Year Portugal Total
WGNEPH Report 2004 153

Summer Autumn
ns 0.7 May-94 2.3
1.3 0.8
ns 0.2
0.7 0.3 Jun-97 2.5
0.7 0.2 Jun-98 1.3
0.3 0.4 Jun-99 2.5
1.0 0.9 Jun-00 1.4
0.6 0.4 Jun-01 0.5
ns 0.1 Jun-02 2.4
ns 0.9 Jun-03 2.6
ns = no survey na = not available
Landings
37.4 33.6
39.3 37.0
36.9 36.6
35.9 32.8
36.8 34.5
38.7 34.6
38.9 35.2
41.6 36.1
40.7 36.2
39.1 36.4
* provisional na = not available
1997
1998
1999
2003*
2000
2002
Females
1994
Males
2001
1997
1995
1996
2000
1996
1995
1994
Year
Note: The 1996 autumn demersal survey and all the 1999 surveys were carried out with
a different research vessel.
1998
1999
2001
No surveys 1995-96
CPUE
(kg/hour)
Month and
year of
survey
2002
Table 5.4.22. - SW and S Portugal (FUs 28-29): Mean sizes (mm CL) of male and
female Nephrops in Portuguese landings, 1994-2003.
2003
Table 5.4.21. - SW and S Portugal (FUs 28-29): Nephrops CPUEs (kg/hour) in research
trawl surveys, 1994-2003.
Demersal surveys
CPUE (kg/hour)
Crustacean surveys
Year
WGNEPH Report 2004
154

Crustacean surveys
Males Females Males Females
ns ns 39.0 33.6 ns ns
42.1 35.6 42.0 34.9 ns ns
ns ns 38.6 32.2 ns ns
40.4 36.9 39.1 31.7 43.7 41.9
36.0 33.9 40.6 35.9 39.5 36.7
45.1 40.4 43.8 32.8 39.7 37.5
40.8 37.1 39.0 35.1 41.7 40.2
40.5 34.5 47.2 41.6 44.5 39.9
41.8 40.6 35.0 39.0 44.8 40.7
na na 37.5 32.3 39.7 36.7
ns = no survey na = not available
2003
1997
1998
1999
2001
2002
2000
Females
Demersal surveys
Autu mnSummerYear Males
Table 5.4.23. - SW and S Portugal (FUs 28-29): Mean sizes (mm CL) of male and
female Nephrops in Portuguese research trawl surveys, 1994-2003.
1996
1994
1995
FU 28 & 29 MA Q
FLEET Portugal GEAR Trawl
Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Qtr 4
Catch
Landings 7 13 12 13 363 12 14 12 13 327
Discards
Year 2003 2002 2001 2000 1999 1998 1997 1996 1995 1994
Catch
Landings 455149432943213930108
Discards
Value
0.00
0.200
70 "
0.3
0.00028
3.2229
0.200
70
0.3
30
0.065
65
0.2
0.00056
3.0288
Figueiredo (pers. comm., 1986)
"
ICES (1994b)
Portuguese data (Bhattacharya method) ; tagging (ICES, 1990a)
"
Figueiredo (1989)
"
Portuguese data (Bhattacharya method) ; tagging (ICES, 1990a)
"
Figueiredo (1989)
Portuguese data (Bhattacharya method) ; tagging (ICES, 1990a)
Figueiredo (1989)
Figueiredo (pers. comm., 1986)
Number of samples Number of samples
Number of samples
Discard Survival
MALES
Growth - K
2003 2002
INPUT PARAMETERS
Parameter
Mean
no. per
sample
Growth - L(inf)
Natural mortality - M
Length/weight - a
Natural mortality - M
Mature Growth
Length/weight - b
FEMALES
Immature Growth
Growth - K
Table 5.4.24. - South-West and South Portugal (FUs 28-29): Input data and parameters.
Length/weight - b
Source
Mean
no. per
sample
Growth - K
Growth - L(inf)
Natural mortality - M
Length/weight - a
Growth - L(inf)
Size at maturity
WGNEPH Report 2004 155

WGNEPH Report 2004
156
Table 5.4.25. – SW and S Portugal (FUs 28-29): Assessment deficiencies 2004.
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
XSA 2
Tuning data 2 Data from trawl fleet (since 1988) and from trawl surveys (since 1997) were used for the tuning. The
last series is too short and the log catchability residuals are higher.
CSA N/A A trial was made. The results point to the same direction as XSA.
Fishery independent
methods
2 Trawl surveys abundance indices are available since 1980. Although the sampling programme was
different along the period, trends can be extracted.
Assessment
method
LCA N/A The method was used until 2001 as an alternative method and to compare the results to the XSA
output. From 2001, the steady state assumption could not be met and the method was not applied.
Definition 3 There are 2 FUs assessed as a unique stock. They are probably two distinct stocks but it is not
possible to differentiate the catches.
Stock
Structure 2 Population structure from the 2 FUs available only from surveys.
Fishery Defi ed, nition (Mix
targeted, multifleet)
2 This is a multifleet and multispecies fishery. Interactions between species and/or fleets are not taken
into account.
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available/Not applicable

WGNEPH Report 2004 157
Table 5.4.25. – SW and S Portugal (FUs 28-29): Assessment deficiencies 2004.
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Catch 2 Obtained from landings and logbooks
Landings 2 Recorded landings are adjusted using a correction factor for weight losses and black landings. It is
not possible to assign to individual FUs.
Discards 1 No Nephrops discards in this fishery.
Effort 2 Total effort estimated from crustacean trawlers’ logbooks and/or number of trips x average no. of
days per trip.
Catch
statistics
CPUE 2 Estimated from crustacean trawlers’ logbooks
Catch N/A No catches sampling programme
Landings 2 Samples are collected at the main crustacean auction place by size categories.
Sampling
levels
Discards N/A No Nephrops discards in this fishery.
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available/Not applicable

WGNEPH Report 2004
158
Table 5.4.25. – SW and S Portugal (FUs 28-29): Assessment deficiencies 2004.
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Age and growth 2 The von Bertalanffy growth parameters used are from ICES (1990)
Maturity 2 Female maturity data are routinely collected under the sampling programme. However, knife-edge
maturity at 30 mm as a fixed vector is used in the XSA assessment. In the male assessment 100%
maturity is assumed. The sensitivity of the assessment to this approach has not been investigated.
Natural mortality 2 Assumed values, based on Figueiredo (1989)
Discard mortality N/A No Nephrops discards in this fishery.
Escape mortality N/A No Nephrops discards in this fishery.
Biological
parameters
Length/weight
coefficients
2 Parameters used were estimated by Figueiredo (pers. comm., 1986). Revision in process.
Availability
of research
survey data
Fishing surveys 1 Species composition, length frequencies and maturity information are available from crustacean trawl
surveys since 1980, yet with different sampling programmes and at different seasons. From 1997, a
stratified trawl survey for crustaceans species is conducted every year in June.
Availability
of other
information
Species composition 2 1. Total species composition for the trawl fleet available from a discards sampling programme started
in 1999.
2. Commercial catch composition can be extracted from fishing logbooks
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available/Not applicable

WGNEPH Report 2004 159
28-29 MA Q Males
First year Last year
1984 2003
Last age Plus group
7Y (8+)
First year Last year
1988 2003
Years used Ages used
1988-2003 2-8
1997-2003 2-8
N
3
6
Yes/No Type
Y tricube, 20 years
Yes/No If Yes: Min. SE for Mean F
Y2.0
If Yes: Year range If Yes: Age range
Final 3 years 2 oldest ages
Yes/No
Y
0.5
N
Minimum Log SE for terminal population estimates
Choices Justification
First age for normal catchability independent analysis
(2) Crustacean surveys
Table 5.4.26. - SW and S Portugal (FUs 28-29): XSA settings used in the assessment - Males.
First age at which q is considered independent of age
Plus-group between 0.3 and 5% of total removals.
Log-book data started in 1988.
(1) Trawl fleet
The regression slope at age 2 is significantly different from 1.
No reasons to change the option from earlier assessments.
The catchability of age 2 dependent on stock size
No reasons to change the option from earlier assessments.
Value chosen according the retrospective analysis
Did tuning converge after 30 iterations or less ?
Prior fleet weighting?
Population shrinkage
F shrinkage
Taper time weighting
applied ?
Fleets used
Tuning range
(3)
The data of 1999 survey were not used because it was carried out with a different
vessel and did not cover the whole area.
The default values were considered too large considering the variation of F in the last
period and the total age range.
FU
Age range
XSA Settings
Year range

WGNEPH Report 2004
160
28-29 MA Q Females
First year Last year
1984 2003
Last age Plus group
12 Y (13+)
First year Last year
1988 2003
Years used Ages used
1988-2003 2-12
1997-2003 2-12
N
4
8
Yes/No Type
Y tricube, 20 years
Yes/No If Yes: Min. SE for Mean F
Y2.0
If Yes: Year range If Yes: Age range
Final 3 years 5 oldest ages
Yes/No
Y
0.5
N
Year range
Taper time weighting
applied ?
Fleets used
Tuning range
F shrinkage
The catchability of age 2 and 3 are dependent on stock size
Did tuning converge after 30 iterations or less ?
Population shrinkage
Minimum Log SE for terminal population estimates
Table 5.4.27. - SW and S Portugal (FUs 28-29): XSA settings used in the assessment - Females.
First age at which q is considered independent of age
Log-book data started in 1988.
(1) Trawl fleet
The regression slopes at age 2 and 3 are significantly different from 1.
Choices Justification
First age for normal catchability independent analysis
(2) Crustacean surveys
Prior fleet weighting?
(3)
Age range
No reasons to change the option from earlier assessments.
The data of 1999 survey were not used because it was carried out with a different
vessel and did not cover the whole area.
The default values were considered too large considering the variation of F in the last
period and the total age range.
Value chosen according the retrospective analysis
FU
XSA Settings

WGNEPH Report 2004 161
Age 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.150.250.130.260.150.170.200.290.340.330.200.020.070.080.080.070.090.040.060.12
3 0.450.530.630.430.440.270.530.560.761.020.540.540.430.390.310.280.250.340.490.51
4 0.590.520.730.580.400.500.780.670.860.840.681.100.450.240.270.310.200.430.690.66
5 0.530.660.980.640.420.880.630.991.140.961.110.450.380.220.300.420.300.470.580.69
6 0.381.080.540.430.340.920.330.870.800.481.140.330.200.110.330.490.420.550.610.82
7 0.460.880.770.540.410.560.460.660.540.470.460.320.320.220.410.300.610.860.780.86
+ grp 0.460.880.770.540.410.560.460.660.540.470.460.320.320.220.410.300.610.860.780.86
Age 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.200.240.160.490.210.200.180.260.250.260.140.010.030.080.080.080.090.040.060.08
3 0.130.190.150.280.190.120.220.220.200.240.190.090.050.140.090.140.080.090.100.09
4 0.230.170.230.230.300.170.280.200.220.200.160.240.070.150.110.140.120.130.240.16
5 0.260.270.220.320.340.270.320.140.190.160.150.490.150.120.120.190.130.130.340.20
6 0.430.240.320.190.290.300.200.110.240.130.150.620.240.130.140.220.160.110.330.24
7 0.360.290.260.260.280.310.340.130.270.150.100.350.160.060.080.210.120.120.270.29
8 0.270.190.150.140.250.200.430.230.210.210.150.610.200.050.150.180.130.200.240.39
9 0.140.160.260.160.120.410.370.240.230.250.200.500.300.060.210.190.160.200.220.43
10 0.25 0.08 0.11 0.28 0.10 0.27 0.33 0.19 0.19 0.21 0.11 0.29 0.19 0.03 0.16 0.13 0.15 0.18 0.26 0.43
11 0.27 0.17 0.16 0.75 0.11 0.28 0.22 0.11 0.20 0.32 0.18 0.36 0.37 0.06 0.24 0.11 0.17 0.20 0.26 0.35
12 0.26 0.18 0.19 0.32 0.19 0.25 0.26 0.22 0.29 0.24 0.14 0.21 0.15 0.04 0.18 0.14 0.21 0.22 0.30 0.30
+ grp 0.260.180.190.320.190.250.260.220.290.240.140.210.150.040.180.140.210.220.300.30
Table 5.4.28. - SW and S Portugal (FU 28-29): VPA Fs-at-age males.
Table 5.4.29. - SW and S Portugal (FU 28-29): VPA Fs-at-age females.

'000 tonnes tonnes tonnes
1984 16884 1027 1027 292 0.28 0.43
1985 14806 999 999 353 0.35 0.65
1986 16624 900 900 315 0.35 0.63
1987 20992 946 946 277 0.29 0.48
1988 16916 1006 1006 249 0.25 0.36
1989 16866 1062 1062 318 0.30 0.55
1990 12433 1010 1010 350 0.35 0.49
1991 11858 868 868 344 0.40 0.67
1992 12524 714 714 305 0.43 0.74
1993 8093 535 535 232 0.43 0.68
1994 4915 379 379 139 0.37 0.69
1995 4002 300 300 98 0.33 0.46
1996 6372 309 309 64 0.21 0.31
1997 7790 434 434 74 0.17 0.21
1998 7999 474 474 88 0.19 0.28
1999 7117 558 558 116 0.21 0.31
2000 7305 590 590 117 0.20 0.31
2001 7326 662 662 190 0.29 0.45
2002 7114 645 645 222 0.34 0.54
2003 7970 562 562 201 0.36 0.61
Average 01-03 0.53
'000 tonnes tonnes tonnes
1984 12781 895 895 169 0.19 0.28
1985 13206 893 893 156 0.17 0.20
1986 13348 915 915 150 0.16 0.22
1987 15561 983 983 232 0.24 0.22
1988 13003 891 891 171 0.19 0.24
1989 12464 849 849 151 0.18 0.28
1990 11147 840 840 174 0.21 0.33
1991 13967 830 830 134 0.16 0.18
Table 5.4.31. - SW and S Portugal (FU 28-29): VPA output females.
Recruits
Age 2
Total
Biomass SSB Catch
Year Fbar
4-10
Yield/SSB
Table 5.4.30. - SW and S Portugal (FU 28-29): VPA output males.
Recruits
Age 2
Total
Biomass SSB Catch
Year Yield/SSB Fbar
2-7
1992 13535 869 869 165 0.19 0.22
1993 9751 834 834 145 0.17 0.19
1994 7707 758 758 97 0.13 0.14
1995 6989 744 744 174 0.23 0.44
1996 8921 661 661 67 0.10 0.19
1997 9168 709 709 62 0.09 0.08
1998 7845 732 732 72 0.10 0.14
1999 7602 734 734 95 0.13 0.18
2000 7835 765 765 84 0.11 0.14
2001 7619 752 752 79 0.11 0.15
2002 8237 778 778 135 0.17 0.27
2003 8749 745 745 126 0.17 0.30
Average 01-03 0.24
WGNEPH Report 2004
162

WGNEPH Report 2004 163
MFYPR version 2a
Run: Males FU 28-29
Time and date: 18:44 26-03-2004
Yield per results
FMult Fbar CatchNos
Y
ield StockNos Biomass SpwnNosJan SSBJan SpwnNosSpwn SSBSpwn
000 0.0000 3.8583 0.2287 3.8583 0.2287 3.8583 0.2287
455 0.0104 3.3778 0.1726 3.3778 0.1726 3.3778 0.1726
397 0.0153 3.0680 0.1392 3.0680 0.1392 3.0680 0.1392
068 0.0177 2.8481 0.1172 2.8481 0.1172 2.8481 0.1172
578 0.0190 2.6819 0.1018 2.6819 0.1018 2.6819 0.1018
981 0.0196 2.5509 0.0904 2.5509 0.0904 2.5509 0.0904
311 0.0199 2.4442 0.0818 2.4442 0.0818 2.4442 0.0818
588 0.0200 2.3554 0.0750 2.3554 0.0750 2.3554 0.0750
823 0.0200 2.2801 0.0695 2.2801 0.0695 2.2801 0.0695
027 0.0199 2.2151 0.0650 2.2151 0.0650 2.2151 0.0650
206 0.0198 2.1586 0.0612 2.1586 0.0612 2.1586 0.0612
364 0.0196 2.1087 0.0580 2.1087 0.0580 2.1087 0.0580
505 0.0195 2.0644 0.0553 2.0644 0.0553 2.0644 0.0553
633 0.0193 2.0247 0.0530 2.0247 0.0530 2.0247 0.0530
748 0.0192 1.9889 0.0509 1.9889 0.0509 1.9889 0.0509
853 0.0191 1.9564 0.0491 1.9564 0.0491 1.9564 0.0491
950 0.0189 1.9268 0.0475 1.9268 0.0475 1.9268 0.0475
038 0.0188 1.8996 0.0461 1.8996 0.0461 1.8996 0.0461
121 0.0187 1.8746 0.0448 1.8746 0.0448 1.8746 0.0448
197 0.0186 1.8515 0.0437 1.8515 0.0437 1.8515 0.0437
268 0.0185 1.8301 0.0426 1.8301 0.0426 1.8301 0.0426
olute F
110
4426
1941
3808
0.0000 0.0000 0.0
0.1000 0.0611 0.1
0.2000 0.1222 0.2
0.3000 0.1833 0.3
0.4000 0.2444 0.3
0.5000 0.3055 0.3
0.6000 0.3666 0.4
0.7000 0.4277 0.4
0.8000 0.4888 0.4
0.9000 0.5499 0.5
1.0000 0.6110 0.5
1.1000 0.6721 0.5
1.2000 0.7332 0.5
1.3000 0.7943 0.5
1.4000 0.8554 0.5
1.5000 0.9165 0.5
1.6000 0.9776 0.5
1.7000 1.0387 0.6
1.8000 1.0998 0.6
1.9000 1.1609 0.6
2.0000 1.2220 0.6
Reference point F multiplier
A
bs
Fbar(2-7) 1.0000 0.6
FMax 0.7245 0.
F0.1 0.3177 0.
F35%SPR 0.6233 0.
Table 5.4.32. - SW and S Portugal (FU 28-29): Long-term yield per recruit analysis of males.

WGNEPH Report 2004
164
MFYPR version 2a
Run: Females FU 28-29
Time and date: 18:50 26-03-2004
Yield per results
FMult Fbar CatchNos
Y
ield StockNos Biomass SpwnNosJan SSBJan SpwnNosSpwn SSBSpwn
000 0.0000 5.5167 0.1884 5.5167 0.1884 5.5167 0.1884
997 0.0038 5.0203 0.1601 5.0203 0.1601 5.0203 0.1601
753 0.0064 4.6440 0.1397 4.6440 0.1397 4.6440 0.1397
349 0.0082 4.3473 0.1245 4.3473 0.1245 4.3473 0.1245
835 0.0094 4.1063 0.1127 4.1063 0.1127 4.1063 0.1127
239 0.0103 3.9059 0.1034 3.9059 0.1034 3.9059 0.1034
582 0.0110 3.7359 0.0958 3.7359 0.0958 3.7359 0.0958
878 0.0116 3.5894 0.0895 3.5894 0.0895 3.5894 0.0895
136 0.0120 3.4616 0.0842 3.4616 0.0842 3.4616 0.0842
365 0.0123 3.3487 0.0797 3.3487 0.0797 3.3487 0.0797
569 0.0126 3.2481 0.0758 3.2481 0.0758 3.2481 0.0758
752 0.0128 3.1577 0.0725 3.1577 0.0725 3.1577 0.0725
919 0.0130 3.0759 0.0695 3.0759 0.0695 3.0759 0.0695
070 0.0132 3.0013 0.0668 3.0013 0.0668 3.0013 0.0668
209 0.0133 2.9330 0.0645 2.9330 0.0645 2.9330 0.0645
337 0.0134 2.8702 0.0623 2.8702 0.0623 2.8702 0.0623
456 0.0135 2.8120 0.0604 2.8120 0.0604 2.8120 0.0604
566 0.0136 2.7580 0.0586 2.7580 0.0586 2.7580 0.0586
669 0.0137 2.7077 0.0570 2.7077 0.0570 2.7077 0.0570
765 0.0138 2.6607 0.0555 2.6607 0.0555 2.6607 0.0555
856 0.0138 2.6166 0.0541 2.6166 0.0541 2.6166 0.0541
olute F
041
7246
2119
4062
0.0000 0.0000 0.0
0.1000 0.0304 0.0
0.2000 0.0608 0.1
0.3000 0.0912 0.2
0.4000 0.1217 0.2
0.5000 0.1521 0.3
0.6000 0.1825 0.3
0.7000 0.2129 0.3
0.8000 0.2433 0.4
0.9000 0.2737 0.4
1.0000 0.3041 0.4
1.1000 0.3345 0.4
1.2000 0.3650 0.4
1.3000 0.3954 0.5
1.4000 0.4258 0.5
1.5000 0.4562 0.5
1.6000 0.4866 0.5
1.7000 0.5170 0.5
1.8000 0.5474 0.5
1.9000 0.5778 0.5
2.0000 0.6083 0.5
Reference point F multiplier
A
bs
Fbar(4-10) 1.0000 0.3
FMax 5.6707 1.
F0.1 0.6967 0.
F35%SPR 1.3355 0.
Table 5.4.33. - SW and S Portugal (FU 28-29): Long-term yield per recruit analysis of females.

MFDP version 1a
Run: Males FU 28-29
NEP MALE(000) PORTUGINDEX FILE
Time and date: 18:20 26-03-2004
Fbar age range: 2-7
2004
Biomass SSB FMult FBar Landings
500 500 1.0000 0.6110 169
2005 2006
Biomass SSB FMult FBar Landings Biomass SSB
474 474 0.0000 0.0000 0 658 658
. 474 0.1000 0.0611 20 633 633
. 474 0.2000 0.1222 39 610 610
. 474 0.3000 0.1833 57 587 587
. 474 0.4000 0.2444 74 566 566
. 474 0.5000 0.3055 90 547 547
. 474 0.6000 0.3666 104 528 528
. 474 0.7000 0.4277 118 511 511
. 474 0.8000 0.4888 132 494 494
. 474 0.9000 0.5499 144 479 479
. 474 1.0000 0.6110 156 464 464
. 474 1.1000 0.6721 167 451 451
. 474 1.2000 0.7332 178 438 438
. 474 1.3000 0.7943 188 426 426
. 474 1.4000 0.8554 197 414 414
. 474 1.5000 0.9165 206 403 403
Table 5.4.34. - SW and S Portugal (FU 28-29): Short-term predictions of landings and
biomass of males. Status quo F in 2004.
. 474 1.6000 0.9776 214 393 393
. 474 1.7000 1.0387 222 383 383
. 474 1.8000 1.0998 230 374 374
. 474 1.9000 1.1609 237 366 366
. 474 2.0000 1.2220 244 357 357
WGNEPH Report 2004 165

WGNEPH Report 2004
166
MFDP version 1a
Run: Females FU 28-29
NEP FEMALE(000) PORTINDEX FILE
Time and date: 09:12 30/03/04
Fbar age range: 4-10
2004
Biomass SSB FMult FBar Landings
716 716 1.0000 0.3041 127
2005 2006
Biomass SSB FMult FBar Landing Yield Biomass SSB
682 682 0.0000 0.0000 0 781 781
. 682 0.1000 0.0304 13 768 768
. 682 0.2000 0.0608 26 754 754
. 682 0.3000 0.0912 39 741 741
. 682 0.4000 0.1217 51 728 728
. 682 0.5000 0.1521 63 716 716
. 682 0.6000 0.1825 75 704 704
. 682 0.7000 0.2129 86 692 692
. 682 0.8000 0.2433 97 681 681
. 682 0.9000 0.2737 108 669 669
. 682 1.0000 0.3041 119 658 658
. 682 1.1000 0.3345 129 648 648
. 682 1.2000 0.3650 139 637 637
. 682 1.3000 0.3954 149 627 627
. 682 1.4000 0.4258 158 617 617
. 682 1.5000 0.4562 168 608 608
. 682 1.6000 0.4866 177 598 598
. 682 1.7000 0.5170 186 589 589
. 682 1.8000 0.5474 195 580 580
. 682 1.9000 0.5778 203 571 571
. 682 2.0000 0.6083 211 563 563
Table 5.4.35. - SW and S Portugal (FU 28-29): Short-term predictions of landings and
biomass of females. Status quo F in 2004.

WGNEPH Report 2004 167
Spain Portugal
Trawl All gears
108 108
132 132
49 49
99 99
86 86
123 123
129 129
178 178
247 247
2814285
* provisional
28203 3.8 895 98.6
32231 4.1 986 104.0
31954 1.5 529 76.1
32679 3.0 935 68.9
32665 2.6 633 68.3
32748 3.8 858 76.0
38322 3.4 1605 53.9
30416 5.9 1669 67.9
30526 8.1 1675 80.7
31643 8.9 2202 67.1
* provisional
2002
Table 5.4.36. - Gulf of Cadiz (FU 30): Landings (tonnes) by country, 1994-2003.
Table 5.4.37. - Gulf of Cádiz (FU 30): Effort for the whole trawl fleet and Nephrops directed
effort (fishing days) and respective LPUEs (kg/fishing day), 1994-2003
1994
1995
Year Total
Effort
1998
1999
2003*
2000
2001
1997
1996
FU 30
LPUE
2000
1996
1997
Directed
effort
Directed
LPUE
1994
1995
1998
1999
2002
2003*
Year
2001

WGNEPH Report 2004
168
March November
0.38 0.19
0.37 ns
0.17 ns
0.38 ns
0.15 0.08
0.13 0.19
0.17 0.21
0.15 0.42
0.18 0.45
0.19 0.14
ns 0.07
ns = no survey
Landings
35.6 34.0
34.9 32.0
33.1 32.6
Males Females Males Females
38.8 32.2 36.2 30.9
39.9 32.9 ns ns
46.9 37.4 ns ns
42.3 34.6 ns ns
35.4 28.9 30.5 28.9
33.9 30.3 36.2 30.7
37.2 29.5 32.1 28.2
36.7 29.0 35.5 30.7
38.1 33.3 35.4 30.0
36.0 30.5 37.3 31.1
ns ns 35.1 28.9
ns = no survey
Year
1995
2003
2001
1996
Females
1994
Males
2001
1997
Year
2000
2003
1997
1998
1999
2001
2002
2000
Spanish research surveys
NovemberMarch
Year
Table 5.4.40. - Gulf of Cádiz (FU30): Mean sizes (mm CL) of male and
female Nephrops in Spanish research trawl surveys, 1993-2003.
Spanish research surveys
CPUE (kg/hour)
1998
1999
1996
1994
1995
1993
2002
2002
Table 5.4.38. - Gulf of Cádiz (FU 30): Nephrops CPUEs (kg/hour) in Spanish research trawl
surveys, 1993-2003.
1993
Table 5.4.39. - Gulf of Cádiz (FU 30): Mean sizes (mm CL) of male and
female Nephrops in Spanish landings, 2001-2003.
2003

WGNEPH Report 2004 169
47
1994
Table 5.4.41. - Gulf of Cádiz (FU30): Input data and parameters.
Mean
no. per
sample
rom FU 30
FU MA
FLEET GEAR
Qtr 1 Qtr 2 Qtr 3 Qtr 4 Qtr 1 Qtr 2 Qtr 3 Qtr 4
Catch
Landings 5788475678
Discards
Year 2003 2002 2001 2000 1999 1998 1997 1996 1995
Catch
Landings 28 26 19
Discards
Value
na
0.160
60
0.2
0.00043
3.160
0.160
60
0.2
28
0.090
58
0.2
0.00043
3.160
Length/weight - b
Source
Mean
no. per
sample
Growth - K
Growth - L(inf)
Natural mortality - M
Length/weight - a
Growth - L(inf)
Natural mortality - M
Size at maturity
Mature Growth
Length/weight - b
FEMALES
Immature Growth
Growth - K
Growth - K
Growth - L(inf)
Natural mortality - M
Length/weight - a
INPUT PARAMETERS
Parameter
Discard Survival
MALES
Not aplicable - few discards (< 1 % on average)
Number of samples Number of samples
Number of samples
2003 2002
Assumed to be in line with FU 25
Derived from length composition in Gulf of Cadiz surveys
Fernández et al. (1986)
Fariña (1984)
"
Assumed to be in line with FU 25
Derived from length composition in Gulf of Cadiz surveys
Fernández et al. (1986)
Fariña (1984)
"
Assumed intermediate between FU 26-27 and FU 28-29
Assumed intermediate between FUs 25 and 26
Derived from length c omposition of commercial landings f
Fernández et al. (1986)
30
Spain
Q
Trawl

Table 5.4.42. – Gulf of Cádiz (FU 30): Assessment deficiencies 2004.
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
XSA N/A Length distribution series was too short (only 3 years) unabling the use of
this methodology.
Tuning data 2 When required Nephrops directed fleet data from the Gulf of Cádiz trawl
fishing trip types defined by Jiménez et al. (2004) can be used. However
a new definition of the fishing trip types classification matrix must be
made due to the changes in fleet composition.
CSA N/A
Fishery independent
methods
3 Bottom trawl surveys in this area are not directed to the species.
Moreover surveys are carried out in March and November while the
commercial bulk of landings take place from April to August.
Assessment
method
LCA 3 A first assessment attemp was carried out in the 2004 WGNEPH. Results
must be treated with caution due to the lack of confidence in the landings
length distribution samplings. Also the biological parameters used do not
belong to this FU (see below).
Definition 2 The stock is distributed in a well know area of the Gulf of Cádiz between
200 and 700 meters depth. There are other stock in South Portugal
(adjacent area FU 29).
Stock
Structure N/A
Fishery Definition (Mixed,
targeted, multifleet)
2 Target and mixed bottom trawl fleet.
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.
WGNEPH Report 2004
170

WGNEPH Report 2004 171
Table 5.4.42. – Gulf of Cádiz (FU 30): Assessment deficiencies 2004 (continued).
Catch N/A
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Catch N/A
Landings 1 Landings data are provided by Spain and in the 2003 also Portugal.
Spanish data are extracted directly for the IEO database.
Discards N/A Discards considered zero (below 1%).
Effort 2 Spanish effort data (fishing days) came from the IEO database. Whole
data can be split in target effort although there is a concern about the
fishing trip types classiffication in recent years.
Catch
statistics
Landings 3 The length frequency distributions of Nephrops landings were obtained
from samples taken by a shelf sampling procedure.
Sampling
levels
Discards N/A
LPUE 2
CPUE N/A
...continued overleaf
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

WGNEPH Report 2004
172
Table 5.4.42. – Gulf of Cádiz (FU 30): Assessment deficiencies 2004 (continued).
Item Sub-item Quality*
(degree of
knowledge)
Considerations and assumptions
Age and growth 3 No biological studies have been carried out in the area yet. Thus its used
parameters estimated for the West Galicia and Portugal populations.
Maturity 3 No biological studies have been carried out in the area yet. Thus its used
a maturity value of 28.0 (derived from an intermediate value of West
Galicia and Portugal).
Natural mortality 3 No estimates of M have been made. It assumed a M=0.2 value for both
sex.
Discard Mortality N/A
Escape Mortality N/A
Biological
parameters
Length/weight
coefficients
3 Only available from a research survey. Thus used the coefficients
estimated for the West Galicia population.
Fishing surveys 2 Not used in the assessment. Data are available but do not be used due to
its general features (not species directed surveys) and also surveys dates
(see above).
Larval surveys N/A
Availability
of research
survey data
TV survey N/A
Availability
of other
information
Species composition 2 It could be described from the specific composition of the Gulf of Cádiz
trawl fishing trip types defined by Jiménez et al. (2004).
* Quality (degree of knowledge): 1 =good, 2=reasonable, 3=poor and N/A=Not available.

Reference peri
Linf (mm CL)
Si Average
(mm CL) ass (kg)
10642
14401
18876
24084
29929
35846
40421
41571
37742
29857
20334
10688
4843
2428
1206
545
323413
Mean F, ca
Table 5.4.43. -
od 2001-2003
60.0 K 0.160
ze Removals M DT F*DT F Z Nos. attaining Average nos. in
('000) (years) aver. size ('000) the sea ('000) biom
18 4 0.2 0.30 0.00 0.00 0.20 7617 2253
20 14 0.2 0.32 0.00 0.01 0.21 7162 2222
22 35 0.2 0.34 0.01 0.02 0.22 6704 2185
24 39 0.2 0.36 0.01 0.02 0.22 6232 2142
26 88 0.2 0.38 0.02 0.04 0.24 5765 2087
28 218 0.2 0.40 0.04 0.11 0.31 5259 1994
30 445 0.2 0.43 0.11 0.24 0.44 4642 1822
32 669 0.2 0.46 0.20 0.44 0.64 3832 1538
34 769 0.2 0.50 0.33 0.67 0.87 2855 1159
36 642 0.2 0.54 0.46 0.84 1.04 1851 769
38 457 0.2 0.60 0.62 1.04 1.24 1053 444
40 297 0.2 0.66 0.99 1.51 1.71 504 199
42 84 0.2 0.74 0.81 1.09 1.29 164 78
44 32 0.2 0.83 0.80 0.96 1.16 63 34
46 12 0.2 0.96 0.80 0.83 1.03 24 15
48 5 0.2 1.14 1.01 0.88 1.08 9 6
Totals, including lengths above + group 18944
lculated across inter-quartile range 0.61
Gulf of Cádiz (FU 30): LCA output males.
WGNEPH Report 2004 173

Reference peri
Linf immat
Linf matures
Transition l
Si Average
(mm CL) ass (kg)
20342
27543
36142
46113
57004
67541
138691
131783
115418
99848
88866
80814
75069
68959
60237
48980
37596
25721
9949
1236615
Mean F, calculated across inter-quartile range 0.13
Table 5.4.44 -
od 2001-2003
ures (mm CL) 60.0 K immatures 0.160
(mm CL) 58.0 K matures 0.090
ength (mm CL) 28.0
ze Removals M DT F*DT F Z Nos. attaining Average nos. in
('000) (years) aver. size ('000) the sea ('000) biom
18 3 0.2 0.30 0.00 0.00 0.20 14557 4306
20 15 0.2 0.32 0.00 0.00 0.20 13693 4250
22 51 0.2 0.34 0.00 0.01 0.21 12828 4183
24 90 0.2 0.36 0.01 0.02 0.22 11940 4101
26 266 0.2 0.38 0.03 0.07 0.27 11030 3975
28 525 0.2 0.40 0.06 0.14 0.34 9969 3758
30 854 0.2 0.82 0.11 0.14 0.34 8692 6250
32 1100 0.2 0.89 0.20 0.23 0.43 6586 4874
34 855 0.2 0.97 0.23 0.24 0.44 4506 3545
36 438 0.2 1.06 0.18 0.17 0.37 2938 2573
38 227 0.2 1.17 0.14 0.12 0.32 1983 1939
40 108 0.2 1.31 0.09 0.07 0.27 1367 1505
42 37 0.2 1.48 0.05 0.03 0.23 958 1203
44 35 0.2 1.71 0.06 0.04 0.24 680 957
46 27 0.2 2.03 0.08 0.04 0.24 453 729
48 24 0.2 2.48 0.12 0.05 0.25 280 519
50 5 0.2 3.20 0.05 0.01 0.21 152 351
52 7 0.2 4.51 0.16 0.03 0.23 77 213
54 8 0.2 7.70 1.05 0.14 0.34 27 73
Totals, including lengths above + group 49302
Gulf of Cádiz (FU 30): LCA output females.
WGNEPH Report 2004
174

FU 26 FU 27 FU 26-27 FU 28-29 FU 30 Other Total
120 22 306 237 107 0 792
117 10 384 273 132 0 916
264 67 132 49 0 512
359 74 136 99 0 668
295 50 161 89 0 595
194 54 211 123 0 581
102 30 201 92 0 425
105 27 271 178 0 582
59 28 359 247 0 693
39 33 362 285 0 719
* provisional
Portugal Spain Total
259 533 792
283 633 916
149 363 512
142 526 668
169 426 595
216 365 581
210 215 425
278 304 582
363 330 693
373 346 719
* provisional
2003*
2002
Table 5.4.46. - Management Area Q (IXa): Total Nephrops landings (tonnes) by country,
1994-2003.
1999
2001
2003*
2000
2002
1995
1996
1997
1998
Table 5.4.45. - Management Area Q (IXa): Total Nephrops landings (tonnes) by Functional
Unit plus Other rectangles, 1994-2003.
Year
1994
1996
Year
2001
1994
1995
1997
1998
1999
2000
WGNEPH Report 2004 175

Run title : FU26+27 West GaliciaINDEX FILE
At 28/03/2004 19:08
Table 1 Catch numbers at age Numbers*10**-3
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0 1787 2797 67 1 4 11 5 10
2 1531 7617 11113 4660 2230 1905 830 2148 2380
3 7324 5041 3512 5854 4757 3869 2976 4866 2264
4 3263 1653 1185 2268 2723 2363 1662 1966 1012
5 913 945 342 494 1526 821 716 493 385
6 244 348 83 136 560 234 239 148 118
7 57 112 34 65 135 61 100 27 39
+gp 54651810553988 117
0 TOTALNUM 13385 17569 19083 13554 11987 9294 6621 9655 6224
TONSLAND 465 437 273 372 474 324 265 293 179
SOPCOF % 99 101 85 100 101 99 99 99 99
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
12004279011
2 661 179 134 387 1312 142 99
3 2456 1440 1077 577 739 480 257
4 1747 1159 694 380 304 273 191
5 878 550 401 150 121 176 121
6 225 303 151 63 45 57 57
7 102 80 57 26 16 12 27
+gp 26 34 24 43 30 8 32
0 TOTALNUM 6098 3745 2538 1668 2645 1147 794
TONSLAND 252 178 115 75 75 48 41
SOPCOF % 9999981121089999
Table 2 Catch weights at age (kg)
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0 0.004 0.005 0.005 0.006 0.006 0.005 0.006 0.006
2 0.015 0.012 0.011 0.013 0.014 0.014 0.014 0.014 0.013
3 0.027 0.026 0.026 0.026 0.026 0.026 0.026 0.026 0.025
4 0.045 0.046 0.045 0.045 0.046 0.045 0.045 0.045 0.046
5 0.068 0.069 0.068 0.069 0.071 0.069 0.069 0.069 0.07
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males.
6 0.096 0.098 0.096 0.095 0.095 0.097 0.098 0.095 0.096
7 0.125 0.124 0.125 0.124 0.123 0.128 0.123 0.121 0.126
+gp 0.219 0.2437 0.2138 0.1828 0.2116 0.1948 0.2002 0.147 0.1617
0 SOPCOFAC 0.9853 1.0053 0.8528 0.9998 1.0087 0.987 0.9942 0.9878 0.9941
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1 0.006 0 0 0.006 0.005 0 0.006
2 0.015 0.015 0.016 0.012 0.012 0.014 0.012
3 0.026 0.028 0.028 0.027 0.026 0.027 0.027
4 0.047 0.046 0.045 0.045 0.044 0.046 0.046
5 0.069 0.07 0.07 0.071 0.071 0.071 0.07
6 0.096 0.098 0.096 0.097 0.095 0.095 0.098
7 0.127 0.125 0.126 0.126 0.129 0.125 0.127
+gp 0.159 0.1793 0.1605 0.2197 0.1985 0.1811 0.2153
0 SOPCOFAC 0.9876 0.9857 0.9821 1.1182 1.0795 0.9931 0.9926
...continued overleaf
WGNEPH Report 2004
176

T
Y
A
Y
A
T
Y
A
Y
A
60.20.20.20.20.20.20.2
70.20.20.20.20.20.20.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2
able 3 Stock weights at age (kg)
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
1 0 0.004 0.005 0.005 0.006 0.006 0.005 0.006 0.006
2 0.015 0.012 0.011 0.013 0.014 0.014 0.014 0.014 0.013
3 0.027 0.026 0.026 0.026 0.026 0.026 0.026 0.026 0.025
4 0.045 0.046 0.045 0.045 0.046 0.045 0.045 0.045 0.046
5 0.068 0.069 0.068 0.069 0.071 0.069 0.069 0.069 0.07
6 0.096 0.098 0.096 0.095 0.095 0.097 0.098 0.095 0.096
7 0.125 0.124 0.125 0.124 0.123 0.128 0.123 0.121 0.126
+gp 0.219 0.2437 0.2138 0.1828 0.2116 0.1948 0.2002 0.147 0.1617
EAR 1997 1998 1999 2000 2001 2002 2003
GE
1 0.006 0 0 0.006 0.005 0 0.006
2 0.015 0.015 0.016 0.012 0.012 0.014 0.012
3 0.026 0.028 0.028 0.027 0.026 0.027 0.027
4 0.047 0.046 0.045 0.045 0.044 0.046 0.046
5 0.069 0.07 0.07 0.071 0.071 0.071 0.07
6 0.096 0.098 0.096 0.097 0.095 0.095 0.098
7 0.127 0.125 0.126 0.126 0.129 0.125 0.127
+gp 0.159 0.1793 0.1605 0.2197 0.1985 0.1811 0.2153
able 4 Natural Mortality (M) at age
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
10.20.20.20.20.20.20.20.20.2
20.20.20.20.20.20.20.20.20.2
30.20.20.20.20.20.20.20.20.2
40.20.20.20.20.20.20.20.20.2
50.20.20.20.20.20.20.20.20.2
60.20.20.20.20.20.20.20.20.2
70.20.20.20.20.20.20.20.20.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
EAR 1997 1998 1999 2000 2001 2002 2003
GE
10.20.20.20.20.20.20.2
20.20.20.20.20.20.20.2
30.20.20.20.20.20.20.2
40.20.20.20.20.20.20.2
50.20.20.20.20.20.20.2
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males (continued).
...continued overleaf
WGNEPH Report 2004 177

T
Y
A
Y
A
T
Y
A
Y
A
able 5 Proportion mature at age
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
1111111111
2111111111
3111111111
4111111111
5111111111
6111111111
7111111111
+gp 111111111
EAR 1997 1998 1999 2000 2001 2002 2003
GE
11111111
21111111
31111111
41111111
51111111
61111111
71111111
+gp 1111111
able 6 Proportion of M before Spawning
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
1000000000
2000000000
3000000000
4000000000
5000000000
6000000000
7000000000
+gp 000000000
EAR 1997 1998 1999 2000 2001 2002 2003
GE
10000000
20000000
30000000
40000000
50000000
60000000
70000000
+gp 0000000
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males (continued).
...continued overleaf
WGNEPH Report 2004
178

T
Y
A
Y
A
60000000
70000000
+gp 0000000
able 7 Proportion of F before Spawning
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
1000000000
2000000000
3000000000
4000000000
5000000000
6000000000
7000000000
+gp 000000000
EAR 1997 1998 1999 2000 2001 2002 2003
GE
10000000
20000000
30000000
40000000
50000000
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males (continued).
Table 8 Fishing mortality (F) at age
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0 0.0581 0.1348 0.005 0.0001 0.0003 0.001 0.0005 0.002
2 0.1377 0.5104 0.6051 0.3477 0.2253 0.2106 0.0798 0.273 0.3505
3 1.1803 0.9002 0.47 0.7657 0.7307 0.7666 0.593 0.9043 0.5175
4 1.1275 0.9725 0.5433 0.6411 1.0603 1.0585 0.9282 1.0589 0.4675
5 0.9756 1.3409 0.5364 0.4583 1.3412 1.186 1.1924 0.8092 0.598
6 0.7693 1.4708 0.3587 0.422 1.6336 0.752 1.6572 0.8663 0.453
7 0.8468 1.051 0.5067 0.5312 1.0096 0.8028 0.8765 0.8701 0.5923
+gp 0.8468 1.051 0.5067 0.5312 1.0096 0.8028 0.8765 0.8701 0.5923
0 FBAR 3- 5 1.0945 1.0712 0.5166 0.6217 1.0441 1.0037 0.9045 0.9241 0.5277
YEAR 1997 1998 1999 2000 2001 2002 2003 FBAR 01-03
AGE
1 0.0007 0 0 0.0139 0.0688 0 0.015 0.0279
2 0.1856 0.0729 0.0764 0.2052 0.7526 0.1701 0.2167 0.3798
3 0.7533 0.7812 0.8086 0.5389 0.7569 0.6954 0.5292 0.6605
4 1.0184 1.0434 1.1944 0.7674 0.6163 0.7163 0.6717 0.6681
5 0.9994 1.1414 1.4978 0.9336 0.5942 0.9173 0.8301 0.7805
6 0.8796 1.2846 1.2575 1.1057 0.8414 0.6306 0.8953 0.7891
7 0.9307 0.9364 0.92 0.7299 0.9301 0.5522 0.6966 0.7263
+gp 0.9307 0.9364 0.92 0.7299 0.9301 0.5522 0.6966
0 FBAR 3- 5 0.9237 0.9887 1.1669 0.7466 0.6558 0.7763 0.677
...continued overleaf
WGNEPH Report 2004 179

WGNEPH Report 2004
180
Table 9 Relative F at age
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0 0.0542 0.261 0.008 0.0001 0.0003 0.0011 0.0006 0.0038
2 0.1258 0.4764 1.1715 0.5592 0.2158 0.2098 0.0882 0.2954 0.6643
3 1.0784 0.8404 0.9099 1.2316 0.6999 0.7638 0.6556 0.9785 0.9807
4 1.0302 0.9079 1.0518 1.0313 1.0155 1.0546 1.0262 1.1458 0.886
5 0.8914 1.2518 1.0383 0.7371 1.2846 1.1816 1.3183 0.8756 1.1333
6 0.7029 1.373 0.6943 0.6788 1.5647 0.7493 1.8321 0.9374 0.8586
7 0.7737 0.9811 0.9808 0.8545 0.967 0.7999 0.9691 0.9415 1.1224
+gp 0.7737 0.9811 0.9808 0.8545 0.967 0.7999 0.9691 0.9415 1.1224
0 REFMEAN 1.0945 1.0712 0.5166 0.6217 1.0441 1.0037 0.9045 0.9241 0.5277
YEAR 1997 1998 1999 2000 2001 2002 2003 MEAN 01-03
AGE
1 0.0008 0 0 0.0186 0.105 0 0.0221 0.0424
2 0.2009 0.0737 0.0655 0.2748 1.1476 0.2191 0.32 0.5623
3 0.8155 0.7902 0.6929 0.7218 1.1541 0.8958 0.7817 0.9439
4 1.1025 1.0554 1.0235 1.0278 0.9398 0.9226 0.9922 0.9515
5 1.0819 1.1545 1.2835 1.2504 0.9061 1.1816 1.2261 1.1046
6 0.9523 1.2994 1.0776 1.4809 1.283 0.8122 1.3225 1.1392
7 1.0076 0.9472 0.7884 0.9775 1.4182 0.7113 1.0289 1.0528
+gp 1.0076 0.9472 0.7884 0.9775 1.4182 0.7113 1.0289
0 REFMEAN 0.9237 0.9887 1.1669 0.7466 0.6558 0.7763 0.677
Table 10 Stock number at age (start of year) Numbers*10**-3
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 25723 35016 24510 14997 13542 14604 12150 10871 5281
2 13158 21060 27051 17536 12218 11086 11953 9938 8895
3 11683 9388 10350 12093 10141 7985 7353 9036 6193
4 5333 2938 3124 5296 4604 3999 3037 3327 2995
5 1619 1414 910 1486 2284 1306 1136 983 945
6 502 500 303 436 769 489 327 282 358
7 110 190 94 173 234 123 189 51 97
+gp 103 108 50 27 94 76 164 2 41
0 TOTAL 58231 70614 66393 52045 43886 39667 36308 34490 24805
YEAR 1997 1998 1999 2000 2001 2002 2003 2004 GM8803 AM8803
AGE
1 3446 2465 2817 3396 1309 685 818 0 8057 12152
2 4315 2820 2018 2307 2742 1000 561 660 7770 10507
3 5130 2935 2146 1531 1538 1058 691 370 5662 6964
4 3022 1977 1100 783 731 591 432 333 2568 3019
5 1536 894 570 273 298 323 236 181 966 1118
6 425 463 234 104 88 134 106 84 329 377
7 186 145 105 54 28 31 59 35 110 127
+gp 4661439153217053
0 TOTAL 18107 11759 9034 8539 6787 3844 2973 1716
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males (continued).
...continued overleaf

WGNEPH Report 2004 181
Table 11 Spawning stock number at age (spawning time) Numbers*10**-3
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 25723 35016 24510 14997 13542 14604 12150 10871 5281
2 13158 21060 27051 17536 12218 11086 11953 9938 8895
3 11683 9388 10350 12093 10141 7985 7353 9036 6193
4 5333 2938 3124 5296 4604 3999 3037 3327 2995
5 1619 1414 910 1486 2284 1306 1136 983 945
6 502 500 303 436 769 489 327 282 358
7 110 190 94 173 234 123 189 51 97
+gp 103 108 50 27 94 76 164 2 41
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1 3446 2465 2817 3396 1309 685 818
2 4315 2820 2018 2307 2742 1000 561
3 5130 2935 2146 1531 1538 1058 691
4 3022 1977 1100 783 731 591 432
5 1536 894 570 273 298 323 236
6 425 463 234 104 88 134 106
7 186 145 105 54 28 31 59
+gp 46614391532170
Table 12 Stock biomass at age (start of year) Tonnes
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0 140 123 75 81 88 61 65 32
2 197 253 298 228 171 155 167 139 116
3 315 244 269 314 264 208 191 235 155
4 240 135 141 238 212 180 137 150 138
5 110 98 62 103 162 90 78 68 66
6484929417347322734
714241221291623 612
+gp 23 26 11 5 20 15 33 0 7
0 TOTALBIO 947 968 943 1026 1012 798 722 690 559
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1210020705
2654232283314 7
3 133 82 60 41 40 29 19
4 142 91 50 35 32 27 20
5 106 63 40 19 21 23 17
641452210 81310
72418137447
+gp 7 11 7 20 11 4 15
0 TOTALBIO 539 352 224 181 155 113 100
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males (continued).
...continued overleaf

WGNEPH Report 2004
182
Table 13 Spawning stock biomass at age (spawning time) Tonnes
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0 140 123 75 81 88 61 65 32
2 197 253 298 228 171 155 167 139 116
3 315 244 269 314 264 208 191 235 155
4 240 135 141 238 212 180 137 150 138
5 110 98 62 103 162 90 78 68 66
6484929417347322734
714241221291623 612
+gp 23 26 11 5 20 15 33 0 7
0 TOTSPBIO 947 968 943 1026 1012 798 722 690 559
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1210020705
2654232283314 7
3 133 82 60 41 40 29 19
4 142 91 50 35 32 27 20
5 106 63 40 19 21 23 17
641452210 81310
72418137447
+gp 7 11 7 20 11 4 15
0 TOTSPBIO 539 352 224 181 155 113 100
Table 14 Stock biomass at age with SOP (start of year) Tonnes
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0 141 105 75 82 86 60 64 31
2 194 254 254 228 173 153 166 137 115
3 311 245 229 314 266 205 190 232 154
4 236 136 120 238 214 178 136 148 137
5 108 98 53 102 164 89 78 67 66
6474925417447322634
713241021291623 612
+gp 2226 9 5201533 0 7
0 TOTALBIO 933 974 804 1026 1020 788 718 682 556
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1200023705
2644232313614 7
3 132 81 59 46 43 28 19
4 140 90 49 39 35 27 20
5 105 62 39 22 23 23 16
640452211 91310
72318138447
+gp 7 11 7 22 11 4 15
0 TOTALBIO 532 347 220 202 168 112 99
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males (continued).
...continued overleaf

WGNEPH Report 2004 183
1996
31
115
154
137
66
634
12
7
556
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
males (continued).
Table 15 Spawning stock biomass with SOP (spawning time) Tonnes
YEAR 1988 1989 1990 1991 1992 1993 1994 1995
AGE
1 0 141 105 75 82 86 60 64
2 194 254 254 228 173 153 166 137
3 311 245 229 314 266 205 190 232
4 236 136 120 238 214 178 136 148
5 108 98 53 102 164 89 78 67
6474925417447322
713241021291623 6
+gp 2226 9 5201533 0
0 TOTSPBIO 933 974 804 1026 1020 788 718 682
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1200023705
2644232313614 7
3 132 81 59 46 43 28 19
4 140 90 49 39 35 27 20
5 105 62 39 22 23 23 16
640452211 91310
72318138447
+gp 7 11 7 22 11 4 15
0 TOTSPBIO 532 347 220 202 168 112 99
...continued overleaf

WGNEPH Report 2004
184
Table 5.4.47. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for males
(continued).
Table 16 Summary (without SOP correction)
Terminal Fs derived using XSA (W ith F shrinkage)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB FBAR 3- 5
Age 1
1988 25723 947 947 465 0.4908 1.0945
1989 35016 968 968 437 0.4512 1.0712
1990 24510 943 943 273 0.2895 0.5166
1991 14997 1026 1026 372 0.3625 0.6217
1992 13542 1012 1012 474 0.4685 1.0441
1993 14604 798 798 324 0.4058 1.0037
1994 12150 722 722 265 0.3669 0.9045
1995 10871 690 690 293 0.4246 0.9241
1996 5281 559 559 179 0.32 0.5277
1997 3446 539 539 252 0.4679 0.9237
1998 2465 352 352 178 0.5052 0.9887
1999 2817 224 224 115 0.5126 1.1669
2000 3396 181 181 75 0.4143 0.7466
2001 1309 155 155 75 0.483 0.6558
2002 685 113 113 48 0.4243 0.7763
2003 818 100 100 41 0.4115 0.677
Arith.
Mean 10727 583 583 242 0.4249 0.8527
0 Units (Thousands) (Tonnes) (Tonnes) (Tonnes)
Table 17 Summary (with SOP correction)
Terminal Fs derived using XSA (W ith F shrinkage)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB SOPCOFAC FBAR 3- 5
Age 1
1988 25723 933 933 465 0.4982 0.9853 1.0945
1989 35016 974 974 437 0.4488 1.0053 1.0712
1990 24510 804 804 273 0.3394 0.8528 0.5166
1991 14997 1026 1026 372 0.3626 0.9998 0.6217
1992 13542 1020 1020 474 0.4645 1.0087 1.0441
1993 14604 788 788 324 0.4111 0.987 1.0037
1994 12150 718 718 265 0.369 0.9942 0.9045
1995 10871 682 682 293 0.4298 0.9878 0.9241
1996 5281 556 556 179 0.322 0.9941 0.5277
1997 3446 532 532 252 0.4737 0.9876 0.9237
1998 2465 347 347 178 0.5125 0.9857 0.9887
1999 2817 220 220 115 0.522 0.9821 1.1669
2000 3396 202 202 75 0.3705 1.1182 0.7466
2001 1309 168 168 75 0.4474 1.0795 0.6558
2002 685 112 112 48 0.4273 0.9931 0.7763
2003 818 99 99 41 0.4146 0.9926 0.677
Arith.
Mean 10727 574 574 242 .4258 .8527
0 Units (Thousands) (Tonnes) (Tonnes) (Tonnes)

WGNEPH Report 2004 185
Run title : 26+27 West Galicia FINDEX FILE
At 25/03/2004 18:09
994 1995 1996
7 1 9
575 1150 1754
054 2249 1305
376 2242 944
026 1281 703
690 512 440
399 278 257
234 154 163
115 109 104
70 57 48
104 37 67
651 8070 5792
184 218 153
97 98 99
003
19
87
142
174
156
137
70
41
26
18
20
888
31
8
Table 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
females.
Table 1 Catch numbers at age Numbers*10**-3
YEAR 1988 1989 1990 1991 1992 1993 1
AGE
1 20 1234 3016 107 4 0
2 998 5286 8314 2967 1087 880
3 2631 2640 2163 3032 1537 1530 1
4 2350 1944 940 1643 1819 1357 1
5 1637 1094 595 1156 956 1199 1
6 790 616 281 629 398 736
7 418 230 202 367 266 410
8 211 132 136 151 121 276
9 61 167 52 86 101 171
10 23 33 22 56 56 77
+gp 62 79 40 71 63 76
0 TOTALNUM 9199 13454 15760 10262 6407 6712 5
TONSLAND 262 271 177 231 162 199
SOPCOF % 99 102 79 93 90 92
YEAR 1997 1998 1999 2000 2001 2002 2
AGE
1000651022
2 207 50 42 415 1139 114
3 830 357 214 254 439 188
4 1381 745 503 325 242 205
5 871 791 584 223 131 137
6 551 531 457 155 105 122
7 335 409 302 123 61 110
8 250 306 260 57 33 82
9 172 198 203 37 23 34
10 116 122 110 21 23 22
+gp 159 221 160 24 20 27
0 TOTALNUM 4871 3730 2835 1701 2316 1044
TONSLAND 180 167 131 58 57 39
SOPCOF % 999898116123999
Table 2 Catch weights at age (kg)
YEAR 1988 1989 1990 1991 1992 1993 1
AGE
1 0.006 0.005 0.005 0.005 0.006 0 0.
2 0.013 0.01 0.01 0.012 0.013 0.012 0.
3 0.019 0.018 0.018 0.018 0.019 0.019 0.
4 0.026 0.026 0.026 0.026 0.026 0.026 0.
5 0.034 0.034 0.034 0.035 0.034 0.035 0.
6 0.044 0.043 0.044 0.044 0.044 0.044 0.
7 0.053 0.053 0.053 0.053 0.053 0.053 0.
8 0.063 0.065 0.064 0.063 0.064 0.064 0.
9 0.074 0.074 0.073 0.074 0.074 0.073 0.
10 0.083 0.084 0.085 0.083 0.083 0.082 0.
+gp 0.1148 0.1092 0.1109 0.1101 0.1008 0.1041 0.
0 SOPCOFAC 0.9942 1.0213 0.7914 0.9267 0.8955 0.9243 0.974
YEAR 1997 1998 1999 2000 2001 2002 2
AGE
1 0 0 0 0.005 0.005 0.006 0.
2 0.013 0.013 0.014 0.01 0.01 0.013 0
3 0.019 0.019 0.019 0.019 0.018 0.019 0.
4 0.026 0.027 0.027 0.026 0.026 0.026 0.
5 0.034 0.035 0.035 0.035 0.035 0.035 0.
6 0.044 0.044 0.044 0.044 0.043 0.044 0.
7 0.053 0.054 0.054 0.054 0.054 0.054 0.
8 0.064 0.064 0.064 0.064 0.063 0.063 0.
9 0.074 0.074 0.074 0.073 0.073 0.073 0.
10 0.083 0.083 0.083 0.084 0.085 0.083 0.
+gp 0.1087 0.1111 0.1097 0.1084 0.1146 0.1203 0.117
994 1995 1996
005 0.004 0.006
012 0.013 0.012
019 0.019 0.018
026 0.026 0.026
034 0.034 0.034
044 0.044 0.044
053 0.053 0.053
063 0.064 0.064
074 0.074 0.073
083 0.082 0.083
102 0.1044 0.107
1 0.9764 0.9862
003
005
.01
019
026
035
044
053
063
074
084
3
0 SOPCOFAC 0.9913 0.9848 0.9819 1.1639 1.2279 0.9936 0.9811
...continued overleaf

Table 3 Stock weights at age (kg)
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0.006 0.005 0.005 0.005 0.006 0 0.005 0.004 0.006
2 0.013 0.01 0.01 0.012 0.013 0.012 0.012 0.013 0.012
3 0.019 0.018 0.018 0.018 0.019 0.019 0.019 0.019 0.018
4 0.026 0.026 0.026 0.026 0.026 0.026 0.026 0.026 0.026
5 0.034 0.034 0.034 0.035 0.034 0.035 0.034 0.034 0.034
6 0.044 0.043 0.044 0.044 0.044 0.044 0.044 0.044 0.044
7 0.053 0.053 0.053 0.053 0.053 0.053 0.053 0.053 0.053
8 0.063 0.065 0.064 0.063 0.064 0.064 0.063 0.064 0.064
9 0.074 0.074 0.073 0.074 0.074 0.073 0.074 0.074 0.073
10 0.083 0.084 0.085 0.083 0.083 0.082 0.083 0.082 0.083
+gp 0.1148 0.1092 0.1109 0.1101 0.1008 0.1041 0.102 0.1044 0.107
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1 0 0 0 0.005 0.005 0.006 0.005
2 0.013 0.013 0.014 0.01 0.01 0.013 0.01
3 0.019 0.019 0.019 0.019 0.018 0.019 0.019
4 0.026 0.027 0.027 0.026 0.026 0.026 0.026
5 0.034 0.035 0.035 0.035 0.035 0.035 0.035
6 0.044 0.044 0.044 0.044 0.043 0.044 0.044
7 0.053 0.054 0.054 0.054 0.054 0.054 0.053
8 0.064 0.064 0.064 0.064 0.063 0.063 0.063
9 0.074 0.074 0.074 0.073 0.073 0.073 0.074
10 0.083 0.083 0.083 0.084 0.085 0.083 0.084
+gp 0.1087 0.1111 0.1097 0.1084 0.1146 0.1203 0.1173
Table 4 Natural Mortality (M) at age
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
10 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1 0.2 0.2 0.2 0.2 0.2 0.2 0.2
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2
10 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2
Table 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
females (continued).
...continued overleaf
WGNEPH Report 2004
186

WGNEPH Report 2004 187
Table 5 Proportion mature at age
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1000000000
2111111111
1995 1996
Table 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
females (continued).
3111111111
4111111111
5111111111
6111111111
7111111111
8111111111
9111111111
10111111111
+gp 111111111
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
10000000
21111111
31111111
41111111
51111111
61111111
71111111
81111111
91111111
101111111
+gp 1111111
Table 6 Proportion of M before Spawning
YEAR 1988 1989 1990 1991 1992 1993 1994
AGE
1000000000
2000000000
3000000000
4000000000
5000000000
6000000000
7000000000
8000000000
9000000000
10000000000
+gp 000000000
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
10000000
20000000
30000000
40000000
50000000
60000000
70000000
80000000
90000000
100000000
+gp 0000000
...continued overleaf

WGNEPH Report 2004
188
Table 7 Proportion of F before Spawning
YEAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
AGE
1000000000
2000000000
1995 1996
0.0001 0.0026
0.1514 0.3382
0.3983 0.2568
0.5026 0.2887
0.45 0.2876
0.2796 0.2721
0.2524 0.22
0.2519 0.2302
0.5263 0.2691
0.4209 0.47
0.4209 0.47
0.3558 0.2592
FBAR 01-03
0.0232
0.2592
0.1932
0.2388
0.2572
0.38
0.3961
0.3653
0.2975
0.3137
Table 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for
females (continued).
3000000000
4000000000
5000000000
6000000000
7000000000
8000000000
9000000000
10000000000
+gp 000000000
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
10000000
20000000
30000000
40000000
50000000
60000000
70000000
80000000
90000000
100000000
+gp 0000000
Table 8 Fishing mortality (F) at age
YEAR 1988 1989 1990 1991 1992 1993 1994
AGE
1 0.0009 0.0452 0.169 0.0076 0.0003 0 0.0007
2 0.09 0.3687 0.4791 0.2501 0.0998 0.0864 0.0665
3 0.3266 0.3629 0.2521 0.3198 0.1982 0.1989 0.1416
4 0.4798 0.4287 0.2111 0.3092 0.3233 0.2697 0.2767
5 0.5729 0.4309 0.2234 0.4353 0.2978 0.367 0.3367
6 0.5236 0.4393 0.1849 0.39 0.2609 0.3951 0.3738
7 0.546 0.281 0.2503 0.3915 0.2832 0.4694 0.3868
8 0.456 0.3297 0.2674 0.3004 0.2138 0.5362 0.5417
9 0.443 0.8201 0.2065 0.2674 0.3352 0.5316 0.4479
10 0.5123 0.4636 0.2276 0.3592 0.2797 0.4633 0.433
+gp 0.5123 0.4636 0.2276 0.3592 0.2797 0.4633 0.433
0 FBAR 3- 8 0.4842 0.3787 0.2315 0.3577 0.2629 0.3727 0.3429
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
10000.0196 0.053 0.0029 0.0137
2 0.0774 0.028 0.0235 0.1778 0.5488 0.0778 0.1511
3 0.2646 0.1855 0.1592 0.1933 0.2895 0.1593 0.1308
4 0.4756 0.404 0.4322 0.3861 0.2853 0.213 0.2181
5 0.4734 0.5555 0.6477 0.3467 0.2634 0.2596 0.2487
6 0.3846 0.6 0.7436 0.3509 0.2706 0.4219 0.4474
7 0.3441 0.5537 0.8437 0.451 0.2234 0.5101 0.4547
8 0.3463 0.6114 0.8551 0.3668 0.2036 0.5357 0.3567
9 0.4061 0.5125 1.1506 0.27 0.2454 0.3344 0.3127
10 0.549 0.5657 0.6055 0.3156 0.2593 0.3908 0.2911
+gp 0.549 0.5657 0.6055 0.3156 0.2593 0.3908 0.2911
0 FBAR 3- 8 0.3814 0.485 0.6136 0.3491 0.256 0.3499 0.3094
...continued overleaf

T
YE
AG
+gp
0 RE
T
YE
AG
+gp
0 RE
T
YE
AG
7 1097 1039 1010 1250 1193 1209 1375 1378 1436
8 636 520 643 644 692 736 619 765 877
9 189 330 306 403 390 458 352 295 487
10 64 99 119 204 252 229 220 184 143
+gp 168 233 214 260 283 223 325 118 196
0 TOTAL 61661 73125 69172 57987 52567 49197 45354 40100 29325
YEAR 1997 1998 1999 2000 2001 2002 2003 2004 GM8803 AM8803
AGE
1 2464 2439 3441 3712 2171 843 1548 0 7653 11052
2 3073 2018 1996 2817 2980 1686 688 1250 7089 9548
3 3944 2328 1606 1597 1931 1409 1277 484 5488 6855
4 4031 2478 1583 1122 1078 1184 984 917 3952 4707
5 2552 2051 1355 841 624 663 783 648 2567 2952
6 1907 1301 964 580 487 393 419 500 1580 1750
7 1272 1063 585 375 335 304 211 219 960 1044
8 943 738 500 206 196 219 150 110 572 622
9 570 546 328 174 117 131 105 86 325 353
10 305 311 268 85 109 75 77 63 166 185
+gp 410 559 384 99 98 92 86 100
0 TOTAL 21471 15833 13011 11608 10124 6998 6326 4376
Tab or
fe
able 9 Relative F at age
AR 1988 1989 1990 1991 1992 1993 1994 1995 1996
E
1 0.002 0.1193 0.73 0.0212 0.0011 0 0.002 0.0004 0.01
2 0.1859 0.9734 2.0692 0.6991 0.3795 0.2318 0.194 0.4255 1.3046
3 0.6746 0.9582 1.0888 0.8941 0.754 0.5337 0.413 1.1195 0.9907
4 0.991 1.1319 0.9118 0.8644 1.23 0.7236 0.8069 1.4126 1.1136
5 1.1833 1.1377 0.965 1.2168 1.1329 0.9846 0.982 1.2646 1.1095
6 1.0814 1.1598 0.7986 1.0902 0.9924 1.0599 1.0902 0.7859 1.0498
7 1.1277 0.7419 1.0811 1.0946 1.0775 1.2594 1.1281 0.7094 0.8486
8 0.9419 0.8705 1.1548 0.8399 0.8132 1.4387 1.5798 0.7079 0.8879
9 0.9149 2.1654 0.8918 0.7477 1.2751 1.4263 1.3063 1.4793 1.0379
10 1.0582 1.2241 0.983 1.0042 1.0641 1.243 1.2628 1.183 1.8132
1.0582 1.2241 0.983 1.0042 1.0641 1.243 1.2628 1.183 1.8132
FMEAN 0.4842 0.3787 0.2315 0.3577 0.2629 0.3727 0.3429 0.3558 0.2592
able 9 Relative F at age
AR 1997 1998 1999 2000 2001 2002 2003 MEAN 01-03
E
10000.0562 0.2072 0.0083 0.0442 0.0865
2 0.203 0.0577 0.0382 0.5093 2.144 0.2224 0.4883 0.9516
3 0.6936 0.3824 0.2594 0.5536 1.131 0.4553 0.4226 0.6697
4 1.247 0.833 0.7044 1.106 1.1145 0.6085 0.7048 0.8093
5 1.2412 1.1454 1.0557 0.9931 1.0292 0.7418 0.8037 0.8582
6 1.0082 1.237 1.2118 1.0051 1.0573 1.2057 1.446 1.2363
7 0.9021 1.1416 1.3751 1.2918 0.8728 1.4578 1.4698 1.2668
8 0.9078 1.2607 1.3936 1.0505 0.7952 1.5308 1.153 1.1597
9 1.0647 1.0566 1.8753 0.7734 0.9586 0.9555 1.0106 0.9749
10 1.4393 1.1664 0.9868 0.9038 1.013 1.1166 0.9411 1.0236
1.4393 1.1664 0.9868 0.9038 1.013 1.1166 0.9411
FMEAN 0.3814 0.485 0.6136 0.3491 0.256 0.3499 0.3094
able 10 Stock number at age (start of year) Numbers*10**-3
AR 1988 1989 1990 1991 1992 1993 1994 1995 1996
E
1 23161 30846 21433 15572 14358 12064 11056 8252 3762
2 12809 18945 24138 14819 12652 11752 9877 9046 6755
3 10434 9584 10728 12240 9448 9375 8825 7566 6366
4 6814 6162 5459 6826 7278 6345 6291 6271 4159
5 4147 3453 3286 3619 4102 4313 3967 3906 3106
6 2143 1914 1837 2152 1917 2494 2446 2319 2039
le 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables f
males (continued).
...continued overleaf
WGNEPH Report 2004 189

T
YE
AG
+gp
YE
AG
+gp
T
YE
AG
10 5 8 10 17 21 19 18 15 12
+gp 192624292823331221
0 TOTALBIO 1053 1023 1027 1057 1029 931 937 863 722
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1000191158
2402628283022 7
375443130352724
4 105 67 43 29 28 31 26
587724729222327
684574226211718
767573220181611
8604732131214 9
942402413 910 8
102526227966
+gp 45624211111110
0 TOTALBIO 630 499 343 225 206 182 155
Tab or
fe
able 11 Spawning stock number at age (spawning time) Numbers*10**-3
AR 1988 1989 1990 1991 1992 1993 1994 1995 1996
E
1000000000
2 12809 18945 24138 14819 12652 11752 9877 9046 6755
3 10434 9584 10728 12240 9448 9375 8825 7566 6366
4 6814 6162 5459 6826 7278 6345 6291 6271 4159
5 4147 3453 3286 3619 4102 4313 3967 3906 3106
6 2143 1914 1837 2152 1917 2494 2446 2319 2039
7 1097 1039 1010 1250 1193 1209 1375 1378 1436
8 636 520 643 644 692 736 619 765 877
9 189 330 306 403 390 458 352 295 487
10 64 99 119 204 252 229 220 184 143
168 233 214 260 283 223 325 118 196
AR 1997 1998 1999 2000 2001 2002 2003
E
10000000
2 3073 2018 1996 2817 2980 1686 688
3 3944 2328 1606 1597 1931 1409 1277
4 4031 2478 1583 1122 1078 1184 984
5 2552 2051 1355 841 624 663 783
6 1907 1301 964 580 487 393 419
7 1272 1063 585 375 335 304 211
8 943 738 500 206 196 219 150
9 570 546 328 174 117 131 105
10 305 311 268 85 109 75 77
410 559 384 99 98 92 86
able 12 Stock biomass at age (start of year) Tonnes
AR 1988 1989 1990 1991 1992 1993 1994 1995 1996
E
1 139 154 107 78 86 0 55 33 23
2 167 189 241 178 164 141 119 118 81
3 198 173 193 220 180 178 168 144 115
4 177 160 142 177 189 165 164 163 108
5 141 117 112 127 139 151 135 133 106
6 94 82 81 95 84 110 108 102 90
7585554666364737376
8403441414447394956
9142422302933262236
le 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables f
males (continued).
...continued overleaf
WGNEPH Report 2004
190

T
Y
A
0 T
Y
A
0 T
T
Y
A
10598161917181512
+gp 192619262621321221
0 TOTALBIO 1047 1045 813 979 922 861 913 843 712
YEAR 1997 1998 1999 2000 2001 2002 2003
AGE
1000221358
2402627333722 7
374443035432724
4 104 66 42 34 34 31 25
586714734272327
683564230261718
767573124221611
8604731151514 9
94240241510 9 8
10 25 25 22 8 11 6 6
+gp 44614112141110
0 TOTALBIO 625 492 337 262 252 181 152
r
fe
able 13 Spawning stock biomass at age (spawning time) Tonnes
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
1000000000
2 167 189 241 178 164 141 119 118 81
3 198 173 193 220 180 178 168 144 115
4 177 160 142 177 189 165 164 163 108
5 141 117 112 127 139 151 135 133 106
6 94 82 81 95 84 110 108 102 90
7585554666364737376
8403441414447394956
9142422302933262236
10 5 8 10 17 21 19 18 15 12
+gp 192624292823331221
OTSPBIO 914 869 920 979 943 931 882 830 700
EAR 1997 1998 1999 2000 2001 2002 2003
GE
10000000
2402628283022 7
375443130352724
4 105 67 43 29 28 31 26
587724729222327
684574226211718
767573220181611
8604732131214 9
942402413 910 8
102526227966
+gp 45624211111110
OTSPBIO 630 499 343 207 195 177 147
able 14 Stock biomass at age with SOP (start of year) Tonnes
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
1 138 158 85 72 77 0 54 32 22
2 166 193 191 165 147 130 115 115 80
3 197 176 153 204 161 165 163 140 113
4 176 164 112 164 169 152 159 159 107
5 140 120 88 117 125 140 131 130 104
6 94 84 64 88 76 101 105 100 88
7585642615759717175
8403533384044384855
9142518282631252135
Table 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables fo
males (continued).
...continued overleaf
WGNEPH Report 2004 191

T
Y
A
0 T
Y
A
0 T
r
fe
able 15 Spawning stock biomass with SOP (spawning time) Tonnes
EAR 1988 1989 1990 1991 1992 1993 1994 1995 1996
GE
1000000000
2 166 193 191 165 147 130 115 115 80
3 197 176 153 204 161 165 163 140 113
4 176 164 112 164 169 152 159 159 107
5 140 120 88 117 125 140 131 130 104
6 94 84 64 88 76 101 105 100 88
7585642615759717175
8403533384044384855
9142518282631252135
10598161917181512
+gp 192619262621321221
OTSPBIO 909 888 728 907 844 861 859 811 690
EAR 1997 1998 1999 2000 2001 2002 2003
GE
10000000
2402627333722 7
374443035432724
4 104 66 42 34 34 31 25
586714734272327
683564230261718
767573124221611
8604731151514 9
94240241510 9 8
10 25 25 22 8 11 6 6
+gp 44614112141110
OTSPBIO 625 492 337 241 239 176 145
Table 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables fo
males (continued).
...continued overleaf
WGNEPH Report 2004
192

T
T
Arith.
Mean
0 Units
T
T
1992 14358 922 844 162 0.1919 0.8955 0.2629
1993 12064 861 861 199 0.2312 0.9243 0.3727
1994 11056 913 859 184 0.2142 0.9741 0.3429
1995 8252 843 811 218 0.2689 0.9764 0.3558
1996 3762 712 690 153 0.2218 0.9862 0.2592
1997 2464 625 625 180 0.2881 0.9913 0.3814
1998 2439 492 492 167 0.3395 0.9848 0.485
1999 3441 337 337 131 0.3886 0.9819 0.6136
2000 3712 262 241 58 0.2411 1.1639 0.3491
2001 2171 252 239 57 0.2383 1.2279 0.256
2002 843 181 176 39 0.2217 0.9936 0.3499
2003 1548 152 145 31 0.2143 0.9811 0.3094
Arith.
Mean 9820 652 609 158 .2594 .3619
0 Units (Thousands) (Tonnes) (Tonnes) (Tonnes)
Tab ales
(con
able 16 Summary (without SOP correction)
erminal Fs derived using XSA (W ith F shrinkage)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB FBAR 3- 8
Age 1
1988 23161 1053 914 262 0.2867 0.4842
1989 30846 1023 869 271 0.3118 0.3787
1990 21433 1027 920 177 0.1924 0.2315
1991 15572 1057 979 231 0.2359 0.3577
1992 14358 1029 943 162 0.1718 0.2629
1993 12064 931 931 199 0.2137 0.3727
1994 11056 937 882 184 0.2087 0.3429
1995 8252 863 830 218 0.2625 0.3558
1996 3762 722 700 153 0.2187 0.2592
1997 2464 630 630 180 0.2856 0.3814
1998 2439 499 499 167 0.3344 0.485
1999 3441 343 343 131 0.3816 0.6136
2000 3712 225 207 58 0.2806 0.3491
2001 2171 206 195 57 0.2926 0.256
2002 843 182 177 39 0.2203 0.3499
2003 1548 155 147 31 0.2102 0.3094
9820 680 635 158 0.2567 0.3619
(Thousands) (Tonnes) (Tonnes) (Tonnes)
able 17 Summary (with SOP correction)
erminal Fs derived using XSA (W ith F shrinkage)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB SOPCOFAC FBAR 3- 8
Age 1
1988 23161 1047 909 262 0.2883 0.9942 0.4842
1989 30846 1045 888 271 0.3053 1.0213 0.3787
1990 21433 813 728 177 0.2432 0.7914 0.2315
1991 15572 979 907 231 0.2546 0.9267 0.3577
le 5.4.48. - West Galicia and North Portugal (FUs 26-27): VPA input and output tables for fem
tinued).
WGNEPH Report 2004 193

WGNEPH Report 2004
194
Lowestoft VPA Version 3.1
25/03/2004 17:03
Extended Survivors Analysis
FU26+27 West GaliciaINDEX FILE
CPUE data from file TUNEFF.DAT
Catch data for 16 years. 1988 to 2003. Ages 1 to 8.
Fleet Fir
s
Last First Last Alpha Beta
year year age age
Mar¡n 1994 20031701
muros 1995 20032701
Time series weights :
Tapered time weighting applied
Power = 3 over 20 years
Catchability analysis :
Catchability independent of stock size for all ages
Catchability independent of age for ages >= 3
Terminal population estimation :
Survivor estimates shrunk towards the mean F
of the final 5 years or the 5 oldest ages.
S.E. of the mean to which the estimates are shrunk = .500
Minimum standard error for population
estimates derived from each fleet = .300
Prior weighting not applied
Tuning converged after 20 iterations
Regression weights
0.751 0.82 0.877 0.921 0.954 0.976 0.99 0.997 1 1
Fishing mortalities
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
1 0.001 0.001 0.002 0.001 0 0 0.014 0.069 0 0.015
2 0.08 0.273 0.351 0.186 0.073 0.076 0.205 0.753 0.17 0.217
3 0.593 0.904 0.517 0.753 0.781 0.809 0.539 0.757 0.695 0.529
4 0.928 1.059 0.468 1.018 1.043 1.194 0.767 0.616 0.716 0.672
5 1.192 0.809 0.598 0.999 1.141 1.498 0.934 0.594 0.917 0.83
6 1.657 0.866 0.453 0.88 1.285 1.257 1.106 0.841 0.631 0.895
7 0.877 0.87 0.592 0.931 0.936 0.92 0.73 0.93 0.552 0.697
Table 5.4.49. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for
males.
...continued overleaf

WGNEPH Report 2004 195
XSA population numbers (Thousands)
AGE
YEAR 1234567
1994 12100 12000 7350 3040 1140 327 189
1995 10900 9940 9040 3330 983 282 51
1996 5280 8900 6190 2990 945 358 97.2
1997 3450 4320 5130 3020 1540 425 186
1998 2470 2820 2930 1980 894 463 145
1999 2820 2020 2150 1100 570 234 105
2000 3400 2310 1530 783 273 104 54.4
2001 1310 2740 1540 731 298 87.8 28.3
2002 685 1000 1060 591 323 134 31
2003 818 561 691 432 236 106 58.6
Estimated population abundance at 1st Jan 2004
0 660 370 333 181 84.4 35.4
Taper weighted geometric mean of the VPA populations:
4070 4190 3440 1700 697 250 87.2
Standard error of the weighted Log(VPA populations) :
1.1807 1.1279 0.9638 0.8512 0.7457 0.6917 0.6961
1
Log catchability residuals.
Fleet : Mar¡n
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
1 -1.38 -2 -1.21 -2.01 99.99 99.99 0.12 3.22 99.99 2.27
2 -1.18 0.17 0.17 -0.36 -0.99 -1.13 -0.05 1.69 0.41 0.92
3 -0.38 0.05 -0.77 -0.36 0.08 -0.01 -0.14 0.47 0.49 0.37
4 0.01 0 -0.96 -0.14 0.21 0.35 0.11 0.08 0.41 0.29
5 0.25 -0.33 -0.71 -0.13 0.22 0.6 0.29 -0.13 0.72 0.38
6 0.55 -0.07 -0.77 -0.19 0.44 0.41 0.26 0.01 0.42 0.17
7 0.1 -0.52 -0.46 -0.06 -0.15 0.01 -0.22 -0.87 0.14 -0.4
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 1234567
Mean Log q -13.8455 -9.9711 -8.6992 -8.6992 -8.6992 -8.6992 -8.6992
S.E(Log q) 2.1705 0.936 0.4081 0.3914 0.4602 0.4105 0.4147
Regression statistics :
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
1 -1.19 -3.45 1.33 0.36 7 1.48 -13.85
2 1.5 -1.003 10.96 0.36 10 1.4 -9.97
3 1.52 -2.87 9.14 0.81 10 0.45 -8.7
4 1.43 -2.062 9.27 0.76 10 0.47 -8.65
5 1.44 -1.498 9.55 0.61 10 0.59 -8.57
6 1.14 -0.561 9.02 0.69 10 0.46 -8.57
7 0.82 1.429 8.12 0.9 10 0.25 -8.95
Table 5.4.49. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for males
continued).
...continued overleaf

WGNEPH Report 2004
196
Fleet : muros
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
1 No data for this fleet at this age
2 99.99 0.53 1.99 -1.1 -0.07 -0.3 -0.81 99.99 99.99 99.99
3 99.99 0.1 0.76 0.32 0.25 0.62 0.72 -1.74 -0.87 99.99
4 99.99 1.49 1.05 1.38 1.02 1.77 1.58 0.41 0.72 99.99
5 99.99 1.21 1.04 1.22 1.65 2.17 1.13 0.87 0.53 99.99
6 99.99 1.61 0 1.22 2.02 2.6 99.99 0.15 -1.36 99.99
7 99.99 2.44 0.23 0.14 2.06 2.03 99.99 99.99 99.99 99.99
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 234567
Mean Log q -13.6273 -11.3934 -11.3934 -11.3934 -11.3934 -11.3934
S.E(Log q) 1.1057 0.9018 1.3418 1.4112 1.6903 1.9166
Regression statistics :
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
2 0.47 1.81 10.8 0.77 6 0.43 -13.63
3 0.64 1.261 10.14 0.69 8 0.55 -11.39
4 0.82 0.857 9.68 0.8 8 0.39 -10.22
5 0.78 0.894 9.35 0.76 8 0.4 -10.17
6 0.45 1.371 7.78 0.58 7 0.59 -10.52
7 -4.7 -0.994 -20.33 0.01 5 5.22 -10.01
Terminal year survivor and F summaries :
Age 1 Catchability constant w.r.t. time and dependent on age
Year class = 2002
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Mar¡n 6362 2.3350010.0430.002
muros 1000000
F shrinkage mean 595 0.5 0.957 0.017
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
660 0.49 2.32 2 4.739 0.015
Age 2 Catchability constant w.r.t. time and dependent on age
Year class = 2001
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Mar¡n 928 0.9850010.1720.092
muros 1000000
F shrinkage mean 306 0.5 0.828 0.257
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
370 0.45 1.01 2 2.259 0.217
Table 5.4.49. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for males
continued).
...continued overleaf

WGNEPH Report 2004 197
Age 3 Catchability constant w.r.t. time and dependent on age
stimated
F
0.37
0.723
stimated
F
0.5
311.187
0.877
stimated
F
0.627
1.202
1.029
stimated
F
0.771
0.667
1.036
Table 5.4.49. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for males
continued).
Year class = 2000
Fleet Estimated Int Ext Var N Scaled E
Survivors s.e s.e Ratio W eights
Mar¡n 519 0.389 0.297 0.76 3 0.487
muros 1000000
F shrinkage mean 219 0.5 0.513
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
333 0.32 0.39 4 1.237 0.529
Age 4 Catchability constant w.r.t. time and age (fixed at the value for age) 3
Year class = 1999
Fleet Estimated Int Ext Var N Scaled E
Survivors s.e s.e Ratio W eights
Mar¡n 267 0.304 0.137 0.45 4 0.515
muros 760.960010.0
F shrinkage mean 123 0.5 0.454
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
181 0.28 0.24 6 0.88 0.672
Age 5 Catchability constant w.r.t. time and age (fixed at the value for age) 3
Year class = 1998
Fleet Estimated Int Ext Var N Scaled E
Survivors s.e s.e Ratio W eights
Mar¡n 125 0.286 0.042 0.15 4 0.467
muros 47 0.722 0.779 1.08 3 0.034
F shrinkage mean 61 0.5 0.5
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
84 0.28 0.2 8 0.715 0.83
Age 6 Catchability constant w.r.t. time and age (fixed at the value for age) 3
Year class = 1997
Fleet Estimated Int Ext Var N Scaled E
Survivors s.e s.e Ratio W eights
Mar¡n 44 0.278 0.144 0.52 5 0.47
muros 54 0.697 0.193 0.28 4 0.026
F shrinkage mean 28 0.5 0.505
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
35 0.28 0.13 10 0.452 0.895
...continued overleaf

WGNEPH Report 2004
198
Age 7 Catchability constant w.r.t. time and age (fixed at the value for age) 3
Table 5.4.49. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for males
continued).
Year class = 1996
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Mar¡n 22 0.256 0.146 0.57 7 0.554 0.749
muros 26 0.812 0.565 0.7 5 0.024 0.66
F shrinkage mean 27 0.5 0.422 0.634
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
24 0.25 0.1 13 0.398 0.697

Low
Ex
Ca
estoft VPA Version 3.1
25/03/2004 17:59
tended Survivors Analysis
26+27 West Galicia FINDEX FILE
CPUE data from file TUNEFF.DAT
tch data for 16 years. 1988 to 2003. Ages 1 to 11.
Fleet Fir
s
Last First Last Alpha Beta
year year age age
Marín1

1994 2003 1 10 0 1
MurosFemaleTU
N
1995 2003 2 10 0 1
me series weights :
Tapered time weighting applied
Power = 3 over 20 years
tchability analysis :
Catchability independent of stock size for all ages
Catchability independent of age for ages >= 5
erminal population estimation :
Survivor estimates shrunk towards the mean F
of the final 5 years or the 5 oldest ages.
S.E. of the mean to which the estimates are shrunk = .500
Minimum standard error for population
estimates derived from each fleet = .300
Prior weighting not applied
Table 5.4.50. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for
females.
Ti
Ca
T
Tuning had not converged after 30 iterations
Total absolute residual between iterations
29 and 30 = .00015
Final year F values
Age 12345678910
Iteration 29 0.0137 0.1511 0.1308 0.2181 0.2487 0.4474 0.4548 0.3567 0.3127 0.2912
Iteration 30 0.0137 0.1511 0.1308 0.2181 0.2487 0.4474 0.4547 0.3567 0.3127 0.2911
Regression weights
0.751 0.82 0.877 0.921 0.954 0.976 0.99 0.997 1 1
Fishing mortalities
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
10.00100.0030000.020.0530.0030.014
2 0.067 0.151 0.338 0.077 0.028 0.023 0.178 0.549 0.078 0.151
3 0.142 0.398 0.257 0.265 0.185 0.159 0.193 0.29 0.159 0.131
4 0.277 0.503 0.289 0.476 0.404 0.432 0.386 0.285 0.213 0.218
5 0.337 0.45 0.288 0.473 0.556 0.648 0.347 0.263 0.26 0.249
6 0.374 0.28 0.272 0.385 0.6 0.744 0.351 0.271 0.422 0.447
7 0.387 0.252 0.22 0.344 0.554 0.844 0.451 0.223 0.51 0.455
8 0.542 0.252 0.23 0.346 0.611 0.855 0.367 0.204 0.536 0.357
9 0.448 0.526 0.269 0.406 0.512 1.151 0.27 0.245 0.334 0.313
10 0.433 0.421 0.47 0.549 0.566 0.605 0.316 0.259 0.391 0.291
...continued overleaf
WGNEPH Report 2004 199

XSA population numbers (Thousands)
AGE
YEAR 123456789
1994 11100 9880 8830 6290 3970 2450 1380 619 352 220
1995 8250 9050 7570 6270 3910 2320 1380 765 295 184
1996 3760 6760 6370 4160 3110 2040 1440 877 487 143
1997 2460 3070 3940 4030 2550 1910 1270 943 570 305
1998 2440 2020 2330 2480 2050 1300 1060 738 546 311
1999 3440 2000 1610 1580 1350 964 585 500 328 268
2000 3710 2820 1600 1120 841 580 375 206 174 84.9
2001 2170 2980 1930 1080 624 487 335 196 117 109
2002 843 1690 1410 1180 663 393 304 219 131 74.8
2003 1550 688 1280 984 783 419 211 150 105 76.6
Estimated population abundance at 1st Jan 2004
0 1250 484 917 648 500 219 110 85.7 62.9
Taper weighted geometric mean of the VPA populations:
4260 4120 3590 2730 1830 1150 722 453 274 156
Standard error of the weighted Log(VPA populations) :
0.9986 1.0048 0.8567 0.8046 0.7634 0.727 0.7054 0.6701 0.6125 0.5522
Log catchability residuals.
Fleet : Marín1
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
1 -2.54 99.99 -1.18 99.99 99.99 99.99 -0.54 2.25 -0.23 1.46
2 -0.95 0.12 0.73 -0.7 -1.55 -1.58 0.29 1.89 0.39 1.08
3 -0.68 0.46 -0.3 -0.07 -0.2 -0.4 0.02 0.68 0.13 0.22
4 -0.45 0.19 -0.6 -0.03 0.05 0.12 0.29 0.15 -0.12 0.26
5 -0.26 -0.01 -0.66 -0.2 0.33 0.46 0.08 -0.06 -0.11 0.28
6 -0.15 -0.68 -0.84 -0.34 0.25 0.53 0.07 -0.15 0.44 0.88
7 -0.15 -0.77 -1.11 -0.53 0.11 0.67 0.44 -0.58 0.7 0.65
8 0.23 -0.88 -1.04 -0.52 0.22 0.7 0.18 -0.82 0.44 0.45
9 -0.08 -0.37 -1.01 -0.36 0.04 0.99 -0.12 -0.5 -0.06 0.24
10 -0.03 -0.1 -0.52 -0.1 0.03 0.23 -0.04 -0.17 -0.09 0.04
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 123456789
Mean Log q -13.1345 -10.4893 -9.8751 -9.3963 -9.3875 -9.3875 -9.3875 -9.3875 -9.3875 -9.3875
S.E(Log q) 1.7171 1.1672 0.3986 0.2923 0.3269 0.5428 0.6707 0.6486 0.5393 0.2057
Regression statistics :
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
1 -3.98 -1.519 -13.18 0.03 6 6.04 -13.13
2 1.19 -0.302 10.97 0.26 10 1.47 -10.49
Table 5.4.50. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for
females (continued).
10
10
3 1.2 -0.862 10.27 0.72 10 0.49 -9.88
4 1.29 -1.872 9.9 0.85 10 0.33 -9.4
5 1.2 -1.087 9.8 0.8 10 0.39 -9.39
6 2.08 -2.705 12.04 0.46 10 0.85 -9.36
7 2.5 -2.452 13.86 0.27 10 1.32 -9.41
8 1.5 -1.093 11.19 0.4 10 0.95 -9.47
9 1.12 -0.356 9.95 0.56 10 0.62 -9.49
10 0.93 0.654 9.14 0.92 10 0.18 -9.46
...continued overleaf
WGNEPH Report 2004
200

Fleet : MurosFemaleTUNEDA
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
1 No data for this fleet at this age
2 99.99 1.07 2.64 -1.11 -0.98 -0.62 -0.64 99.99 99.99 99.99
3 99.99 0.67 1.54 -0.08 -0.16 0.27 -0.05 99.99 -1.89 99.99
4 99.99 0.49 0.79 0.31 0.03 0.4 0.86 -1.98 -0.67 99.99
5 99.99 0.25 0.06 0.24 -0.38 0.39 0.49 -0.78 -0.2 99.99
6 99.99 0.39 0.4 0.65 0.24 0.82 0.89 -0.12 0.34 99.99
7 99.99 0.47 0.41 0.88 0.2 1.07 0.91 0.44 0.29 99.99
8 99.99 0.13 0.12 0.77 0.46 1.04 1.02 0.5 0.2 99.99
999.99 0.40.150.910.861.570.740.530.0399.
10 99.99 -0.42 0.97 1.28 1.32 1.59 -0.31 0.45 0.42 99.99
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 2345678910
Mean Log q -14.9304 -12.7405 -12.0131 -11.1315 -11.1315 -11.1315 -11.1315 -11.1315 -11.1315
S.E(Log q) 1.4781 1.0502 0.9628 0.4419 0.5908 0.7115 0.6955 0.8613 1.0423
Regression statistics :
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
2 0.34 2.806 10.44 0.84 6 0.31 -14.93
3 0.48 2.136 10.24 0.79 7 0.39 -12.74
4 0.58 1.372 10.21 0.66 8 0.53 -12.01
5 0.81 0.945 10.41 0.82 8 0.36 -11.13
6 0.93 0.384 10.41 0.83 8 0.34 -10.68
7 1.03 -0.16 10.68 0.8 8 0.37 -10.54
8 1.12 -0.481 11.13 0.74 8 0.45 -10.59
9 0.79 0.867 9.46 0.76 8 0.4 -10.48
10 0.53 2.242 7.92 0.8 8 0.31 -10.46
Terminal year survivor and F summaries :
Age 1 Catchability constant w.r.t. time and dependent on age
Year class = 2002
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1
99

5401 1.8640010.0660.003
MurosFemaleTU
N
1000000
Table 5.4.50. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for
females (continued).
F shrinkage mean 1127 0.5 0.934 0.015
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
1250 0.48 1.51 2 3.136 0.014
...continued overleaf
WGNEPH Report 2004 201

Age 2 Catchability constant w.r.t. time and dependent on age
Year class = 2001
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

961 1.026 0.603 0.59 2 0.17 0.079
MurosFemaleTU
N
1000000
F shrinkage mean 421 0.5 0.83 0.172
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
484 0.45 0.56 3 1.244 0.151
Age 3 Catchability constant w.r.t. time and dependent on age
Year class = 2000
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

1256 0.389 0.276 0.71 3 0.589 0.097
MurosFemaleTU
N
1000000
F shrinkage mean 584 0.5 0.411 0.198
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
917 0.31 0.33 4 1.079 0.131
Age 4 Catchability constant w.r.t. time and dependent on age
Year class = 1999
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

828 0.243 0.147 0.61 4 0.738 0.174
MurosFemaleTU
N
981.1280010.0310.958
F shrinkage mean 381 0.5 0.231 0.346
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
Table 5.4.50. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for
females (continued).
648 0.22 0.24 6 1.12 0.218
Age 5 Catchability constant w.r.t. time and dependent on age
Year class = 1998
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

599 0.202 0.167 0.83 4 0.773 0.211
MurosFemaleTU
N
257 0.881 0.015 0.02 2 0.036 0.438
F shrinkage mean 272 0.5 0.191 0.418
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
500 0.19 0.18 7 0.975 0.249
,,,continued overleaf
WGNEPH Report 2004
202

Age 6 Catchability constant w.r.t. time and age (fixed at the value for age) 5
Year class = 1997
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

251 0.193 0.201 1.04 5 0.633 0.401
MurosFemaleTU
N
144 0.394 0.336 0.85 4 0.155 0.62
F shrinkage mean 200 0.5 0.212 0.481
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
219 0.17 0.15 10 0.852 0.447
Age 7 Catchability constant w.r.t. time and age (fixed at the value for age) 5
Year class = 1996
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

127 0.197 0.168 0.86 6 0.556 0.402
MurosFemaleTU
N
88 0.341 0.306 0.9 5 0.187 0.539
F shrinkage mean 92 0.5 0.257 0.521
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
110 0.18 0.13 12 0.711 0.455
Age 8 Catchability constant w.r.t. time and age (fixed at the value for age) 5
Year class = 1995
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

101 0.209 0.113 0.54 8 0.523 0.31
MurosFemaleTU
N
106 0.323 0.135 0.42 6 0.197 0.297
F shrinkage mean 54 0.5 0.279 0.519
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
86 0.19 0.11 15 0.6 0.357
Table 5.4.50. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for
females (continued).
Age 9 Catchability constant w.r.t. time and age (fixed at the value for age) 5
Year class = 1994
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Marín1

74 0.239 0.111 0.47 8 0.507 0.271
MurosFemaleTU
N
99 0.327 0.13 0.4 7 0.198 0.209
F shrinkage mean 35 0.5 0.296 0.507
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
63 0.2 0.14 16 0.678 0.313
...continued overleaf
WGNEPH Report 2004 203

Age 10 Catchability constant w.r.t. time and age (fixed at the value for age) 5
Year class = 1993
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Marín1

47 0.213 0.092 0.43 10 0.664 0.291
MurosFemaleTU
N
70 0.358 0.167 0.47 8 0.134 0.204
F shrinkage mean 36 0.5 0.202 0.366
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
47 0.18 0.08 19 0.448 0.291
Table 5.4.50. - West Galicia and North Portugal (FUs 26-27): XSA tuning diagnostics for
females (continued).
WGNEPH Report 2004
204

At
0
0
0
0
Run title : NEP MALE(000) PORTUGINDEX FILE
7/04/2004 12:43
Table 1 Catch numbers at age Num bers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 2069 2837 1752 4102 2057 2307 1931 2543 3139 1952
3 2870 3773 3425 3260 3692 2163 3709 2780 3033 3616
4 1892 1511 2086 1272 1465 1942 2851 1930 1591 1116
5 750 852 1017 686 414 1301 1030 1118 1020 530
6 309 517 278 158 165 353 196 509 271 134
7 153 295 107 121 74 128 64 177 114 62
+gp 6111142785810850966747
TOTALNUM 8104 9895 8707 9677 7924 8303 9830 9153 9234 7457
TONSLAND 292 353 315 277 249 318 350 344 305 232
SOPCOF % 99 99 99 99 99 99 100 100 100 100
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 778 57 352 534 510 395 545 251 362 765
3 1549 1067 877 1219 1218 1139 937 1232 1746 1709
4 745 1071 401 257 453 663 487 862 1121 985
5 419 206 126 104 182 372 349 607 518 415
6 167 43 48 20 86 151 179 314 339 273
761162233454380148172171
+gp 46 6 27 70 27 49 101 187 229 183
TOTALNUM 3765 2466 1853 2236 2521 2811 2678 3602 4486 4502
TONSLAND 139 98 64 74 88 116 117 190 222 201
SOPCOF % 99 99 98 101 100 100 100 102 102 101
Table 2 Catch weights at age (kg)
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.014 0.015 0.014 0.014 0.015 0.012 0.015 0.014 0.014 0.015
3 0.028 0.026 0.027 0.026 0.027 0.027 0.026 0.025 0.026 0.026
4 0.044 0.044 0.045 0.045 0.043 0.046 0.045 0.046 0.045 0.044
5 0.066 0.067 0.064 0.064 0.066 0.065 0.064 0.066 0.065 0.065
6 0.087 0.088 0.087 0.087 0.088 0.088 0.086 0.087 0.086 0.086
7 0.108 0.108 0.108 0.109 0.108 0.108 0.11 0.109 0.109 0.11
+gp 0.135 0.132 0.135 0.137 0.136 0.139 0.131 0.132 0.144 0.145
SOPCOFAC 0.9942 0.991 0.9927 0.9861 0.991 0.994 1 1.0003 0.9968 0.9999
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.015 0.016 0.014 0.015 0.015 0.015 0.014 0.016 0.016 0.015
3 0.026 0.028 0.027 0.026 0.026 0.027 0.027 0.026 0.027 0.027
4 0.046 0.045 0.045 0.044 0.046 0.045 0.045 0.047 0.045 0.045
5 0.065 0.065 0.066 0.065 0.065 0.066 0.066 0.065 0.066 0.066
6 0.088 0.087 0.087 0.09 0.089 0.088 0.089 0.089 0.088 0.089
7 0.106 0.107 0.107 0.11 0.108 0.109 0.108 0.108 0.107 0.108
+gp 0.137 0.133 0.139 0.146 0.136 0.138 0.141 0.142 0.142 0.143
SOPCOFAC 0.9866 0.9935 0.9813 1.0089 0.9987 1.0025 1.003 1.0187 1.0172 1.0139
Table 5.4.51. - SW and S Portugal: VPA input and output tables for males.
...continued overleaf
WGNEPH Report 2004 205

Table 3 Stock weights at age (k g)
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.014 0.015 0.014 0.014 0.015 0.012 0.015 0.014 0.014 0.015
3 0.028 0.026 0.027 0.026 0.027 0.027 0.026 0.025 0.026 0.026
4 0.044 0.044 0.045 0.045 0.043 0.046 0.045 0.046 0.045 0.044
5 0.066 0.067 0.064 0.064 0.066 0.065 0.064 0.066 0.065 0.065
6 0.087 0.088 0.087 0.087 0.088 0.088 0.086 0.087 0.086 0.086
7 0.108 0.108 0.108 0.109 0.108 0.108 0.11 0.109 0.109 0.11
+gp 0.135 0.132 0.135 0.137 0.136 0.139 0.131 0.132 0.144 0.145
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.015 0.016 0.014 0.015 0.015 0.015 0.014 0.016 0.016 0.015
3 0.026 0.028 0.027 0.026 0.026 0.027 0.027 0.026 0.027 0.027
4 0.046 0.045 0.045 0.044 0.046 0.045 0.045 0.047 0.045 0.045
5 0.065 0.065 0.066 0.065 0.065 0.066 0.066 0.065 0.066 0.066
6 0.088 0.087 0.087 0.09 0.089 0.088 0.089 0.089 0.088 0.089
7 0.106 0.107 0.107 0.11 0.108 0.109 0.108 0.108 0.107 0.108
+gp 0.137 0.133 0.139 0.146 0.136 0.138 0.141 0.142 0.142 0.143
Table 4 Natural Mortality (M) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
4 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
5 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
6 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
7 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
+gp 0.3 0. 3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
4 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
5 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
6 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
7 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
+gp 0.3 0. 3 0.3 0.3 0.3 0.3 0.3 0.3 0.3 0.3
Table 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004
206

60000000000
70000000000
+gp 0000000000
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
+gp 0000000000
Table 5 Proportion mature at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
21111111111
31111111111
41111111111
51111111111
61111111111
71111111111
+gp 1111111111
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
21111111111
31111111111
41111111111
51111111111
61111111111
71111111111
+gp 1111111111
Table 6 Proportion of M befor e Spawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
30000000000
40000000000
50000000000
Table 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004 207

Table 7 Proportion of F before Spawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
+gp 0000000000
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
+gp 0000000000
Table 8 Fishing mortality (F) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.1536 0.2518 0.1306 0.2575 0.1523 0.1731 0.199 0.2866 0.3442 0.3288
3 0.453 0.5253 0.6286 0.4316 0.4413 0.266 0.5278 0.5585 0.7641 1.0183
4 0.5874 0.5227 0.7252 0.5775 0.3964 0.5007 0.781 0.6699 0.862 0.8437
5 0.5348 0.6649 0.9779 0.6396 0.421 0.8755 0.6256 0.9851 1.1412 0.9555
6 0.3753 1.0754 0.537 0.4283 0.3442 0.923 0.3344 0.8665 0.7969 0.4755
7 0.4606 0.8848 0.7694 0.5411 0.4139 0.5596 0.4642 0.6617 0.5374 0.471
+gp 0.4606 0.8848 0.7694 0.5411 0.4139 0.5596 0.4642 0.6617 0.5374 0.471
0 FBAR 2- 7 0.4274 0.6542 0.6281 0.4793 0.3615 0.5496 0.4887 0.6714 0.741 0.6821
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 FBAR 01-03
AGE
2 0.2033 0.0167 0.0664 0.0829 0.077 0.0667 0.0906 0.0407 0.061 0.1183 0.0733
3 0.5397 0.5401 0.43 0.3868 0.3099 0.2758 0.2494 0.342 0.4929 0.5117 0.4489
4 0.6772 1.1013 0.4518 0.2384 0.2705 0.3101 0.2027 0.4337 0.6942 0.6644 0.5974
5 1.1123 0.4479 0.3838 0.2226 0.298 0.4215 0.2994 0.4748 0.5798 0.6948 0.5831
6 1.1356 0.3316 0.1968 0.1063 0.3252 0.4939 0.4167 0.5512 0.613 0.821 0.6617
7 0.4638 0.3201 0.3193 0.2221 0.4149 0.2975 0.6065 0.857 0.7815 0.8557 0.8314
+gp 0.4638 0.3201 0.3193 0.2221 0.4149 0.2975 0.6065 0.857 0.7815 0.8557
0 FBAR 2- 7 0.6887 0.4596 0.308 0.2099 0.2826 0.3109 0.3109 0.4499 0.5371 0.611
Table 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004
208

T
YE
AG
+gp
0 RE
YE
AG
+gp
0 RE
T
YE
AG
+gp
0 TO
YE AM8403
AG
11157
7140
3433
1503
600
264
+gp
0 TO
Ta
able 9 Relative F at age
AR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
E
2 0.3594 0.3849 0.208 0.5373 0.4212 0.3149 0.4072 0.4268 0.4646 0.482
3 1.0597 0.8031 1.0009 0.9005 1.2208 0.4839 1.0801 0.8319 1.0312 1.4929
4 1.3742 0.7991 1.1545 1.205 1.0966 0.9109 1.5983 0.9978 1.1633 1.2369
5 1.2512 1.0164 1.5568 1.3347 1.1645 1.5928 1.2801 1.4673 1.5401 1.4007
6 0.8779 1.644 0.8549 0.8936 0.952 1.6793 0.6844 1.2906 1.0755 0.6971
7 1.0775 1.3526 1.2249 1.129 1.1449 1.0182 0.95 0.9856 0.7253 0.6904
1.0775 1.3526 1.2249 1.129 1.1449 1.0182 0.95 0.9856 0.7253 0.6904
FMEAN 0.4274 0.6542 0.6281 0.4793 0.3615 0.5496 0.4887 0.6714 0.741 0.6821
AR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 MEAN 01-03
E
2 0.2952 0.0363 0.2156 0.3952 0.2723 0.2144 0.2914 0.0904 0.1136 0.1936 0.1325
3 0.7838 1.1752 1.3959 1.8431 1.0965 0.8872 0.8022 0.7602 0.9178 0.8376 0.8385
4 0.9834 2.3961 1.4667 1.1359 0.9573 0.9975 0.6519 0.9639 1.2926 1.0874 1.1146
5 1.6152 0.9746 1.246 1.0609 1.0545 1.3557 0.9629 1.0553 1.0796 1.1372 1.0907
6 1.649 0.7214 0.6389 0.5064 1.1509 1.5886 1.3405 1.2252 1.1414 1.3437 1.2368
7 0.6735 0.6964 1.0368 1.0585 1.4683 0.9567 1.951 1.9049 1.4551 1.4006 1.5869
0.6735 0.6964 1.0368 1.0585 1.4683 0.9567 1.951 1.9049 1.4551 1.4006
FMEAN 0.6887 0.4596 0.308 0.2099 0.2826 0.3109 0.3109 0.4499 0.5371 0.611
able 10 Stock number at age (start of year) Numbers*10**-3
AR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
E
2 16884 14806 16624 20992 16916 16866 12433 11858 12524 8093
3 9154 10727 8527 10807 12021 10762 10509 7549 6596 6576
4 4948 4311 4699 3369 5200 5728 6111 4592 3199 2276
5 2102 2037 1894 1686 1401 2591 2572 2073 1741 1001
6 1146 912 776 528 659 681 800 1019 573 412
7 482 583 231 336 255 346 201 424 317 191
190 215 89 213 195 288 153 227 183 143
TAL 34905 33591 32840 37931 36647 37263 32778 27742 25134 18692
AR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 GM8403
E
2 4915 4002 6372 7790 7999 7117 7305 7326 7114 7970 0 10056
3 4315 2971 2915 4417 5312 5487 4933 4943 5211 4958 5246 6535
4 1760 1863 1283 1405 2223 2887 3085 2848 2601 2358 2202 3096
5 725 662 459 605 820 1256 1568 1866 1367 962 899 1337
ble 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
6 285 177 313 232 359 451 611 861 860 567 356 532
7 190 68 94 191 154 192 204 298 368 345 185 233
143 26 111 403 90 218 252 368 479 360 222
TAL 12333 9770 11547 15043 16956 17608 17958 18511 18000 17521 9110
...continued overleaf
WGNEPH Report 2004 209

0
0
Table 11 Spawning stock number at age (spawning time) Numbers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 16884 14806 16624 20992 16916 16866 12433 11858 12524 8093
3 9154 10727 8527 10807 12021 10762 10509 7549 6596 6576
4 4948 4311 4699 3369 5200 5728 6111 4592 3199 2276
5 2102 2037 1894 1686 1401 2591 2572 2073 1741 1001
6 1146 912 776 528 659 681 800 1019 573 412
7 482 583 231 336 255 346 201 424 317 191
+gp 190 215 89 213 195 288 153 227 183 143
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 4915 4002 6372 7790 7999 7117 7305 7326 7114 7970
3 4315 2971 2915 4417 5312 5487 4933 4943 5211 4958
4 1760 1863 1283 1405 2223 2887 3085 2848 2601 2358
5 725 662 459 605 820 1256 1568 1866 1367 962
6 285 177 313 232 359 451 611 861 860 567
7 190 68 94 191 154 192 204 298 368 345
+gp 143 26 111 403 90 218 252 368 479 360
Table 12 Stock biomass at age ( start of year) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 236 222 233 294 254 202 186 166 175 121
3 256 279 230 281 325 291 273 189 171 171
4 218 190 211 152 224 263 275 211 144 100
5 139 136 121 108 92 168 165 137 113 65
6 100 80 68 46 58 60 69 89 49 35
752632537283722463521
+gp 26281229274020302621
TOTALBIO 1027 999 900 946 1006 1062 1010 868 714 535
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 74 64 89 117 120 107 102 117 114 120
3 112 83 79 115 138 148 133 129 141 134
4 81 84 58 62 102 130 139 134 117 106
54743303953831041219064
625152721324054777650
7 20 7 10 21 17 21 22 32 39 37
+gp 20 4 15 59 12 30 36 52 68 51
TOTALBIO 379 300 309 434 474 558 590 662 645 562
Table 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004
210

0
0
0
0
Table 13 Spawning stock biomass at age (s pawning time) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 236 222 233 294 254 202 186 166 175 121
3 256 279 230 281 325 291 273 189 171 171
4 218 190 211 152 224 263 275 211 144 100
5 139 136 121 108 92 168 165 137 113 65
6 100 80 68 46 58 60 69 89 49 35
752632537283722463521
+gp 26281229274020302621
TOTSPBIO 1027 999 900 946 1006 1062 1010 868 714 535
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 74 64 89 117 120 107 102 117 114 120
3 112 83 79 115 138 148 133 129 141 134
4 81 84 58 62 102 130 139 134 117 106
54743303953831041219064
625152721324054777650
7 20 7 10 21 17 21 22 32 39 37
+gp 20 4 15 59 12 30 36 52 68 51
TOTSPBIO 379 300 309 434 474 558 590 662 645 562
Table 14 Stock biomass at age with SOP (s tart of year) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 235 220 231 290 251 201 186 166 175 121
3 255 276 229 277 322 289 273 189 171 171
4 216 188 210 149 222 262 275 211 143 100
5 138 135 120 106 92 167 165 137 113 65
699806745576069894935
752622536273722463421
+gp 26281229264020302621
TOTALBIO 1021 990 894 933 997 1056 1010 868 712 535
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 73 64 88 118 120 107 103 119 116 121
3 111 83 77 116 138 149 134 131 143 136
4 80 83 57 62 102 130 139 136 119 108
54743304053831041249264
625152721324055787751
7 20 7 10 21 17 21 22 33 40 38
+gp 19 3 15 59 12 30 36 53 69 52
TOTALBIO 374 298 303 437 474 560 592 674 656 570
Table 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004 211

0
0
T
Table 15 Spawning stock biomass with SOP (spawning time) T onnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 235 220 231 290 251 201 186 166 175 121
3 255 276 229 277 322 289 273 189 171 171
4 216 188 210 149 222 262 275 211 143 100
5 138 135 120 106 92 167 165 137 113 65
699806745576069894935
752622536273722463421
+gp 26281229264020302621
TOTSPBIO 1021 990 894 933 997 1056 1010 868 712 535
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 73 64 88 118 120 107 103 119 116 121
3 111 83 77 116 138 149 134 131 143 136
4 80 83 57 62 102 130 139 136 119 108
54743304053831041249264
625152721324055787751
7 20 7 10 21 17 21 22 33 40 38
+gp 19 3 15 59 12 30 36 53 69 52
TOTSPBIO 374 298 303 437 474 560 592 674 656 570
able 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
...continued overleaf
WGNEPH Report 2004
212

Arit
Table 16 Summary (without SOP cor rection)
Terminal F s derived using XSA (With F shrink age)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB FBAR 2- 7
Age 2
1984 16884 1027 1027 292 0.2845 0.4274
1985 14806 999 999 353 0.3534 0.6542
1986 16624 900 900 315 0.35 0.6281
1987 20992 946 946 277 0.2928 0.4793
1988 16916 1006 1006 249 0.2474 0.3615
1989 16866 1062 1062 318 0.2994 0.5496
1990 12433 1010 1010 350 0.3464 0.4887
1991 11858 868 868 344 0.3965 0.6714
1992 12524 714 714 305 0.427 0. 741
1993 8093 535 535 232 0.4338 0.6821
1994 4915 379 379 139 0.367 0.6887
1995 4002 300 300 98 0.3264 0.4596
1996 6372 309 309 64 0.2073 0.308
1997 7790 434 434 74 0.1707 0.2099
1998 7999 474 474 88 0.1855 0.2826
1999 7117 558 558 116 0.2077 0.3109
2000 7305 590 590 117 0.1984 0.3109
2001 7326 662 662 190 0.287 0.4499
2002 7114 645 645 222 0.3442 0.5371
2003 7970 562 562 201 0.3575 0.611
h.
Mean 10795 699 699 217 0.3041 0.4926
0 Units (Thousan
d
(Tonnes) (T onnes) (Tonnes)
Table 17 Summary (with SO P correction)
Terminal F s derived using XSA (With F shrink age)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB
S
OPCOFAC FBAR 2- 7
Age 2
1984 16884 1021 1021 292 0.2861 0.9942 0.4274
1985 14806 990 990 353 0.3566 0.991 0.6542
1986 16624 894 894 315 0.3525 0.9927 0.6281
1987 20992 933 933 277 0.2969 0.9861 0.4793
1988 16916 997 997 249 0.2497 0.991 0.3615
1989 16866 1056 1056 318 0.3012 0. 994 0.5496
1990 12433 1010 1010 350 0.3464 1 0.4887
1991 11858 868 868 344 0.3964 1.0003 0.6714
1992 12524 712 712 305 0.4284 0.9968 0.741
1993 8093 535 535 232 0.4338 0.9999 0.6821
1994 4915 374 374 139 0.372 0.9866 0.6887
1995 4002 298 298 98 0.3285 0.9935 0.4596
1996 6372 303 303 64 0.2113 0.9813 0.308
1997 7790 437 437 74 0.1692 1.0089 0.2099
1998 7999 474 474 88 0.1857 0.9987 0.2826
1999 7117 560 560 116 0.2072 1.0025 0.3109
2000 7305 592 592 117 0.1978 1.003 0.3109
2001 7326 674 674 190 0.2817 1.0187 0.4499
2002 7114 656 656 222 0.3384 1.0172 0.5371
2003 7970 570 570 201 0.3526 1.0139 0.611
h.
Mean 10795 698 698 217 .3046 .4926
0 Units (Thousan
Arit
d
(Tonnes) (T onnes) (Tonnes)
Table 5.4.51. - SW and S Portugal: VPA input and output tables for males (continued).
WGNEPH Report 2004 213

R
At
0 T
T
S
0 T
T
S
Ta
un title : NEP FEMALE(000) PORTIN DEX FILE
7/04/2004 13:19
Table 1 Catch numbers at age Number s*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 2059 2584 1743 5411 2234 2073 1693 2856 2695 2004
3 1022 1324 1065 2049 1235 866 1492 1342 1451 1693
4 1204 969 1102 1094 1353 767 1404 883 905 995
5 1038 909 848 928 1013 763 905 463 564 431
6 844 597 655 486 511 538 368 213 538 277
7 526 329 426 323 463 335 357 165 343 218
8 199 179 110 154 205 216 265 149 182 171
9 75 80 157 83 95 194 244 84 98 141
10 35 31 41 104 38 142 89 78 45 59
11 19 15 46 143 29 70 72 19 55 48
1210 81259184340493444
+gp 1 4 5 10 136 45 89 30 50 137 107
OTALNUM 7046 7029 6212 10970 7238 6097 6960 6350 7047 6186
ONSLAND 169 156 150 232 171 151 174 134 165 145
OPCOF % 101 100 99 100 100 101 100 100 103 102
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 908 87 201 663 568 558 621 281 412 577
3 955 441 246 831 518 696 392 437 510 503
4 725 797 265 544 460 597 415 469 862 601
5 500 1353 335 326 311 585 400 342 815 459
6 295 1165 382 204 262 403 339 257 561 350
7 153 431 168 61 95 273 149 187 412 292
8 156 550 153 40 126 156 116 175 245 361
9 105 313 138 31 113 108 96 126 131 259
10 41 99 68 10 64 50 60 76 106 150
11 33 88 76 16 56 32 44 52 69 88
12142623 6332242395151
+gp 36 36 39 15 47 30 154 98 157 176
OTALNUM 3920 5385 2095 2746 2653 3508 2827 2539 4332 3865
ONSLAND 97 174 67 62 72 95 84 79 135 126
OPCOF % 100 101 100 99 99 100 101 100 100 102
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females.
Table 2 Catch weights at age (kg)
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.013 0.014 0.014 0.014 0.014 0.012 0.014 0.014 0.013 0.014
3 0.019 0.019 0.02 0.019 0.02 0.019 0.02 0.019 0.019 0.019
4 0.024 0.023 0.024 0.024 0.024 0.024 0.024 0.023 0.023 0.023
5 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028
6 0.033 0.033 0.033 0.032 0.032 0.033 0.033 0.033 0.033 0.032
7 0.037 0.037 0.037 0.037 0.037 0.037 0.037 0.037 0.037 0.038
8 0.042 0.043 0.042 0.042 0.043 0.043 0.042 0.042 0.042 0.043
9 0.047 0.046 0.047 0.047 0.046 0.047 0.048 0.048 0.047 0.047
10 0.052 0.052 0.053 0.054 0.053 0.052 0.053 0.052 0.053 0.053
11 0.057 0.057 0.057 0.057 0.057 0.056 0.057 0.058 0.057 0.057
12 0.062 0.062 0.061 0.061 0.062 0.062 0.062 0.062 0.062 0.062
+gp 0.072 0.069 0.073 0.072 0.073 0.072 0.07 0.073 0.075 0.073
SOPCOFAC 1.0064 1.0025 0.9908 1.0001 0.9971 1.0061 0.9987 1 1.0324 1.0164
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.014 0.016 0.014 0.014 0.014 0.014 0.014 0.015 0.015 0.014
30.020.020.020.020.020.020.020.020.020.02
4 0.023 0.024 0.024 0.023 0.024 0.024 0.024 0.024 0.024 0.024
5 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028
6 0.032 0.032 0.033 0.032 0.032 0.032 0.032 0.032 0.033 0.033
7 0.037 0.037 0.037 0.037 0.038 0.037 0.037 0.037 0.037 0.037
8 0.042 0.043 0.042 0.043 0.042 0.042 0.042 0.042 0.042 0.042
9 0.047 0.046 0.047 0.047 0.047 0.047 0.047 0.047 0.047 0.047
10 0.053 0.053 0.054 0.054 0.053 0.053 0.053 0.053 0.052 0.052
11 0.056 0.057 0.056 0.057 0.056 0.057 0.057 0.057 0.057 0.057
12 0.062 0.061 0.061 0.061 0.062 0.062 0.062 0.062 0.062 0.062
0
+gp 0.073 0.07 0.07 0.074 0.071 0.072 0.072 0.073 0.074 0.074
0 SOPCOFAC 1.0046 1.0066 0.9958 0.9936 0.9923 1 1.0148 1.0031 1.0044 1.0161
...continued overleaf
WGNEPH Report 2004
214

Ta
Table 3 Stock weights at age (kg)
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.013 0.014 0.014 0.014 0.014 0.012 0.014 0.014 0.013 0.014
3 0.019 0.019 0.02 0.019 0.02 0.019 0.02 0.019 0.019 0.019
4 0.024 0.023 0.024 0.024 0.024 0.024 0.024 0.023 0.023 0.023
5 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028
6 0.033 0.033 0.033 0.032 0.032 0.033 0.033 0.033 0.033 0.032
7 0.037 0.037 0.037 0.037 0.037 0.037 0.037 0.037 0.037 0.038
8 0.042 0.043 0.042 0.042 0.043 0.043 0.042 0.042 0.042 0.043
9 0.047 0.046 0.047 0.047 0.046 0.047 0.048 0.048 0.047 0.047
10 0.052 0.052 0.053 0.054 0.053 0.052 0.053 0.052 0.053 0.053
11 0.057 0.057 0.057 0.057 0.057 0.056 0.057 0.058 0.057 0.057
12 0.062 0.062 0.061 0.061 0.062 0.062 0.062 0.062 0.062 0.062
+gp 0.072 0.069 0.073 0.072 0.073 0.072 0.07 0.073 0.075 0.073
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.014 0.016 0.014 0.014 0.014 0.014 0.014 0.015 0.015 0.014
30.020.020.020.020.020.020.020.020.020.02
4 0.023 0.024 0.024 0.023 0.024 0.024 0.024 0.024 0.024 0.024
5 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028 0.028
6 0.032 0.032 0.033 0.032 0.032 0.032 0.032 0.032 0.033 0.033
7 0.037 0.037 0.037 0.037 0.038 0.037 0.037 0.037 0.037 0.037
8 0.042 0.043 0.042 0.043 0.042 0.042 0.042 0.042 0.042 0.042
9 0.047 0.046 0.047 0.047 0.047 0.047 0.047 0.047 0.047 0.047
10 0.053 0.053 0.054 0.054 0.053 0.053 0.053 0.053 0.052 0.052
11 0.056 0.057 0.056 0.057 0.056 0.057 0.057 0.057 0.057 0.057
12 0.062 0.061 0.061 0.061 0.062 0.062 0.062 0.062 0.062 0.062
+gp 0.073 0.07 0.07 0.074 0.071 0.072 0.072 0.073 0.074 0.074
Table 4 Natural Mortality (M) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
10 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
11 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
12 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
3 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
4 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
5 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
6 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
7 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
8 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
9 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
10 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
11 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
12 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
+gp 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2 0.2
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
...continued overleaf
WGNEPH Report 2004 215

30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
110000000000
120000000000
+gp 0000000000
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
110000000000
120000000000
+gp 0000000000
Ta
Table 5 Proportion mature at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
21111111111
31111111111
41111111111
51111111111
61111111111
71111111111
81111111111
91111111111
101111111111
111111111111
121111111111
+gp 1111111111
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
21111111111
31111111111
41111111111
51111111111
61111111111
71111111111
81111111111
91111111111
101111111111
111111111111
121111111111
+gp 1111111111
Table 6 Proportion of M before S pawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
...continued overleaf
WGNEPH Report 2004
216

Table 7 Proportion of F befo re Spawning
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
110000000000
120000000000
+gp 0000000000
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
20000000000
30000000000
40000000000
50000000000
60000000000
70000000000
80000000000
90000000000
100000000000
110000000000
120000000000
+gp 0000000000
Table 8 Fishing mortality (F) at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.1961 0.2437 0.1558 0.485 0.2106 0.2032 0.1837 0.2561 0.2486 0.2576
3 0.1265 0.1864 0.1495 0.2772 0.1911 0.1176 0.2207 0.2173 0.1998 0.244
4 0.2281 0.1697 0.2336 0.2261 0.2979 0.174 0.2839 0.1964 0.2231 0.2049
5 0.2611 0.2695 0.2203 0.3157 0.3384 0.2732 0.3205 0.1419 0.1857 0.1571
6 0.4286 0.235 0.3175 0.1893 0.2871 0.3025 0.2045 0.1148 0.2436 0.1304
7 0.3552 0.2936 0.2625 0.2552 0.2779 0.3099 0.3378 0.133 0.2734 0.1469
8 0.2656 0.1946 0.1509 0.1418 0.2547 0.2019 0.433 0.2288 0.2126 0.2123
9 0.1391 0.1621 0.2614 0.1609 0.1229 0.4099 0.3683 0.2353 0.2307 0.2528
10 0.2538 0.0777 0.1147 0.2786 0.1034 0.2711 0.3315 0.1905 0.1923 0.2109
11 0.2718 0.1691 0.1592 0.7461 0.1134 0.2812 0.2158 0.11 0.2007 0.3231
12 0.2585 0.1803 0.1907 0.3186 0.1875 0.2521 0.2569 0.2195 0.2877 0.2445
+gp 0.2585 0.1803 0.1907 0.3186 0.1875 0.2521 0.2569 0.2195 0.2877 0.2445
0 FBAR 4-10 0.2759 0.2003 0.223 0.2239 0.2403 0.2775 0.3256 0.1772 0.2231 0.1879
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 FBAR 01-03
AGE
2 0.1395 0.0139 0.0252 0.0832 0.0835 0.0845 0.0916 0.0415 0.0568 0.0756 0.058
3 0.1875 0.0929 0.0495 0.1381 0.0865 0.1394 0.0787 0.0861 0.0989 0.0912 0.0921
4 0.1562 0.2361 0.0743 0.1469 0.1055 0.1361 0.1154 0.1275 0.2442 0.1622 0.178
5 0.1505 0.4865 0.1472 0.123 0.1172 0.1895 0.1271 0.1316 0.3406 0.1984 0.2235
6 0.1533 0.6194 0.2434 0.1254 0.1375 0.2189 0.1601 0.1124 0.3304 0.2394 0.2274
7 0.0988 0.3501 0.1639 0.0556 0.0786 0.2081 0.1175 0.1241 0.2651 0.2858 0.225
8 0.1486 0.6083 0.2004 0.0526 0.1543 0.1796 0.128 0.1969 0.2383 0.393 0.2761
9 0.1965 0.4987 0.2971 0.056 0.208 0.1917 0.1601 0.1999 0.2213 0.4251 0.2821
10 0.1072 0.2859 0.1882 0.0323 0.1587 0.1342 0.1548 0.1834 0.2581 0.425 0.2888
11 0.1755 0.3561 0.3694 0.061 0.2424 0.1099 0.1652 0.1967 0.2554 0.3531 0.2684
Table 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
12 0.1403 0.2074 0.1472 0.0413 0.1761 0.1389 0.2104 0.219 0.3023 0.3013 0.2742
+gp 0.1403 0.2074 0.1472 0.0413 0.1761 0.1389 0.2104 0.219 0.3023 0.3013
0 FBAR 4-10 0.1444 0.4407 0.1878 0.0846 0.1371 0.1797 0.1376 0.1537 0.2712 0.3041
...continued overleaf
WGNEPH Report 2004 217

0
0
0
8403
10692
7480
5334
3720
2468
1601
1041
681
424
277
171
0
Ta
Table 9 Relative F at age
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 0.7107 1.2166 0.6988 2.1657 0.8763 0.732 0.5642 1.445 1.1144 1.3707
3 0.4583 0.9306 0.6706 1.238 0.7953 0.4239 0.6777 1.2261 0.8959 1.2982
4 0.8267 0.8472 1.0476 1.0097 1.2396 0.6271 0.8719 1.1083 1.0002 1.0905
5 0.9461 1.3453 0.988 1.4096 1.4081 0.9845 0.9841 0.8003 0.8325 0.836
6 1.5534 1.1731 1.4239 0.8453 1.1945 1.0899 0.628 0.6476 1.0923 0.6942
7 1.2873 1.4661 1.1772 1.1398 1.1565 1.1167 1.0375 0.7503 1.2255 0.7819
8 0.9626 0.9714 0.6766 0.633 1.0599 0.7277 1.3296 1.2909 0.953 1.13
9 0.5041 0.8093 1.172 0.7186 0.5112 1.4771 1.1309 1.3278 1.0344 1.3452
10 0.9198 0.3877 0.5145 1.2439 0.4302 0.9771 1.0181 1.0748 0.8622 1.1222
11 0.9852 0.8444 0.7137 3.3317 0.4719 1.0131 0.6627 0.6206 0.8999 1.7196
12 0.937 0.9 0.855 1.4226 0.78 0.9085 0.7891 1.2383 1.2898 1.3013
+gp 0.937 0.9 0.855 1.4226 0.78 0.9085 0.7891 1.2383 1.2898 1.3013
REFMEAN 0.2759 0.2003 0.223 0.2239 0.2403 0.2775 0.3256 0.1772 0.2231 0.1879
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 MEAN 01-03
AGE
2 0.9657 0.0315 0.1341 0.9845 0.6087 0.4703 0.6658 0.2703 0.2096 0.2487 0.2429
3 1.298 0.2108 0.2634 1.6328 0.6312 0.7758 0.5718 0.5604 0.3648 0.2999 0.4084
4 1.0812 0.5357 0.3955 1.7375 0.7695 0.7575 0.8385 0.8298 0.9006 0.5334 0.7546
5 1.0418 1.1038 0.7838 1.4549 0.8545 1.0546 0.9242 0.856 1.2563 0.6523 0.9215
6 1.0613 1.4056 1.2962 1.4825 1.0027 1.2179 1.1641 0.7316 1.2186 0.7872 0.9125
7 0.6839 0.7944 0.8729 0.6577 0.573 1.1576 0.8539 0.8073 0.9777 0.9397 0.9083
8 1.0289 1.3803 1.0673 0.6223 1.1255 0.9992 0.9301 1.2813 0.8787 1.2923 1.1508
9 1.3605 1.1315 1.5823 0.6628 1.5171 1.0667 1.1637 1.3008 0.8161 1.3977 1.1716
10 0.7424 0.6487 1.002 0.3822 1.1576 0.7464 1.1256 1.1932 0.952 1.3973 1.1809
11 1.2151 0.8081 1.967 0.7219 1.768 0.6114 1.2006 1.2797 0.9419 1.161 1.1275
12 0.9714 0.4707 0.7836 0.4888 1.2846 0.7729 1.5295 1.4248 1.1151 0.9908 1.1769
+gp 0.9714 0.4707 0.7836 0.4888 1.2846 0.7729 1.5295 1.4248 1.1151 0.9908
REFMEAN 0.1444 0.4407 0.1878 0.0846 0.1371 0.1797 0.1376 0.1537 0.2712 0.3041
Table 10 Stock number at age (s tart of year) Numbers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 12781 13206 13348 15561 13003 12464 11147 13967 13535 9751
3 9508 8601 8474 9351 7844 8624 8329 7595 8852 8642
4 6524 6859 5844 5974 5803 5305 6277 5469 5003 5934
5 4993 4252 4740 3788 3901 3527 3649 3869 3679 3277
6 2676 3149 2659 3113 2262 2277 2197 2169 2749 2502
7 1944 1427 2038 1585 2109 1390 1378 1466 1583 1764
8 945 1116 871 1284 1005 1308 835 805 1051 986
9 637 593 752 613 912 638 875 443 524 696
10 171 454 413 474 428 660 347 496 287 341
11 89 109 344 301 294 316 412 204 335 194
12 49 56 75 240 117 215 195 272 149 225
+gp 69 35 60 548 288 440 147 281 602 541
TOTAL 40387 39856 39618 42833 37966 37164 35788 37034 38349 34852
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004 GM8403 AM
AGE
2 7707 6989 8921 9168 7845 7602 7835 7619 8237 8749 0 10342
3 6170 5488 5643 7122 6907 5908 5720 5854 5984 6372 6644 7353
4 5544 4188 4095 4397 5079 5186 4208 4329 4397 4438 4764 5270
5 3958 3883 2708 3113 3108 3742 3706 3070 3120 2820 3092 3680
6 2293 2788 1954 1914 2253 2263 2535 2672 2203 1817 1895 2445
7 1798 1611 1229 1254 1382 1608 1489 1768 1955 1296 1172 1582
8 1247 1333 929 854 971 1046 1069 1084 1279 1228 798 1029
9 653 880 594 623 663 682 716 770 729 825 679 671
10 442 439 437 361 482 441 461 499 516 478 442 410
11 226 325 270 297 286 337 316 323 340 327 256 260
12 115 155 187 153 229 184 247 219 217 216 188 155
+gp 302 212 315 411 322 258 889 546 662 741 580
TOTAL 30455 28292 27283 29667 29528 29258 29190 28752 29640 29306 20512
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
...continued overleaf
WGNEPH Report 2004
218

0 T
0 T
Ta
Table 11 Spawning stock number at age (spawning time) Numbers*10**-3
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 12781 13206 13348 15561 13003 12464 11147 13967 13535 9751
3 9508 8601 8474 9351 7844 8624 8329 7595 8852 8642
4 6524 6859 5844 5974 5803 5305 6277 5469 5003 5934
5 4993 4252 4740 3788 3901 3527 3649 3869 3679 3277
6 2676 3149 2659 3113 2262 2277 2197 2169 2749 2502
7 1944 1427 2038 1585 2109 1390 1378 1466 1583 1764
8 945 1116 871 1284 1005 1308 835 805 1051 986
9 637 593 752 613 912 638 875 443 524 696
10 171 454 413 474 428 660 347 496 287 341
11 89 109 344 301 294 316 412 204 335 194
12 49 56 75 240 117 215 195 272 149 225
+gp 69 35 60 548 288 440 147 281 602 541
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 7707 6989 8921 9168 7845 7602 7835 7619 8237 8749
3 6170 5488 5643 7122 6907 5908 5720 5854 5984 6372
4 5544 4188 4095 4397 5079 5186 4208 4329 4397 4438
5 3958 3883 2708 3113 3108 3742 3706 3070 3120 2820
6 2293 2788 1954 1914 2253 2263 2535 2672 2203 1817
7 1798 1611 1229 1254 1382 1608 1489 1768 1955 1296
8 1247 1333 929 854 971 1046 1069 1084 1279 1228
9 653 880 594 623 663 682 716 770 729 825
10 442 439 437 361 482 441 461 499 516 478
11 226 325 270 297 286 337 316 323 340 327
12 115 155 187 153 229 184 247 219 217 216
+gp 302 212 315 411 322 258 889 546 662 741
Table 12 Stock biomass at age ( start of year) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 166 185 187 218 182 150 156 196 176 137
3 181 163 169 178 157 164 167 144 168 164
4 157 158 140 143 139 127 151 126 115 136
5 140 119 133 106 109 99 102 108 103 92
6 88 104 88 100 72 75 73 72 91 80
772537559785151545967
840483754435635344442
930273529423042212533
10 9242226233418261518
11 5 6 20 17 17 18 23 12 19 11
12335157131217914
+gp 5 2 4 39 21 32 10 20 45 39
OTALBIO 895 893 915 983 891 849 840 830 869 834
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 108 112 125 128 110 106 110 114 124 122
3 123 110 113 142 138 118 114 117 120 127
4 128 101 98 101 122 124 101 104 106 107
5 111 109 76 87 87 105 104 86 87 79
673896461727281857360
767604546535955657248
852573937414445465452
931402829313234363439
10 23 23 24 20 26 23 24 26 27 25
11 13 19 15 17 16 19 18 18 19 19
12 7 911 9141115141313
+gp 22152230231964404955
OTALBIO 758 744 661 709 732 734 765 752 778 745
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
...continued overleaf
WGNEPH Report 2004 219

0 T
0 T
0 T
0 T
Ta
Table 13 Spawning stock biomass at age (s pawning time) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 166 185 187 218 182 150 156 196 176 137
3 181 163 169 178 157 164 167 144 168 164
4 157 158 140 143 139 127 151 126 115 136
5 140 119 133 106 109 99 102 108 103 92
6 88 104 88 100 72 75 73 72 91 80
772537559785151545967
840483754435635344442
930273529423042212533
10 9242226233418261518
11 5 6 20 17 17 18 23 12 19 11
12335157131217914
+gp 5 2 4 39 21 32 10 20 45 39
OTSPBIO 895 893 915 983 891 849 840 830 869 834
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 108 112 125 128 110 106 110 114 124 122
3 123 110 113 142 138 118 114 117 120 127
4 128 101 98 101 122 124 101 104 106 107
5 111 109 76 87 87 105 104 86 87 79
673896461727281857360
767604546535955657248
852573937414445465452
931402829313234363439
10 23 23 24 20 26 23 24 26 27 25
11 13 19 15 17 16 19 18 18 19 19
12 7 911 9141115141313
+gp 22152230231964404955
OTSPBIO 758 744 661 709 732 734 765 752 778 745
Table 14 Stock biomass at age with SOP (s tart of year) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 167 185 185 218 182 150 156 196 182 139
3 182 164 168 178 156 165 166 144 174 167
4 158 158 139 143 139 128 150 126 119 139
5 141 119 131 106 109 99 102 108 106 93
6 89 104 87 100 72 76 72 72 94 81
772537559785251546068
840483654435735344643
930273529423042212533
10 9242226233518261618
11 5 6 19 17 17 18 23 12 20 11
123351571312171014
+gp 5 2 4 39 21 32 10 20 47 40
OTALBIO 901 895 906 983 888 854 839 830 897 847
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 108 113 124 128 109 106 111 115 124 124
3 124 110 112 142 137 118 116 117 120 129
4 128 101 98 100 121 124 102 104 106 108
5 111 109 76 87 86 105 105 86 88 80
674906461727282867361
767604546525956667349
853583936404446465452
931412829313234363439
10 24 23 24 19 25 23 25 27 27 25
11 13 19 15 17 16 19 18 18 19 19
12 7 10 11 9 14 11 16 14 14 14
+gp 22152230231965404956
OTALBIO 761 749 658 704 726 734 777 754 781 757
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
...continued overleaf
WGNEPH Report 2004
220

0 T
0 T
Ta
Table 15 Spawning stock biomass with SOP (spawning tim e) Tonnes
YEAR 1984 1985 1986 1987 1988 1989 1990 1991 1992 1993
AGE
2 167 185 185 218 182 150 156 196 182 139
3 182 164 168 178 156 165 166 144 174 167
4 158 158 139 143 139 128 150 126 119 139
5 141 119 131 106 109 99 102 108 106 93
6 89 104 87 100 72 76 72 72 94 81
772537559785251546068
840483654435735344643
930273529423042212533
10 9242226233518261618
11 5 6 19 17 17 18 23 12 20 11
123351571312171014
+gp 5 2 4 39 21 32 10 20 47 40
OTSPBIO 901 895 906 983 888 854 839 830 897 847
YEAR 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
AGE
2 108 113 124 128 109 106 111 115 124 124
3 124 110 112 142 137 118 116 117 120 129
4 128 101 98 100 121 124 102 104 106 108
5 111 109 76 87 86 105 105 86 88 80
674906461727282867361
767604546525956667349
853583936404446465452
931412829313234363439
10 24 23 24 19 25 23 25 27 27 25
11 13 19 15 17 16 19 18 18 19 19
12 7 10 11 9 14 11 16 14 14 14
+gp 22152230231965404956
OTSPBIO 761 749 658 704 726 734 777 754 781 757
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
...continued overleaf
WGNEPH Report 2004 221

1999 7602 734 734 95 0.1294 0.1797
2000 7835 765 765 84 0.1098 0.1376
2001 7619 752 752 79 0.105 0.1537
2002 8237 778 778 135 0.1736 0.2712
2003 8749 745 745 126 0.169 0.3041
Arith.
Mean 10472 809 809 132 0.1601 0.2198
0 Units (Thousan
Table 16 Summary (without SOP correc tion)
Terminal Fs derived using XSA (With F shrink age)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB FBAR 4-10
Age 2
1984 12781 895 895 169 0.1888 0.2759
1985 13206 893 893 156 0.1747 0.2003
1986 13348 915 915 150 0.164 0.223
1987 15561 983 983 232 0.236 0.2239
1988 13003 891 891 171 0.192 0.2403
1989 12464 849 849 151 0.1778 0.2775
1990 11147 840 840 174 0.2071 0.3256
1991 13967 830 830 134 0.1615 0.1772
1992 13535 869 869 165 0.1899 0.2231
1993 9751 834 834 145 0.1739 0.1879
1994 7707 758 758 97 0.128 0.1444
1995 6989 744 744 174 0.234 0.4407
1996 8921 661 661 67 0.1014 0.1878
1997 9168 709 709 62 0.0875 0.0846
1998 7845 732 732 72 0.0983 0.1371
ble 5.4.52. - SW and S Portugal: VPA input and output tables for females (continued).
d
(Tonnes) (Tonnes) (T onnes)
Table 17 Summar y (with SOP correction)
Term inal Fs derived using XSA (With F shrinkage)
RECRUITS TOTALBIO TOTSPBIO LANDINGS YIELD/SSB
S
OPCOFAC FBAR 4-10
Age 2
1984 12781 901 901 169 0.1876 1.0064 0.2759
1985 13206 895 895 156 0.1743 1.0025 0.2003
1986 13348 906 906 150 0.1655 0.9908 0.223
1987 15561 983 983 232 0.236 1.0001 0.2239
1988 13003 888 888 171 0.1925 0.9971 0.2403
1989 12464 854 854 151 0.1767 1.0061 0.2775
1990 11147 839 839 174 0.2073 0.9987 0.3256
1991 13967 830 830 134 0.1615 1 0.1772
1992 13535 897 897 165 0.1839 1.0324 0.2231
1993 9751 847 847 145 0.1711 1.0164 0.1879
1994 7707 761 761 97 0.1274 1.0046 0.1444
1995 6989 749 749 174 0.2325 1.0066 0.4407
1996 8921 658 658 67 0.1018 0.9958 0.1878
1997 9168 704 704 62 0.088 0.9936 0.0846
1998 7845 726 726 72 0.0991 0.9923 0.1371
1999 7602 734 734 95 0.1294 1 0.1797
2000 7835 777 777 84 0.1082 1.0148 0.1376
2001 7619 754 754 79 0.1047 1.0031 0.1537
2002 8237 781 781 135 0.1728 1.0044 0.2712
2003 8749 757 757 126 0.1664 1.0161 0.3041
Arith.
Mean 10472 812 812 132 .1593 .2198
0 Units (Thousan
d
(Tonnes) (Tonnes) (T onnes)
Ta
WGNEPH Report 2004
222

Lowestoft VPA Version 3.1
26/03/2004 15:26
Extended Survivors Analysis
NEP MALE(000) PORTUGINDEX FILE
CPUE data from file TUNEFF.DAT
Catch data for 20 years. 1984 to 2003. Ages 2 to 8.
Fleet Fir
s
Last First Last Alpha Beta
year year age age
Trawl fleetEffort d 1988 20032701
Summer surveys - nu
m
1997 2003 2 7 0.41 0.47
Time series weights :
Tapered time weighting applied
Power = 3 over 20 years
Catchability analysis :
Catchability dependent on stock size for ages < 3
Regression type = C
Minimum of 5 points used for regression
Survivor estimates shrunk to the population mean for ages < 3
Catchability independent of age for ages >= 6
Terminal population estimation :
Survivor estimates shrunk towards the mean F
of the final 3 years or the 2 oldest ages.
S.E. of the mean to which the estimates are shrunk = 2.000
Minimum standard error for population
estimates derived from each fleet = .500
Prior weighting not applied
Tuning had not converged after 30 iterations
Total absolute residual between iterations
29 and 30 = .00065
Final year F values
Age 234567
Iteration 29 0.1183 0.5118 0.6644 0.6949 0.8212 0.856
Iteration 30 0.1183 0.5117 0.6644 0.6948 0.821 0.8557
Regression weights
0.751 0.82 0.877 0.921 0.954 0.976 0.99 0.997 1 1
Table 5.4.53. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for males.
...continued overleaf
WGNEPH Report 2004 223

Fishing mortalities
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.203 0.017 0.066 0.083 0.077 0.067 0.091 0.041 0.061 0.118
3 0.54 0.54 0.43 0.387 0.31 0.276 0.249 0.342 0.493 0.512
4 0.677 1.101 0.452 0.238 0.271 0.31 0.203 0.434 0.694 0.664
5 1.112 0.448 0.384 0.223 0.298 0.422 0.299 0.475 0.58 0.695
6 1.136 0.332 0.197 0.106 0.325 0.494 0.417 0.551 0.613 0.821
7 0.464 0.32 0.319 0.222 0.415 0.297 0.607 0.857 0.782 0.856
XSA population numbers (Thousands)
AGE
YEAR 234567
1994 4920 4320 1760 725 285 190
1995 4000 2970 1860 662 177 67.9
1996 6370 2920 1280 459 313 93.9
1997 7790 4420 1410 605 232 191
1998 8000 5310 2220 820 359 154
1999 7120 5490 2890 1260 451 192
2000 7310 4930 3080 1570 611 204
2001 7330 4940 2850 1870 861 298
2002 7110 5210 2600 1370 860 368
2003 7970 4960 2360 962 567 345
Estimated population abundance at 1st Jan 2004
0 5250 2200 899 356 185
Taper weighted geometric mean of the VPA populations:
7730 5160 2480 1100 470 209
Standard error of the weighted Log(VPA populations) :
0.346 0.344 0.4056 0.5004 0.5208 0.5103
Log catchability residuals.
Fleet : Trawl fleetEffort d
Age 1988 1989 1990 1991 1992 1993 1994 1995
2 -0.25 -0.15 -0.07 0.17 0.16 0.42 0.62 -0.33
3 0.06 -0.34 -0.04 0.17 0.35 0.68 0.31 0.24
4 -0.16 0.18 0.24 0.24 0.36 0.39 0.42 0.83
5 -0.15 0.68 -0.04 0.56 0.58 0.46 0.85 -0.11
6 -0.22 0.86 -0.52 0.56 0.35 -0.1 1 -0.27
7 -0.04 0.37 -0.2 0.3 -0.03 -0.11 0.12 -0.31
Age 1996 1997 1998 1999 2000 2001 2002 2003
2 0.08 0.17 -0.09 0.05 0.04 -0.4 -0.29 -0.07
3 0.27 0.43 -0.29 -0.08 -0.5 -0.43 -0.25 -0.18
4 0.22 -0.15 -0.54 -0.07 -0.81 -0.31 -0.02 -0.04
5 0 -0.28 -0.5 0.17 -0.48 -0.27 -0.25 -0.05
6 -0.54 -0.89 -0.28 0.46 -0.02 0 -0.07 0.25
7 -0.05 -0.15 -0.04 -0.04 0.35 0.44 0.17 0.29
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 34567
Mean Log q -9.2797 -9.1713 -9.1148 -9.2451 -9.2451
S.E(Log q) 0.3592 0.4324 0.4154 0.4978 0.2439
Table 5.4.53. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for males (continued).
...continued overleaf
WGNEPH Report 2004
224

Regression statistics :
Ages with q dependent on year class strength
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Log q
2 0.42 2.166 9.72 0.58 16 0.29 -10.81
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
3 1.19 -0.481 9.42 0.38 16 0.44 -9.28
4 1.21 -0.527 9.46 0.38 16 0.54 -9.17
5 0.94 0.245 8.99 0.62 16 0.41 -9.11
6 0.77 1.052 8.53 0.68 16 0.38 -9.25
7 0.76 3.035 8.25 0.94 16 0.13 -9.17
Fleet : Summer surveys - num
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 99.99 99.99 99.99 -0.04 -0.03 99.99 0.01 -0.03 0.02 0.07
3 99.99 99.99 99.99 0.04 0.17 99.99 -0.07 -1.02 0.32 0.58
4 99.99 99.99 99.99 0.57 -0.31 99.99 -0.25 -0.96 0.54 0.44
5 99.99 99.99 99.99 0.99 -0.26 99.99 -0.5 -0.87 0.21 0.49
6 99.99 99.99 99.99 0.93 -0.05 99.99 -0.1 -0.83 -0.22 0.34
7 99.99 99.99 99.99 0.42 0.02 99.99 -0.46 -0.44 0.41 0.33
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 34567
Mean Log q -6.9362 -6.0791 -5.8524 -5.6616 -5.6616
S.E(Log q) 0.5581 0.6205 0.6785 0.5833 0.4166
Regression statistics :
Ages with q dependent on year class strength
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Log q
2 0.09 2.197 8.88 0.6 6 0.05 -8.32
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
3 0.42 0.308 7.84 0.07 6 0.26 -6.94
4 -4.36 -1.275 15.14 0.01 6 2.55 -6.08
5 -3.57 -2.632 11.22 0.08 6 1.63 -5.85
6 15.22 -2.802 -3.13 0.01 6 5.72 -5.66
7 0.79 0.471 5.6 0.56 6 0.36 -5.62
Table 5.4.53. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for males (continued).
...continued overleaf
WGNEPH Report 2004 225

Fleet disaggregated estimates of survivors :
Age 2 Catchability dependent on age and year class strength
Year class = 2001
Trawl fleetEffort d
Age 2
Survivors 4882
Raw Weights 3.554
Summer surveys - num
Age 2
Survivors 5603
Raw Weights 3.554
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Trawl fleetEffort d 4882 0.50010.2250.127
Summer surveys - nu
m
5603 0.50010.2250.111
P shrinkage mean 5161 0.34 0.535 0.12
F shrinkage mean 9900 2 0.016 0.064
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
5246 0.25 0.05 4 0.219 0.118
Age 3 Catchability constant w.r.t. time and dependent on age
Year class = 2000
Trawl fleetEffort d
Age 3 2
Survivors 1832 1647
Raw Weights 2.398 2.255
Summer surveys - num
Age 3 2
Survivors 3918 2247
Raw Weights 1.644 2.255
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Trawl fleetEffort d 1740 0.354 0.053 0.15 2 0.529 0.613
Summer surveys - nu
m
2840 0.385 0.275 0.71 2 0.443 0.417
F shrinkage mean 3336 2 0.028 0.365
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
2202 0.26 0.16 5 0.603 0.512
Table 5.4.53. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for males (continued).
...continued overleaf
WGNEPH Report 2004
226

Age 4 Catchability constant w.r.t. time and dependent on age
Year class = 1999
Trawl fleetEffort d
Age 4 3 2
Survivors 868 703 601
Raw Weights 2.058 1.257 1.204
Summer surveys - num
Age 4 3 2
Survivors 1399 1233 872
Raw Weights 1.142 0.862 1.204
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Trawl fleetEffort d 742 0.298 0.109 0.37 3 0.567 0.762
Summer surveys - nu
m
1132 0.345 0.148 0.43 3 0.402 0.559
F shrinkage mean 1497 2 0.031 0.449
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
899 0.23 0.12 7 0.513 0.664
Age 5 Catchability constant w.r.t. time and dependent on age
Year class = 1998
Trawl fleetEffort d
Age 5432
Survivors 339 350 231 369
Raw Weights 1.997 0.997 0.706 0.64
Summer surveys - num
Age 5432
Survivors 578 611 128 360
Raw Weights 0.926 0.553 0.484 0.64
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Trawl fleetEffort d 325 0.28 0.089 0.32 4 0.603 0.741
Summer surveys - nu
m
393 0.341 0.332 0.97 4 0.362 0.646
F shrinkage mean 617 2 0.035 0.457
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
356 0.22 0.14 9 0.629 0.695
Table 5.4.53. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for males (continued).
...continued overleaf
WGNEPH Report 2004 227

Age 6 Catchability constant w.r.t. time and dependent on age
Year class = 1997
Trawl fleetEffort d
Age 65432
Survivors 237 144 136 113 195
Raw Weights 1.638 0.985 0.637 0.493 0.455
Summer surveys - num
Age 65432
Survivors 261 229 70 172 0
Raw Weights 1.105 0.457 0.353 0.338 0
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Table 5.4.53. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for males (continued).
Trawl fleetEffort d 174 0.258 0.14 0.54 5 0.627 0.856
Summer surveys - nu
m
194 0.371 0.266 0.72 4 0.336 0.793
F shrinkage mean 334 2 0.037 0.534
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
185 0.22 0.12 10 0.567 0.821
Age 7 Catchability constant w.r.t. time and age (fixed at the value for age) 6
Year class = 1996
Trawl fleetEffort d
Age 765432
Survivors 145 102 83 48 100 99
Raw Weights 1.7 0.856 0.571 0.463 0.347 0.313
Summer surveys - num
Age 765432
Survivors 151 87 46 84 0 105
Raw Weights 1.7 0.578 0.265 0.257 0 0.313
Fleet Estimated Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio Weights F
Trawl fleetEffort d 105 0.248 0.152 0.61 6 0.558 0.877
Summer surveys - nu
m
113 0.313 0.184 0.59 5 0.409 0.834
F shrinkage mean 127 2 0.033 0.77
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
109 0.2 0.11 12 0.527 0.856
WGNEPH Report 2004
228

Lowestoft VPA Version 3.1
26/03/2004 15:26
Extended Survivors Analysis
NEP FEMALE(000) PORTINDEX FILE
CPUE data from file TUNEFF.DAT
Catch data for 20 years. 1984 to 2003. Ages 2 to 13.
Fleet Fi Last First Last Alpha Beta
year year age age
Trawl fleetEffort d 1988 2003 2 12 0 1
Summer surveys - num 1997 2003 2 12 0.41 0.47
Time series weights :
Tapered time weighting applied
Power = 3 over 20 years
Catchability analysis :
Catchability dependent on stock size for ages < 4
Regression type = C
Minimum of 5 points used for regression
Survivor estimates shrunk to the population mean for ages < 4
Catchability independent of age for ages >= 8
Terminal population estimation :
Survivor estimates shrunk towards the mean F
of the final 3 years or the 5 oldest ages.
S.E. of the mean to which the estimates are shrunk = 2.000
Minimum standard error for population
estimates derived from each fleet = .500
Prior weighting not applied
Tuning had not converged after 30 iterations
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females.
Total absolute residual between iterations
29 and 30 = .00408
Final year F values
Age 2 3 4 5 6 7 8 9 10 11 12
Iteration 29 0.0757 0.0912 0.1623 0.1986 0.2397 0.2861 0.3935 0.4257 0.4257 0.3537 0.3019
Iteration 30 0.0756 0.0912 0.1622 0.1984 0.2394 0.2858 0.393 0.4251 0.425 0.3531 0.3013
Regression weights
0.751 0.82 0.877 0.921 0.954 0.976 0.99 0.997 1 1
...continued overleaf
WGNEPH Report 2004 229

Fishing mortalities
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 0.139 0.014 0.025 0.083 0.083 0.085 0.092 0.042 0.057 0.076
3 0.187 0.093 0.049 0.138 0.087 0.139 0.079 0.086 0.099 0.091
4 0.156 0.236 0.074 0.147 0.106 0.136 0.115 0.128 0.244 0.162
5 0.15 0.486 0.147 0.123 0.117 0.19 0.127 0.132 0.341 0.198
6 0.153 0.619 0.243 0.125 0.137 0.219 0.16 0.112 0.33 0.239
7 0.099 0.35 0.164 0.056 0.079 0.208 0.117 0.124 0.265 0.286
8 0.149 0.608 0.2 0.053 0.154 0.18 0.128 0.197 0.238 0.393
9 0.197 0.499 0.297 0.056 0.208 0.192 0.16 0.2 0.221 0.425
10 0.107 0.286 0.188 0.032 0.159 0.134 0.155 0.183 0.258 0.425
11 0.176 0.356 0.369 0.061 0.242 0.11 0.165 0.197 0.255 0.353
12 0.14 0.207 0.147 0.041 0.176 0.139 0.21 0.219 0.302 0.301
XSA population numbers (Thousands)
AGE
YEAR 23456789101112
1994 7710 6170 5540 3960 2290 1800 1250 653 442 226 115
1995 6990 5490 4190 3880 2790 1610 1330 880 439 325 155
1996 8920 5640 4090 2710 1950 1230 929 594 437 270 187
1997 9170 7120 4400 3110 1910 1250 854 623 361 297 153
1998 7840 6910 5080 3110 2250 1380 971 663 482 286 229
1999 7600 5910 5190 3740 2260 1610 1050 682 441 337 184
2000 7840 5720 4210 3710 2530 1490 1070 716 461 316 247
2001 7620 5850 4330 3070 2670 1770 1080 770 499 323 219
2002 8240 5980 4400 3120 2200 1950 1280 729 516 340 217
2003 8750 6370 4440 2820 1820 1300 1230 825 478 327 216
Estimated population abundance at 1st Jan 2004
- 6640 4760 3090 1900 1170 798 679 442 256 188
Taper weighted geometric mean of the VPA populations:
8860 6570 4780 3360 2290 1540 1060 690 439 296 191
Standard error of the weighted Log(VPA populations) :
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
00000000000
Log catchability residuals.
Fleet : Trawl fleetEffort d
Age 1988 1989 1990 1991 1992 1993 1994 1995
2 0 0.05 -0.01 -0.04 -0.06 0.2 0.27 -0.31
3 0.07 -0.12 -0.01 0.09 -0.08 0.03 0.24 0.05
4 0.68 0.25 0.36 0.14 0.14 0.11 0.09 0.43
5 0.65 0.55 0.32 -0.34 -0.2 -0.31 -0.11 1
6 0.41 0.57 -0.2 -0.63 -0.01 -0.57 -0.17 1.16
7 0.57 0.79 0.49 -0.29 0.3 -0.26 -0.41 0.79
8 0.28 0.16 0.53 0.05 -0.15 -0.1 -0.21 1.13
9 -0.45 0.86 0.37 0.08 -0.07 0.07 0.07 0.93
10 -0.62 0.45 0.27 -0.13 -0.25 -0.11 -0.53 0.38
11 -0.53 0.48 -0.16 -0.68 -0.21 0.32 -0.04 0.6
12 -0.03 0.38 0.01 0.01 0.15 0.04 -0.27 0.06
Age 1996 1997 1998 1999 2000 2001 2002 2003
2 -0.25 0.13 0.1 0.22 0.13 -0.13 -0.15 -0.11
3 -0.1 0.2 -0.12 0.26 -0.03 -0.1 -0.13 -0.19
4 -0.46 0.48 -0.36 0.23 -0.25 -0.41 0.07 -0.31
5 0.07 0.15 -0.41 0.4 -0.31 -0.53 0.25 -0.27
6 0.49 0.09 -0.33 0.47 -0.16 -0.77 0.14 -0.16
7 0.29 -0.53 -0.69 0.61 -0.28 -0.47 0.11 0.21
8 0.28 -0.79 -0.22 0.26 -0.4 -0.22 -0.2 0.32
9 0.67 -0.73 0.07 0.32 -0.17 -0.2 -0.28 0.4
10 0.22 -1.28 -0.2 -0.03 -0.21 -0.29 -0.12 0.4
11 0.89 -0.64 0.23 -0.23 -0.14 -0.22 -0.13 0.21
12 -0.03 -1.03 -0.09 0 0.1 -0.11 0.04 0.06
...continued overleaf
WGNEPH Report 2004
230

Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 4 5 6 7 8 9 10 11 12
Mean Log q -10.286 -10.132 -10.052 -10.247 -10.04 -10.04 -10.04 -10.04 -10.04
S.E(Log q) 0.3391 0.431 0.5122 0.4894 0.4627 0.4618 0.4721 0.434 0.3216
Regression statistics :
Ages with q dependent on year class strength
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Log q
2 0.28 2.465 9.6 0.54 16 0.19 -10.96
3 0.35 2.143 9.42 0.52 16 0.16 -10.59
Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
4 0.52 1.218 9.41 0.39 16 0.17 -10.29
5 0.46 1.178 9.04 0.32 16 0.19 -10.13
6 1.08 -0.061 10.24 0.06 16 0.58 -10.05
7 0.88 0.13 9.91 0.11 16 0.45 -10.25
8 0.48 1.235 8.44 0.36 16 0.22 -10.04
9 0.65 0.659 8.73 0.26 16 0.3 -9.94
10 0.53 1.115 8.27 0.37 16 0.24 -10.18
11 1.25 -0.267 11.12 0.1 16 0.57 -10.03
12 0.65 1.376 8.42 0.61 16 0.19 -10.12
Fleet : Summer surveys - num
Age 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
2 -0.14 0.11 -0.05 -0.05 -0.08 0.21
3 -0.31 0.14 0 -0.37 0.16 0.36
4 0.03 0.22 -0.39 -1 0.26 0.88
5 -0.27 -0.04 0.06 -1.02 0.51 0.73
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
6 0.17 -0.5 0.31 -1.56 0.68 0.89
7 0.48 -0.43 0.34 -1.44 0.24 0.83
8 0.52 -0.3 0.05 -0.79 0.28 0.27
9 1.17 -0.07 0.52 -0.58 0.67 0.44
10 1.84 -0.29 0.6 -0.31 0.79 0.94
11 1.66 0.27 0.74 -0.56 0.95 0.7
12 2.2 -0.23 0.81 -0.57 1.35 0.98
Mean log catchability and standard error of ages with catchability
independent of year class strength and constant w.r.t. time
Age 4 5 6 7 8 9 10 11 12
Mean Log q -7.9252 -7.2209 -6.8901 -6.5864 -6.243 -6.243 -6.243 -6.243 -6.243
S.E(Log q) 0.6461 0.6267 0.9093 0.8257 0.4783 0.7217 1.0295 0.9995 1.3017
Regression statistics :
Ages with q dependent on year class strength
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Log q
2 0.17 0.884 8.93 0.23 6 0.15 -8.52
3 0.44 0.347 8.65 0.09 6 0.32 -8.52
...continued overleaf
WGNEPH Report 2004 231

Ages with q independent of year class strength and constant w.r.t. time.
Age Slope t-value Intercept RSquare No Pts Reg s.e Mean Q
4 0.23 0.721 8.3 0.18 6 0.15 -7.93
5 -5.92 -0.335 12.99 0 6 4.11 -7.22
6 -0.32 -1.844 7.97 0.33 6 0.24 -6.89
7 -0.82 -1.068 7.92 0.08 6 0.67 -6.59
8 1.05 -0.03 6.2 0.08 6 0.56 -6.24
9 -0.65 -0.901 7.03 0.07 6 0.41 -5.89
10 -0.28 -2.05 6.27 0.4 6 0.17 -5.66
11 -2.85 -0.231 6.11 0 6 2.34 -5.63
12 -0.33 -1.681 5.31 0.29 6 0.28 -5.5
Fleet disaggregated estimates of survivors :
Age 2 Catchability dependent on age and year class strength
Year class = 2001
Trawl fleetEffort d
Age 2
Survivors 5956
Raw Weights 3.709
Summer surveys - num
Age 2
Survivors 8186
Raw Weights 3.709
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 5956 0.5 0 0 1 0.081 0.084
Summer surveys - num 8186 0.5 0 0 1 0.081 0.062
P shrinkage mean 6572 0.16 0.832 0.076
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
F shrinkage mean 7961 2 0.005 0.063
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
6644 0.15 0.05 4 0.334 0.076
...continued overleaf
WGNEPH Report 2004
232

Age 3 Catchability dependent on age and year class strength
Year class = 2000
Trawl fleetEffort d
Age 3 2
Survivors 3949 4093
Raw Weights 3.651 3.448
Summer surveys - num
Age 3 2
Survivors 6835 4378
Raw Weights 3.651 3.448
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 4018 0.354 0.018 0.05 2 0.101 0.107
Summer surveys - num 5505 0.354 0.223 0.63 2 0.101 0.079
P shrinkage mean 4779 0.13 0.795 0.091
F shrinkage mean 4933 2 0.004 0.088
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
4764 0.12 0.05 6 0.384 0.091
Age 4 Catchability constant w.r.t. time and dependent on age
Year class = 1999
Trawl fleetEffort d
Age 4 3 2
Survivors 2256 2722 2703
Raw Weights 3.401 3.08 2.946
Summer surveys - num
Age 4 3 2
Survivors 7452 3610 2941
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
Raw Weights 1.74 3.08 2.946
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 2538 0.289 0.063 0.22 3 0.54 0.194
Summer surveys - num 3929 0.316 0.251 0.8 3 0.445 0.13
F shrinkage mean 3073 2 0.014 0.163
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
3092 0.21 0.13 7 0.629 0.162
...continued overleaf
WGNEPH Report 2004 233

Age 5 Catchability constant w.r.t. time and dependent on age
Year class = 1998
Trawl fleetEffort d
Age 5 4 3 2
Survivors 1448 2028 1713 2167
Raw Weights 3.28 2.569 2.35 2.129
Summer surveys - num
Age 5 4 3 2
Survivors 3939 2462 1307 1799
Raw Weights 1.784 1.314 2.35 2.129
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 1778 0.254 0.093 0.37 4 0.569 0.21
Summer surveys - num 2069 0.29 0.241 0.83 4 0.417 0.183
F shrinkage mean 1869 2 0.014 0.201
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
1895 0.19 0.11 9 0.566 0.198
Age 6 Catchability constant w.r.t. time and dependent on age
Year class = 1997
Trawl fleetEffort d
Age 6 5 4 3 2
Survivors 997 1497 781 1138 1461
Raw Weights 2.767 2.239 1.965 1.804 1.635
Summer surveys - num
Age 6 5 4 3 2
Survivors 2842 1953 432 1176 0
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
Raw Weights 0.813 1.217 1.006 1.804 0
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 1129 0.233 0.12 0.51 5 0.672 0.247
Summer surveys - num 1259 0.336 0.365 1.09 4 0.312 0.224
F shrinkage mean 1415 2 0.016 0.202
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
1172 0.19 0.14 10 0.71 0.239
...continued overleaf
WGNEPH Report 2004
234

Age 7 Catchability constant w.r.t. time and dependent on age
Year class = 1996
Trawl fleetEffort d
Age 7 6 5 4 3 2
Survivors 984 913 470 619 1035 885
Raw Weights 2.894 1.898 1.888 1.67 1.433 1.288
Summer surveys - num
Age 7 6 5 4 3 2
Survivors 1823 1572 288 542 0 890
Raw Weights 0.942 0.558 1.027 0.855 0 1.288
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 794 0.217 0.128 0.59 6 0.692 0.287
Summer surveys - num 784 0.324 0.336 1.04 5 0.292 0.29
F shrinkage mean 1428 2 0.016 0.17
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
798 0.18 0.13 12 0.737 0.286
Age 8 Catchability constant w.r.t. time and dependent on age
Year class = 1995
Trawl fleetEffort d
Age 8 7 6 5 4 3 2
Survivors 935 758 316 497 850 600 774
Raw Weights 2.7 1.994 1.622 1.614 1.389 1.244 1.106
Summer surveys - num
Age 8 7 6 5 4 3 2
Survivors 886 865 143 723 0 783 589
Raw Weights 2.521 0.649 0.477 0.877 0 1.244 1.106
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 658 0.201 0.147 0.73 7 0.621 0.403
Summer surveys - num 695 0.266 0.203 0.76 6 0.366 0.385
F shrinkage mean 1574 2 0.013 0.189
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
679 0.16 0.11 14 0.704 0.393
...continued overleaf
WGNEPH Report 2004 235

Age 9 Catchability constant w.r.t. time and age (fixed at the value for age) 8
Year class = 1994
Trawl fleetEffort d
Age 9 8 7 6 5 4 3 2
Survivors 658 361 275 376 660 309 539 343
Raw Weights 2.615 2.06 1.747 1.349 1.252 1.101 0.926 0.86
Summer surveys - num
Age 9 8 7 6 5 4 3 2
Survivors 689 582 104 602 0 550 323 0
Raw Weights 1.072 1.923 0.568 0.397 0 0.563 0.926 0
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 429 0.192 0.127 0.66 8 0.676 0.435
Summer surveys - num 453 0.29 0.249 0.86 6 0.309 0.416
F shrinkage mean 1089 2 0.014 0.195
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
442 0.16 0.11 15 0.716 0.425
Age 10 Catchability constant w.r.t. time and age (fixed at the value for age) 8
Year class = 1993
Trawl fleetEffort d
Age 10 9 8 7 6 5 4 3 2
Survivors 381 194 206 194 408 170 414 231 187
Raw Weights 2.615 2.095 1.716 1.459 1.055 1.043 0.87 0.788 0.727
Summer surveys - num
Age 10 9 8 7 6 5 4 3 2
Survivors 652 500 116 358 0 246 263 0 0
Raw Weights 0.527 0.859 1.602 0.475 0 0.567 0.445 0 0
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 253 0.185 0.121 0.65 9 0.724 0.429
Summer surveys - num 253 0.31 0.292 0.94 6 0.262 0.429
F shrinkage mean 613 2 0.015 0.2
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
256 0.16 0.12 16 0.738 0.425
...continued overleaf
WGNEPH Report 2004
236

Age 11 Catchability constant w.r.t. time and age (fixed at the value for age) 8
Year class = 1992
Trawl fleetEffort d
Age 11 10 9 8 7 6 5 4 3 2
Survivors 233 166 153 126 345 135 218 118 197 247
Raw Weights 2.81 2.17 1.772 1.548 1.194 0.928 0.902 0.797 0.679 0.541
Summer surveys - num
Age 11 10 9 8 7 6 5 4 3 2
Survivors 377 412 105 198 0 114 143 0 0 0
Raw Weights 0.601 0.437 0.727 1.445 0 0.273 0.49 0 0 0
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 184 0.181 0.102 0.56 10 0.76 0.359
Summer surveys - num 195 0.332 0.215 0.65 6 0.226 0.342
F shrinkage mean 346 2 0.014 0.207
Weighted prediction :
Survivors Int Ext N Var F
at end of year s.e s.e Ratio
188 0.16 0.09 17 0.564 0.353
Age 12 Catchability constant w.r.t. time and age (fixed at the value for age) 8
Year class = 1991
Trawl fleetEffort d
Age 12 11 10 9 8 7 6 5 4 3 2
Survivors 138 114 98 110 169 65 143 140 202 166 160
Raw Weights 2.959 2.292 1.903 1.61 1.326 1.154 0.897 0.839 0.619 0.47 0.324
Summer surveys - num
Age 12 11 10 9 8 7 6 5 4 3 2
Survivors 350 338 96 220 0 85 155 0 0 0 0
Raw Weights 0.373 0.49 0.383 0.66 0 0.375 0.264 0 0 0 0
Fleet Estimate
d
Int Ext Var N Scaled Estimated
Survivors s.e s.e Ratio W eights F
Trawl fleetEffort d 123 0.178 0.084 0.47 11 0.837 0.317
Summer surveys - num 189 0.43 0.242 0.56 6 0.148 0.217
F shrinkage mean 100 2 0.015 0.379
Weighted prediction :
Survivors Int Ext N Var F
Table 5.4.54. - SW and S Portugal (FUs 28-29): XSA tuning diagnostics for females
(continued).
at end of year s.e s.e Ratio
131 0.16 0.09 18 0.524 0.301
WGNEPH Report 2004 237

WGNEPH Report 2004
238
Figure 5.4.1. - West Galicia (FU 26): Long-term trends in landings, effort, CPUEs and/or LPUEs, and mean sizes of Nephrops .
Landings - International
Data up to 1995 include some landings from FU 27
1965 1970 1975 1980 1985 1990 1995 2000 2005
0
200
400
600
800
1000
1960
Landings (tonnes)
International but
exclusively Spain
Effort - Spanish trawlers
0
2000
4000
6000
8000
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Effort (trips)
Home port Marín
Muros
Riveira
Vigo
LPUE - Spanish trawlers
1965 1970 1975 1980 1985 1990 1995 2000 2005
0
30
60
90
120
1960
LPUE (kg/trip)
Home port Marín
Muros
Riveira
Vigo
Mean sizes - Spanish trawlers
22
26
30
34
38
42
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Mean size (mm carapace length)
Landings Mal
Landings Fem

Figure 5.4.2. - West Galicia and North Portugal (FUs 26-27): VPA diagnostics males:
Log catchability residuals for Marín tuning fleet
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
6 7
WGNEPH Report 2004 239

Figure 5.4.3. - West Galicia and North Portugal (FUs 26-27): VPA diagnostics males:
Log catchability residuals for Muros tuning fleet.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
2 3 4 5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
6 7
WGNEPH Report 2004
240

Figure 5.4.4. - West Galicia and North Portugal (FUs 26-27): VPA diagnostics females:
Log catchability residuals for Marín tuning fleet.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
678910
WGNEPH Report 2004 241

Figure 5.4.5. - West Galicia and North Portugal (FUs 26-27): VPA diagnostics females:
Log catchability residuals for Muros tuning fleet.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
2 3 4 5
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1990 1995 2000 2005
678910
WGNEPH Report 2004
242

Recruitment
0
5000
10000
15000
20000
25000
30000
35000
40000
1980 1985 1990 1995 2000 2005
Recruits (millions)
Spawning Stock Biomass
0
200
400
600
800
1000
1200
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 3-5
0.20
0.40
0.60
0.80
1.00
1.20
1.40
Fbar
0.00
1980 1985 1990 1995 2000 2005
Figure 5.4.6. - West Galicia & North Portugal (FUs 26-27): VPA diagnostics males:
Retrospective analyses.
WGNEPH Report 2004 243

Recruitment
0
5000
10000
15000
20000
25000
30000
35000
40000
1980 1985 1990 1995 2000 2005
Recruits (millions)
Spawning Stock Biomass
0
200
400
600
800
1000
1200
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 3-8
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
Fbar
0.00
1980 1985 1990 1995 2000 2005
Figure 5.4.7. - West Galicia & North Portugal (FUs 26-27): VPA diagnostics females:
Retrospective analyses.
WGNEPH Report 2004
244

WGNEPH Report 2004 245
Fi
g
ure 5.4.8. - West Galicia and North Portu
g
al
(
FUs 26-27
)
: Output VPA males: Trends
in Landin
g
s, Fbar, Total Stock Biomass and Recruitment.
Fishing Mortality Fbar 3-5
1990 1995 2000 2005
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1985
Fbar
Recruitment (age 1)
1990 1995 2000 2005
0
5
10
15
20
25
30
35
40
1985
Recruits (millions)
Total Stock Biomass
0
200
400
600
800
1000
1200
1400
1985 1990 1995 2000 2005
TB (tonnes)
Catches
0
100
200
300
400
500
600
1985 1990 1995 2000 2005
Catches (tonnes)

WGNEPH Report 2004
246
Fi
g
ure 5.4.9. - West Galicia and North Portu
g
al
(
FUs 26-27
)
: Output VPA females: Trends in Landin
g
s, Fbar, Total Stock Biomass and Recruitment.
Catche
0
100
200
300
400
500
600
1985 1990 1995
Catches (tonnes)
s
2000 2005
Fishing Mortality Fbar 3-8
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1.40
1985 1990 1995 2000 2005
Fbar
Recruitment (age 1)
0
5
10
15
20
25
30
35
40
1985 1990 1995 2000 2005
Recruits (millions)
Total Stoc
0
200
400
600
800
1000
1200
1400
1985 1990 1995
TB (tonnes)
k Biomass
2000 2005

WGNEPH Report 2004 247
Males Females
Figur
R = 0.403 R = 0.113
e 5.4.10. - West Galicia and North Portugal (FUs 26-27): Effort and Fbar, and relationship between them, for males and females.
0
3
6
9
12
15
1980
Effort ('000 days fishing)
1985 1990 1995 2000 2005
0.00
0.30
0.60
0.90
1.20
1.50
Fbar
Effort Fbar
0.00
0.30
0.60
0.90
1.20
1.50
4 5
Fbar
6 7 8 9 10 11 12 13
Effort ('000 days fishing)
0
3
6
9
12
15
1980 1985 1990 1995 2000 2005
Effort ('000 days fishing)
0.00
0.30
0.60
0.90
1.20
1.50
Fbar
Effort Fbar
0.00
0.30
0.60
0.90
1.20
1.50
4 5 6 7 8 9 10 11 12 13
Effort ('000 days fishing)
Fbar

F0.1 0.4616 0.1428
Fbar(3-8) 1.0000 0.3094
FMax 0.8720 0.2698
0.2048 0.1386
FMax
Reference point F multiplier
A
bsolute Fbar
Figure 5.4.11. - West Galicia & North Portugal (FUs 26-27): Y/R analysis based on output VPA:
Relative changes in long-term Y/R and long-term SSB/R upon relative changes in effort.
Males and females shown separately.
F multiplier
A
bsolute FbarReference point
Fbar(3-5) 1.0000 0.6770
0.3297 0.2232
F0.1
Males
-50
-40
-30
-20
-10
0
10
20
30
40
50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
% Change in Effort
% Change in Y/R and SSB/R
SSB/R long-term Landings Y/R long-term
Females
-50
-40
-30
-20
-10
0
10
20
30
40
50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
% Change in Effort
% Change in Y/R and SSB/R
SSB/R long-term Landings Y/R long-term
WGNEPH Report 2004
248

WGNEPH Report 2004 249
Figure 5.4.12. - West Galicia and North Portugal (FUs 26-27): Short-term predictions of relative
changes in landings and SSB over two years, based on output of VPA with status quo F in the
intermediate year.
Males
-100
-80
-60
-40
-20
0
20
40
60
80
100
-100 -80 -60 -40 -20 0 20 40 60 80 100
% change in effort
% change in landings or SSB
Landings in 2005 vs 2003 SSB in 2006 vs 2004
Females
-100
-80
-60
-40
-20
0
20
40
60
80
100
-100 -80 -60 -40 -20 0 20 40 60 80 100
% change in effort
% change in landings or SSB
Landings in 2005 vs 2003 SSB in 2006 vs 2004

WGNEPH Report 2004
250
Figure 5.4.13. - SW and S Portugal (FUs 28-29): Long-term trends in landings, effort, CPUEs and mean sizes of Nephrops in landings.
Landings - International
1990 1995 2000 2005
0
100
200
300
400
500
600
1980 1985
Landings (tonnes)
Effort - Total
0
2000
4000
6000
8000
10000
12000
1980 1985 1990 1995 2000 2005
Effort (fishing days)
CPUE - Portuguese trawlers
1990 1995 2000 2005
0
20
40
60
80
100
120
140
1980 1985
CPUE (kg/day)
Mean sizes
22
26
30
34
38
42
1980 1985 1990 1995 2000 2005
Mean size (mm carapace length)
Landings Males
Landings Females

WGNEPH Report 2004 251
Figure 5.4.14. - SW and S
Portugal (FUs 28-29): Landings, effort and CPUEs by semester and sex from Portuguese Nephrops trawlers.
CPUE - Females
0
20
40
60
80
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
CPUE (kg/day)
Qtr 1+2 Annual
Landings
1998 1999 2000 2001 2002 2003
0
50
100
150
200
250
300
350
400
1994 1995 1996 1997
Landings (t)
Total
CPUE - M
0
20
40
60
80
1994 1995 1996 1997
CPUE (kg/day)
ales
1998 1999 2000 2001 2002 2003
Annual
Effort
0
1
2
3
4
1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Quarterly effort ('000 days)
0
1
2
3
4
5
6
7
8
Annual effort ('000 days)
Qtr 1+2 Total
Qtr 3+4
Females
Qtr 3+4
Qtr 3+4
Qtr 1+2
Males

WGNEPH Report 2004
252
Figure 5.4.15. - SW and S Portugal (FUs 28-29): Mean sizes of Nephrops in Portuguese surveys, 1991-2002.
Crustacean surv
25
30
35
40
45
50
1991 1992 1993 1994 1995
Mean size (mm CL)
eys - Summer
1996 1997 1998 1999 2000 2001 2002 2003
Females
Groundfish surveys - Autumn
25
30
35
40
45
50
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Mean size (mm CL)
Males Females
Groundfish surv
25
30
35
40
45
50
1991 1992 1993 1994 1995
Mean size (mm CL)
eys - Summer
1996 1997 1998 1999 2000 2001 2002 2003
Females
Males
Males

Figure 5.4.16. - SW and S Portugal (FU 28-29): VPA diagnostics males:
Log catchability residuals from trawl fleet data.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
6 7
WGNEPH Report 2004 253

Figure 5.4.17. - SW and S Portugal (FU 28-29): VPA diagnostics males:
Log catchability residuals from survey data.
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
6 7
WGNEPH Report 2004
254

-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
678910
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
11 12
Figure 5.4.18. - SW and S Portugal (FU 28-29): VPA diagnostics females:
Log catchability residuals from trawl fleet data.
WGNEPH Report 2004 255

-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
12345
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
1980 1985 1990 1995 2000 2005
678910
-2.0
-1.5
-1.0
-0.5
0.0
0.5
1.0
1980 1985 1990 1995 2000 2005
1.5
2.0
11 12
Figure 5.4.19. - SW and S Portugal (FU 28-29): VPA diagnostics females:
Log catchability residuals from survey data.
WGNEPH Report 2004
256

Recruitment
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1980 1985 1990 1995 2000 2005
Recruits (thousands)
Spawning Stock Biomass
0
200
400
600
800
1000
1200
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 2-7
0.40
0.60
0.80
1.00
1.20
Fbar
0.00
0.20
1980 1985 1990 1995 2000 2005
Figure 5.4.20. - SW and S Portugal (FU 28-29): VPA diagnostics males:
Retrospective analyses.
WGNEPH Report 2004 257

Recruitment
0
2000
4000
6000
8000
10000
12000
14000
16000
18000
20000
1980 1985 1990 1995 2000 2005
Recruits (thousands)
Spawning Stock Biomass
0
200
400
600
800
1000
1200
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 4-10
0.40
0.60
0.80
1.00
1.20
Fbar
0.00
0.20
1980 1985 1990 1995 2000 2005
Figure 5.4.21. - SW and S Portugal (FU 28-29): VPA diagnostics females:
Retrospective analyses.
WGNEPH Report 2004
258

WGNEPH Report 2004 259
Fi
g
ure 5.4.22. - SW and
S Portu
g
al
(
FU 28-29
)
: Output VPA males: Trends in Landin
g
s, Fbar, Total Stock Biomass and Recruitment.
Catches
0
100
200
300
400
1980 1985 1990
Catches (tonnes)
1995 2000 2005
Fishing Mortality Fbar 2-7
0.00
0.20
0.40
0.60
0.80
1.00
1980 1985 1990 1995 2000 2005
Fbar
Recruitment
0
5
10
15
20
25
1980 1985 1990 1995 2000 2005
Recruits (millions)
Total Stoc
0
200
400
600
800
1000
1200
1980 1985 1990
TB (tonnes)
k Biomass
1995 2000 2005

WGNEPH Report 2004
260
Fi
g
ure 5.4.23. - SW and S Portu
g
al
(
FU 28-29
)
: Output VPA females: Trends in Landin
g
s, Fbar, Total Stock Biomass and Recruitment.
Catches
0
100
200
300
400
1980 1985 1990
Catches (tonnes)
1995 2000 2005
Fishing Mortality Fbar 4-10
0.00
0.20
0.40
0.60
0.80
1.00
1980 1985 1990 1995 2000 2005
Fbar 4-10
Recruitment
0
5
10
15
20
25
1980 1985 1990 1995 2000 2005
Recruits (millions)
Total Stoc
0
200
400
600
800
1000
1200
1980 1985 1990
TB (tonnes)
k Biomass
1995 2000 2005

WGNEPH Report 2004 261
Males Females
Figure 5.4.24. -
R = 0.616 R = 0.420
SW and S Portugal (FU 28-29): Effort and Fbar, and relationship between them, for males and females.
0
1000
2000
3000
4000
5000
6000
7000
8000
1980 1985 1990
Effort (fishing days)
1995 2000 2005
0.00
0.20
0.40
0.60
0.80
1.00
1.20
Fbar 2-7
ffort Fbar
0.00
0.20
0.40
0.60
0.80
1.00
2000 3000 4000
Effort (fishin
Fbar 2-7
5000 6000 7000
g days)
0
1000
2000
3000
4000
5000
6000
7000
8000
1980 1985 1990 1995 2000 2005
Effort (fishing days)
0.00
0.20
0.40
0.60
0.80
1.00
1.20
Fbar 4-10
Effort Fbar
0.00
0.20
0.40
0.60
0.80
1.00
2000 3000 4000 50 00 6000 7000
Effort (fishing days)
Fbar 4-10
E

WGNEPH Report 2004
262
Figure 5.4.25. - SW and S Portugal (FU 28-29): Y/R analysis based on output VPA:
Relative changes in long-term Y/R and long-term SSB/R upon relative changes in effort.
Males and females shown separately.
F multiplier
A
bsolute FbarReference point
Fbar(2-7) 1.0000 0.6110
0.7245 0.4426
F0.1 0.3177 0.1941
FMax
Reference point F multiplier
A
bsolute Fbar
F0.1 0.6967 0.2119
Fbar(4-10) 1.0000 0.3041
FMax 5.6707 1.7246
-50
-40
-30
-20
-10
0
10
20
30
40
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40
% Change in Effort
% Change in Y/R and SSB/R
SSB/R long-term Landings Y/R long-term
Females
-50
-40
-30
-20
-10
0
10
20
30
40
50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40
% Change in Effort
% Change in Y/R and SSB/R
50
SSB/R long-term Landings Y/R long-term
Males
50
50

Figure 5.4.26. - SW and S Portugal (FU 28-29): Short-term predictions of relative changes in landings
and SSB over two years, based on output of VPA with status quo F in the intermediate year.
Males
-100
-80
-60
-40
-20
0
20
40
60
80
100
-100 -80 -60 -40 -20 0 20 40 60 80 100
% change in effort
% change in landings or SSB
Landings in 2005 vs 2003 SSB in 2006 vs 2004
Females
-100
-80
-60
-40
-20
0
20
40
60
80
100
% change in landings or SSB
-100 -80 -60 -40 -20 0 20 40 60 80 100
% change in effort
Landings in 2005 vs 2003 SSB in 2006 vs 2004
WGNEPH Report 2004 263

WGNEPH Report 2004
264
Figure 5.4.27. - Gulf of Cádiz (FU 30): Long-term trends in landings, effort, LPUEs and mean sizes of Nephrops .
Landings
0
50
100
150
200
250
300
350
1960 1965 1970 1975 1980 1985 1990
Landings (tonnes)
1995 2000 2005
Nephrops directed effort
0
500
1000
1500
2000
2500
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Effort (days)
LPUE
0
20
40
60
80
100
120
1960 1965 1970 1975 1980 1985 1990
LPUE (kg/day)
1995 2000 2005
Mean sizes
22
26
30
34
38
42
1960 1965 1970 1975 1980 1985 1990 1995 2000 2005
Mean size (mm carapace length)
Landings Mal < 35
Landings Fem < 35

WGNEPH Report 2004 265
Figure 5.4.28. - Gulf of C
ádiz (FU 30): Mean sizes of Nephrops in Spanish surveys, 1993-2003.
Groundfish surveys - November
25
30
35
40
45
50
1991 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003
Mean size (mm CL)
Males Females
Groundfish surveys - March
25
30
35
40
45
50
1991 1992 1993 1994 1995 1996 1997 1998 1999
Mean size (mm CL)
2000 2001 2002 2003
Males Femal es

F multiplier
A
bsolute FbarReference point
Fbar 1.0000 0.6103
0.5350 0.3265
F0.1 0.2949 0.1800
FMax
Males
-50
-40
-30
-20
-10
0
10
20
30
40
50
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
% Change in Effort
% Change in Y/R and SSB/R
SSB/R long-term Y/R 1 year Y/R long-term
Females
-30
-20
-10
0
10
20
30
40
50
% Change in Y/R and SSB/R
-50
-40
-90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50
% Change in Effort
SSB/R long-term Y/R 1 year Y/R long-term
Reference point F multiplier
A
bsolute Fbar
F0.1 1.7343 0.2154
Fbar 1.0000 0.1242
FMax 3.5089 0.4358
Figure 5.4.29. - Gulf of Cádiz (FU 30): Output LCA: Relative changes in short-term Y/R
(i.e. after 1 year), long-term Y/R and long-term SSB/R upon relative changes in effort.
Males and females shown separately.
WGNEPH Report 2004
266

6 REPORTING LEVELS FOR LANDINGS
6.1 Data on reporting levels
At the 2003 meeting of WGNEPH some concern was expressed that official landings data for some Nephrops stocks
may not reflect the true levels of landings (ICES, 2003a). It was considered that this would not necessarily mean that
wrong conclusions would be drawn about relative stock status and the direction of trends, since Nephrops assessments
are based on multiple lines of evidence, many of which are independent of the absolute level of landings. However,
uncertainty about reporting levels for landings has strong implications for the setting of TACs. WGNEPH thus
considered that it would be essential to examine the extent to which official landings statistics reflect the true levels of
landings in Nephrops fisheries.
Some UK processors and fish producers organisations have expressed concern that any attempt to reconcile
recorded landings with buyer’s figures would result in restriction of harvests that have in fact been sustained over many
years. This concern has arisen particularly in the light of prospective UK legislation on the registration of first-time
buyers and sellers. Reacting to this concern, the UK Nephrops Industry Action Group (mainly composed of
representatives of concerned processors and fish producers organisations) has proposed to employ an independent
research organisation to collate relevant sales information in an attempt to evaluate the real level of Nephrops landings
around the UK and how they are distributed between areas. This potentially would allow revision of landings data with
consequences for assessments and advice. WGNEPH recommended that this data collation exercise should be
attempted during 2003 and that at the 2004 WG meeting the findings of the exercise be considered in relation to the
assessments and advice provided for relevant stocks.
Accordingly, the Terms of Reference for the 2004 meeting include: evaluating the extent to which official landings
statistics reflect the true levels of landings in Nephrops fisheries, considering the implications for assessment and advice
(ToR b); revising the landings data for Sub-areas IV and VII and Division VIa in the light of any new information (ToR
c); and updating the relevant assessments and catch options as appropriate (ToR d). It was reported to the WG that in
the light of other priorities and concerns about Nephrops management in 2003 the UK Nephrops Industry Action Group
did not feel that they were in a position to attempt the proposed data collation exercise at this stage. No new data were
made available to the WG to allow revision of landings statistics or assessments, thus there is no basis to address ToRs
c) and d). The WG recommends that the collation of data on the true levels of landings in Nephrops fisheries be
attempted at the earliest opportunity, and that any relevant data be made available to be considered in relation to stock
assessments and management advice.
Considerable anecdotal and circumstantial evidence exists to indicate that misreporting of landings does occur in a
number of Nephrops fisheries (in this respect, Nephrops fisheries are unlikely to be a special case), but there are
currently no data that would allow any statement to be made about the likely extent of misreporting and its distribution
amongst stocks. Given the current tightening of controls on effort on finfish, the pressures for misreporting in
Nephrops fisheries are likely to be increased.
In the past, WGNEPH has repeatedly flagged that the tightening of quota for round- and flatfish in many areas
may result in considerable shifts in fishing effort, with effort being redirected from finfish towards Nephrops.
WGNEPH is particularly concerned about this increase in fishing pressure on the Nephrops stocks and the associated
problems in terms of data recording, not only from a data quality point of view, but also for the consequences this may
have for the state of exploitation of Nephrops stocks. If misreporting in the Nephrops fisheries is not properly
remedied, the increases in fishing pressure cannot properly be assessed and any worsening of the state of exploitation of
the Nephrops stocks may remain unnoticed. Eventually, this could put scientists and managers in a position that they
are unable to detect the signs of unsustainable levels of exploitation in time to propose appropriate conservation
measures.
6.2 Implications of reporting levels for analytical stock assessments
The effects of misreporting of landings on analytical stock assessments could depend on the variability of reporting
levels between years. If reporting levels remain relatively stable, it is clear that inferences about relative stock status
and trends would be valid, but that absolute stock estimates would be incorrect. In other words, reporting levels would
simply act as a scaling factor for assessments. Fishing mortality estimates would not be sensitive to reporting levels
provided that those levels remained stable.
A relatively constant level of under-reporting is a plausible scenario for some fisheries. However, given increased
pressures to misreport, there is cause for concern that the discrepancy between recorded statistics and true landings
levels may actually increase over time. The WG examined the implications of such a scenario for the example of the
WGNEPH Report 2004 267

South Minch stock (FU 12). Landings for this stock show a downward trend between the mid-1990s and 2002 (ICES,
2003a). The assessment data for males of this stock were revised under the scenario that, instead of decreasing, the
landings for the seven year period 1996-2002 remained stable at the average of the previous seven year period 1989-95.
XSA was performed for the revised landings data using the same settings as for the original assessment (ICES, 2003a).
The tuning data (Scottish Nephrops trawl fleet) was left unchanged, reflecting the scenario that under-reporting affected
landings and effort statistics equally, thus did not influence the measurement of CPUE.
The scenario is for increasing discrepancy between recorded and ‘true’ landings after 1995, amounting to around
+ 60% in 2002 (Figure 6.2.1). Estimates of recent stock biomass and recruitment are revised upwards by as much as
30%, and the upward revision extends 3-4 years prior to the revision of landings. Revised Fbar fluctuates within ± 10-
15% of the unrevised values for years up to 2001, reflecting a trade-off between greater landings and greater biomass of
the exploited stock. The increased Fbar for the final year is likely to be an assessment bias rather than a natural
consequence of the landings adjustment (retrospective analysis shows upwards bias of F in the final year). Y/R analysis
based on these assessment outputs shows results very similar to the unrevised analysis.
The conclusions from this very limited simulation exercise are:
(1) that systematic changes in reporting levels are likely to cause biases in estimates of recruitment and stock biomass
– increased levels of under-reporting would cause both recruitment and stock biomass to be underestimated in an
assessment based on reported data; and
(2) that estimates of fishing mortality are relatively insensitive to changes in reporting levels, such that Y/R analyses
can continue to be used to assess stock status with respect to growth overfishing.
The first conclusion is no more than could have been predicted from common sense; the second is not unexpected
given that inferences about fishing mortality and Y/R depend more on the composition than quantity of fishery
removals. Nevertheless, given the importance of these conclusions for advice and management (see below), the WG
recommends that the effects of misreporting on the estimation of stock biomass, recruitment and fishing mortality be
explored in more detail.
6.3 Implications for advice
The extent to which uncertainty about reporting levels for landings affects the validity of catch options and management
advice is clearly of concern to the WG. Even if assessments provide a good indication of relative stock status and
trends, for fisheries managed by TAC there remains the problem of setting an absolute number for that TAC. This
problem could be circumvented if the emphasis of management was changed from output controls to input controls.
Whilst TAC management is in place, conclusions about appropriate harvest levels that can be drawn from fishery-
independent sources are of increased value.
6.3.1 Utility of underwater TV survey data
Fishery-independent surveys can and do provide an important contribution to the evidence on stock status and trends.
For some Nephrops stocks underwater TV surveys of burrows provide a fishery independent index of abundance which
can be used simply to indicate trends in the stock, or with more refinement to provide an estimate of the total stock
biomass. The underwater TV technique is now being utilised by a number of nations exploiting Nephrops, and through
further development of the technique is hoped to provide useful tuning indices for analytical assessments. At the
present meeting, presentations were made on the results from underwater TV surveys in Scotland, England and Ireland
(see Section 12 and Appendices 2 and 3).
Landings of Nephrops from the Fladen Ground (FU 7) expanded rapidly during the 1980s and 1990s, often
exceeding perceptions of available fishing opportunities. However, TV surveys indicated that the stock was very large
and consequently the level of exploitation was relatively low. An alternative approach for providing advice was
therefore suggested by the WG in 1999, based on the estimated stock size from TV surveys rather than historical
reported landings (ICES, 1999a). This approach used a conservative harvest ratio (= removals number / stock
abundance) of 7.5 % of the TV estimated abundance to provide advice for the TAC (this percentage is below the lower
end of the range of harvest ratios estimated from reported landings and VPA outputs for other stocks). The method was
also used to provide catch options for this stock in 2001 and 2003 (ICES, 2001a, 2003a) and is further described in a
working paper presented in 2004 (Appendix 1).
The same approach could be applied to other stocks for which a TV survey is conducted, although there is
currently some uncertainty over what would be an appropriate harvest ratio for these stocks. Estimates of harvest ratios
based on reported landings and VPA outputs should be robust to misreporting when reporting levels have been
consistent over recent years. The tentative conclusion that fishing mortality estimates are relatively insensitive even to
changing reporting levels (Section 6.2) suggests that estimated harvest ratios may be fairly robust even in this case. The
WG recommends that the sensitivity of estimated harvest ratios to misreporting should be explored further.
WGNEPH Report 2004
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WGNEPH Report 2004 269
6.4 Conclusions
Although there is little objective information about the levels of misreporting of Nephrops landings and how it varies
between stock areas, it seems likely that it is both common and widespread. It also seems likely that this is not a
problem that will be solved quickly, either in terms of gathering evidence for its occurrence or of ensuring the absolute
quantitative reliability of official statistics. This means that there is a strong imperative to develop approaches to advice
and management that are both robust to the existence of misreporting and conducive to the development of good
reporting practice.
The robust calculation of harvest ratios coupled with fishery-independent estimates of stock biomass or abundance
offers a strong possibility for future advice for many stocks. This would require decisions about what would be an
appropriate target value of harvest ratio for a particular stock. The past history of harvest levels sustained by a stock
(e.g. based on VPA estimates and reported landings) would provide strong guidance in this respect. Some further
investigation may also be needed into the quantitative reliability and spatial applicability of the fishery-independent
estimates. If it is a management objective to maintain stability of catch levels between years, there would need to be
some consideration of how to deal with the variability of stock estimates between years. Other issues that would need
to be examined include the non-random distribution of fishing effort in relation to stock density, and the mixed fishery
context for management.
The WG considers that setting TACs on the basis of estimates of available stock biomass rather than reported
landings might offer an improved basis for management of Nephrops fisheries. It is recommended that the applicability
of this type of management be examined for all stocks for which there are appropriate fishery-independent data.

WGNEPH Report 2004
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of Figure 6.2.1. - South Minch (FU 12): Revised landings and assessment outputs under a scenario
under-reporting of landings increasing over time.
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1981 1984 1987 1990 1993 1996 1999 2002
revised value / unadjusted value
1.8
landings
recruits
biomass
Fbar

WGNEPH Report 2004 271
7 APPLICATION OF MEDIUM-TERM CATCH PROJECTIONS TO
NEPHROPS
7.1 Introduction
In 2002 the Working Group (ICES, 2002a) was asked to consider the application of both short- and medium-term catch
projections to Nephrops. Short-term predictions within spreadsheets had been carried out occasionally by the WG in
previous years (ICES, 1999a, 2001a), but had not routinely been employed.
The two software tools routinely used by ICES Working Groups for stock projections (MFDP - Multi Fleet
Deterministic Projection - and routines within the MLA suite) were applied to Nephrops stocks with varying success.
While the short-term deterministic projections were found to be relatively successful, the usefulness of the medium term
projections was less convincing. It was concluded that in the absence of better information on the appropriate form and
parameters of a stock-recruitment relationship, these projections could not be regarded as meaningful, and that given the
general uncertainty about stock-recruitment relationships for Nephrops it seemed unlikely that there would be any
benefit in implementing medium-term projections.
In the 2003 meeting the WG was asked to explore further of applicability of medium-term catch projections to
Nephrops. This was undertaken through limited implementation of the ‘CS’ model, a method to evaluate the outcomes
of harvest control rules, to FUs 28-29 (SW and S Portugal). The projections used the ‘hockey stick’ stock-recruitment
relationship, which was considered to be the most appropriate approach, although none of the available functions
provided satisfactory fits to the data.
As in previous investigations, the over-riding difficulty in the implementation of medium-term projections for Nephrops
stocks remains the lack of information on stock-recruitment relationships. This topic has been examined on a number of
occasions by the WG, with generally little progress being made. Until stock-recruitment relationships can be
successfully investigated there seems little value in routinely applying medium-term projections, since results are at best
tentative. Further research along these lines should be encouraged, since medium-term projections (and other uses for
stock-recruitment relationships) would undoubtedly be of great benefit to managers. Given the previous difficulties
encountered by the WG in using stock and recruitment estimates output from analytical assessments, however,
alternative approaches should also be considered, including use of data from fishery independent surveys. The ‘knife-
edge’ slicing into age groups currently used by the WG leads to a merging of year classes, and will underestimate the
variability in recruitment, hampering the identification of stock-recruitment relationships (see also Section 10).
7.3 Conclusions
In the present meeting, the WG was asked to continue investigations into the application of medium-term
projections to Nephrops. This was carried out by applying the ‘CP’ model, a stochastic approach presented to the
SGMOS meeting in Lisbon in June 2003 (Azevedo & Jardim, 2003). CP was developed to simulate recovery plans,
based on an F strategy. Recruitment is selected at random from a specified distribution (based on recently observed
data).
7.2 ‘CP’ model implementation
The CP model was applied to the male stock from FUs 28-29 (SW and S Portugal). This stock is currently the subject of
a recovery plan (although that recovery plan has yet to be implemented).
The F strategy investigated was an F multiplier of 1 in the current year (2004), with an F multiplier of 0.9 applied
on each subsequent year. Numbers-at-age for the start of 2004 were taken from the final XSA assessment, with the
estimate of recruits taken as the arithmetic mean of the period 1997-2003. F values were taken from the final XSA
assessment, averaged over the period 2001-2003, and scaled to the last year.
The output from the CP projection is shown in Figure 7.1. The F strategy is indicated in the top right figure, in
relation to the target F (F0.1 of about 0.2). The projection indicates that given average recruitment and the proposed F
strategy, stock biomass will decrease in the first year, but will recover to current levels by 2007, and continue to
increase thereafter. By 2014, the projection indicates a 44% increase in biomass. Yield decreases steadily throughout
the projection time series, but the rate of decline decreases after the initial years. By 2014, the projection indicates a
25% decrease in yield
Despite the problems of medium-term projections for Nephrops, the WG nevertheless considers that they may be
of value in deriving conservative prognoses of future stock trajectories for recovering stocks. Thus, for example,

medium-term projections for Nephrops in FUs 23-24 (Bay of Biscay) were considered in 2003 (ICES, 2003a) and again
at the current WG meeting (Section 5.2.1). With respect to the investigation of the recovery plans for Nephrops in
southern areas, it was considered that the ‘CP’ model approach could be considered. For FUs 28-29 (SW and S
Portugal), recent recruitment appears low and relatively stable, and therefore the assumption that future recruitment
might follow the same distribution appears valid, and precautionary. Given the need for projections for recovery stocks,
the use of this approach, rather than applying a stock-recruitment model which implies improved recruitment as the
stock recovers, provides a precautionary projection, but may overestimate stock recovery times. This approach could
also be adopted for other recovery stocks, until more detailed information is available on stock-recruitment
relationships.
Owing to the concern over the lack of knowledge on stock-recruit relationships, the routine use of medium-term
projections for Nephrops stocks is not recommended by the WG. However, for recovery stocks does have some merits,
and can be considered to provide indications of the potential consequences of fishing strategies.
WGNEPH Report 2004
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2004 2006 2008 2010 2012 2014
0 4000 8000
year
n(x1000)
Stochastic Pro
j
ections - probabilit
y
profile
(
10%, 25%, 50% , 75% , 90%
)
Recruitment
2004 2006 2008 2010 2012 2014
0.0 0.2 0.4 0.6
year
Fishing mortality
2004 2006 2008 2010 2012 2014
0 200 400 600 800
year
Spawning Stoc k Biomass
[t]
2004 2006 2008 2010 2012 2014
0 50 100 150
year
[t]
Yield
2006 2008 2010 2012 2014
-0.2 0.0 0.1 0.2
year
SSB differences from previous year
%
2006 2008 2010 2012 2014
-0.2 0.0 0.1 0.2
year
%
Yield differences from previous y ear
Figure 7.1.- SW and S Portugal (FUs 28-29): Output from CP stochastic projection.
WGNEPH Report 2004 273

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One of the approaches presented at SGASAM, a modified catch-at-size analysis (previously used in the assessment of
Northern Shelf Anglerfish, ICES, 2003d) has been applied to the Firth of Forth Nephrops and is discussed in Section 12
and in more detail in a working document submitted to this WG (Appendix 8). The method is based on that of Sullivan
et al. (1990) and uses a size-transition matrix approach to model growth, which is assumed to be sex and maturity
specific. The growth transition matrices are derived using assumed von Bertalanffy growth parameters which are used
in the L2AGE slicing procedure for this stock. In brief, the method gives very similar stock trends and levels to the
XSA assessment (biomass estimates, fishing mortality), with the exception of estimated recruitment which shows much
greater fluctuations than seen in the age-based assessment results. This appears to highlight the inability of catch-at-age
data derived by length-slicing to pick up fluctuations in year class strength. The model is also able to make use of
auxiliary information in the form of survey data (length distributions, indices of abundance in terms of biomass or
numbers). Model runs which incorporated estimates of total stock biomass based on TV surveys gave similar trends in
recruitment and fishing mortality to those without, but rather different estimated biomass. The TV survey estimates of
stock biomass show a downward trend which is not apparent from the commercial catch data. Reasons for this are
discussed further in the working document.
A model for Metanephrops challengeri based on similar stock dynamics, but incorporating uncertainty into
estimates of the input parameters (natural mortality and growth) using a Bayesian framework, is described below (see
also Appendix 7).
One of the key difficulties with the assessment of Nephrops is that they cannot easily be aged and yet the most widely
accepted stock assessment methods are all age-based. The current approach for most stocks is therefore to apply an
age-structured method following slicing of the catch-at-length distributions into age-classes using fixed growth
parameters. In general, length-slicing reduces the contrast in the catch-at-age data, therefore there is likely to be less
distinction of year class strength and as a consequence estimated trends in stock biomass may be smoothed out. This
section considers two alternative approaches which do not require age-disaggregated data: dynamic length-based
methods and catch survey analysis (based on Collie & Sissenwine, 1983).
8.1 Introduction
8 APPLICABILITY OF ALTERNATIVE ASSESSMENT METHODS TO
NEPHROPS STOCKS
8.2.1 A size-transition matrix approach to the assessment of Firth of Forth Nephrops
The WG was asked to consider any outcomes of the 2003 Study Group on Age-length Structured Assessment Models
(SGASAM, ICES, 2003c) which may be relevant to Nephrops. The main tasks of this study group were to investigate
model formulation, sensitivity and goodness of fit; and evaluate the usefulness of such tools in particular stocks with
differing life histories and data availability. SGASAM considered the incorporation of length-structure into stock
assessment models to be particularly important in situations when problems with age determination do not permit the
use of age-structured models, or make such models less reliable. In addition, a length-based model may, in any case, be
a better representation of many biological and fishery processes than an age-structured model.
A number of length-structured methods were presented to SGASAM (some incorporating both age and length
structure) which could be applied to Nephrops stocks. As well as making direct use of catch-at-length data these
models have the added advantage that they are able to make use of many different sources of information (short time
series of data with missing years) which may improve parameter estimates. However, it was concluded that unless the
data were particularly informative (i.e. obvious modal structure in length distributions), growth parameters estimated
using only length structured data were likely to be very uncertain and should therefore be derived from external data
sources and fixed within the model. Few of the methods are able to make use of tagging data, which would be
particularly useful in estimation of Nephrops growth parameters. In relation to Nephrops, specific comments were made
to the effect that the direct use of length-distribution data is likely to be more effective at picking up fluctuations in year
class strength than length-sliced catch-at-age data. However estimates of recruitment are likely to be confounded with
estimates of the selection curve parameters unless there is auxiliary information on either of these quantities.
8.2 Length-based approaches

WGNEPH Report 2004 275
After many years of relatively cursory treatment, NIWA (New Zealand) is developing a Bayesian, length based model
for one stock of Metanephrops challengeri in northern New Zealand. Much data has been collected in the 17 year
history of this fishery, including commercial CPUE and catch-at-length, multiple fishery-independent trawl surveys,
tag- and aquarium-based growth studies and, most recently, a series of quantitative photographic surveys. As with
Nephrops, no direct methods of ageing have been developed, and the variability of growth-at-length suggests that any
relationship between length and age will be imprecise. An entirely length-based approach was therefore chosen, based
on growth transition matrices (one for each sex). To incorporate disparate data sources and to propagate their respective
errors through to parameter estimates, a Bayesian model structure was chosen, implemented in NIWA’s CASAL (C++
Algorithmic Stock Assessment Laboratory) software suite. Most priors were uninformative except for that on M, and
the growth model (which was fitted outside the model using a maximum likelihood, mixed-error method). Observation
error for each data set is supplied to the model, but additional process error can be supplied or fitted within the model.
The model is used to estimate unfished biomass, M, selectivity and maturity ogives, and a vector of annual recruitment
terms using an autodifferentiation function, betadiff, as a minimizer. The model fits to all supplied data sets or a
specified subset. Uncertainty in estimated parameters is estimated using a Markov chain Monte Carlo (McMC)
procedure to explore the likelihood surface. A burn-in of 500,000 iterations is followed by a chain of 1,000,000
iterations that is systematically thinned to 1000 samples assumed to represent the error structure of estimated
parameters (e.g., M) and derived quantities (e.g., biomass at intermediate years).
At this early stage the model has been considered by just one meeting of the NZ Ministry’s Shellfish Fishery
Assessment Working Group, and a number of issues have been raised for exploration or development. It was noted that
the model estimates of biomass were very similar to estimates of minimum absolute biomass (based on the density and
size of animals visible in photographs) but substantially less than photographic biomass estimates base on burrow
density. Also, the model did not reproduce systematic changes in sex ratio seen in both commercial and research trawl
samples and apparently related to changes in trawl catch rates. Further, the model did not reproduce these marked
changes in commercial and research trawl catch rates, although the NZ working group did not feel this was necessarily
a big problem because trawl catch rates are thought to be driven as much by catchability (emergence) as by stock
density. The working group had a preference for fitting growth within the model (because imposing a growth model
restricts the model’s ability to explore many options for M and B0), whether or not the source data for growth are fitted.
The use of multinomial error structure for length frequency distributions was recommended (for more transparent
treatment of zero observations than the current robustified lognormal allows), and it was agreed to restrict the
assessment to the area covered by the photographic surveys.
(1) The explicitly length-based approach (already under investigation within SGASAM) is consistent with the length-
based data collected on growth, and precludes the ‘slicing’ necessary to generate ‘ages’ for input to XSA (and the
smoothing of recruitment that this inevitably entails).
In this early stage of its development, the model has not been accepted as a stock assessment for the Metanephrops
stock to which it has been applied. Considerable further development is anticipated, however, following the success of
this approach in New Zealand’s important rock lobster and paua (abalone) fisheries.
Although considerable development is still required, this approach offers a significant advance over methods
previously used in New Zealand (depletion analyses and surplus production modelling) and throughout the ICES area
(equilibrium LCA and dynamic XSA modelling) for the following reasons:
8.2.2 Developing a Bayesian, length based model for Metanephrops challengeri.
(5) Proper handling of variance also allows more realistic stochastic stock projections under different management
regimes and could form the basis for ‘risk analysis’ as well as simple projection.
(3) Fitting to all data sources simultaneously rapidly illuminates conflicts, data problems, and poorly-fitted
observations. These conflicts can be merely a nuisance or can guide thoughts on model development and
weighting.
(2) Integrated models allow simultaneous fitting to a wide variety of different data sources, many of which cannot be
incorporated in simpler models. This is important because data can sometimes act synergistically.
(7) The downside of this approach is that models invariably become very complex, the software is costly to produce
and support, and analyses (especially McMC) are highly computer intensive.
(6) Integrated modelling and exploration of model sensitivity provides guidance on where future research might most
profitably be concentrated (e.g. in areas of greatest uncertainty or to test hypotheses generated from conflicts
between data sources).
(4) Variance and uncertainty are readily incorporated and propagated to generate confidence estimates for estimates of
model parameters and quantities of management interest.
This model was developed under contract SCI2003/02 let by the New Zealand Ministry of Fisheries.

WGNEPH Report 2004
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8.3 Catch Survey Analysis
Catch Survey Analysis (CSA, Mesnil, 2003) is an implementation of the ‘modified DeLury method’ proposed by
Conser (1995). In contrast to the highly structured methods described above, CSA has much reduced data demands. It
requires only a time-series of recruitment and stock indices, and total catch numbers, together with some idea of the
relative catchability (s) of recruits to fully recruited individuals. For species where the abundance indices are derived
from trawl survey data, it may be appropriate to assume s=1.0, but when commercial CPUE data are used, estimating
this parameter is a problem. It has been suggested that this value should be estimated from external information on the
mean length of recruits and gear selectivity parameters. However, these are not always known and furthermore, initial
attempts at estimating s based on these assumptions made at the Working Group on Methods on Fish Stock Assessment
(ICES, 2003e) were not always found to be reliable. In such cases the only way forward is to check the sensitivity of
the results to a range of values of s.
At a previous WG meeting, this method was applied to the Skagerrak stock of Nephrops using commercial CPUE
data and indicated similar fishing mortality trends to XSA, but much more variation in biomass and recruitment trends
(ICES, 2003a). Further investigations of this method are carried out here, with a trial CSA for Firth of Forth Nephrops
(FU 8) (males only).
The two indices are derived by assuming that the estimated numbers from the TV survey are representative of the
whole population and that this can be split into ‘recruits’ and ‘fully selected’ on the basis of the commercial catch-at-
length frequency data. The commercial data from quarter 3 is used as this most closely agrees with the timing of the
survey. Due to problems with the slicing routine, a number of nominal cut off lengths (20 mm and 25 mm CL) for size
of recruits were chosen for comparison purposes. Figure 8.3.1 shows the two sets of indices for males. Missing values
which occur in 1995 and 1997 are filled by linear interpolation. The CSA is able to deal with missing values, but
requires a minimum of 10 years of survey data.
Although this method of deriving abundance indices overcomes some of the problems which may be associated
with the use of commercial CPUE as an index of population abundance, an estimate of s is still required as the
allocation of total numbers to recruits and fully recruited is based on the catch-at-length distribution data. This method
also makes the assumption that the TV survey estimates of population numbers are representative of the whole
population so that it can be assumed that the changes in year class strength from the length distribution data are being
picked up in the survey. This rather ad hoc derivation of the abundance indices requires further scrutiny and the results
should therefore be regarded as illustrative only. Furthermore, the filling of the missing values using interpolation
creates artificial values which would not have been necessary had the time series been available for a longer period.
A range of values of s were tried for each data set, yet in only a limited number of cases did the routine converge.
A comparison of the resulting stock trends with the XSA output is shown in Figure 8.3.3 (although residuals do appear
to show some blocks of positive and negative values - see Figure 8.3.2). The broad trends in fishing mortality are
similar for CSA and XSA; however, the trends in biomass and recruitment show few similarities. Model runs with
alternative recruitment cut-off points differ in the size of the fluctuations in stock trends, with the lower cut-off length
giving greater fluctuations.
The results are unsurprising in that the fishing mortality fluctuations are likely to be driven mostly by the annual
number removed from the population, which is the same in both XSA and CSA. However, the estimates of biomass
and recruitment are constrained to the abundance indices which are dependent on the TV survey data as well as the
catch-at-age distribution data and may indicate rather different trends.
The effect of altering the assumed value of s on the absolute estimates of stock trends was also investigated.
Figure 8.3.4 shows a comparison of runs with s set to 0.2, 0.25 and 0.3 (which were the only values for which the
routine converged). The value of s acts as a scaling factor on the absolute value of estimated stock trends with higher
values giving higher estimates of recruitment and biomass and lower estimates of fishing mortality. In fact, increasing
the catchability of recruits from 0.2 to 0.3 has the effect of almost doubling the estimates of stock biomass and halving
estimated fishing mortality.
This method appears to be useful for picking up fluctuations in estimated fishing mortality and possibly stock
biomass and recruitment. However, unless external information is available and the value of s can be derived with
some confidence, it would seem unwise to rely on CSA as a stand-alone assessment method as the results are so
sensitive to the value of s that is chosen. Such problems are not unique to this method. In cases where there is no
external information from which to derive s, but there are enough data to apply an age-based assessment, CSA could be
considered a useful way of verifying results. At this WG an exploratory CSA was carried out for Nephrops in FUs 28-
29 and confirmed the trends which appeared in the XSA assessment.
The WG considers both of the methods described above to be valuable in certain situations. There are other methods
which may also be worth considering, for example Integrated Catch-at-Age Analysis (ICA), (Patterson, 1998) which
assumes a separable fishing mortality model for the most recent years. The parameters are estimated using tuning
8.4 Conclusions
The other major difficulty in applying this method is how to derive the abundance indices. In many stocks of
Nephrops, the only available length-frequency data are from the commercial catch and there is often no clear distinction
in the distributions between recruits and fully recruited individuals. Rather than considering commercial length-
frequency data which is cumulative over time, it may be worthwhile exploring whether length-frequency data collated
over a shorter time scale better distinguishes between recruits and fully recruited individuals.

indices which can be age-structured or non-age structured – for example measures of biomass, which currently cannot
be incorporated as tuning indices in XSA. Furthermore, the incorporation of uncertainty into the input parameters such
as those defining growth and natural mortality is also considered highly desirable and further investigation of CASAL is
anticipated. It should be mentioned here that all of the models described above make dynamic pool assumptions about
the population dynamics which may not be appropriate for Nephrops stocks due to the spatial heterogeneity of the
stocks and fisheries (see Section 10). So, although the development of non-age-structured assessment methods is
considered a useful and important task, it would be helpful if models could be developed which account for these spatial
aspects.
(b)
0
20
40
60
80
100
120
140
0
50
100
150
200
250
300
350
400
93 94 95 96 97 98 99 00 01 02
Stock
(a)
0
5
10
15
20
25
30
93 94 95 96 97 98 99 00 01 02
0
50
100
150
200
250
300
350
400
450
Stock
Recruitment
Recruitment
Figure 8.3.1. - Firth of Forth Nephrops (FU 8): Males. Indices of recruitment and stock size
as calculated using TV survey estimates of total numbers and the quarter 3 commercial
catch-at-length distribution data with cut-off lengths of a) 20 mm CL and b) 25 mm CL.
WGNEPH Report 2004 277

Figure 8.3.2. - Firth of Forth Nephrops (FU 8): Males. Residuals from CSA run.
-2
-1.5
-1
-0.5
0
0.5
1
1.5
2
93 94 95 96 97 98 99 00 01
Recruits
Fully recruited
WGNEPH Report 2004
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Figure 8.3.3. - Firth of Forth (FU 8): Males. Results of CSA for 2 different recruitment cut-
off lengths compared with XSA estimates. The results are all mean standardized for ease
of comparison.
Fishing Mortality
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1.6
1992 1994 1996 1998 2000 2002
XSA
25 mm
20 mm
Total Biomass
0
0.2
0.4
0.6
0.8
1
1.2
1.4
1992 1994 1996 1998 2000 2002
XSA
25 mm
20 mm
Recruitment
0
0.5
1
1.5
2
2.5
3
3.5
1992 1994 1996 1998 2000 2002
XSA
25 mm
20 mm
WGNEPH Report 2004 279

Figure 8.3.4. - Firth of Forth (FU 8): Males. Results of CSA for alternative values of the
relative catchability of recruits.
Fishing Mortality
0
0.1
0.2
0.3
0.4
0.5
0.6
1992 1994 1996 1998 2000 2002
s=0.2
s=0.25
s=0.3
Total Biomass
0
2
4
6
8
10
1992 1994 1996 1998 2000 2002
s=0.2
s=0.25
s=0.3
Recruitment
0
100
200
300
400
500
1992 1994 1996 1998 2000 2002
s=0.2
s=0.25
s=0.3
WGNEPH Report 2004
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9 IMPLICATIONS OF DIFFERING SELECTION PATTERNS FOR
DATA COLLECTION AND ASSESSMENT
9.1 Introduction
The size structure and sex ratio of catch and landed Nephrops in sampling will depend on a number of factors. The
relative importance of these factors varies by Functional Unit and by metier, mainly driven by management measures
(both technical and catch restrictions), market reason, fleet characteristics and the biology of Nephrops (see Figure
9.1.1). These external drivers may vary between different countries fishing the same Functional Unit and/or over time,
potentially leading to unrepresentative sampling of the population structure which may result in either inaccurate or
biased stock assessments.
The current spatial resolution (i.e. statistical rectangle) of catch and effort data available from EU logbooks is
almost certainly not sufficient to properly identify metier-specific spatio-temporal fishing patterns for most Functional
Units. There may be some scope in the future to improve this situation as the VMS programme is extended to smaller
vessels (<25 m) and data currently collected by enforcement agencies become more readily available for scientific
purposes. Even if such data were currently available, some type of spatially explicit modelling would be required for
the historical time series of assessment data. If metiers fish in different areas during individual trips then the resultant
population structure of sample landed catch may be a composite of different stock units. The problem of inappropriate
spatial resolution of data is a general problem with fish stock assessment within ICES which may be exacerbated in
Nephrops stocks because of their discrete and relatively sedentary nature. This may result in both inaccurate sampling
and violation of the dynamic pool assumptions (see Section 10).
Data are lacking on selection parameters for most gears employed by different metiers targeting Nephrops. In the
literature there are different views of how well Nephrops are selected. Graham & Fero (in prep.) concluded that in
general the size selection of Nephrops is poor, resulting in a high degree of discarding in certain fisheries. Nephrops
may have a low L50 or an absence of length-related selection because of their shape, spiny nature, tendency to cluster in
trawls (using their claws to hold together) and their passive escapement from gear (unlike the active escapement of
some fish species). Some studies however, suggest that cod-end selectivity in Nephrops trawls may be rather steep, but
also that selectivity depends on many factors, such as mesh size, twine properties, quantities caught, weather conditions,
etc. (Polet & Redant, 1994). The use of selective grids has been tested in the Bay of Biscay Nephrops fishery with
promising results. In certain cases selectivity patterns can be adapted by fishers to increase catches when technical
measures are introduced and theoretical improvements in selection may not always be realised.
Past studies have shown that high-grading or crew selection (discarding of animals above MLS for economic
reasons) of Nephrops is extremely variable both between and within different fisheries. In some cases data on
discarding are lacking for some of the main metiers exploiting Nephrops stock. The availability of these data is
expected to improve significantly in the future since sampling of discards has been made mandatory by the DCR (Data
Collection Regulation, EC1639/2001). However, as this happens it will lead to dilemmas on how to integrate discard
data into the assessments which currently have no or poor discard data.
9.2 Celtic Sea FUs 20-22
The fishery in the Celtic Sea is mainly involves metiers from France, Ireland and the UK (landings by other countries
are minor). Spatial and temporally resolved landings and discard data by metier are not currently available to
WGNEPH. However, the spatial distribution of landings from these countries was previously investigated by
WGNEPH in 2002 (ICES, 2002a) to investigate the appropriateness of Functional Units. These data show significant
differences in the spatial distribution of landings by country during the period 1996-99. The majority (80%) of the Irish
catches were restricted to 31E3 where the ‘Smalls’ grounds occur. French catches from this rectangle were also high
(~40%) but landings generally were from a wider spatial distribution. France accounted for 65% of the total reported
landings during this period, whereas Ireland accounted for 34% (ICES, 2003a). There are also significant trends in the
landings by country with and increasing trend in Irish landings from around 500 t in the early 1990s to around 1800 t in
the early 2000s.
There are no parameterised selection curves available for either the French or Irish metiers operating in the Celtic
Sea. The fleet structure and some information on the gears used by these metiers have been described in previous
WGNEPH reports (ICES,1999a, 2003a). The French fleet is a multi-purpose fleet which alternates between targeting
whitefish and Nephrops depending on number of factors. The Irish fleet is mainly a Nephrops-directed fleet that targets
Nephrops in several different FUs, also depending on number of factors.
WGNEPH Report 2004 281

Several management changes through various EC regulations have affected both fleets in recent years, with the
increase in towed gear mesh sizes from 80 mm to 100 mm under some conditions and in part of FUs 20-22 as part of
the hake recovery plan. Adequate data are not available on the actual impact of these regulations in terms of uptake of
larger mesh sizes and realised changes in selection by metiers. However, WGNEPH in 2003 indicated that French
vessels have been mainly using 100 mm mesh since 2000, giving them the flexibility to switch between targeting
Nephrops and finfish. Irish vessels on the other hand may be using smaller mesh sizes.
Investigation of the data available for 2002 indicates that discarding and high-grading occurs in the French fishery
and Irish fisheries. The fisher selection pattern in the Irish fleet indicates that the L50 (24 mm) is close to the 25 mm CL
minimum landing size. In the French fishery there is also discarding of underside Nephrops but there is also substantial
high grading (L50 35 mm) due to a 35 mm minimum landing size set by the French Producers Organisation (Figure
9.2.2). Estimated parameters for logistic selection curves are given in Table 9.2.1, where pl is the proportion retained at
length l by fishers, as described by the equation below.
lba
lba
e
e
*
*
+
+
+
l
p1
=
Within FUs 20-22 are three separate FUs which ideally which should be assessed independently. As WGNEPH has
warned previously, the impact of including data from several spatially and reproductively isolated populations in one
assessment may lead to an inaccurate assessment. WGNEPH recommend that trends in catch, effort and CPUE should
be monitored on a smaller spatial scale as possible changes in these stock indicators may be masked in the aggregated
data. Fishery independent data from UWTV surveys or other sources on the distribution of Nephrops populations within
FUs 20-22 are also required.
Since fishing vessels may fish in several FUs during the same voyage in the Celtic Sea, in the past it was not
possible to adequately sample the landed catches by FU. Catches for different countries appear to indicate that the
fleets may not be exploiting these FUs evenly. WGNEPH recommend that national sampling programmes should be
modified/implemented so that data on the origin of each sample on a finer spatial scale are also collected. Sampling
levels should be modified such that reasonable precision of sampling of Nephrops is achieved an appropriate spatial
scale. This might involve self-sampling of catches and discards by fishers or dedicated observer trips.
Although gear selection parameters of the different metiers involved in this fishery are not available it seems likely
that these differences will be insignificant compared with the substantially different fisher selection patterns. These led
to substantial differences in the raised length frequency distributions for the two countries in 2002 (ICES, 2003a).
Historical data on the size composition of landings and discards for the Irish fleet are not available. Therefore there
could also be potential bias in the input catch numbers-at-age, with more individuals being removed from the stock due
to the increasing trend catches taken by the Irish fleet since 1990. This could manifest itself as unaccounted mortality in
XSA causing a retrospective bias in the assessment. Although there is a poor retrospective pattern in both F and SSB
estimates for this stock, there is not much evidence of a systematic bias (ICES, 2003a). WGNEPH recommend that the
potential impact of different selection patterns on trends in F and SSB be investigated using a simulation approach.
The available data for this stock are likely to improve in coming years since sampling of catches are required
under the DCR. WGNEPH recommend that during this interim phase there will be a need to carefully evaluate
potential ways of integrating newer data with the historical time series for this stock. The introduction of data from
previously unsampled metiers or improved discard information could lead to large changes in recruit estimates in XSA.
Several options are likely and the sensitivity of the realised assessments to these should be tested.
9.3 Porcupine Bank FU 16
An examination of the available landings data shows spatial differences between the countries exploiting Nephrops in
the Porcupine Bank area. Again, WGNEPH recommend that sampling programmes should be modified to account for
this, and that catch, effort and CPUE trends should be examined on a finer spatial scale. This might involve self-
sampling of catches and discards by fishers or dedicated observer trips. As in the Celtic Sea, large differences are
observed in the length composition of landings sampled by the three main countries exploiting this stock (Spain, France
and Ireland). There are no data available on metier or fisher selection patterns and it is not clear what are the underlying
factors and at what level the differences in selection occur. There are significant differences in fishing patterns and
vessel characteristics of the different metiers. The limited data available for this stock has meant that an acceptable
assessment has not been possible in recent years. However, WGNEPH are hopeful that the data situation will improve
with the implementation of the DCR. Due consideration (i.e. simulations and sensitivity analysis) of the potential
impact of combining heterogeneous sampling data into an assessment dataset should occur before an analytical
assessment could be accepted for this stock.
9.4 Botney Gut-Silver Pit area (FU 5)
The Nephrops fishery in FU 5 is international. Up to the mid 1990s, most of the Nephrops landings from FU 5 were
made by Belgian trawlers (usually over 90 % of the international landings). Since then however, the situation has
changed, and nowadays most of the Nephrops from FU 5 are taken by Dutch vessels. The share of the Danish fleet in
the landings has been generally modest (< 10 % of the international landings), while that of UK vessels has gone up
WGNEPH Report 2004
282

WGNEPH Report 2004 283
On the west coast of Scotland, the majority of landings are made by inshore trawlers, but a valuable creel fishery for
Nephrops also exists, generally catching larger individuals for the live export market. The high unit value of the live
product has attracted extra effort to this fishery, and the proportion of total landings made by creel fishermen has
increased in recent years. Figure 9.5.1 shows the trends in total landings from the North and South Minch Functional
Units, and the percentage contributed by creel activity. For the North Minch it can be seen that the while the percentage
contributed by the creel fleet has been quite variable, levels in the most recent years (about 17%) are higher than those
recorded through most of the 1990s. In the South Minch, the percentage contribution of the creel fishery appears to have
been generally less variable historically, but has shown a dramatic increase in the most recent years, from an average of
about 12% through much of the 1980s and 1990s to over 22% in 2002.
Catchability in the two metiers relies on different aspects of Nephrops behaviour, and selectivity is also different.
While catchability in the trawl fishery is related to animal emergence patterns, leading to marked seasonal shifts in the
sex ratio of catches, catchability in the creel fishery is related to bait attraction and interactions between animals. Creel
catches do not show the same seasonal fluctuations in sex ratio, and may include high numbers of ovigerous females
through the winter, a component of the population largely absent from trawl catches. Nephrops selectivity in trawls is
generally poor, but the open nature of meshes on creels means that smaller individuals can escape from creels.
9.5 North Minch (FU 11) and South Minch (FU 12)
considerably in the most recent years (from less than 5 % of the international landings up to 1998, to about 15-20 % in
2000-2002) (ICES, 2003a).
Although FU 5, as it was defined by WGNEPH, comprises 10 statistical squares, the actual extent of the Nephrops
grounds is much smaller, with most of the population being confined to the muddy depression of the Silver Pit in the
north and the trenches of the Botney Gut and Markham’s Hole in the south. Some Nephrops are also seen to inhabit the
coarser sandy sediments on the shallows around the Silver Pit and the Botney Gut, but densities in these areas are
generally very low.
Fishing for Nephrops in FU 5 is very diverse in terms of gears used. In the Belgian fleet, which nowadays has
shrunk to less than 10 vessels (specialist and occasional Nephrops trawlers combined), at least four different types of
Nephrops and combined Nephrops-whitefish trawls are used: single rigs, twin-rigs, double twin-rigs and light beam
trawls (the latter typically being operated by Eurocutters). There is little information on the gears used by the Dutch and
the UK fleets, but the data available suggest that at least in the Dutch fleet, several types of gear are being used too,
including single and multi-rig otter trawls and light beam trawls.
Similarly, there is little information on the spatial distribution of effort over the actual Nephrops grounds in FU 5.
Most skippers do have their preferred ‘spots’, and some vessels are known to shift seasonally between different parts of
the grounds (depending on weather conditions and catch rates). In general however, all vessels and fleets seem to cover
most of the area most of the year, and there is no indication of spatial segregation between gears.
If the rules to identify metiers (as laid down by SGDFF – ICES, 2003b) were strictly to be applied to the fisheries
in FU 5, this may well lead to the identification of a very large number of metiers, all however comprising a very small
number of vessels only. From a modelling and management point of view, this may be highly impractical. Therefore, it
is likely that the metiers will have to be grouped in some sort of ‘super-family’ of metiers, which all have in common
however that they are primarily directed towards Nephrops.
From an assessment point of view, this does not seem to pose a major problem, provided that the different national
landings and discard sampling programmes properly cover all metiers. The problems associated with the Nephrops
fisheries in FU 5 therefore seem to be mostly a problem of sampling stratification, rather than a methodological
assessment problem in the strict sense.
The potential for conflict between static and mobile gear means that the two metiers (trawl and creel) are generally
active in spatially distinct areas, with the creel activity usually concentrated in more coastal areas, and the trawl fleet
operating further offshore. It must be assumed, however, that within a FU, both metiers exploit the same population of
Nephrops. The sedentary nature of Nephrops, and the generally spatial distinct nature of the metiers means that there is
scope for the parts of the populations exploited by the different fleets to be experiencing different states of exploitation,
and there is anecdotal evidence of this in the South Minch. While both the analytical assessments and TV surveys
suggest a relatively stable population (based on data from the trawl fishery and a survey largely covering the area of
trawl activity), the creel fishermen report considerable declines in CPUE and a reduction in the mean size in catches
indicative of a population in decline.
While the two metiers generally operate in different locations, in some areas seasonal closures to mobile gear
mean that both metiers exploit the same area, but at different times of the year, and in some cases both metiers are
active simultaneously.
Historically the WG has dealt with the two metiers separately in terms of assessment. This has largely been due to
the fact that the two activities have been considered spatially distinct, and although landings from both are sampled at
markets, no meaningful effort data is available for the creel fisheries. However, where the two fisheries are active in the
same area (a possibility becoming more likely as creel activity expands), the effects of both should be taken into
account for the same population.

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284
9.6 Kattegat (FU 4) and Skagerrak (FU 3)
In Skagerrak and Kattegat the Nephrops stocks are primarily exploited by Danish and Swedish vessels. Information on
the two national fleets’ temporal and spatial effort allocation exist only from logbook information. Due to the low
spatial resolution from the Danish log books in terms of ICES rectangles, the WG was unable to analyse for any
differences in the two fleets’ spatial allocation of effort. However, based on ad hoc knowledge of the fleets, spatial
distribution the Danish fleet is mainly distributed around the Læsø Deep and northeast of Denmark, whereas the
Swedish Nephrops fleet mainly operates in the eastern part of Skagerrak.
Based on a recently study by Ulrich & Andersen, two different types of Nephrops-related fisheries have been
identified within the Danish fleet: a 70-89 mm mesh fishery primary targeting Nephrops; and a 90-104 mm fishery
targeting both Nephrops and demersal fish species. Within those fisheries various types of netting structure (e.g. square
or diamond mesh, different thread thickness, single/double thread etc.) are used, but at present time no such information
can be separated into different fisheries/fleets.
In the Swedish fleet four different Nephrops-related fisheries exist. An inshore creel fishery targeting only
Nephrops, a single trawl fishery (70 mm square or 90 mm diamond mesh) primarily targeting Nephrops, a twin trawl
fishery (70 mm square mesh or 90 mm diamond mesh) targeting both Nephrops and, to an increasing extent, demersal
fish. A nationally regulated Nephrops-directed trawl fishery is allowed in special areas inside the trawling border using
trawls equipped with 35 mm species selective grid together with 70 mm square mesh in 8 m of codend and extension
piece.
Due to the observed differences in mesh size, netting structure and catch composition among the identified
fisheries, we may expect different exploitation patterns between the fisheries in terms of size selection on the Nephrops
stock both within and between the national fleets.
The fishers selection ogive curve of the landings of male and female from the Danish and Swedish fishers are
represented in Figure 9.6.1. For both nations the L25 of the selection ogive match esthe minimum landing size.
However, it seems that the Danish fishers select for a slightly higher proportion of smaller Nephrops compared to the
Swedish fishers. These observed differences in size compositions in the landings could be due to either differences in
gear riggings or the behaviour of fishers.
Comparing the length frequency of the discards between the two national fleets show that the Danish fleet are
catching and discarding a higher proportion of smaller Nephrops (both male and females) (Figure 9.6.2). The higher
proportion of smaller Nephrops in the discards of the Danish fleet are most probably due to the geographical differences
in stock composition on the main fishing grounds (as described above).
From an assessment point of view, different trends in size selection pattern among the identified fisheries may be a
problem when aggregating and raising the input data and also in tuning of the assessment.
New regulation from 1 March 2004 now requires vessels in Skagerrak and Kattegat using mesh size 70-89 mm to
use square meshed netting (Council regulation (EC) No. 2287/2003) in order to reduce the amount of undersized
Nephrops in the catch. As an alternative to a square mesh codend and extension piece, it is allowed to use diamond
mesh of 90 mm or more. The new regulation will most probably change size selection patterns in the Nephrops fishery
for both the Danish and the Swedish fleet.
9.7 General conclusions and recommendations
The various factors determining the realised selection pattern in Nephrops fisheries are complex and widespread. These
may result in significant selection differences between within and between metiers. Given that several of the factors
affecting selection are not routinely investigated, changes may occur without being noticed. This will have implications
for Nephrops data collection and raising procedures.
Slight differences in shape, range and L50 can result in substantial changes in the proportions of catch landed and
discarded. This can have implication for how catch compositions are aggregated and raised. WGNEPH therefore
recommend that impacts of selection variation on assessment inputs should be fully evaluated on a stock-by-stock level.
Changes in assessment outputs should also be examined through simulations. Therefore WGNEPH recommend that
this be taken up as a term of reference in future meetings.
Where necessary ,sampling should be modified to improve the spatial coverage of catch and discard sampling.
Sampling levels should be modified such that reasonable precision of sampling of Nephrops is achieved an appropriate
spatial scale.

WGNEPH Report 2004 285
Table 9.2.1. Celtic Sea (FUs 20-22): The parameters for the fishers selection curves with estimated L50 and
bootstrapped 95% confidence intervals .
Country a b L50 lower 95% CL L50 L
50 upper 95% CL
Ireland -15.66 0.66 22.7 23.8 24.86
France -33.13 0.96 32.2 34.7 37.19

Figure 9.1.1. - Potential factors affecting the selection patterns and resulting sampled
population structure for Nephrops stocks.
Management Measures
Gear restrictions
Closed areas & seasons
Quota restrictions
Catch composition limits
Market reasons
Producer organisation rules
Demand for size categori
Prices for size categories
Fleet Characteristics
Vessel size, power gears
Availability of other targe
Species/Stocks
Vessel Skipper & Crew
Weather effects on
catchability
Biology of Nephrops
Emergence patterns/volume
in tow
Sex ratio & Maturity stage
Moult phase
es
t
Population Structure
Metier spatio-temporal
Fishing Pattern
Gear Selection
Parameters
Fisher Selection Pattern
Sampled Population Structure
WGNEPH Report 2004
286

Fi y
gure 9.2.1. - Cumulative logbook landings 1996-99 by ICES statistical rectangle in FUs 20-22 b
country.
0
1000
2000
3000
4000
5000
6000
7000
8000
28E1 28E2 29E1 29E2 30E1 30E2 31E2 31E3 31E4 32E3
ICES Statistical Rectangle
Cumulative Landings 1996-99 (t)
UK E&W
Ireland
France
Figure 9.2.2. - Celtic Sea (FUs 20-22): High-grading selection curves for Nephrops . The
parameters for the fitted curves are shown in Table 9.2.1.
0
0.5
1
10 20 30 40 50 60
CL (mm)
Proportion Retained
Ireland France
WGNEPH Report 2004 287

WGNEPH Report 2004
288
d Figure 9.5.1. - North Minch (FU 11) and South Minch (FU 12): Trends in total landings an
the percentages contributed by creel activity.
North Minch
2000
2500
3000
3500
4000
4500
1975 1980 1985 1990 1995 2000 2005
Tonnes
7.5%
10.0%
12.5%
15.0%
17.5%
20.0%
Total % Creel
South Minch
2000
2500
3000
3500
4000
4500
5000
1975 1980 1985 1990 1995 2000 2005
Tonnes
7.5%
10.0%
12.5%
15.0%
17.5%
20.0%
22.5%
Total % Creel

WGNEPH Report 2004 289
n ogive of the landings for the Danish and Swedish fleet
d on the average for 1991-2002.
Figure 9.6.1. - Skagerrak (FU 3): The fisher's selectio
spilt by sex. The data are base
0.00
0.25
0.50
0.75
1.00
0 10203
Le
Proportion obtained
Danish fleet (male)
Swedish fleet (male)
Selection Ogive of the landing for the Danish and the Swedish
fleet
04050607080
ngth (mm)
Swedish fleet (female)
MLS
Danish fleet (female)

WGNEPH Report 2004
290
Figure 9.6.2. - Skagerrak (FU 3): The length frequency of the discards of the Danish and Swedish fleet split by sex. The data are based on the average for
1991-2002.
Male discard
0.000
0.010
0.020
0.030
0.040
0.050
0.060
0.070
0.080
0.090
20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Length (mm)
Frequncy
Sweden
Female discard
0.000
0.010
0.020
0.030
0.040
0.050
0.060
20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50
Length (mm)
Frequncy
Sweden
Denmark
Denmark

10 Assessment Deficiencies for NEPHROPS Stocks
10.1 Generic assessment problems for Nephrops stocks
10.1.1 Age determination
The principle source of information on the structure and dynamics of Nephrops stocks is the length composition of
catches, landings and discards. Inferences about age rely on the application of growth curves to apply a temporal scale
to transitions between length-classes. The most commonly applied analytical methods of stock assessment are age-
based, and depend on the conversion of length-classes into age-classes. WGNEPH practice is to use von Bertalanffy
growth parameters in a deterministic ‘slicing’ of length compositions, whereby sharp length boundaries to ‘age’-classes
are defined as points on a growth curve. It is, of course, recognised that in fact no such clear boundaries exist – age-
classes are likely to overlap widely in size. Various empirical (e.g. MIX) and model-based (e.g. MULTIFAN)
approaches have been attempted for resolving length-compositions in terms of mixtures of component distributions,
each of which is interpreted as an age-class. In practice, however, the method of deterministic slicing has been retained,
since length-composition of Nephrops samples rarely show clear modes so that identification of putative age-classes is
highly subjective.
The principle consequence of deterministic slicing for stock assessment is that year-class signals in the data
become indistinct. Each nominal ‘age’-class contains a mixture of year-classes, with the effect that estimates of stock
biomass and recruitment from age-based assessments tend to be smoothed towards their recent average values.
Underestimation of the true variability of biomass and recruitment has adverse consequences for the identification of
biological reference points and application of the Precautionary Approach, and also hampers early detection of
unfavourable stock trends.
It would not be reasonable to expect that methods of direct age determination for Nephrops will be routinely
available in the foreseeable future. Measurement of lipofuscin (‘age pigment’) and radiometric methods have been
applied to Nephrops with varying degrees of success, but these techniques are too expensive and labour-intensive to be
routine monitoring tools. Realistically, improvements in the quality of inferences about age in Nephrops stock
assessments depend on two types of development: firstly, the collection of good quality, stock-specific information on
growth (see Section 12); secondly, the use of such data in length-based assessment approaches with explicit modelling
of transitions between length-classes (see Section 8).
10.1.2 Sampling levels for catch, landings and discards
Sampling levels for the landings are generally assumed to be sufficient to produce reliable length frequency
distributions (LFDs) of the landed Nephrops, but there is little or no statistical evidence that this is really the case.
Routine discard sampling programmes have been in operation for a small number of stocks (see tables ‘Input data and
parameters’ in earlier WGNEPH reports), but the reliability of the discard LFDs is likely to be lower than that of the
landings in view of the limited number of discard samples that is usually available compared to the number of landings
samples. As for landings however, there is little or no statistical evidence on the actual reliability of the discard LFDs.
The issue of precision levels has recently been addressed by the Workshop on Precision Levels, as sub-group of
the ICES Planning Group on Commercial Catch, Discards and Biological Sampling (PGCCDBS). This workshop has
recommended a number of possible approaches to calculate precision levels (ICES, 2004), and it is expected that
countries will apply these techniques to assess the accuracy/reliability of their landings and discard sampling
programmes. In this context, it is worth noting that EU Member States are compelled to provide precision levels for all
their sampling programmes as part of the annual technical reports on their Data Gathering Programmes (see EC
Regulation 1639-2001).
As already mentioned, long-term discard data series are available for a small number of Nephrops stocks only.
This situation is likely to improve over time, since all EU Member States are now expected to collect information on (a)
the quantities of Nephrops discarded, and (b) the length composition of these discards, in all their major Nephrops
fisheries. WGNEPH notices that several countries have recently started routine discard sampling programmes on their
Nephrops fisheries, many of which cover not only the Nephrops discards but also the discards of associated finfish
species. It will take some time before these data series will be sufficiently long to be useful for assessment purposes but,
on the whole, these initiatives could mean a major step forward in the quality improvement of the database to the
assessments.
WGNEPH Report 2004 291

10.1.3 Quality of landings and effort statistics
Official landings data for some Nephrops stocks may not reflect the true levels of landings and corresponding effort.
The implications and potential deficiencies in assessments are discussed in Section 6.
10.1.4 Validity of information on biological parameters
In the assessments as such and in the associated pre-processing of the data (slicing of the length frequency distributions
into ‘age’ groups), several biological parameters are being used, including length-weight-relationships, growth
parameters, sexual maturity rates and natural mortality rates.
Length-weight relationships (LWR)
LWRs are available for most stocks, although not all of these were actually derived from stock-specific length and
weight measurements. For most stocks, separate LWRs are used for males and females. Although when plotted in a
graph, these relationship show the same overall shape, there appear to be major differences in the weight-at-length
between FUs (Figure 10.1.1). These amount to almost 30 % in males and almost 40 % in females between the upper and
the lower LWRs in the plots. It is difficult to believe that there would be such a high degree of variability in the
biometric features of a single species, the more so since there is no consistent (e.g. latitudinal) pattern in the observed
differences. There could be many explanations to this (differences in methodology, time of the year over which the
length and weight data were collected, etc.), but it is definitely worth revisiting the issue, in an attempt to sort out the
likely reasons for the observed differences in LWRs.
For a number of stocks (FUs 20-22, 25, 31, 26+27), the same LWR is used for both males and females. In view of
the marked morphological differences between the two sexes, and the associated differences in weight-at-length, this
does not seem to be a justifiable approach. Regardless whether an ‘average’ LWR is being calculated and then used for
either sex, or a ‘single sex’ LWR is being calculated and then applied to the other sex, it may lead to erroneous
estimates of stock biomass for both sexes or for either males or females. Since LWRs by sex are easy to obtain,
WGNEPH recommends that such data be collected for all stocks where both males and females represent a significant
proportion of the catches and/or landings.
Growth parameters
Growth parameters (von Bertalanffy’s K and L-infinity) are used to generate nominal age groups as an input to the age-
based assessments, and to introduce a time-scale in the length-based assessments.
Growth studies are extremely scarce in the case of Nephrops, mostly because they are laborious, time-consuming
and expensive, and because the outcome is far from being guaranteed (tagging experiments e.g. may yield
disappointingly low recapture rates, in the order of 1 % only, which is not exactly an incentive to set up such studies).
The most recent growth studies on Nephrops are from the mid-1990s and the early 2000s (Tuck et al., 1997;
Ulmestrand & Eggert, 2001), but most go back to the late 1970s and early 1980s (Conan, 1978; Hillis, 1979; Bailey &
Chapman, 1983).
In the absence of stock-specific growth parameters for most FUs, these parameters have often been ‘borrowed’ from
other stocks with similar geographical features and size compositions (see the tables ‘Input data and parameters’ in earlier
WGNEPH reports). Besides, even for those stocks for which stock-specific growth parameters are available, there is little
or no information on issues such as year-to-year variability in growth rates, density dependence, etc.
The uncertainty on the growth parameters is one of the most important sources of uncertainty in the Nephrops
assessments (together with the uncertainty on the estimates of natural mortality – see further). The use of slightly different
values of K and L-infinity can seriously affect the slicing procedure and hence the estimates of the numbers-at-age. This, in
turn, has an impact on the perceived age structure of the population and hence on the estimates of the Fs-at-age. WGNEPH
is aware of this, but in the absence of better estimates of the growth parameters, there is little that can be done to improve
the quality of the assessments (also see paragraph ‘Improving the estimates of biological parameters’).
Sexual maturity
Estimates of the size at 50 % maturity (L50) for both males and females are used in the computations of the spawning stock
biomass.
Estimates of the L50 are available for most stocks for females but not for males, mostly because sexual maturity is
easier to measure in females (where it can be studied by visual examination of the ovaries and/or the egg bearing
condition) than in males (where extensive histological and/or morphometric studies are required – see working paper by
McQuaid & Briggs, Appendix 6). For most stocks however, even the most recent estimates of the female L50 values go
back to the 1980s or 1990s (see the tables ‘Input data and parameters’ in earlier WGNEPH reports), and as for growth,
there is no information on year-to-year variability. The impact of the uncertainty over L50 on the assessments however, is
generally assumed to be relatively small, since in most stocks most Nephrops landed are well above the L50.
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Natural mortality
Traditionally, WGNEPH has been using a natural mortality (M) rate of 0.3 for males and immature females, and 0.2 for
mature females.
The 0.3 value for males was derived from a study performed in the early 1980s on total mortality in virgin and
quasi-unexploited Nephrops stocks (Morizur, 1982). Since in virgin and quasi-unexploited stocks, fishing mortality is
zero or close to zero, all mortality could be assumed to be natural mortality. The use of a lower value of 0.2 for mature
females, was justified on the basis that mature females spend more time in their burrows than males and immature
females (particularly during the ovigerous period), and hence that, on an annual basis, they are less vulnerable to
predation.
Since Morizur's study, no attempts have been made to calculate new estimates of natural mortality, nor to adjust
the values to the likely changes in predation pressure that may have resulted from the decline in e.g. the cod stocks in
many Nephrops areas.
Improving the estimates of biological parameters
Under the provisions of EC Regulation 1639-2001, EU Member States are compelled to regularly update the estimates
of a number of biological parameters, amongst which sexual maturity and growth, for all major commercial fish and
shellfish stock, amongst which Nephrops. The sexual maturity estimates for Nephrops need to be updated every three
years, and the growth estimates every six years (see Appendix XVI of EC Regulation 1639-2001).
In an attempt to streamline these updates, WGNEPH agreed in 2001 to set up a framework for the co-ordination of
the sexual maturity and growth studies. Following this idea, an extra meeting day was 'hooked up' to the meeting of the
WG, to discuss data collection issues and to further elaborate joint sexual maturity and growth studies on Nephrops.
Once these studies will be completed, they will help to improve the quality of the biological input parameters to the
assessments and hence to the overall quality of the assessments. A copy of the minutes of this extra meeting day on data
collection is issued as an annex to the WG report (Appendix 9). WGNEPH endorses the recommendations of this
meeting with respect to internationally co-ordinated studies into growth and maturity of Nephrops.
10.1.5 Sedentary nature, the potential for spatial targeting of fishing effort, and spatial differences in fleet
selection patterns
Nephrops is a relatively sedentary and territorial animal, and is not thought to undertake large scale migrations. The
dynamic pool assumptions that underlie many of the analytical assessment approaches commonly applied to fish species
are therefore invalid, compromising their application to Nephrops stocks to some extent. Following fishing in one area,
individuals do not redistribute from surrounding areas, and animals do not have an equal probability of capture. As with
many crustacean species, local environmental variability appears to affect the population biology of Nephrops, and
parameters including growth and density vary over quite small spatial scales (10s of kms), with growth (and mean size)
being density-dependent. Given this variability, one would expect there to be considerable scope for spatial targeting of
effort into particular areas within a stock. For both inshore and offshore Nephrops fisheries where fine scale mapping of
fishing activity has been possible, spatial targeting of effort has been observed (Marrs et al., 2000, 2002). Effort is not
highest in areas where individuals are largest, or animal density is highest, but appears to be targeted in areas where
growth and density combine to maximise financial yield. Such spatial variability in effort will lead to spatial variability
in fishing mortality, as observed by Bell et al. (submitted) in the Farn Deeps fishery (see Section 12.8). Spatial
variability in fishing mortality within stocks complicates the relationship between effort and fishing mortality, and the
use of standard fisheries theory may overestimate fishing mortality.
If fishing effort does show spatial variability, then the information gathered from market and observer sampling on
the size composition of the removals will be biased towards areas with higher than average fishing mortality.
Simulation exercises may be required to evaluate the full consequences of this for the levels of variability in effort
observed in Nephrops fisheries, but it is likely that fishing mortality for the stock as a whole will be overestimated, and
stock size underestimated, unless the spatial aspects of the fishery can be taken into account.
Nephrops stocks are generally exploited by trawler fleets, but baited trap (creel) fisheries are also important in
some areas, contributing up to 20% of landings by weight in some stocks on the west coast of Scotland. Catchability in
creels is poorly understood (there is currently an EU FP6 project (NECESSITY) covering some aspects of this topic),
but is related to the attraction of animals to a bait, rather than emergence from their burrows, which is the case for trawl
fisheries. Creel fisheries tend to catch a different component of the stock than trawl fisheries, often taking larger
individuals, with a higher proportion of mature females. Therefore where the two fisheries interact, it is clearly
important to take account of the fisheries appropriately.
Even within trawl fisheries, differences in selection patterns can be expected. Nephrops are exploited by dedicated
Nephrops trawler fleets, but also feature in a number of mixed fisheries, where gears are often designed to catch both
fish and Nephrops. Where these activities occur in the same stock, then there are implications for data collection and
assessment. These issues are considered more fully in Section 9 of the current report.
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10.1.6 Seasonal and diurnal differences in availability and their consequences for assessment models
Nephrops shows distinct sex- and age-dependent diurnal and seasonal patterns in emergence from the burrows and
hence in availability to trawling. Seasonal patterns in catch composition (male and female catch components) and
CPUE and/or LPUE (for males and females separately) have routinely been documented by WGNEPH as part of its
stock evaluations (see e.g. ICES 2001a, 2003a). Cyclic changes in availability to trawling could result in changes in
annualized catchability, especially if the pattern or the amplitude of the cyclic changes differs from one year to another,
or if there are changes between years in the seasonal distribution of fishing effort. In the current analytical assessments,
such changes are hardly taken into account, and it cannot be excluded that persistent changes in seasonal behaviour or
in the seasonal distribution of fishing effort are erroneously ‘interpreted’ by the assessment models as changes in stock
biomass. One possible means to avoid this could be by running quarterly VPAs. Such an approach however, is even
more data hungry than the current one, and it is unlikely that the existing data sets are sufficiently extensive to allow
quarterly VPAs for all stocks.
10.1.7 Methodological/software limitations
The current method of slicing catch-at-length composition data to obtain ‘catch-at-age data’ has known problems in that
year classes are often indistinct and consequently important trends in stock biomass may not be identified (see above).
A number of methods which may overcome this problem by making direct use of catch-at-length distribution data are
described in Section 8. However, the use of these methods in routine stock assessment is likely to be more time
consuming and involve a much steeper learning curve than the standard age-based methods.
Stock assessment models are simple representations of reality and therefore by definition there is no correct model.
The idea is to apply a model which is a close approximation to reality and one for which, if the assumptions are
violated, do not have a significant effect on the results. As already stated, the dynamic pool assumptions which are
made by currently implemented methods, and other analytic assessment methods commonly applied to fish species, are
likely to be invalid for Nephrops. If the spatial aspects of the dynamics and fishery are found to affect the results then
spatially explicit models may be required. Such models do exist, but inevitably these require much larger amounts of
data to parameterise than standard single area models. Alternative methods of supplying scientific advice may be
required which do not rely on a detailed reconstruction of the historical stock dynamics.
Tuning fleets
Most assessment methods assume that catchability-at-age of the tuning fleets is stable. For commercial fleets, this
assumption is likely to be violated when increases in efficiency and/or changes in strategy are not taken into account in
the elaboration of the effort data used in assessments (see, for example, Section 5.2, Figure 5.2.18). The problem of
different selection patterns for metiers prosecuting the same fishery is discussed in more detail in Section 9.
10.2 Stock-specific assessment problems
To identify key deficiencies and highlight problems in the assessment of each stock the WG has drawn up a standard
table to be completed for each assessed FU. The table lists the problem areas discussed in section 10.1. Against each of
these is provided a score on the quality or knowledge of that parameter and, where appropriate, a summary of
assumptions and considerations. The completed tables are presented in each of the assessment sections (Tables 5.2.6,
5.3.6, 5.4.8, 5.4.25 and 5.4.42).
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WGNEPH Report 2004 295
Figure 10.1.1. - Length-weight relationships for male and female Nephrops in different FUs.
Body weight (g)
Body size (mm CL)
Males Females
Body size (mm CL)
0
20
40
60
80
100
120
140
160
180
200
15 20 25 30 35 40 45 50 55 60
FUs 3+4
FU 5
FU 6
FUs 7,8,9,11,12,13
FU 14
FUs 15,17
FUs 23-24
FUs 28-29
0
20
40
60
80
100
120
140
160
180
200
15 20 25 30 35 40 45 50 55 60
FUs 3+4
FU 5
FU 6
FUs 7,8,9,11,12,13
FU 14
FUs 15,17
FUs 23-24
FUs 28-29

11 ALLOCATION OF NEPHROPS FUs TO AREA-BASED
ASSESSMENT WGs
Over the past years, the problems associated with the management of mixed fisheries have become a prime issue in the
discussions on fisheries management. So far however, these problems have only poorly been dealt with in the case of
the Nephrops directed fisheries. Technical interactions between stocks and fisheries have repeatedly been in the ToR of
several ICES assessment WGs, but time constraints and/or the lack of adequate data have prevented most WGs from
providing advice that actually did take into account such interactions.
In an attempt to resolve the problem, the EC has asked the Mixed Fisheries Sub-group of STECF to make short-
term mixed fisheries predictions, using the outputs of the ICES assessments WGs, complemented with additional
information on the age composition of the landings of all key species in all relevant fleets or fisheries. So far, these
exercises have mostly been restricted to the North Sea and the Irish Sea fisheries, and in the first attempts the Nephrops
fisheries were not at all taken into account because of a lack of data on the age compositions of their finfish by-catches.
WGNEPH recognizes the problem, but it also wishes to emphasize that the proper dealing with the mixed fisheries
issues will require that steps are being taken at different levels of the data gathering and assessment process.
Regardless of the expert group that will eventually be asked to address the mixed fisheries issues (ICES
assessment WGs, STECF Sub-group or another), the success of any such approach will largely depend on the
availability of adequate data, i.e. age compositions for all key species by metier or fishery. The decision to set up data
gathering programmes on the finfish by-catches in the Nephrops-directed fisheries is far beyond the capacity of
WGNEPH, but the WG understands that several countries have already started such programmes or are planning to do
so in the near future. WGNEPH also was informed that the advisory groups which are responsible for the revision of EC
Regulation 1639-2001 (the ‘Data Regulation’) have picked up the issue, and that EU Member States will be encouraged
to set up fishery-based data collection programmes. In the mid-term, this can be expected to largely resolve the data
availability problem.
WGNEPH also discussed the fora that would be most suitable to deal with the mixed fisheries issues, and
concluded that the area-based assessment WGs are probably the best place to do so. This then poses the problem of how
to allocate the Nephrops FUs to the existing area-based assessment WGs within ICES. A proposal for such an allocation
is given in Table 11.1. For each Nephrops FU, this table shows the ICES area where the FU is located, the most
prominent linkages between Nephrops and its associated by-catch species (information taken from last year's WG
report), and the proposed allocation of the FU to the area based WGs (WGNSSK, WGNSDS, WGSSDS or WGHMM).
For most FUs, the allocation is straightforward (WGNSSK for all FUs in Sub-areas IIIa and IV, and WGNSDS for all
FUs in Sub-areas VI and VIIa). For the FUs in Sub-areas VII (except VIIa), VIII and IX, the choice between either
WGSSDS or WGHMM was based on the species of finfish that prevail in the by-catches of the Nephrops fisheries.
Following this rationale, it is suggested to allocate FUs 20-22 to WGSSDS (because of the predominance of cod and
whiting in the by-catches), and all other FUs in Sub-areas VII (except VIIa), VIII and IX to WGHMM (because of the
predominance of hake in the by-catches).
WGNEPH recognizes that allocating the Nephrops FUs to the area-based WGs bears the risk of considerably
increasing the workload of these WGs. However, since most Nephrops FUs are currently being exploited by one
country only (which implies that there is no need for extensive data pooling across countries), WGNEPH assumes that it
might be possible to run most of the Nephrops assessments prior to the meetings of the area-based WGs. WGNEPH
also understands that this is becoming common practice for most finfish assessments as well, thus leaving more time for
the mixed fisheries issues.
WGNEPH also recognizes that the proposed changes may imply a shift from the current system of biennial
assessments for most Nephrops stocks to a system of regular benchmark assessments and annual update assessment for
all Nephrops stocks. Such a shift however, is not expected to pose major problems.
WGNEPH decided that, for the time being, it will keep the NephStat system for the collation and exchange of
landings statistics for Nephrops. The Sea Fisheries Department (Belgium) agreed to further maintain and manage the
system.
The allocation of the Nephrops FUs and the associated assessment work to the area-based assessment WGs, does
not necessarily mean that WGNEPH should cease to exist. Over the past decades, WGNEPH has built up considerable
expertise on biological and methodological issues associated with Nephrops, and it would be regrettable to lose this
expertise. Therefore, it is proposed that WGNEPH should continue to operate, and that it should be given the task of
carrying on its biological and methodological work (also see Section 13). This could be done on a need-to-meet basis,
with biennial or triennial meetings, depending on the need to review biological data and the state of progress of
methodological developments.
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Cod
Haddock
Whiting
Hake
Blue whiting
Plaice
Megrim
Lemon sole
Sole
Monk
WGNSSK
WGNSDS
WGSSDS
3 IIIa M m m -- -- m -- m m -- X
4 IIIa M m M -- -- m -- m m -- X
5 IVbc M m P -- -- M -- m m -- X
6 IVbc M M P -- -- m -- m -- -- X
7 IVa MMm--------m--mX
8 IVbc mM----------------X
9 IVa -- m -- -- -- m -- -- -- -- X
10 IVa X
11 VIa m M m -- -- m -- m -- -- X
12 VIa m M M -- -- m -- m -- -- X
13 VIa M M m m -- m -- -- -- -- X
14 VIIa M m M -- -- M -- -- m -- X
15 VIIa MMM----m-------- X
16 VIIbcjk------m----M----P
17 VIIbcjk --mmM-- mMm--M
18-19 VIIbcjk m M M m -- m P m -- M
20-22 VIIfgh M m M m -- -- M -- m M X
23-24 VIIIab -- -- -- M -- -- M -- M M
25 VIIIc
26-27 IXa
Table 11.1. - Major by-catch species in the Nephrops fisheries
and proposed allocation of Nephrops FUs to area-based assessment WGs
Little or no information available
Nephrops is by-catch of finfish directed fisheries
Nephrops is by-catch of finfish directed fisheries
Proposed alloc
to area-based W
Nephrops
Functional Unit
ICES Sub-area
Major species in by-landings and/or
discards of the Nephrops-directed fisheries (*)
WGHMM
X
X
X
X
X
X
28-29 IXa -- -- -- P P -- m -- -- m X
30 IXa X
31 VIIIc X
32 IVa M m -- m -- -- -- -- -- M X
33 IVbc X
(*) P
M
m
-- By-catches marginal or nil
Little or no information available
Predominant by-catch species
Major by-catch species, without however being predominant
Minor by-catch species
Little or no information available
ation
Gs
Nephrops is by-catch of finfish directed fisheries
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12 WORKING DOCUMENTS AND PRESENTATIONS
12.1 STECF Recovery Plans for Southern Hake and Norway Lobster in IXa and VIIIc
Celso Fariña (La Coruña, Spain) reported on the recovery plans for southern hake and Nephrops put forward by the
Subgroup on Management Objectives (SGMOS) of STECF in Lisbon, 9-13 June 2003 (SGMOS, 2003). The Terms of
Reference for the meeting were:
(1) advise on possible recovery targets both for the southern hake stock and Norway lobster stocks (FUs 26-30 and
FUs 25-31 in the Atlantic Iberian peninsula; ICES areas IXa and VIIIc), and the acceptable time-span needed to
rebuild the stocks to safe biological limits;
(2) evaluate different recovery strategies based on SSB increments or F reduction and explore the effect of
implementing constraints on annual variation in TAC, taking into account the time needed to rebuild the stock;
(3) advise on management measures suitable for implementing the recovery strategies paying special attention to
quota, effort and/or technical measures, taking into consideration the characteristics of the fisheries (multispecies
and multifleet);
(4) identify areas suitable for permanent or temporary closures suitable for Norway lobster stocks;
(5) evaluate possible technical measures (mesh size or other selectivity measures, closed areas, gear size) to improve
the exploitation pattern for the southern hake stock;
(6) define criteria to evaluate the performance of the different recovery strategies, including criteria for when the
recovery target has been met.
For Nephrops, annual reductions in F were proposed based on the strategy for hake – gradual F reduction (10 %
p.a.) to achieve F0.1 for hake of 0.15 over a recovery time of 5-10 years. Since this was deemed insufficient to allow
effective recovery of Nephrops stocks, additional technical measures were proposed (closed areas).
The main conclusions of the SGMOS meeting were:
• An effort control scheme represents the best overall management scheme for the fisheries for southern hake and
Iberian Nephrops.
• Any such effort control scheme needs to account for the particular problems associated with defining and
regulating effort in artisanal fleet.
• If any additional measures are required to help ensure the recovery of Nephrops stocks, then area closures
represent the best option.
• There is only limited scope for use of additional fishing gear regulations given the mixed-species nature of the
fisheries, but a number of minor changes were suggested.
12.2 Major developments in data collection and related issues, and their impact on Nephrops-work
A presentation was made by Frank Redant (Oostende, Belgium), in his capacity of Chair of the STECF Sub-group on
Research Needs (SGRN) and Member of the ICES Planning Group on Commercial Catch, Discards and Biological
Sampling (PGCCDBS).
First, the presentation reviewed the ongoing revision of EC Regulation 1639-2001, and its implications with
respect to the data collection on Nephrops and the Nephrops directed fisheries. New or modified provisions in the
proposed revised version of the Regulation with relevance to Nephrops-workers include:
• The obligation to collect annual discard data for all stocks that are assessed annually or that are under a recovery
plan.
• Changes in the priority status of a number of surveys, and the inclusion of a number of new surveys with priority
status 2 (i.e. surveys that are eligible for co-funding by the EC under the extended programme requirements of the
Regulation).
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• Modified exemption rules for Nephrops, that better match the spatial disaggregation levels at which data collection
should be organised (FUs in the case of Nephrops as opposed to management units in the case of most finfish
stocks).
• A new approach to length and age sampling, based on target precision levels instead of pre-set sampling intensities.
• A clearer distinction between mandatory and optional species/stocks throughout the Regulation, and a better
linkage between Modules E (Quantities caught, landed and discarded), H (Length and age sampling) and I (Other
biological sampling) of the Regulation.
Next, the presentation gave an overview of the role and task of PGCCDBS, the workshops that took place or are
planned to take place under its auspices (Workshop on Discard Sampling in 2003, Workshop on Precision Levels in
2004, Workshop on Small-scale Fisheries in 2004 or 2005, several ring-tests and workshops on age reading), and the
recent decision to establish four Regional Planning Groups (RPGs) in support of the data collection programmes (one
for the Baltic, one for the North Sea, one for the Western Seas and one for the Mediterranean). The task of these RPGs
would be to:
• Promote and improve international co-operation on data gathering.
• Establish bilateral agreements and task sharing between countries on the length and age sampling of landings by
foreign flag vessels.
• Promote joint study programmes and organise task sharing for the collection of data on length-age keys, growth,
sexual maturity, fecundity, etc.
• Inventory and standardise sampling procedures.
• Report to PGCCDBS on ‘problem areas’ for which pan-European workshops could be organised.
In order to ensure maximum operational flexibility, it was agreed to keep the RPGs independent from existing
scientific or management bodies such as ICES, CIESM, the European Commission, etc. As far as the EU Member
States are concerned, participation in the activities of the RPGs would be eligible for funding under the National Data
Gathering Programmes. As a response to the general feeling that international co-ordination and co-operation in relation
to data gathering is an absolute must, it was decided not to wait any longer with the organisation of the RPG-meetings,
and to have the first meetings already in 2004. A provisional list of the planned RPG-meetings and their venues is given
below:
• Baltic Sea RPG: Denmark, May 2004.
• North Sea RPG: UK England, 4th quarter 2004.
• Western Seas RPG: Ireland, September 2004.
Following the WGNEPH meeting, an additional meeting, chaired by Frank Redant (Oostende, Belgium) was held
in Lisbon on 2 April 2004 to discuss national plans for studies on sexual maturity and growth in Nephrops. Notes from
this meeting are attached at Appendix 9. WGNEPH endorses the recommendations of this meeting with respect to
internationally co-ordinated studies into growth and maturity of Nephrops.
12.3 Nephrops and the ICES-FAO Working Group on Fishing Technology and Fish Behaviour
A presentation was made by Norman Graham (Bergen, Norway) in his capacity as chair of the ICES-FAO Working
Group on Fishing Technology and Fish Behaviour (WGFTFB). He reported on “The Nephrops fisheries of the NE
Atlantic and Mediterranean – A review and assessment of fishing gear design”. An abstract is given below:
A review of the commercial trawl fisheries where Nephrops are a component of the catch was undertaken. These
have considerable geographical coverage, ranging from Iceland to Portugal and into the Mediterranean. Nephrops are a
highly important commercial species, valued at €208 million in 2001. The fisheries, with a few exceptions, are typically
multi-species, with the relative economic importance of Nephrops varying considerably between fisheries. Due to the
smaller mesh size used in comparison to demersal fish fisheries, the degree of discarding of other species can be high.
Additionally, due to the poor trawl selection characteristics, high grading and legislative restrictions, the discarding of
Nephrops is considerable in certain fisheries. A range of gear related technical measures are applied in order to mitigate
discard levels, but further improvements are required. There is a lack of parameterised selectivity data for many of the
existing technical measures, making any population independent assessment of their effectiveness impossible. The
report is divided into geographical areas and, for each of these, the fisheries are described, fleet adaptations to
legislation are discussed and a review of the remedial measures that have been tested or applied is provided. Based on
this information, fishery or area specific recommendations are made. In addition to the fishery specific
recommendations, more general recommendations are also given.
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The full report is available in Appendix 1 of ICES CM 2003/B:07.
Some more general remarks were also made, with some proposals for future work relevant to WGNEPH. A large
proportion of data from recent Nephrops selectivity experiments fail to demonstrate length-dependency. This is contrary
to the model developed by WGFTFB sub-group in 1995. It would be beneficial if WGFTFB re-examine historic and
recent Nephrops selection data to:
(1) Examine possible reasons for this failure considering both methodological aspects for estimating selectivity and
physical cod-end design characteristics.
(2) If data are available, refine the 1995 model considering additional parameters such as twine thickness, cod-end
circumference and mesh shape and propose further research if required.
(3) In fisheries where fisherman and market selection exceeds current MLS criteria, model the potential stock impacts
of altering cod-end selection to mirror those of commercial selection practices.
12.4 Use of underwater TV survey data in formulating management advice for Nephrops stocks
Ian Tuck (Aberdeen, UK, Scotland) made a presentation on possible future directions for TAC advice for Nephrops
stocks based on the use of abundance estimates based on underwater TV surveys of burrows. A Working Document is
attached at Appendix 1 (Ian, Tuck and Nick Bailey, Aberdeen, UK, Scotland), and the topic is also raised in Section
6.3.1.
12.5 New underwater TV survey data
Ian Tuck (Aberdeen, UK, Scotland) presented new underwater TV survey results for Scottish Nephrops stocks
indicating substantial increases in abundance in the northern North Sea and off the west coast of Scotland over recent
years. A Working Document is attached at Appendix 2 (Ian Tuck, Nick Bailey and Adrian Weetman, Aberdeen, UK,
Scotland).
Colm Lordan (Galway, Ireland) presented the results of the first underwater TV survey of Nephrops stocks in the
western Irish Sea. The survey was a successful collaboration between the Marine Institute (Ireland) and DARDNI
(Northern Ireland) and demonstrated the applicability of the technique for this stock. Results showed very high
densities in some areas. The preliminary biomass estimate of 103 thousand t was approximately three times higher than
a comparable VPA estimate. A Working Document is attached at Appendix 3 (Colm Lordan and Jennifer Doyle,
Galway Ireland; Richard Briggs, Belfast, UK, Northern Ireland).
12.6 Review of Nephrops stock assessment in the western Irish Sea
A comprehensive review of the Nephrops assessment in FU 15 is attached at Appendix 4 (Colm Lordan, Galway,
Ireland). The review concluded that XSA assessment appears to give a fairly consistent view of stock trends, but that
there are concerns about the applicability of the method to a species for which age structure is not directly estimated.
12.7 New data on Nephrops to the north of Ireland
Appendix 5 gives a Working Document submitted by Emmet Jackson and Conor Nolan (Dun Laoghaire, Ireland) on
biological observations of Nephrops in catches to the north of Ireland.
12.8 Spatial patterns of Nephrops exploitation
A presentation was made by Mike Bell (Lowestoft, UK, England) on spatial patterns of depletion of Nephrops density
in the Farn Deeps stock (FU 6). Survey results indicated effective targeting of fishing effort at the highest density areas
of the stock, and provided evidence that M is currently close to the values assumed for this stock.
Fishers exploiting a sedentary stock are likely to visit the most profitable (highest catch rate) areas first.
Simulation models demonstrated that this type of spatially non-random ‘foraging’ behaviour can cause the relationship
between commercial CPUE and overall population abundance to be highly non-linear. There is thus a risk that stock
assessments based on commercial catch data may either exaggerate or be slow to detect important stock changes.
Modelling predicted that a sedentary stock should show two measurable indications of effective targeting of fishing
effort:
(i) decreased spatial variance in density after fishing; and
(ii) higher depletion rates in the areas of highest density.
To find out whether either of these signs of targeting was apparent in Farn Deeps Nephrops, underwater TV surveys
were used to describe the distribution of stock density at the beginning and the end of a winter fishing season.
The overall spatial variance of burrow density was lower at the end of the fishing season, but not significantly so.
However, geostatistical analysis demonstrated a decrease in variance along an axis parallel to the coast and consistent
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with the predominant direction of commercial trawl tows. Location of fishing along the inshore-offshore axis appears
to be influenced by factors other than (or additional to) Nephrops density.
There was a strong positive relationship between initial density and overwinter depletion of density. Above a
threshold density of about 0.6 burrows .m-2, overwinter depletion increased with density, consistent with fishing effort
being targeted at the highest densities. Below this threshold, the constant level of overwinter depletion was assumed to
represent natural mortality, yielding an estimate of M very close to the value currently assumed in stock assessments.
It was concluded that Nephrops fishers are able to find and exploit the highest densities of their target species.
The findings suggested that CPUE statistics for the Farn Deeps Nephrops stock should be viewed at a finer spatial scale
(10-20 km) than is currently possible (50-60 km), and that stock trends inferred from commercial catch data preferably
should be corroborated by fishery-independent surveys.
12.9 Sexual maturity in male Nephrops
Richard Briggs (Belfast, UK, Northern Ireland) reported on Northern Ireland studies examining the size at onset of
sexual maturity for male Nephrops from primary sexual characteristics and from morphometric traits. Physiological
maturity determined by histological examination of the reproductive system indicated that 50% of male Nephrops had
spermatophores in the vasa deferentia at 15.1mm carapace length (L50). Morphometric maturity, where males are
physically able to copulate and characterised by the appendix masculina reaching optimal length, occurred at 24.3-
26.9 mm carapace length. Functional maturity, represented by a relative increase in claw growth with the onset of
maturity, varied spatially in the Irish Sea and ranged from 25.9 to 31.0 mm carapace length in Nephrops from different
areas. Until the relationship between claw size and maturity is more fully understood the change in allometry of the
appendix masculina appears to be the most appropriate measure of sexual maturity in males.
A Working Document is attached at Appendix 6 (Nuala McQuaid and Richard Briggs, Belfast, UK, Northern
Ireland).
12.10 Length-based assessment methods
Martin Cryer (Auckland, New Zealand) made a presentation on a Bayesian length-based assessment of the New
Zealand species Metanephrops challengeri. A Working Document is attached at Appendix 7, and a summary is given
in Section 8.2.2.
Helen Dobby (Aberdeen, UK, Scotland) made a presentation on a length-based assessment method applied to Firth
of Forth (FU 8) Nephrops. A Working Document is attached at Appendix 8 and summaries are given below and in
Section 8.2.1. This preliminary assessment of the Firth of Forth Nephrops used a size-transition matrix approach based
on the catch-at-size analysis (CASA) of Sullivan et al. (1990). The method was developed for Northern Shelf
anglerfish and following a number of years of exploratory work (Dobby, 2000, 2002; ICES, 2001b, 2002b, 2003c), the
anglerfish assessment was accepted by ICES in 2002 and used as the basis for advice.
The population is described by a vector of numbers-at-length, which is projected forwards in time using a size
transition matrix (sex and maturity specific) obtained from a stochastic growth model with externally estimated
parameters. All population dynamics processes (e.g. recruitment, fishing mortality) are assumed to be dependent on
length rather than age. Parameter estimates and historical trends in stock abundance (annual recruitment, mean and
standard deviation of recruitment distribution, selectivity parameters, temporal component of fishing mortality) are then
obtained by fitting the model to the observed data. In contrast to the age-based assessments currently used, this length-
based approach carries out the assessment of males and females simultaneously. The population model links the males
and females by assuming identical numbers recruit to the male and female populations and also that the fishing
mortality fluctuates in a similar way. The reduced fishing mortality on the female population due to reduced emergence
is modelled by introducing a quarterly dependent ‘catchability’ parameter (fixed from year to year) which calculates
female fishing mortality as a proportion of the male fishing mortality. The parameters can then be used (together with
estimates of maturity and individual weight) to obtain short-term predictions of catch and biomass and in yield-per-
recruit analysis.
The resulting estimates of biomass and fishing mortality are very similar to those obtained from the XSA
assessment which may not be surprising since the assessment is based on the same catch-at-length data. However,
although the estimated recruitment has the same trends, it shows much greater fluctuations, possibly due to the
application of length-slicing to obtain the age-structured data. Incorporation of TV survey biomass data alters the
perception of the stock biomass in that estimates are increased in early years, but then show a downward trend which
was not observed in runs based only on the commercial data. Possible explanations for this mismatch are that
commercial catchability may have increased (not accounted for in the model) or that the low values in the TV survey
data may have been due to weather conditions rather than any particular downward trend in stock biomass.
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13 RECOMMENDATIONS
On the identification of Nephrops metiers and fisheries
Although there is general recognition amongst fisheries scientists and managers that fisheries management and data
collection should move from a stock-based to a fishery-based approach, little progress has been made on this in the case
of the Nephrops fisheries. However, before fishery-based management and sampling schemes can be implemented, it is
essential that the Nephrops directed metiers and fisheries be properly defined. Therefore, WGNEPH recommends that
countries undertake the necessary steps to identify their Nephrops metiers and fisheries without any further delay,
following the general guidelines laid down by SGDFF (ICES, 2003b).
On discard sampling
Many if not most Nephrops assessments would benefit from improved estimates of the quantities of Nephrops discarded
and the length composition of these discards. WGNEPH notes that several countries have Nephrops discard sampling
programmes in operation now or are planning to set up such programmes in the near future. WGNEPH strongly
supports any such initiatives and recommends that these be continued unabated.
On biological parameters
Most estimates of the biological parameters that are used in the Nephrops assessments (sexual maturity, growth, natural
mortality, etc.) go back to the 1970s and 1980s, and may no longer correctly reflect the biological characteristics of the
stocks to which they are applied. WGNEPH notes that regular updates of several of these parameters (amongst which
sexual maturity and growth) are required under the provisions of EC Regulation 1639-2001. Although this Regulation
only applies to EU Member States, in practice it does affect the vast majority of the Nephrops stocks in the ICES area
(all except FUs 1, Iceland; 2, Faroe; and 32, Norwegian Deeps). WGNEPH notes that initiatives are underway to set up
joint research programmes to update the estimates of sexual maturity and growth in Nephrops, and it strongly
recommends that these initiatives be fully supported (see Appendix 9).
On the allocation of the Nephrops FUs to the area-based assessment WGs
Following the arguments given in Section 11 of this report, WGNEPH suggests that the Nephrops assessments be
assigned to the area-based assessment working groups, according to the allocation proposal given in Table 11.1.
On the development of fishery-independent methods of stock assessment
WGNEPH notes that the use of underwater TV surveys for assessing Nephrops stocks is increasingly (see Section 12.5
and Appendices 2-3), and there is a recognition that such fishery-independent data may form an important basis for
management advice in future (see Sections 6.3.1 and 12.4 and Appendix 1). It is timely to consider how widely
applicable the method is to stocks throughout the ICES area (and the Mediterranean), to develop common standards and
to examine possible applications for the data. WGNEPH recommends that an international workshop be convened in
the near future, meeting possibly under the aegis of PGCCDBS.
On the future of the Nephrops Working Group
The proposed allocation of the Nephrops FUs and the associated assessment work to the area-based assessment WGs,
does not necessarily mean that WGNEPH should cease to exist. Over the past decades, WGNEPH has built up
considerable expertise, and it would be regrettable to lose this. Therefore, WGNEPH proposes that it continues to
operate with a clear focus on biological and methodological issues. This could be done on a need-to-meet basis, with
biennial or triennial meetings, depending on the need to review biological data and the state of progress of
methodological developments.
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WGNEPH suggests that it meets again late 2005 or early 2006 (venue to be decided), to:
(1) Review progress made on the identification of Nephrops metiers and fisheries, and the likely consequences this
may have on the stock assessments.
(2) Review progress made on the calculation of precision levels for the Nephrops landings and discard sampling
programmes, and the consequences this may have on the design of these programmes.
(3) Review new information on reporting levels for landings and examine the implications for assessments and advice.
(4) Review progress made on the updates of sexual maturity parameters.
(5) Further develop alternative assessment techniques.
On the new Chair of WGNEPH
WGNEPH expressed its appreciation to the outgoing Chairman, Mike Bell (Lowestoft, UK, England) for “a job well
done”, and unanimously proposes Ian Tuck (Aberdeen, UK, Scotland) to become the new Chair of the Working Group.
WGNEPH Report 2004 303

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APPENDIX 1
Working Document to WGNEPH, March 2004
Using Underwater Television and Harvest Ratio’s to provide Nephrops TAC advice – a
Scottish example.
Ian Tuck and Nick Bailey
FRS Marine Laboratory, Aberdeen
Summary
Uncertainty over landings figures, and concerns over some of the assumptions upon which analytical assessments are
based, have lead to investigations into alternative approaches for providing Nephrops advice. A Harvest Ratio, based on
an underwater TV survey estimate of abundance, was first applied to the Fladen Ground in 1999. This method is
described, and applied to other stocks around Scotland.
Uneven spatial distribution of fishing effort may result in VPA underestimating stock size, and overestimating F.
TV surveys are able to sample over the whole spatial distribution of a stock, and may provide a more reliable estimate
of stock size than analytical approaches.
Introduction
Given the complexity of gathering information on quantities of landings from diverse and remote Nephrops fisheries,
there are some uncertainties about the accuracy of reported landings figures. This naturally raises the question ‘how
much does uncertainty about the true level of landings affect the quality of assessments, and what impact does this have
on the nature of management advice for affected fisheries?’
Using multiple lines of evidence to gain an appreciation of the status of a Nephrops stock and the likely directions
of stock trajectories, it appears that uncertainty in landings does not compromise the assessment of stock trajectories.
Stock indicators, such as CPUE and LPUE are to some extent independent of reporting levels, and many inferences are
drawn from the length and age compositions, rather than the quantities, of fishery removals. In the case of many stocks
for which the UK has the main share of the fishery, underwater TV burrow counts provide an assessment that is
completely independent of the fishery. It seems that in the case of trends derived from analytical estimates of stock
biomass and recruitment, that reported landings levels act more as a scaling than a confounding factor. Taken together,
the available information on the major Nephrops stocks is considered to provide an adequate basis from which to draw
conclusions about stock status. Recent advice suggests that current levels of exploitation are sustainable for the North
Sea and west coast of Scotland stocks, with scope for expansion at the Fladen Ground (ICES, 2003).
The effect of uncertainty in landings may be more profound in the setting of Nephrops TACs. Although TACs for
Nephrops are precautionary, (mostly based on historic landings interpreted in the context of stock indicators rather than
determined explicitly from an analytical procedure), there comes a point when the relative interpretation of sustainable
exploitation levels must be translated into an absolute number for the TAC. As such, TAC recommendations are mainly
given in terms of official landings statistics. Where the quality of landings is uncertain, then the TAC based on these
data will underestimate the amount that can be sustainably removed, and could lead to increased levels of discarding.
Setting aside concerns over the accuracy of landings statistics, other factors call into question the appropriateness
of the analytical approaches applied to Nephrops. Nephrops are a relatively sedentary species, and so dynamic pool
assumptions are invalid. Micro-scale effort mapping studies (Marrs et al., 2000; 2002) have shown considerable spatial
variability in the levels of effort, which will lead to spatial variability in fishing mortality. This complicates the
relationship between effort and fishing mortality, and the use of standard fisheries theory may overestimate fishing
mortality.
Owing to the variety of concerns over the current assessment and advice process, alternative approaches have been
investigated. Since 2000, the ACFM advice for the Fladen Ground in the North Sea has been based on a conservative
harvest ratio of the abundance estimated from underwater TV surveys. This paper documents the approach used for this
stock, and applies it to other Scottish stocks, to provide alternative advice, independent of landings statistics.
Methods
TV survey
Nephrops is a mud-burrowing species that is protected from trawling while inside its burrow. Burrow emergence is
known to vary with environmental (ambient light level, tidal strength) and biological (moult cycle, females reproductive
condition) factors. This means that trawl catch rates may bear little resemblance to population abundance. Trawl
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surveys are therefore not ideal for Nephrops, and the use of underwater TV has been developed as a means of
estimating stock size from burrow densities.
The data described in this study are derived from surveys carried out from the FRS RV Scotia and Clupea, and the
survey vessel RV Alkaid. An underwater colour TV camera (Kongsberg-Simrad OE1364) is mounted on an aluminium
sledge (Shand and Priestly, 1999), and towed slowly (< 1kt) astern of the survey vessel. The camera is arranged on the
sledge to view obliquely forwards between the runners of the sledge, with a width of view of approximately 1m.
Lighting for the camera is provided by underwater lights mounted on the sledge, and powered from the vessel through
the umbilical. A range finder is mounted vertically on the sledge to provide information on the height of the camera
above the seabed, and the degree of sinking of the sledge runners into the mud sediment. These data, together with
camera lens angle specifications, are used to calculate the dimensions of the camera field of view. An odometer wheel is
used to measure the distance travelled along the seabed during a TV run, typically lasting for 10 minutes. Data on the
vessel location, elapsed time, sledge depth, range finder and odometer readings are recorded during a TV run with ‘in
house’ data logging software. During the earliest surveys the umbilical cable was manually secured to the towing warp,
but since 1993 a kevlar strengthened towing umbilical cable has been used on a slip winch, greatly reducing the time
involved in sledge deployment, and improving survey efficiency.
Video tape recordings are made of each TV run, and burrow counts made both at the time of recording, and by at
least two experienced observers under controlled conditions. The later counts are converted into densities using
information on the width of view of the camera and length of the tow. Burrow occupancy is assumed to be 100% in TV-
based stock estimates, although it is straightforward to provide a range of estimates, allowing for different occupancy
rates (Tuck et al., 1997). SCUBA observations in unfished areas have indicated that unoccupied burrows do occur
(Marrs et al., 1996). However, since trawling collapses the entrances to both occupied and unoccupied burrows, and
occupied burrows are rapidly re-excavated (Marrs et al., 1996), occupancy rate is expected to be close to 100% in
trawled areas. Overall animal abundance is estimated by raising the mean densities to the appropriate area.
Survey design
A variety of survey designs are employed for the Nephrops stocks presently surveyed using underwater TV techniques.
While the majority use some form of random stratified design, the basis of stratification varies between stocks,
including the use of a regular grid, BGS strata sediment maps and sediment data stratified at other levels (Afonso-Dias,
1997). The use of habitat strata based on RoxAnnTM surveys has also recently been undertaken for the Clyde stock
(Marrs et al., 2000). The stratification choice is generally based on convenience, except for that of the Fladen Ground,
where a more comprehensive study into the data has taken place (Afonso-Dias, 1997). In 1999, the use of an adaptive
survey design with a regular grid stratification was attempted for two Scottish stocks, with varying results (ICES, 2000),
and has been applied to the Fladen Ground since then when time allows. Adaptive approaches have potential to improve
precision in survey estimates through allocating additional sample stations to strata that are larger or more variable, and
therefore contribute more to the overall survey estimate variance (Francis, 1984). The most appropriate basis for
stratification may vary between stocks, however, depending on the heterogeneity of population parameters in the area,
and the factors causing it.
Data series
Annual underwater TV surveys of the Scottish Nephrops stocks (Figure 1) started at the Fladen Ground in 1992, and
included all the main grounds by 1995. Details of the surveys carried out in each year are provided in Table 1. All
surveys of the main stocks have been undertaken during the summer months (June to September). All burrow counts are
made by experienced observers, and to maintain consistency, one individual has been involved in counts in every year.
Harvest ratio
At the 1999 meeting of the WG, concern was expressed that the TAC set at the time was unrealistically low for the
Fladen Ground stock, given its large size and the expanding fishery (ICES, 1999). It was feared that this would
encourage mis-reporting and lead to deterioration of the information for the stock, and ultimately the chance of not
detecting future problems that might arise. As a consequence, the advice moved away from the previous reliance on the
historical landings data as a basis for providing a TAC recommendation. Instead, the independent estimates of stock
abundance provided by the TV survey were used to estimate a likely landings level. This estimate was based on a
'harvest ratio' (defined here as catch in numbers/stock abundance) from the lower end of the harvest ratios observed
across a range of other Nephrops stocks, as calculated during the 1998 Nephrops Study Group (ICES, 1998). This
approach was also adopted at the 2001 and 2003 meetings of the WG. Given the generally low density of Nephrops at
the Fladen Ground, and greater uncertainty over the reliability of recruitment compared to more intensively studied
inshore stocks, a conservative harvest ratio of 7.5% of the abundance was considered appropriate by the WG, and
accepted by ACFM. Estimated harvest ratio’s for other Nephrops stocks range from 9.7 – 33% of the biomass, based on
reported landings and stock sizes from analytical assessments (ICES, 1998).
Details of the estimation procedure for the Fladen Ground 2003 assessment is provided below and in Table 2.
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Average length frequency distributions (calculated over the three most recent years) for the two sexes from
monthly Fladen Ground market samples were raised to annual removals (landings + dead discards) using discard
estimates from quarterly observer trips (with 25% discard survival) and reported landings figures. This provided an
indication of the length structure of the animals of each sex removed from the population. The total weight of the
reported landings representative of this number of removals (232.4 million animals) amounted to about 5960 t, and is
about 3.5% of the population abundance estimated by TV survey (averaged over the three most recent years). The TV
abundance estimate, 6613 million individuals, was multiplied by the harvest ratio (7.5%) to estimate a suitable limit on
the number of animals removed. This limit was then divided by the estimated current removals to provide a raising
factor by which to adjust the estimated current reported landings, to provide a potential landings figure.
Using the data for 2000-2002, this approach provides an estimate of potential landings of 12,720 tonnes for the
Fladen Ground.
Application of method to other areas
TV surveys for assessment of Nephrops stocks were started at the Fladen Ground in 1992, and regular surveys of the
other main areas around Scotland started 1994 or 1995, with an unbroken time series available since 1998 (Table 1).
The approach is providing consistent data on the abundance of Nephrops in the populations, and it is now considered
that sufficient data is available to investigate the harvest ratio approach for other stocks. As described above, the harvest
ratio considered appropriate for the Nephrops population at the Fladen Ground was 7.5%. This is lower than any of the
harvest ratio’s previously estimated for Nephrops (ICES, 1998), but although this stock is very large, the actual density
of animals is low, and the rapid development of the fishery since the mid 1980’s means that a long time series of length
or age structure data in the population are unavailable. There is therefore a greater level of uncertainty over the
reliability of recruitment than for some of the inshore stocks, for which regular sampling started in the 1960’s. For these
more intensively studied inshore stocks a harvest ratio of 7.5% would be considered overly cautious, and a more
appropriate figure would be between 20 - 30%, which roughly equates to an overall F of 0.22 - 0.36. These values of F
are within the range of estimates of F0.1 and F30%, which have been considered as reference points for Nephrops stocks
(ICES 1998). A harvest ratio of 20 – 30% is also within the range previously estimated for Nephrops (9.7 – 33%; ICES,
1998), and is at a level generally considered to be appropriate for many stocks.
Although the two sexes are exploited together, they are subject to different exploitation rates, owing to behavioural
differences in relation to burrow emergence while the mature females carry eggs. It is therefore appropriate to
investigate the effects of an overall harvest ratio on each sex individually. From market sample and observer data, the
numbers of animals of each sex removed (landings plus dead discards) each year are estimated. Assuming the accuracy
of landings data is consistent through the year, then the sex ratio estimated from these data is independent of landings
statistics. Over the last decade, males have typically contributed 54-55% of individuals to the total number removed,
although this is slightly higher for the Fladen Ground, and lower for the Moray Firth (Table 3). Based on these removals
figures, VPA conducted on each sex separately estimates stock numbers, and the % males in the stock from this analysis
is also presented in Table 3. There are concerns over the quality of females assessments in some areas, but the outputs
from the assessments are relatively consistent, in that males are estimated to contribute between 38-46% of the
population, which is in line with the contribution to the removals. Overall F on each sex is calculated for a range of
scenarios for male contribution to removals and stock number is examined in relation to an overall harvest ratio of 25%
in Table 4. The scenarios closest to observed values (52.5-55% males in removals, 40-45% males in stock) are
highlighted in bold font, and result in F values ranging from 0.34-0.40 and 0.21-0.24, for males and females
respectively. This equates to a harvest ratio of 31-34% and 19-22%, for males and females respectively.
A summary of the potential landings estimated from the harvest ratio approach for each of the stocks considered is
provided in Table 5. Fbar values for the male assessments conducted in 2003 (ICES 2003) and current harvest ratio
estimates (removals estimated from reported landings / TV abundance) are also provided. Interestingly, although the
Fbar values are considerably higher than would be expected from the estimated harvest ratios (even taking into account
the likely bias towards males in the catches), the harvest ratio and Fbar data show a positive linear relationship (Figure
2). This suggests that while the absolute levels of F may be overestimated by the analytical approach, the relative levels
between stocks do appear to relate to the fishing pressure.
Discussion
The traditional analytical assessment approaches currently employed for Nephrops are potentially hampered by
accuracy of landings and the biological characteristics of the species. Consistent under-reporting of landings will lead to
lower estimates of stock size, and also the rolling over of advice on the basis of historical landings will underestimate
the potential of the stock. The relatively sedentary nature of individuals means that the dynamic pool assumption is
invalid, and stock redistribution does not occur to any great extent. Given that effort is not even over the stock, this
means that while the standard VPA approach can provide information on levels of mortality on areas fished, it is likely
to underestimate the overall stock size, and overestimate the overall fishing mortality. TV surveys cover the whole
distribution of the stock, and therefore provide a more accurate indication of the stock size. The apparent dramatic
increases in potential landings from adopting the harvest ratio approach described above simply reflect a more
appropriate estimate of overall stock size. Given the uncertainty over current landings, the reduction in the trawler fleet,
WGNEPH Report 2004
308

and the demand for Nephrops, it is actually quite unlikely that shifting to the proposed advisory approach with larger
permitted landings would lead to increased effort on Nephrops grounds.
References
Afonso-Dias, M. (1997). Variability of Nephrops norvegicus (L.) populations in Scottish waters in relation to the
sediment characteristics of the seabed. Ph.D. Thesis, University of Aberdeen. 282pp.
Francis, R.I.C.C. (1984). An adaptive strategy for stratified random trawl surveys. New Zealand Journal of Marine and
Freshwater Research, 18, 59-71.
ICES (1998). Report of the Study Group on Life History of Nephrops. ICES CM 1998/G:9.
ICES (1999). Report of the Working Group on Nephrops stocks. ICES CM 1999/ACFM:13.
ICES (2000). Report of the Study Group on Life History of Nephrops. ICES CM 2000/G:6.
ICES (2003). Report of the Working Group on Nephrops stocks. ICES CM 2003/ACFM:18.
Marrs, S.J., Atkinson, R.J.A., Smith, C.J. and Hills, J.M. (1996). Calibration of the towed underwater TV technique for use in
stock assessment of Nephrops norvegicus. (94/069) Study project in support of the Common Fisheries Policy call for
proposals, 94/C144.
Marrs, S.J., Tuck, I.D., Arneri, E., Atkinson, R.J.A., Santojanni, A. and Stevenson, T.D.I. (2000). Improvement of Nephrops
stock assessment by use of micro-scale mapping of effort and landings. (97/0100) Study project in support of the
Common Fisheries Policy call for proposals, 97/C205.
Marrs, S.J., Tuck, I.D., Arneri, E., La Mesa, M., Atkinson, R.J.A., Ward, B., Santojanni. A. (2002). Technical Improvements
in the assessment of Scottish Nephrops and Adriatic clam fisheries.(99/077 Study Project in support of the Common
Fisheries Policy call for proposals 99/OJ C122)
Shand, C.W. and Priestly, R. (1999) A towed sledge for benthic surveys. Scottish Fisheries Information Pamphlet, No.
22.
Tuck, I.D., Chapman, C.J., Atkinson, R.J.A., Bailey, N. & Smith, R.S.M. (1997). A comparison of methods for stock
assessment of the Norway lobster, Nephrops norvegicus, in the Firth of Clyde. Fish. Res., 32:89-100.
WGNEPH Report 2004 309

Table 1. Nephrops TV surveys: Numbers of stations sampled in each area in each year. Main areas in bold type.
Stock 1992 1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 Area
Total
Fladen Ground 69 73 58 61 55 59 60 68 51 57 57 668
Firth of Forth 37 30 27 23 49 50 51 44 40 351
Moray Firth 31 28 27 34 31 52 38 33 46 36 356
Noup 10 10 20
North Minch 41 38 38 37 39 57 39 43 332
South Minch 33 21 40 36 37 39 56 39 36 337
Firth of Clyde 28 38 31 38 39 40 44 46 46 350
Sound of Jura 7 10 13 12 13 55
Sealochs 121 46 64 231
West of
Hebrides
31 21 52
Annual Total 69 141 167 129 161 160 225 284 426 305 350 335 2752
WGNEPH Report 2004
310

Table 2. Fladen Ground: Predicted landings potential based on Nephrops abundance estimate using TV surveys, current
landings and discard length distributions, and a harvest ratio of 7.5%.
CL Landings Discards Removals wt (g) Landings (t) CL Landings Discards Removals wt (g) Landings (t)
('000) ('000) ('000) ('000) ('000) ('000)
11 0 1.3 0.98 0.96 0.00
13 0.0 0.70 0.53 1.59 0.00
15 0.0 0.80 0.60 2.46 0.00 15 0 0.3 0.23 2.39 0
17 0.2 0.80 0.80 3.60 0.72 17 6.3 6.50 11.18 3.37 21.24
19 56.7 102.30 133.43 5.08 287.77 19 62.3 109.70 144.58 4.58 285.46
21 382.0 485.60 746.20 6.92 2642.76 21 886.8 435.40 1213.35 6.05 5362.13
23 1426.8 1519.50 2566.43 9.18 13096.97 23 2492.3 1594.80 3688.40 7.79 19412.27
25 3897.4 3576.50 6579.78 11.91 46404.45 25 5976.8 3366.80 8501.90 9.83 58762.79
27 8116.0 5323.00 12108.25 15.15 122949.54 27 10680.3 4874.50 14336.18 12.20 130279.05
29 12087.2 5085.50 15901.33 18.96 229134.79 29 15750.8 3706.00 18530.30 14.91 234847.93
31 17748.8 3326.80 20243.90 23.38 414980.49 31 15448.9 1559.50 16618.53 17.99 277936.29
33 18648.5 1165.00 19522.25 28.47 530972.02 33 12867.5 749.00 13429.25 21.46 276158.93
35 17168.7 335.10 17420.03 34.29 588629.19 35 8509.9 274.70 8715.93 25.35 215688.01
37 12714.2 140.10 12819.28 40.87 519645.27 37 5031.7 68.60 5083.15 29.66 149260.97
39 9440.2 81.50 9501.33 48.29 455824.25 39 2685.9 7.60 2691.60 34.44 92500.84
41 6447.5 64.90 6496.18 56.58 364815.09 41 1476.6 11.60 1485.30 39.69 58611.06
43 4070.4 21.70 4086.68 65.82 267904.21 43 745.3 1.70 746.58 45.45 33871.91
45 3068.8 20.40 3084.10 76.05 233374.17 45 429.4 3.20 431.80 51.72 22210.00
47 1966.3 1.70 1967.58 87.33 171713.74 47 150.6 8.60 157.05 58.54 8816.54
49 1328.2 1.30 1329.18 99.72 132445.51 49 95.8 0.00 95.80 65.93 6315.82
51 807.3 0.00 807.30 113.27 91446.50 51 24.7 0.00 24.70 73.90 1825.27
53 394.4 0.00 394.40 128.06 50505.41 53 3.2 0.00 3.20 82.48 263.92
55 299.3 0.00 299.30 144.12 43135.92 55 4.7 0.00 4.70 91.68 430.91
57 174.9 0.00 174.90 161.53 28252.19 57 0.0 0.00 0.00 101.54 0.00
59 114.8 0.00 114.80 180.35 20704.02
61 87.4 0.00 87.40 200.63 17535.00
63 37.9 0.00 37.90 222.44 8430.35
65 48.6 0.00 48.60 245.83 11947.45
Total 136473.4 4366.78 95913.7 1592.86
Total (males & females) 232387 5959.64
TV abundance 6613333
Landings potential with
7.5% removals
12720
Table 3. Estimated % of males in removals (from market and observer samples) and estimated % males in the stock
(from VPA output).
Stock % males in removals
(1993-2002)
% males in stock
(1993-2002)
Fladen Ground 62.4% *
Firth of Forth 55.1% 46.1%
Moray Firth 48.8% 37.9%
North Minch 54.8% 43.8%
South Minch 54.3% 38.0%
Firth of Clyde 54.8% 45.3%
*- trial analytical assessment conducted, but not considered reliable
WGNEPH Report 2004 311

Table 4. Scenarios investigating influence of contribution of males to removals and stock number on overall F for each
sex, assuming an overall harvest ratio (sexes combined) of 25%.
% of males in population
0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65
% males in
removals
M F M F M F M F M F M F M F M F
0.45 0.47 0.22 0.39 0.24 0.33 0.26 0.29 0.29 0.25 0.32 0.23 0.36 0.21 0.42 0.19 0.50
0.475 0.50 0.21 0.41 0.23 0.35 0.25 0.31 0.27 0.27 0.30 0.24 0.34 0.22 0.40 0.20 0.47
0.50 0.54 0.20 0.44 0.21 0.37 0.23 0.33 0.26 0.29 0.29 0.26 0.33 0.23 0.37 0.21 0.44
0.525 0.58 0.19 0.47 0.20 0.40 0.22 0.34 0.24 0.30 0.27 0.27 0.31 0.25 0.35 0.23 0.41
0.55 0.61 0.18 0.50 0.19 0.42 0.21 0.36 0.23 0.32 0.25 0.29 0.29 0.26 0.33 0.24 0.39
0.575 0.65 0.16 0.53 0.18 0.45 0.19 0.38 0.21 0.34 0.24 0.30 0.27 0.27 0.31 0.25 0.36
0.60 0.69 0.15 0.56 0.17 0.47 0.18 0.41 0.20 0.36 0.22 0.32 0.25 0.29 0.29 0.26 0.34
0.625 0.74 0.14 0.59 0.16 0.50 0.17 0.43 0.19 0.37 0.21 0.33 0.23 0.30 0.27 0.27 0.31
0.65 0.78 0.13 0.62 0.14 0.52 0.16 0.45 0.17 0.39 0.19 0.35 0.22 0.32 0.25 0.29 0.29
0.675 0.83 0.12 0.66 0.13 0.55 0.15 0.47 0.16 0.41 0.18 0.37 0.20 0.33 0.23 0.30 0.26
0.70 0.88 0.11 0.69 0.12 0.58 0.13 0.49 0.15 0.43 0.16 0.38 0.18 0.34 0.21 0.31 0.24
Table 5. Fbar estimate from most recent assessment, current landings and harvest ratio based on TV abundance estimate,
along with summary of potential landings estimation using TV abundance data based on harvest ratios of 20%, 25% and
30% (2000-2002 average).
Stock Fbar **
(males
)
Current harvest
ratio (reported
removals/TV
abundance)
Average
reported
landings (2000-
2002)
Potential
landings (20%
harvest ratio)
Potential
landings (25%
harvest ratio)
Potential
landings
(30% harvest
ratio)
Firth of Forth 0.95 22.8% 1574 1380 1724 2069
Moray Firth 0.47 12.9% 1292 2000 2500 3000
North Minch 0.58 17.2% 2835 3295 4119 4942
South Minch 0.52 7.5% 3119 8290 10362 12434
Firth of Clyde 0.77 14.4% 3023 4195 5243 6292
*- trial analytical assessment conducted, but not considered reliable
** - Fbar averaged over 2000-2002.
WGNEPH Report 2004
312

Figure 1. Main Nephrops Grounds around Scotland surveyed annually with underwater TV.
MF
SM
NM
CL
FF
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
0% 5% 10% 15% 20% 25%
Observed Harvest ratio
Male F bar
Figure 2. Plot of male Fbar and observed harvest ratio for Scottish Nephrops stocks. Point labels refer to stocks (FF –
Firth of Forth, CL – Firth of Clyde, NM – North Minch, SM – South Minch, MF – Moray Firth).
WGNEPH Report 2004 313

APPENDIX 2
Working Document to WGNEPH, March 2004
New survey information on Scottish Nephrops stocks.
Ian Tuck, Nick Bailey and Adrian Weetman
FRS Marine Laboratory, Aberdeen
Summary
Underwater TV survey data indicate increases in the abundance of Nephrops in the northern North Sea (15%) and off
the West Coast of Scotland (30%). The TAC for the North Sea has increased since the mid 1990’s, while for the West
Coast, the TAC has reduced. If levels of effort have remained constant then the reduction in TAC, in conjunction with
higher catch rates, will almost certainly lead to increased discarding or under-reporting. Given these circumstances it is
unlikely that the current TAC level is appropriate and that a figure more in line with availability should be seriously
considered.
Data from both TV surveys and more recent analytical assessments suggests that Nephrops stock trajectories may
be more variable than previously realised. Provision of assessments and advice on an annual basis may be more
appropriate than the current biennial programme for most stocks.
Introduction
The Nephrops Working Group has met biennially in recent years to provide advice on the state of Nephrops stocks, and
catch options for the various Nephrops stocks within the ICES area. The biennial timing of the meetings was suggested
because of the apparent stability of the stocks through the early 1990’s. The inclusion of discard data in more recent
assessments has, however, suggested that recruitment is more variable than previously thought, and the decline in some
stocks has lead to the provision of annual advice.
For stocks still assessed on a biennial basis, there remains the scope for considerable changes in the stock before
new advice is provided. This working paper investigates recent changes in Nephrops abundance data from TV surveys
of the stocks of interest to Scotland, conducted by FRS, paying particular attention to data collected in the summer of
1993, after the WG met.
New fishery independent TV survey data
TV surveys of the main Scottish Nephrops stocks are conducted on an annual basis, although a series of annual data
from all stocks is only available since 1998. Mean burrow density for each stock, and estimated total abundance for the
North Sea (Scottish stocks) and West Coast are provided in Figure 1 & 2 and Table 1 & 2.
North Sea (Area IV)
In the North Sea, three Functional Units (FU’s) are of importance to Scottish fisheries (Fladen Ground, Firth of Forth
and Moray Firth), and these are included in the FRS TV survey programme. Although there are a number other FU’s in
Area IV, these three contribute about 63% of the total North Sea Nephrops landings. Therefore, while the data presented
here cannot be considered to represent all the Area IV Nephrops stocks, it does represent almost two thirds.
Although higher than average values were recorded in 1993 and 1994, densities observed in the latter half of the
1990’s remained relatively stable. An increase in density was noted at the Fladen Ground in 2001, and this was
continued into 2002, when increases were also recorded in the Firth of Forth and Moray Firth. Data for the most recent
year shows a continued increase in these smaller areas, but a return to levels closer to the long term average for the
Fladen Ground. Average burrow densities for 2001-2003 are 17-21 % higher than those averaged over the period prior
to 2001 (Table 1).
For the North Sea Nephrops stocks of Scottish interest, the overall abundance figures are heavily influenced by
data for the Fladen Ground. Although the densities for this stock are generally low, the area over which the stock
extends is very large (nine time combined area of other two stocks surveyed). Total estimated Nephrops abundance
across the three North Sea FU’s included in the surveys has increased by 15% in recent years, compared to the period
prior to 2001 (Table 1). This observed increase in abundance, however, is likely to be related to an increase in recruits,
and will not be reflected in an increase in biomass of the same magnitude. It is not clear whether similar trends have
occurred in other North Sea Nephrops stocks, but the increase observed here is likely to result in increased catch rates
for these stocks.
WGNEPH Report 2004
314

West Coast (Area VIa)
The three FU’s contributing to Area VIa (North Minch, South Minch, Firth of Clyde) are all of major importance to
Scottish fisheries, and are therefore included within the FRS TV survey programme. Although in recent years the
reported landings for the area from outside the FU’s have increased, they remain <4% of the total, and the data provided
here therefore represent the vast majority of the Area VI Nephrops fishery.
During the 1990’s the TV surveys showed a relatively stable density, with levels observed since 2000 at the higher
end of the range (Figure 2, Table 2). Inclusion of the most recent data collected since the 2003 ICES Nephrops WG,
reinforces the impression that Nephrops abundance is currently at a higher level than observed in the 1990’s (Figure 2).
Data for the South Minch suggests density has stabilised at a higher level, while data for the North Minch and Firth of
Clyde show a trend of increasing density. Average burrow densities for 2001-2003 are 32-43 % higher than those
averaged over the period prior to 2001 (Table 2).
Total estimated Nephrops abundance across West Coast FU’s has increased by 30% over the same period (Table
2). As with the North Sea, this observed increase in abundance would not be wholly reflected in an increase in biomass.
It does appear quite clear, however, that overall abundance has increased, and catch rates would also be expected to
increase.
Recent anecdotal reports also suggest that activity and landings may be greater in the ‘Other rectangles’ area (in Area
VI but outside FU’s) than reported, and possibly expanding. Increases in Nephrops abundance have also been observed at
the Stanton Bank (an area outside FU’s) and therefore increased landings might also be expected from this area.
Underwater TV observations were carried out in 2000 and 2002 on the shelf edge to the west of the Hebrides and Nephrops
burrow densities were found to be low. The area over which Nephrops are distributed in this area is uncertain but potentially
large, and if the fishery in this area develops further, a re-examination of the ‘Other rectangles’ allowance in relation to the
deep water stocks may also be appropriate. At present the underlying dynamics of the offshore populations are not yet
well understood however, and further investigations are required before anything other than modest increases are
introduced.
Conclusions
Underwater TV survey results suggest substantial increases in the abundance of Nephrops in the northern North Sea
(15%) and off the West Coast of Scotland (30%) in recent years. Although this increase in abundance will not be totally
reflected in increased biomass, higher catch rates would be expected, leading to increased catches for the same effort.
The advised and adopted TAC for the North Sea has increased over a number of years, through adoption of a new
approach for advice provision at the Fladen Ground, and increased opportunity in expanding fisheries elsewhere.
However, while the advice for Nephrops on the West Coast has not changed, the TAC has decreased. This reduction in
TAC, in conjunction with higher catch rates, will almost certainly lead to increased discarding or under-reporting. A
TAC figure in line with availability would be more appropriate, and should be seriously considered.
The relatively rapid increase in abundance observed from the TV surveys would suggest that Nephrops stock
trajectories may not be as stable as in previously assumed. These assumptions were often based on analytical
assessments excluding annual discard data, and therefore may have considerably underestimated inter annual variability
in recruitment. Given the levels of variability currently observed, routine assessment and advice provision on an annual
basis may be more appropriate than the current biennial programme for most stocks.
WGNEPH Report 2004 315

Table 1. Table of average burrow densities for the Area IV FU’s of Scottish interest, and estimated total abundance for
period 1992-2003. Average values for the periods 1992-2000 and 2001-2003 are also provided, along with % increases
observed.
Average burrow density
Year FL FF MF
Abundance
(millions)
1992 0.17
1993 0.21 0.72 0.19 7080
1994 0.3 0.58 0.39 9708
1995 0.24
1996 0.48 0.26
1997 0.13 0.14
1998 0.18 0.38 0.18 5917
1999 0.2 0.6 0.22 6627
2000 0.17 0.57 0.212 5888
2001 0.23 0.54 0.19 7636
2002 0.29 0.66 0.29 9447
2003 0.21 0.80 0.32 7331
1992-2000 0.20 0.56 0.23 7044
2001-2003 0.24 0.67 0.27 8138
% increase 21.54% 20.30% 17.48% 15.53%
Table 2. Table of average burrow densities for the Area VIa FU’s and estimated total abundance for period 1994-2003.
Average values for the periods 1994-2000 and 2001-2003 are also provided, along with % increases observed.
Average burrow density
Year NM SM CL
Abundance
(millions)
1994 0.38
1995 0.30 0.33
1996 0.25 0.38 0.54 3497
1997 0.28 0.68
1998 0.41 0.38 0.72 4146
1999 0.32 0.23 0.43 2607
2000 0.41 0.37 0.63 3890
2001 0.39 0.44 0.66 4287
2002 0.49 0.42 0.73 4497
2003 0.64 0.42 0.83 4981
1994-2000 0.35 0.32 0.56 3535.00
2001-2003 0.51 0.43 0.74 4588.40
% increase 43.17% 32.59% 33.11% 29.80%
WGNEPH Report 2004
316

0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1990 1992 1994 1996 1998 2000 2002 2004
Average burrow density
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
Total abundance (millions)
FL
FF
MF
TOT
Figure 1. Plot of average burrow density for Area IV FU’s and estimated total abundance for period 1994-2003.
0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1
1993 1994 1995 1996 1997 1998 1999 2000 2001 2002 2003 2004
Average burrow density
0
500
1000
1500
2000
2500
3000
3500
4000
4500
5000
Total abundance (millions)
NM
SM
CL
TOT
Figure 2. Plot of average burrow density for Area VIa FU’s and estimated total abundance for period 1994-2003.
WGNEPH Report 2004 317

1
The International Council for the Exploration of the Sea
Working Document
Preliminary Results of the joint MI-DARDNI
UWTV Survey on the Western Irish Sea
Nephrops Grounds.
By
Colm Lordan, Jennifer Doyle and Richard Briggs
RV Lough Foyle 18th to 22nd August 2003
RV Lough Foyle 1st to 5th September 2003
RV Celtic Voyager 15th to 27th September 2003
Marine Fisheries Services Division,
Galway Technology Park, Parkmore, Galway, Ireland
E-mail: colm.lordan@marine.ie
Web: www.marine.ie
Working Group on
Nephrops
Stocks
Lisbon Portugal, 29 March-
1 April 2004
Not to be cited without prior reference to the authors

2
Introduction:
The Norway lobster, Nephrops norvegicus, is exploited throughout its
geographic range, from Icelandic waters to the Mediterranean and the Moroccan
coast. The western Irish Sea stock is by far the most productive of all the Nephrops
stocks currently fished yielding landings of between 7,000-10,000 tonnes annually
from a relatively small geographic area (ICES, 2003). The western Irish Sea
Nephrops stock is fished by around 50 vessels from the Republic and around 160
vessels from Northern Ireland (ICES, 2003). Nephrops landings by Irish vessels from
the Irish Sea were worth approximately € 11.1 m at first sale in 2002. There is also a
lucrative processing industry for Nephrops both in the Republic and in the North.
Nephrops stock collapse in other areas has meant that this resource requires
careful assessment and management to ensure future sustainability (Anon, 2001).
Stock assessment is currently carried out of several of the stocks using commercial
fisheries catch and effort data to tune the VPA assessments. The Marine Laboratory
in Aberdeen developed fishery independent tuning datasets using underwater
television (UWTV) surveys to estimate stock size from burrow densities (Bailey et
al., 1993; Marrs et al., 1996; Froglia et al., 1997; Tuck et al., 1997). This method was
pioneered in Scotland and has now been applied elsewhere (Farn Deeps, Adriatic).
The ICES Advisory Committee for Fisheries Management (ACFM) have
recommended that TV surveys should be used to provide biomass estimates for non-
assessed and poorly assessed stocks. The method has great potential, and given the
economic importance of Nephrops stocks to Ireland, it is important that survey series
are developed for the stock exploited by Ireland.
In recent years the Fladden UWTV Nephrops surveys have be used by ACFM
to give a new ‘type’ of management advice for Nephrops. This advice based on
harvest ratios rather than deterministic forecasts from an analytical assessment. The
recommended TAC is in line with a precautionary harvest ratio of the estimated stock
size i.e. the UWTV estimate of stock size is 10000 t the fishery can safely harvest
1,000 t. This type of approach is particularly relevant stocks around Ireland where a
historical time series of data for full analytical assessments either do not exist or of
dubious quality.
During an UWTV surveys a sledge-mounted TV system is towed slowly
across the sea bed. The numbers of Nephrops burrows are counted and these data are
used to estimate a mean density for a stock. A mean weight (based on known
relationship with mean animal size and size structure of the Nephrops in the stock) is
then used to calculate abundance and stock biomass. Trawling is also normally
conducted to examine biological features at different sites. The survey technique is
reliant on good underwater visibility for accurate identification and counting of
Nephrops burrows. The UWTV footage can also be used for ancillary purposes such
as habitat mapping and to assess the effects of trawling activity on the benthos.
Background to 2003 Irish Sea survey:
In a fisheries context the Irish Sea Nephrops supports the majority of fishing
vessels operating in the Irish Sea and as such is of considerable socio-economic
importance. The Irish Sea Nephrops stock has been routinely assessed using an

3
analytical VPA approach. The reliability of this approach is increasingly been
questioned and it has never been considered a good enough basis for short-term
deterministic catch forecasts that can be used by managers to set a TAC. Recently,
the Department of Agriculture and Rural Development Northern Ireland (DARDNI)
have also estimated stock size using an egg production method. The results were
broadly inline with the VPA point estimates of stock size (Briggs et. al, 2002). A
second fishery independent method (i.e. the UWTV) offers another opportunity to test
a VPA estimate of stock size and may in itself be a more robust estimator of stock
size.
The Marine Institute carried out the two Nephrops UWTV surveys of the
Outer Galway Bay and Aran fishing grounds in June/July of 2002 and 2003 using RV
Celtic Voyager. As a result of these surveys the Marine Institute decided to extend
the survey programme into the Irish Sea in co-operation with the Department of
Agriculture and Rural Development Northern Ireland. This joint survey was planned
in three legs on RV Celtic Voyager and RV Lough Foyle in August September 2003.
The primary objectives are listed below.
Specific Objectives:
1. Technology and protocol transfer between Marine Institute and Department of
Agriculture and Rural Development Northern Ireland.
2. To develop a fishery independent survey to produce a relative index for the
Nephrops stock.
3. To develop a fishery independent survey to a biomass estimate for the
Nephrops stock.
4. To map the Irish Sea Nephrops grounds.
5. To gather data on the abundance, distribution and patchiness of Nephrops
burrows in the Irish Sea.
6. To collect secondary data on the seabed in the Irish Sea using benthic grabs
and multibeam.

4
Scientific Personnel List:
Leg 1: RV Lough Foyle 18th to 22nd August 2003
Dr. Richard Briggs DARDNI SIC
Dr. Colm Lordan MI
Jennifer Doyle MI
Michael McAliskey, DARDNI
John Peel, DARDNI
Gerrard Curran ANIFPO Observer
Leg 2: RV Lough Foyle 1st to 5th September 2003
Dr. Richard Briggs DARDNI SIC
Dr. Colm Lordan MI
Jennifer Doyle MI
Peter McCorriston, DARDNI
John Peel, DARDNI
Leg 3: RV Celtic Voyager 15th to 27th September 2003
Dr. Colm Lordan MI SIC
Jennifer Doyle MI
Dr. Richard Briggs DARDNI (15-21st)
Peter McCorriston, DARDNI (22-27th)
Ayesha Power MI
Ross Fitzgerald MI
Gerry Sutton CRC/UCC (15-21st)
Gerrard Curran ANIFPO Observer (22-27th)
Survey Area:
The Western Irish Sea Nephrops stock occurs in an area of sandy muddy
sediment. Figure 1 is a map interpolating existing DARDNI sediment data in an
attempt to map this area. It was decided that a regularly spaced grid would be the
most appropriate for post survey geostatistical analysis of the results. The primary
survey stations where the sledge was deployed are indicated on Figure 2. The stations
are at approximately 3.5 nautical mile intervals along a transect 3.5 nautical miles
apart. Stations were added in an adaptive way to ensure that the boundaries of the
ground were surveyed. In addition some stations were moved slightly because of
fishing activity or other external information i.e. information from industry or RV
officers on locations of fast and or obstacles.

5
6.4 6.0 5.6 5.2 4.8
Longitude (decimal °W)
53.5
54.0
54.5
L
a
t
i
t
u
d
e
(
d
e
c
i
m
a
l
°
N
)
Dublin
Belfast
I.O.M
North Channel
Figure 1: Map of Western Irish Sea sediment data (contours represent % sediment
<63µm).

6
53°24 N
53°36 N
53°48 N
54°00 N
54°12 N
54°24 N
54°36 N
06°00W 05°30W 05°00W
Figure 2: Distribution of the UWTV Stations in Western Irish Sea Nephrops survey
2003. (Leg 1, 2 and 3 stations are indicated with green, red and yellow dots
respectively. Stations where the sledge was deployed but no counts were possible are
indicated with an ‘x’ symbol)

7
Materials and Methods:
Towed Sledge and UWTV Equipment
The towed sledge used during the survey on RV Lough Foyle is described in
Service and Golding (2002). The sledge and main equipment used during the survey
on RV Celtic Voyager is listed below and shown in Figure 3:
Marine Institute UWTV Benthic sledge
1 OE14-108 Underwater Digital Stills Camera
1 OE11-142 Underwater Flashgun
1 OE1366-MK II Underwater Video Camera (supplied by Kongsberg-SIMRAD)
4 OE11-135 Miniature Underwater Lamp
2 OE1232 Control Unit
1 500 Metre NC 13 Cable
1 300 Metre NC 13 Cable
1 10 Metre Test Lead NC 13 Cable
DVDs
DVD Recorder
DVD Player
2 Monitors
In addition a GPS-Video encoded recording and processing system supplied by Blue
Glen Ltd. was set up in the dry laboratory during the survey.
Figure 3: The Marine Institute UWTV sledge ready for deployment in the Irish Sea
on RV Celtic Voyager September 2003.

8
Deployment and Towing of the Sledge
Sledge deployment on RV Lough Foyle was described in Service and Golding
(2002). The sledge was deployed and towed on RV Celtic Voyagers port trawl drum
using 10mm non-rotating transducer armoured cable (Figure 3). The amount of cable
shot was quantified using a mechanical cable meter, which served as the towing
block. The umbilical cable (yellow cable in Figure 3), which is non-load bearing, was
paid out manually as the warp was shot. Every 10 m the umbilical was secured to the
transducer cable using cable ties.
RV Celtic Voyager was making between 2-3 knots for shooting into the
weather. Once in the water the camera lights were switched on and warp was paid out
until the seabed came into view. Shortly before touch down the vessel was slowed
back to 0.8-1.0 knots. A warp-depth ratio of around between 1.4:1 and 1.8:1 was used
at most stations. Once stable on the bottom the sledge was towed at between 0.8-1.0
knots for around 10-14 minutes.
Video Methodology
The same methodology was employed on both research vessels. Once the
sledge was stable on the bottom video recording on to DVD disk. Start times,
positions and depth were recorded on the data sheet shown in Appendix 1. Positional
data from the ships GPS were logged using the HyperTerminal software and
summarised binned every 5 seconds using a specifically written MS Excel macro.
Two scientists made preliminary counts the Nephrops and their burrows observed
passing off the bottom of the screen during the 10-14 minute run. Feedback was
given to the officer on watch and the deck crew throughout the run. Warp out and
speed were adjusted as necessary to obtain the best possible conditions for counting
burrows. In addition at selected stations footage was captured using the GPS-Video
encoded recording and processing system supplied by Blue Glen Ltd.
Analysis of UWTV Burrow and Nephrops Count Data
Recounts were conducted by two experienced scientists independent of each other.
During this review process the visibility, ground type and speed of the sledge during
one-minute intervals were subjectively classified using the classification criteria in the
text table below. In addition the numbers of Nephrops burrows, Nephrops in and
Nephrops out of burrows counted by each scientist for each one-minute interval was
recorded. Notes were also made on the occurrence of trawl marks, fish species and
other species during the one-minute interval. Finally, if any there was any time
during the one-minute were counting was not possible this was also estimated.
The resultant recount data was screened for any one minute intervals with an
unusually large deviation between recounts. Means of the burrow and Nephrops
recounts were standardised by dividing by the area observed. This area was
calculated by multiplying the Distance over Ground (DoG) by the length of seabed
viewed at the bottom of the screen with the sledge flat on the seabed underwater
(assuming no sinking into the seabed). The DoG of the sledge was estimated as

9
approximately the same as that of the vessel this distance was calculated at one
minute intervals for the duration of the UWTV recording using the MS Excel macro.
Visibility Ground Type Speed
Excellent Very Soft Mud Stopped
Good Mud Slow
OK Sandy Mud OK
OK-Poor Shelly Mud Fast
Poor Sand Gliding
Very poor Gravely-sand Jumpy
Nil Gravel Variable
Stones Good
Rock
Shelly Sand
Collection of Multibeam data
Data on the Nephrops stations surveyed was collected at many of the UWTV stations
using the Kongsberg Simrad EM1002 multibeam on RV Celtic Voyager. Although
the multibeam was not calibrated regularly during the survey a previous calibration
file was used and the sound speed at transducer, temperature and salinity were
adjusted regularly. The multibeam was primarily used to identify obstacles on the sea
bed before sledge deployment and to monitor speed, course and DoG while carrying
out UWTV stations. No Roxanne data were collected on either vessel.
Sediment sampling
Samples of seabed sediment from the top 10 cm of the seabed were collected
at each UWTV station for granulometric analysis during the survey. These samplese
were obtained using a Day-Grab on RV Lough Foyle and the Reineck Box-Core on
RV Celtic Voyager. Samples were labelled and frozen for analysis at a later stage.

10
Preliminary Results and Discussion:
This was the first systematic UWTV survey of the Western Irish Sea Nephrops
grounds. The survey was very successfully completed on both the RV Celtic Voyager
and Lough Foyle involving scientists, equipment and protocols from both DARDNI
and MI thus achieving the first objective. The leg on RV Celtic Voyager offered the
opportunity to test new technology (i.e. the GPS-Video encoded recording and
processing system) in conjunction with Gerry Sutton of CRC–UCC. The survey was
also an important training exercise where scientists were trained in the use of UWTV
equipment, burrow recognition and survey protocols.
Data and UWTV footage required for objectives 2-5 were collected at 192
individual UWTV station as shown in Figure 2. The stations cover the entire
distribution of the stock at reasonably regular intervals and also extend beyond the
distribution thus making it possible to identify the stock boundary. Data and UWTV
footage required for objectives 2-5 were collected at 192 individual UWTV stations
shown in Figure 2. Video footage was obtained for an estimated total of 35,851m2
during the survey. A total of 32.8 hours of footage was collected.
Approximately 80% was classified as having OK-Poor or better visibility
(Table 1). Only those minutes classified with having OK-Poor or better visibility was
used further in the analysis. Counts made in poor or worse visual conditions were
deemed unreliable since burrow identification became uncertain. Similarly all those
one-minute intervals with more than 30 uncountable seconds were excluded form
further analysis (Table 2). Burrow counts were adjusted for the stations with between
1-29 uncountable seconds to reflect the total number of burrows that may have been
seen if all 60 seconds were countable. The result was that usable video footage was
obtained for 27,566m2.
Table 1: The visual clarity and percentage of the area surveyed.
Visibility Percentage of area
Excellent 5
Good 26
OK 45
OK-Poor 4
Poor 14
Very poor 1
Nil 3
Not Clasified 3
Table 2: The numbers of one minute intervals with uncountable seconds.
Uncountable
Seconds Number of
Minute intervals Percentage
0 1584 80
1-29 185 9
30-59 53 3
60 147 7

11
In terms of quality of the UWTV footage it became obvious for the outset that
visibility near the seabed is not as good as on the Aran grounds. The strong tides, fine
sediment and fishing activity meant that often there were considerable amounts of
suspended material in the water near the sea bed. Having said that repeat tows were
made a 27 (14%) of stations often with much improved visibility and no counts were
made at only two stations because of poor visibility. Future surveys should however
be planned carefully around periods of slack tides.
There was reasonable agreement between recounts made by the two
independent counters with some evidence of a systematic bias at larger burrow
densities (Figure 4). The distribution of burrow densities from these recounts on
usable footage are shown in Figure 5. Nephrops were widespread all over the western
Irish Sea. However there are observable patterns to this distribution which might be
investigate in relation to other parameters such as sediment and hydrography.
Extremely high densities were observed on the southwestern part of the grounds.
Overall these preliminary densities are significantly higher than those observed by all
previous UWTV surveys on other Nephrops grounds. A frequency distribution of the
preliminary burrow densities is presented in Figure 7. This indicates a modal
distribution around 1.6-2.0 burrow systems per meter squared. This grounds has
yielded substantial reported landings of around 8,000 t over the last 10 years from a
relatively small area. The UWTV survey seems to confirm the Nephrops occur at
higher densities than in other areas.
0
100
200
300
400
500
600
700
800
900
0 200 400 600 800 1000
JD Station Counts
CL Station Counts
Figure 4. A scatterplot of the recounts made for each station by two burrow counters
independently. The solid red line indicate a 1-1 relationship the dotted line is a fitted
linear regression.

12
53°24 N
53°36 N
53°48 N
54°00 N
54°12 N
54°24 N
54°36 N
06°00W 05°30W 05°00W
Nephrops Burrow
Density no/m2
0.00 1.71 3.42 5.12
Figure 5: Station positions (+) and preliminary Nephrops burrow densities based on
live counts.

13
0
5
10
15
20
25
0
0.4
0.8
1.2
1.6
2
2.4
2.8
3.2
3.6
4
4.4
4.8
5.2
Burrow Density (No/m2)
Numbers of stations
Figure 5: A frequency distribution of the preliminary Nephrops burrow densities
based on live counts.
A very rough estimate of the total area covered by this survey was around
5,791 km2. The total numbers of burrows counted during the survey could be raised
to this area to give an estimate of the total number of individual burrows in the
western Irish Sea. Assuming 100% burrow occupancy (as has been done in other
areas) the total number of Nephrops in the western Irish Sea was estimated to be
around 8.9 billion individuals. This is approximately 75% higher than the average
population numbers between 1997-2002 from the XSA carried out by WGNEPH
2003. Assuming a mean weight of 12.0±2.0 gr (the mean weight from the August
2003 DARDNI Nephrops trawl survey) the total biomass of Nephrops in the western
Irish Sea would be estimated to be (102KT). This is significantly higher the combined
male female biomass estimate from recent XSA assessments (~35KT) suggesting that
the mean weight is not entirely appropriate. There are a number of assumptions in
both the XSA and UWTV which will have a significant bearing on these results. In
addition the estimate of surveyed area should be improved. The results here should be
considered very preliminary.
The final objective involved the collection of ancillary data including
multibeam data and samples of the sediment at each UWTV station. On RV Celtic
Voyager the multibeam was running almost continuously throughout the survey and
proved to be a useful tool in evaluating the seabed before camera deployment.
Multibeam data were collected on many but not all of the UWTV stations completed
in leg 3 on RV Celtic Voyager. Garb samples for granulometric analysis were
obtained at 194 stations during the survey. These samples will be sent for lazer
particle size analysis in the near future so that the relationship between Nephrops
burrow density and sediment type can be investigated.

14
Overall this joint MI-DRADNI survey proved very successful although further
analysis of the data and samples is required. It is expected that the full results will be
submitted for publication in a peer review journal in the interim further information
and a DVD containing some of the footage collected is available from the authors.
Acknowledgements:
The authors would like to acknowledge the invaluable contributions of all those who
made this survey a success. Firstly, thanks to the master (Ray Lavery) and the crew
of RV Celtic Voyager and the master (Andrew Niblock) and the crew of RV Lough
Foyle. Thanks to all the scientists and the ANIFPO observer listed in the text for their
extremely hard work throughout the survey.
Thanks to Mike Armstrong, Michelle Allen, Bill Clake and Matt Service for advice
on survey design and help with survey equipment. Thanks to Paul Connolly
(Fisheries Science Services Director MI) and Ivan Heany (Head of Aquatics Section
DARDNI) who agreed to fund this ambitious survey. Thanks to the Marine Institute
RVOPs team in particular John Breslin and Conor Mowlds who helped with the
logistics and Diplomatic clearance. Thanks to Barry Kavanagh the MTDS shore team
for their excellent work in particular to Pat Myer and Bill Dwyer.
References:
ICES (2002). Report of Working Group on the assessment of Nephrops stocks. ICES
CM 2002/ACFM:16 (www.ices.dk).
ICES (2003). Report of Working Group on the assessment of Nephrops stocks. ICES
CM 2003/ACFM:16 (www.ices.dk).
Bailey, N., Chapman, C.J., Kinnear, J. Bova, D. & Weetman, A. (1993). Estimation
of Nephrops stock biomass on the Fladen ground by TV survey. ICES CM
1993/K:34.
Briggs, R.P., Armstrong, M.J., Dickey-Collas, M., Allen, M., McQuaid, N. and
Whitmore, J. 2002. The application of fecundity estimates to determine the
spawning stock biomase of Irish Sea Nephrops norvegicus (L.) using the
annual larval production method. ICES Journal of Marine Science, 59: 109-
199.
Froglia, C., Atkinson, R.J., Tuck. I. & Arneri, E. (1997). Underwater television survey,
a tool to estimate Nephrops stock biomass on the Adriatic trawling grounds.
In: Tisucu godina prvoga spomena ribarstva u Hrvata (ed. B. Finka). Hrvatska
Akademija Ananosti i Umjetnosti, Zagreb 1997.
Marrs, S.J., Atkinson, R.J.A., Smith, C.J. & Hills, J.M. (1996). Calibration of the
towed underwater TV technique for use in stock assessment of Nephrops
norvegicus. Report to the EC for Study Project in support of the CFP,
94/069. 155pp.
Service, M., and Golding, N. (2002). Procedural Guideline No. 3-14 In situ survey of
sublittoral epibiota using towed sledge video and still photography, Marine

15
Monitoring Handbook, pp. 331-337. Department of agriculture and rural
development Northern Ireland, Belfast.
Tuck, I.D., Chapman, C.J., Atkinson, R.J.A., Bailey, N. & Smith, R.S.M. (1997). A
comparison of methods for stock assessment of the Norway lobster,
Nephrops norvegicus, in the Firth of Clyde. Fish. Res., 32:89-100.

APPENDIX 4
Working Document to WGNEPH, March 2004
A Review of Western Irish Sea Nephrops Assessment (FU 15)
Colm Lordan
Marine Institute Ireland
Methods
The assessment methods currently applied by the WGNEPH on the Western Irish Sea Nephrops are:
(1) The analysis of long-term trends in fishery data (landings, effort, CPUE, LPUE, mean sizes of Nephrops by sex in
catches <35 mm, and in landings < 35 mm and >35 mm).
(2) A separate sex age-based XSA assessment tuned using two commercial fleets, applied to “pseudo-age groups”
obtained by slicing the length compositions of the removals. Total removals were calculated as landings plus 90 %
of the discards, assuming a discard survival of 10 %.
(3) Age structured yield-per-recruit analyses based on the inputs and output of the XSA.
Multiple lines of evidence from the above analysis are then used to formulate management advice. To date the advice
has been average landings as the stock “appears to be exploited at sustainable levels”. Short-term predictions have been
investigated but not used up to now to give advice as their reliability is still under investigation. However in recent
weeks the results of the separate sex assessments XSA for Western and Eastern Irish Sea have been used in a mixed
fisheries forecast using the MTAC model.
Previously the WG used Length Cohort Analysis (LCA) as an assessment tool. However, the steady-state
assumptions may no be met and the method gives no information on recruitment over-fishing so the WG no longer use
this method where and XSA assessment is considered reliable.
Landings statistics
Landings data are provided for the Irish Sea by Functional Unit by Ireland, UK England & Wales, UK Northern Ireland,
UK Scotland, UK Isle of Man, France and Belgium. These data are extracted directly for the database containing EU
logbook data of the various nations. Landings data are not corrected for misreporting. The accuracy of these data has
not been investigated however given the nature of the fishery where a large proportion of the catch is landed, as tails
there are probably opportunities to misreport landings. Data are available since 1986 to the present. The homogeneity
raising factors used by various countries have not been investigated.
Discards
Discards are included in this assessment. There is an assumption that a fixed proportion (10%) of the discards survive.
The Nephrops Study Group comprehensively reviewed the sampling procedures used by different countries (ICES,
1996). The same sampling methodology is employed Northern Ireland and Ireland which involves sampling unsorted
catch and sampling small discarded Nephrops and heads of landed Nephrops to generate a discarding ogive. This ogive
is then applied to the catch length frequency data to generate landed and discarded component length frequencies.
Sampling rates have been relatively high discards ogives and rates appear to be stable over time but precision estimates
of discard rates and frequencies are not available.
Sampling protocols for Length and for Age
The length frequency distributions of Nephrops catches, landings and discards were obtained from samples taken at sea
on commercial vessels or by in a self sampling procedure. Details of sampling and raising procedures are described in
the 1996 Nephrops SG report (ICES, 1996). Detailed protocols are available for both Ireland and Northern Ireland
(Lordan & Doyle, Marine Institute Protocols Document and Briggs DARDNI Protocols Document). Precision
estimates length frequencies data are not available.
WGNEPH Report 2004 333

Fixed length-weight parameters are used to derive the weight of the landed and discarded components of the catch.
These parameters were estimated from data for Scottish stocks (Pope and Thomas 1955). No precision estimates are
available.
In the absence of routine methods of direct age determination in Nephrops, age compositions of removals were
inferred from length compositions by means of ‘slicing’. This procedure, introduced at the 1991 WG, uses von
Bertalanffy growth parameters to determine length boundaries between age classes. All animals in length classes
between boundaries are assigned deterministically to the same age class. The method is implemented in the L2AGE
programme which automatically generates the VPA input files. The programme was modified in 1992 to accommodate
the two-stage growth pattern of female Nephrops (ICES, 1992) and again in 2001 to separate ‘true’ as opposed to
‘nominal’ age classes (ICES, 2001). The age classes are ‘true’ to the extent that the first slicing boundary, i.e. lower
length boundary
for ‘age’ 0, is the length-at-age zero rather than the lowest length in the data. This ensures comparability of ‘age’
classes across stocks. Mean weights at age are also calculated in the programme. The von Bertalanffy growth
parameters used are from Hillis (1979) the appropriateness of these has not been investigated in recent years and no
precision estimates are available.
Commercial CPUEs and their derivation
Commercial CPUE data are available for Ireland (1995-2002) and UK Northern Ireland (1984-2002). Both effort data
sets are for Nephrops directed fishing only. These are not particularly well standardised or described. The Irish fleet
effort and catch is only for vessels where Nephrops accounted for over 35% of the total daily landings. These vessels
were considered to be ‘targeting Nephrops’ on that day. These vessels account for over 95% of the total Irish Nephrops
landings from FU 15 in most years. The Northern Irish vessels effort and catch data are for vessels using a ‘Nephrops
trawl’. There is anecdotal evidence of increased efficiency of the Irish and Northern Ireland fleets in recent years with
more efficient vessels, improved gears and technology. Neither data set is corrected for this.
Age structure of the commercial fleets is derived using the same parameters and programme (L2AGE) as the catch
at age matrix.
Surveys' protocols and construction of indices
Survey data are not used in the assessment. Northern Ireland has conducted a directed Nephrops fishing survey for
around 10 years. These data are not used to tune the assessment due to concerns about variability in catches due to tidal
and deil factors. Ireland also conducted a directed Nephrops fishing survey for several years but similarly these data
were not used in the assessment. Various biological data including recruit size structure, maturity, disease prevalence,
emergency activity, sex ratio, etc. are used from these surveys in biological studies.
Other survey methods are currently under investigation. A female SSB estimates from an egg production survey
was found to be similar with the XSA estimates in 2000. In 2003 Ireland and Northern Ireland successfully conducted a
joint Underwater Television (UWTV) survey of the Western Irish sea Nephrops grounds. This method has been used
with very promising results in several in other areas. The results of the 2003 survey are not finalised yet.
Biological data (with the same items as in the Table)
Maturity
Female maturity data are routinely collected during catch sampling as the female component of the catch is staged when
sampled. However, knife-edge maturity at 24 mm as a fixed vector is used in the XSA assessment. In the male
assessment 100% maturity is assumed. The sensitivity of the assessment to this approach has not been investigated.
Weight at age
Weight sampling is not routinely carried out. Fixed parameter are used in the L2AGE programme to calculate catch
weights and stock weights. These parameters were estimated from data for Scottish stocks (Pope and Thomas 1955).
Natural Mortality
A fixed natural mortality vector is used in the XSA assessment; 0.3 in Females and 0.2 in males (Brander and Bennett
1986, 1989). Natural mortality may have declined in recent years as the cod stock (one of the main predators of
Nephrops in the Irish Sea) has declined. No new estimates of M have been made.
WGNEPH Report 2004
334

Migration/mixing
There may be a very minor amount of mixing with the neighbouring FU 14 stock at the larval stage. However once the
juveniles settle on the seabed they are not thought to move very far during their lifetime. It is general thought that adult
Nephrops movements would be in the order of 10-100 m only.
Stock ID
Although there have not been detailed genetic structure of this Nephrops stock. The discrete nature of the
stock on sandy/muddy ground means the stock boundary is very well defined.
Environmental data
There is a gyre in the western Irish Sea and this is thought to limit the dispersion of larval Nephrops during their 3-week
pelagic phase after hatching. This retention mechanism has been studied extensively. The distribution of the sand and
mud in which the Nephrops make their burrows has also been investigated.
Mixed fishery Interactions
The Nephrops fishery has a major impact on the Irish Sea whiting stock. There is considerable discarding of juvenile
whiting in the fishery as the distribution of Nephrops overlaps with a whiting nursery area. By-catches of other species
in the fishery are not as large. The recent implementation of the MTAC model with mixed fishery data for the western
Irish Sea allows the formulation mixed fisheries management scenarios to be evaluated.
Conclusion on the performance of recent assessments.
The approach of WGNEPH is to draw on multiple lines of evidence to gain an appreciation of stock status and the
direction of stock trends rather than being based on the quantitative output of analytical assessments. Given the tentative
nature of some of the input data the WGNEPH consider it inadvisable to treat the terminal estimates from XSA as a
quantitative basis to derive catch options. In recent years the catch advice is given in line with recent landings for this
stock.
A retrospective analysis for this assessment was carried out for the first time in 2003. Because one of the tuning
series was short it was only possible to run the analysis for the last four years (Figure 1 and 2). There is no real
evidence of retrospective bias although there is relatively large revision in F and recruitment estimates from year to
year. Quality control sheets are not routinely provided by WGNEPH. The assessments are carried out every two years
rather than annually so the QCDs data are more sparse than normal. In Figure 3 and 4 the QCD data for the last four
assessments are plotted. There have been revisions to the landings data between the 1999 and 2001 resulting in an
upward revision of SSB and recruitment levels for both sexes. The 2003 and 2001 assessments show some divergence
compared with previous assessments this probably because in 2003 more consideration was given to the XSA settings
where as previously all the defaults were used. Given the short nature of both the retrospective and QCD data sets
meant that it was not possible to apply the Jónsson and Hjörleifsson metrics to quantify both the bias and uncertainty of
the retrospective patterns.
The length frequency data used in this assessment includes discards and is considered to be of good quality. There
are some concerns about the quality of all the other input data. Although multiple lines of evidence are used by the
ACFM to justify their advice the data used are not independent and wholly fishery dependent. For example the CPUE
trends observed are also used in the XSA tuning and these may give biased perception due to increased efficiency.
Fishery independent data such as those from UWTV surveys may be a better basis to give management advice for
Nephrops.
Overall the XSA assessment appears to give a fairly consistent picture of stock trends. However there are major
concerns about the applicability of the method to a species where the age structure of the population is not directly
estimated. The slicing may act as a smoother through the age structure possibly explaining the relatively stable trends
in recruitment and biomass observed in the results of the XSA. If this is the case the method may not be sensitive to
sudden changes in the recruitment and the S/R relationship may not be accurate. To date WGNEPH have not proposed
biomass reference points for Nephrops because of these concerns.
WGNEPH Report 2004 335

Checklist : Nephrops in the Western Irish Sea FU 15.
1. General
step Item Considerations
1.1 Stock definition The stock is distributed in a well know patch of suitable sand and mud
sediment in the western Irish Sea. Catches ICES Rectangles 36E3; 35-37
E4-E5; 38E4 or FU 15 are all considered to be from this stock. The are other
stocks in adjacent areas FU 14 Eastern Irish Sea and FU 13 the Clyde.
1.2 Stock structure Nephrops are burrow dwelling and territorial and not thought to migrate
far from their burrows during their lifetime. A gyre is know to retain
larvae over the mud patch although there may be some minor advection
to other areas at the larval stage.
1.3 Single/multi-species Single species and separate sex XSA assessments are conducted every
two years.
2. Data
step Item Considerations
2.1 Removals: catch, discarding,
fishery induced mortality
Landings data come from the official statistics. The discard component
are estimated from self sampling schemes and observer trips and
are included in this assessment. There is an assumption that a
fixed proportion (10%) of the discards survive
2.2 Indices of abundance
Catch per unit effort Data available on commercial CPUE from UK Northern Ireland and Irish
Nephrops directed trawlers are used in the assessment.
Gear surveys (trawl, longline) UK Northern Ireland conduct a trawl survey annually in August. This
survey is not used to tune the assessment due to highly variable catch
rates related to the emergence patterns of Nephrops from their Burrows.
A trawl survey series was discontinued by Ireland in 2000
Acoustic surveys N/A
Egg surveys N/A
Larvae surveys A larval survey was used experimentally in 1995 to estimate the female
biomass (Briggs et. al 2002)
Underwater Television Survey An underwater television survey was conducted for the first time in
August-September 2003 the results are currently being analysed and
should also produce a fishery independent biomass estimate (Lordan et al
in prep.)
2.3 Age, size and sex-structure:
catch-at-age,
weight-at-age,
Maturity-at-age,
Size-at-age,
age-specific reproductive
information
Routine age estimation is not currently possible for Nephrops. Historical
growth parameters are used to estimate age structure from length-
frequency data Hillis (1979). Mean weights are derived from fixed
parameters. Female maturity data are routinely collected during catch
sampling as the female component of the catch is staged when sampled.
However, knife-edge maturity at 24 mm as a fixed vector is used in the
XSA assessment. In the male assessment 100% maturity is assumed.
2.4 Tagging information Limited historic information.
2.5 Environmental data The western Irish Sea gyre is thought to be a retention system for
Nephrops (Hill et all 1996).
2.6 Fishery information The majority of the landings are made by otter trawlers in a directed
Nephrops fishery. These vessels use single or twin trawls with either
70 mm mesh with a square mesh panel or 80 mm mesh. There are by
catches of finfish including whiting, plaice, haddock and cod. Effort for
these fleets is form EU logbook data.
WGNEPH Report 2004
336

Table 1.4.5 (Cont’d)
3. Assessment model
step Item Considerations
3.1 Age, size, length or sex-
structured model
Age-structured based on ‘sliced’ length compositions; XSA has been
used for routine assessment since 1997.
3.2 Spatially explicit or not Not
3.3 Key model parameters:
natural mortality,
vulnerability,
fishing mortality,
catchability
Fishing mortality and stock numbers at age
Recruitment From VPA
3.4 Statistical formulation:
- what process errors
- what observation errors
- what likelihood distr.
VPA-based approach, so no real statistical formulation.
3.5 Evaluation of uncertainty:
- asymptotic estimates of
variance,
- likelihood profile
– bootstrapping
- bayes posteriors
No analytic estimates of variance.
3.6 Retrospective evaluation Introduced as part of assessment procedure in 2003.
4. Prediction model(s)
Step Item Considerations
4.1 Age, size, sex or fleet-structured
prediction model
No forecasts are carried out
4.2 Spatially explicit or not
4.3 Key model parameters
4.4 Recruitment
4.5 Evaluation of uncertainty
4.6 Evaluation of predictions
WGNEPH Report 2004 337

Figure 1. - Irish Sea West (FU 15): XSA diagnostics males: Retrospective analyses.
Recruitment
0
200000
400000
600000
800000
1000000
1200000
1400000
1600000
1800000
1980 1985 1990 1995 2000 2005
Recruits (thousands
)
Spawning Stock Biomass
0
5000
10000
15000
20000
25000
30000
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 3-5
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1980 1985 1990 1995 2000 2005
Fbar
WGNEPH Report 2004
338

Figure 2. - Irish Sea West (FU 15): XSA diagnostics females: Retrospective
analyses.
Recruitment
0
500000
1000000
1500000
2000000
2500000
1980 1985 1990 1995 2000 2005
Recruits (thousands
)
Spawning Stock Biomass
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
1980 1985 1990 1995 2000 2005
SSB (tonnes)
Fbar 3-5
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1980 1985 1990 1995 2000 2005
Fbar
WGNEPH Report 2004 339

Figure 3. - Irish Sea West (FU 15): QCD diagnostics males.
Recruitment
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
Recruits (thousands)
Spawning Stock Biomass
0
5000
10000
15000
20000
25000
30000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
SSB (tonnes)
Fbar 3-5
0.00
0.20
0.40
0.60
0.80
1.00
1.20
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
Fbar
Removals
0
1,000
2,000
3,000
4,000
5,000
6,000
7,000
8,000
9,000
10,000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 200 5
Removals (tonnes)
WGNEPH Report 2004
340

Figure 4. - Irish Sea West (FU 15): QCD diagnostics females.
Recruitment
0
200
400
600
800
1000
1200
1400
1600
1800
2000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
Recruits (thousands)
Spawning Stock Biomass
0
1000
2000
3000
4000
5000
6000
7000
8000
9000
10000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
SSB (tonnes)
Fbar 3-5
0.00
0.10
0.20
0.30
0.40
0.50
0.60
0.70
0.80
0.90
1.00
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
Fbar
Removals
0
1,000
2,000
3,000
4,000
5,000
6,000
1985 1987 1989 1991 1993 1995 1997 1999 2001 2003 2005
Removals (tonnes)
WGNEPH Report 2004 341

References:
Hillis, J. P. (1979). "Growth studies on the prawn, Nephrops norvegicus." Rapp. P.-v. Reun. Cons. int. Explor. Mer.
175: 170-175.
ICES, 1991, 1996, 2001, 2002. The report of the Working Group on Nephrops stocks.
Pope, J. A. and H. J. Thomas (1960). "Nephrops V - Some biometric observations on Nephrops norvegicus (L.)."
International Council for the Exploration of the Sea Council Meeting (180): 1-5.
WGNEPH Report 2004
342

Observations on Nephrops norvegicus catches from
grounds to the north of Ireland (ICES sub-area VIa).
Working document to WGNEPH 2004
Prepared by
Jackson, E. and Nolan*, C.P.
Irish Sea Fisheries Board (BIM), Crofton Road, Dun Laoghaire, Co. Dublin.
Tel.: +353 1 2144 146
Fax : +353 1 2300 564
Email: cnolan@bim.ie

Executive summary
Data on the size frequency, sex and maturity of Nephrops norvegicus,
taken in the catches of two commercial vessels from grounds to the north
of Ireland, were collected by scientific observers between August and
October 2003. Summary data are presented for each of the 5 voyages
observed during this period.
For further information on the data presented or any associated aspect of
these cruises please contact;
Dr Conor P. Nolan,
Irish Sea Fisheries Board (BIM)
Crofton Road,
Dun Laoghaire,
Co. Dublin.
Tel.: +353 1 2144 146
Fax : +353 1 2300 564
Email: cnolan@bim.ie

BIM Nephrops norvegicus 2003
1. 11th August 2003 – 16th August 2003
Target species: Nephrops norvegicus
‘
Prawn Grounds
’
Stanton Banks
Figure 1.1 Fishing positions for the 11 August to the 16 August 2003 in ICES
area VIa.

BIM Nephrops norvegicus 2003
Table 1.1 Summary statistics for male and female N. norvegicus length
measurements (mm).
Female
Maturity
Minimum
Maximum
Mean
Pale (n=9)
39
52
45.33
Medium (n=1)
52
52
52
Male (n=148)
Minimum 42
Maximum 74
Mean 57.08
34
23
11
1
5
8
18
26
37
0
5
10
15
20
25
30
35
40
35 40 45 50 55 60 65 70
Carapace Length (mm)
Frequency
Femal e
Ma le
Figure 1.2 Number of male and female N. norvegicus in 5mm carapace length
categories.

BIM Nephrops norvegicus 2003
2. 30th August 2003 - 04th September 2003
Target species: Nephrops norvegicus
Stanton Banks
‘
Prawn Grounds
’
Figure 2.1 Fishing positions for the 30th August to the 04th September 2003 in
ICES area VIa.

BIM Nephrops norvegicus 2003
Table 2.1 Summary statistic for male and female Nephrops norvegicus length
measurements (mm).
Female
Pale
(n=18)
Medium
(n=9)
Dark
(n=79)
Eggs
(n=16)
Minumum 26 29 23 31
Maximum 38 43 47 43
Mean 31.88 35.22 37.56 37.37
Male (n=873)
Minumum 26
Maximum 62
Mean 38.81
0
10
20
30
40
50
60
70
25 30 35 40 45
Carapace Length
Number in each maturity stage
Eggs
Dark
Medium
Pale
Figure 2.2 Number of female N. norvegicus by maturity classes in 5 m
m
carapace length categories.

BIM Nephrops norvegicus 2003
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
20 25 30 35 40
Carapace Length (mm)
Percentage
Eggs
Dark
Medium
Pale
Figure 2.3 Percentage maturity class in 5 mm carapace length
categories.
25
27
29
31
33
35
37
39
41
43
Pale Medium Dark Eggs
Maturity Stage
Average carapace length (mm)
Figure 2.4 Average female N. norvegicus carapace lengths (mm) with
standard deviations for each maturity class.

BIM Nephrops norvegicus 2003
12
147
359
268
83
12 3
0
50
100
150
200
250
300
350
400
20 25 30 35 40 45 50
Carapace Length (mm)
Number in Length Catagories
Figure 2.5 Number of male N. norvegicus in 5mm carapace length
categories.

BIM Nephrops norvegicus 2003
3. 27th September 2003 - 2nd October 2003
Target species: Nephrops norvegicus
‘
Prawn Grounds
’
Stanton Banks
Figure 3.1 Fishing position from the 27th October to the 2nd November in ICES
area VIa.

BIM Nephrops norvegicus 2003
Table 3.1 Summary statistics for male and female Nephrops norvegicus
carapace length measurements (mm).
Female
Pale
(n=12)
Medium
(n=16)
Dark
(n=62)
Eggs
(n=26)
Minumum 22 28 28 32
Maximum 45 43 48 48
Mean 33.16 36.06 39.74 39.30
Male (n=782)
Minumum 14
Maximum 59
Mean 38.92
50
0
5
10
15
20
25
30
35
40
45
20 25 30 35 40 45
Carapace Le ngth (mm)
Number of Nephrops in length category
Eggs
Dar k
Medium
Pale
Figure 3.2 Number of female N. norvegicus by maturity classes in 5m
m
carapace length categories.

BIM Nephrops norvegicus 2003
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
10 15 20 25 30 35 40 45 50 55
Carapace Length (mm)
Percentage of female maturity classes
Eggs
Dark
Medium
Pale
Figure 3.3 Percentage maturity class in 5 mm carapace length categories.
20
25
30
35
40
45
50
Pa le Me d i u m Da r k Egg s
Maturi ty Stage
Average carapace length (mm
)
Figure 3.4 Average female N. norvegicus carapace lengths (mm) with standar
d
deviations for each maturity class.

BIM Nephrops norvegicus 2003
1034
113
319
240
86
12 4
0
50
100
150
200
250
300
350
10 15 20 25 30 35 40 45 50 55
Carapace Length (mm)
Frequency
Figure 3.5 Number of male N. norvegicus in 5mm carapace length categories.
R2 = 0.5852
0
20
30
40
50
60
70
20 25 30 35 40 45 50 55
Carapace Length (mm)
Weight (g)
Figure 3.6 Carapace length (mm) versus weight (g) for N. norvegicus (n=266).
10

BIM Nephrops norvegicus 2003
4. 10th October 2003 - 16th October 2003
Target species: Nephrops norvegicus
Stanton Banks
‘
Prawn Grounds
’
Figure 4.1 Fishing positions from the 10th October to the 16th October 2003 in
ICES area VIa.

BIM Nephrops norvegicus 2003
Table 4.1 Summary statistics for male and female N. norvegicus length
measurements (mm).
Female
Pale
(n=193)
Medium
(n=13)
Dark
(n=44)
Eggs
(n=90)
Minimum 19 29 24 25
Maximum 36 45 45 42
Mean 25.35 32.29 36.11 33.78
Male (n=1285)
Minimum 15
Maximum 58
Mean 33.45
0
20
40
60
80
100
120
140
160
15 20 25 30 35 40
Carapace Length (mm)
Numbers of Nephrops in each length
category
Eggs
Dark
Medium
Pale
Figure 4.2 Number of female N. norvegicus by maturity classes in 5m
m
carapace length categories.

BIM Nephrops norvegicus 2003
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
15 20 25 30 35 40
Carapace Length (mm)
Percentage Maturity per length
category
Eggs
Dark
Medium
Pale
Figure 4.3 Percentage maturity class in 5mm carapace length categories.
20
25
30
35
40
45
Pale Medium Dark Eggs
Maturity Class
Average Crapace Length (mm)
Figure 4.4 Average female N. norvegicus carapace lengths (mm) with standar
d
deviations for each maturity class.

BIM Nephrops norvegicus 2003
1
47
299
377 379
154
22
51
0
50
100
150
200
250
300
350
400
15 20 25 30 35 40 45 50 55
Carapace Length (mm)
Number of Males in each size class
Figure 4.5 Number of male N. norvegicus in 5mm carapace length categories.

BIM Nephrops norvegicus 2003
5. 24th October 2003 - 29th October 2003
Target species: Nephrops norvegicus
Stanton Banks
‘
Prawn Grounds
’
Figure 5.1 Fishing positions for the 24th October to the 29th October 2003 in
ICES area VIa.

BIM Nephrops norvegicus 2003
Table 5.1 Summary statistics for male and female N. norvegicus length
measurements (mm).
Female
Pale
(n=45)
Medium
(n=4)
Dark
(n=6)
Eggs
(n=38)
Minimum 27 31 30 35
Maximum 38 35 43 45
Mean 30.28 33.00 37.83 39.39
Male (n=506)
Minimum 23
Maximum 51
Mean 37.54
0
5
10
15
20
25
30
35
25 30 35 40 45
Carapace Length (mm)
Number of Nephrops in length category
Eggs
Dark
Medium
Pale
Figure 5.2 Number of female N. norvegicus by maturity classes in 5mm carapace
length categories.

BIM Nephrops norvegicus 2003
0%
10%
20%
30%
40%
50%
60%
70%
80%
90%
100%
25 30 35 40 45
Carapace Length (mm)
Percentage fremales in each cohort
Eggs
Dark
Medium
Pale
Figure 5.3 Percentage maturity class in 5mm carapace length categories.
25
27
29
31
33
35
37
39
41
43
45
Pale Medium Dark Eggs
Maturity Class
Average carapace length (mm)
Figure 5.4 Average female N. norvegicus carapace lengths (mm) with standar
d
deviations for each maturity class.

BIM Nephrops norvegicus 2003
1
17
122
211
106
44
5
0
50
100
150
200
250
20 25 30 35 40 45 50
Carapace Length (mm)
Number of males in each size class
Figure 5.5 Number of male N. .norvegicus in 5mm carapace length categories.
0%
20%
40%
60%
80%
100%
20 25 30 35 40 45 50
Carapace Length (m m)
Percentage
Whole
Tailed
Discard
Figure 5.6 Percentage of N. norvegicus discarded, tailed or kept whole in 5
mm carapace length categories.

APPENDIX 6
Working Document to WGNEPH, March 2004
Sexual maturity of male Nephrops norvegicus (L.) in the Irish Sea
Nuala McQuaid1 and Richard Briggs2*
1Department of Biology and Biochemistry, The Queen's University of Belfast.
2Agriculture, Food and Environmental Science Division, Department of Agriculture and Rural Development for
Northern Ireland. *E-mail: richard.briggs@dardni.gov.uk
ABSTRACT
Size at onset of maturity was estimated for male Nephrops from primary sexual characteristics and from morphometric
traits. Maturity estimated from primary sexual characteristics based on histological examination of the gonad indicated
sexual maturity at 15.1mm carapace length. Morphometric maturity, or change in allometric growth of body parts, was
estimated from appendix masculina and cutter claw lengths from two sites in the Irish Sea. Two regression techniques
were used to estimate morphometric maturity and the results compared. Estimated sexual maturity from morphometric
characteristics ranged from 25.9 - 31.0mm CL.
INTRODUCTION
The size at onset of sexual maturity (SOM) is an important factor in reproductive strategy and overall fitness of a
species. It is also an important factor in the effective management of commercial fisheries by providing a guide for the
setting of technical conservation measures such as minimum mesh sizes in trawl nets. Studies of sexual maturity in
female Nephrops are well documented (eg Tessier, 1960; Figueiredo & Barraca, 1963; Thomas, 1964; Bailey, 1984;
Farmer, 1974a,b,c; Briggs, 1988; and Tuck et al., 2000). Morizur (1981) and Figueiredo (1982) suggested that the most
accurate estimates of size at first maturity would be the size at which 50% of animals display mature gonads. Maturity
in male decapods cannot generally be readily determined from macroscopic examination and few studies have been
documented. Storrow (1912) studied Nephrops in the North Sea and concluded that the presence of spermatophores in
the vasa deferentia (Figure 1 &2) was an indicator of sexual maturity. He found that males reached sexual maturity at
30mm carapace length. O' Neill (1992) carried out a histological examination of male Nephrops from the Irish Sea and
found that the smallest individuals examined (17mm carapace length) had spermatophores in the vasa deferentia.
Estimates of the size at onset of maturity from morphometric characteristics are based on changes in the relative growth
of body parts such as the chela in relation to overall body size (Watters and Hobday, 1998). The inflexion point at
which a change in relative growth occurs gives the size of maturity. Farmer (1974 c) found that changes in the relative
growth of the chela propodal length in males occurred at sexual maturity. Changes in allometry of cheliped size were
also recorded in the American lobster Homarus americanus and was related to functional maturity, i.e. the ability of a
male to inseminate a female (Aiken and Waddy, 1989). Other allometric studies in Nephrops have included estimates of
the relationship between body size (usually carapace length) and appendix masculina length (Hillis, 1977, 1981 and O'
Neill, 1992); number of segments on the antennule (O' Neill, 1992) and crusher claw propodal length (Tuck et al.,
2000).
METHODS
Presence of spermatophores
The DARD vessel RV Lough Foyle performs trawl surveys during spring (April) and summer (August) using a custom
built Nephrops trawl of 50mm mesh size throughout. Juvenile Nephrops are also captured using a 2-metre beam trawl
with a 12mm mesh. A pooled sample of small Nephrops was made from all stations surveyed (Figure 3) to investigate
the size at onset of maturity from primary sexual characteristics. Samples of small males were fixed in alcoholic Bouins
solution (Mahoney, 1965) to investigate the presence of spermatophores in the vasa deferentia using histological
techniques. Gonads were removed from the largest males and stored and fixed in 70% alcohol. They were then
dehydrated and embedded in wax and sections of 8µm thickness were cut and stained using haematoxylin and eosin.
Below carapace length of 16.9mm the entire thorax/abdomen was processed. Presence or absence of spermatophores in
the vasa deferentia was estimated for each 1mm carapace length category and L50 estimated using probit analysis. Probit
analysis was used to estimate size at onset of sexual maturity from primary sexual characteristics. A logarithmic curve
was fitted to the data and 95% confidence intervals were calculated for the carapace length categories so that the
estimated L50 could be generated (Figure 6).
WGNEPH Report 2004 363

Morphometric analysis
The size at onset of maturity in males was also estimated by measuring the appendix masculina and the propodus of the
cutter claw lengths. The appendix masculina is found on the endopodite of the second pleopod in male Nephrops
(Figure 4). The second pleopods were removed at their base to ensure the intact removal of the endopodite and the
appendix masculina. The pleopods were stored in 70% alcohol and appendix masculina lengths measured on a glass
slide using a "Wild Heerbrugg" microscope with a calibrated ocular micrometer. The cutter claw (Figure 5) was chosen
as it had a more streamlined shape and therefore the less likely claw to be damaged during processing.
Morphometric data were log-log transformed so that linear regression lines could be calculated. This was done by
applying a least squares regression model (MATURE 2), which assigns individuals of known maturity to an upper and
lower regression line (Somerton (1980) and Somerton & MacIntosh (1983). Tuck et al. (2000) developed a model
based on Lovett and Felder (1989) using reduced major axis regression (RMA). This model separates the data into two
sets with a carapace length greater than or less than a hypothesised transition point. A separate regression function is
calculated for each of the two groups after relocating the transition point using an iterative computer technique across
the carapace length size range. The size at onset of maturity is the point at which the regression functions of the two
groups best fit the combined data. The two lines of best fit are compared with a single line through the data set in the
same way as in the MATURE 2 model to determine if two lines are significantly better than one through the data. Both
models were applied to the morphometric data obtained from two of the stations fished during research vessel surveys
(stations 8 and 102 in Figure 3).
One drawback of both techniques is that they do not generate confidence limits about the inflexion point, making
it difficult to compare the size of maturity estimates from each technique. To overcome this, a method of numerical re-
sampling was used; in which 6 sub-set samples were created with replacement using the same size of sample as the
original data set for each maturity parameter measured. Inflexion points were calculated for each sub-set using the
MATURE and RMA computer programs. Inflexion points were combined to provide a mean and standard deviation to
allow comparisons to be made using a paired t-test.
RESULTS
Primary sexual characteristics
The smallest male Nephrops with spermatophores present in the vasa deferentia had a carapace length of 15.0mm. The
length at which 50% of males are mature (L50)was calculated using probit analysis and estimated to be 15.1 (+1.1/-
3.0mm, 95% confidence limits) carapace length (Figure 6).
Morphometric characteristics
Size at onset of maturity was estimated using appendix masculina and cutter claw propodus lengths. Data for two
selected stations (8 & 102) were analysed using two computer techniques, MATURE 2 and RMA. These techniques
estimate an inflexion point, ie the point at which there is a change in the level of allometry or relative growth rate, as
occurs at the onset of maturity.
a) Appendix Masculina Length
The appendix masculina showed a marked change in growth with carapace length for both stations investigated (Figure
7). Unlike cutter claw length the relative growth rate (represented by slope b, in Table 1) of appendix masculina
decreases at the inflexion point. There were no significant differences between the MATURE and RMA estimates of
SOM based on appendix masculina length for Nephrops from either station (t-test, P> 0.05).
b) Cutter Claw length
Claw length has been used successfully by other authors (Farmer, 1974 c; Tuck et al., 2000). The relationship between
cutter claw propodus length and carapace length for the two stations investigated are illustrated in Figure 8. The two
computer techniques identify an inflexion point at which a change in the relative growth occurs. The relative growth
rate indicated by the slope b, in the regression equation (Table 1) increases in the upper regression line suggesting that
the claw length of males increases more rapidly after the onset of maturity.
DISCUSSION
In male Nephrops the only maturity diagnostic comparable to the presence of eggs in females, is the presence of
spermatophores in the vasa deferentia (Storrow, 1912). Farmer (1974 a) noted that although males from the Irish Sea
as small as 18mm carapace length had fully developed spermatozoa, spermatophores in the vasa deferentia were
unusual. More recently however, O' Neill (1992) found that males of 17mm carapace length had spermatophores
present in the vasa deferentia. In the present study it was possible to collect males down to 6mm CL from small mesh
beam trawl catches and the smallest male captured with a spermatophore was <15.0mm CL. A male maturity ogive
WGNEPH Report 2004
364

gave a L50 significantly lower (15.1mm CL) than the value of 23.5mm CL published for Irish Sea female Nephrops
(Briggs, 1988; McQuaid, 2002).
Appendix masculina and cutter claw propodus lengths were used as indicators of male maturity. Data were
analysed using two computer-based regression programs, MATURE and reduced major axis regression (RMA). A t-test
comparing estimated size at onset of maturity for all of the data showed no significant difference between the two
techniques. The RMA program is more suitable where the relationship between the two sets of data are linear, while the
MATURE program is more suited to curvilinear data, because it automatically log-log transforms the data to carry out
LSR. The MATURE program also requires two values to be input; a lower limit below which individuals are known to
be immature and an upper limit above which individuals are known to be mature. The
RMA program does not require this information and therefore is not biased by the user, suggesting a more objective
technique where upper and lower maturity boundaries are unknown.
Hillis (1981) investigated the appendix masculina length : carapace length ratio as a method of identifying
immature and mature age groups in male Nephrops, but omitted to describe a size at onset of maturity. O'Neill (1992)
also examined the relationship between appendix masculina length and carapace length in two areas within the Irish Sea
and found a significant decrease in the slope of the regression of appendix masculina length and carapace length at
21mm CL and 24mm CL in the two areas respectively. The two stations examined here also showed a significant
difference in allometry at 24.0-26.3mm CL (station 8) and 25.5-26.9mm CL (station 102) respectively. The increased
growth rate in the appendix masculina therefore occurs before sexual maturity so the male is physically capable of
mating with a female. Increase in appendix masculina length, after this point appears to be a function of overall growth.
Both Farmer (1974 c) and Tuck et al. (2000) noted a change in allometry using cheliped length data which they
associated with the onset of sexual maturity. In the current study, two sampling stations from the western Irish Sea
were investigated using regression techniques. Table 2 shows the size at onset of maturity observed from the current
and previous studies carried out using claw length data. The inflexion points calculated here from cutter claw data from
Irish Sea Nephrops falls within the range estimated for Clyde Nephrops using crusher claw length Tuck (2000).
Farmer (1974 c) however, estimated a smaller size of maturity using LSR method. One possible reason for this is that
he used an average of both cutter and crusher claw lengths and included all female claw lengths with immature males.
It appears therefore that males are physiologically capable of reproduction at a smaller size than females. Changes
in allometric growth relationships may be a more useful method of estimating maturity in males and have been used
successfully in previous maturity studies for females (Farmer, 1974 c; Tuck et al., 2000). The increase in relative
growth of claw length in males has been related to mating behaviour in Nephrops (Farmer, 1974 c). Cheliped size is
known to undergo changes in allometry in the male American lobster (Homarus americanus) as it matures (Aiken and
Waddy, 1989). These authors related the change in cheliped size of the American male lobsters to functional maturity
defined as the ability of a male to inseminate a female. Farmer (1974b) observed that males have much larger claws
than females of the same size and that large males displayed their claws to rivals as well as to mature females.
Maturity in male Nephrops can be divided into three stages. (i) physiological maturity in which males are capable
of producing spermatophores in the vasa deferentia, estimated at 15.1mm CL. (ii) morphometric maturity, where males
are physically able to copulate, characterised by the appendix masculina reaching optimal length (24.3-26.9mm CL).
(iii) functional maturity represented by a relative increase in claw growth with the onset of maturity. Although not well
understood, this increase in claw size is thought to be related to mating behaviour, as males have been observed using
their claws to ward off rival males (Farmer 1974 c). Functional maturity was estimated in the present study to occur at
25.9-28.7mm CL at station 8 and 29.4-31.0mm CL at station 102. Until the relationship between claw size and maturity
is more fully understood the change in allometry of the appendix masculina appears to be the most appropriate measure
of sexual maturity in males. This was found to be 24.3-26.9mm CL in western Irish Sea Nephrops.
This study was funded by a Department of Agriculture and Rural Development (NI) postgraduate scholarship.
REFERENCES
Aiken, D. E., and Waddy, S. L. (1989). Allometric growth and the onset of maturity in male. American lobsters
(Homarus americanus): The crusher propodite index. Journal of Shellfish 8, 7-11.
Bailey, N. (1984). Some aspects of reproduction in Nephrops. ICES Shellfish Committee CM 1984/ K:33, (mimeo.).
Briggs, R. P. (1988). A preliminary analysis of maturity data for northwest Irish Sea Nephrops fishery. ICES Shellfish
Committee CM 1988/ K:21, (mimeo.).
Farmer, A. S. D. (1974 a). Reproduction in Nephrops norvegicus (Decapoda: Nephropidae). Journal of Zoology London
174, 161-183.
Farmer, A. S. D. (1974 b). The development of the external sexual characters of Nephrops norvegicus(L.). (Decapoda:
Nephropidae). Journal of natural history 8, 241-255.
Farmer, A. S. (1974 c). Relative Growth in Nephrops norvegicus (L.) (Decapoda: Nephropidae). Journal of Natural
History 8, 605-620.
Figueiredo, M. J. (1982). The occurrence of reabsorbtion in the ovaries of Nephrops norvegicus (L.) in Portuguese
waters. ICES Shellfish and Benthos Committee CM 1982/ K:28, (mimeo.).
Figueiredo, M. J., and Barraca, I. F. (1963). Contribucoa para o conhecimento da pesca e da biologia do langostim
(Nephrops norvegicus L,) na costa portuguesa. Notas Estudos de l'Instituto de Biologia Marina de Lisboa 28, 1-
44.
WGNEPH Report 2004 365

Hillis, J. P. (1977). Observations on age and growth in Nephrops norvegicus. ICES Shellfish and Benthos Committee
CM 1977/ K12, (mimeo.).
Hillis, J. P. (1981). Maturity in male Nephrops norvegicus: a study in secondary sexual characters. ICES Shellfish
Committee CM 1981/K:22, (mimeo.).
Lovett, D. L., and Felder, D. L. (1989). Application of regression techniques to studies of relative growth in
crustaceans. Journal of Crustacean Biology 9, 529-539.
Mahoney, R (1965). Laboratory Techniques in Zoology. Butterworth & Co. (Publishers) Ltd., press, London. pp 404.
McQuaid, N. (2002). Reproduction, development and growth of Nephrops norvegicus. PhD Thesis, Queen’s University
of Belfast. pp 205.
Morizur, Y. (1981). Evolution du taux de presence de spermatophore chez les femelles de Nephrops norvegicus(L.)
(Decapoda:Reptantia) et developpement ovarien. Journal of experimental marine biology and ecology 52, 15-24.
O'Neill, M. F. (1992). Physiological and morphological maturity in male Nephrops norvegicus(L.) 1758. B.A. Thesis:
Trinity College Dublin.
Somerton, D. A. (1980). A computer technique for estimating the size of sexual maturity in crabs. Canadian Journal of
Fisheries and Aquatic Science 37, 1488-1494.
Somerton, D. A., and MacIntosh, R. A. (1983). The size at sexual maturity of blue King crab, Paralithodes platypus, in
Alaska. Fishery Bulletin 81, 621-628.
Storrow, B. (1912). The prawn (Norway lobster, Nephrops norvegicus (L.), and the prawn fishery of North Shields.
Report for the Dove Marine Laboratory, North Shields 1, 10-31.
Tessier, G. (1960). Relative growth. In The Physiology of Crustacea, T. H. Waterman, ed. (New York: Academic
Press), pp. 537-560.
Thomas, H. J. (1964). The spawning and fecundity of the Norway lobster (Nephrops norvegicus (L.)) around the
Scottish Coast. Journal du Conseil Permanent International pour l'Exploration de la Mer. 29, 221-229.
Tuck, I. D., Atkinson, R. J. A., and Chapman, C. J. (2000). Population Biology of the Norway lobster, Nephrops
norvegicus (L.) in the Firth of Clyde, Scotland II: fecundity and size at onset of maturity. ICES Journal of Marine
Science 57, 1227-1239.
Watters, G., and Hobday, A. J. (1998). A new method for estimating morphometric size at maturity of crabs. Canadian
Journal of Fisheries and Aquatic Science 55, 704-714.
WGNEPH Report 2004
366

Table 1: Regression parameters estimated using MATURE and RMA. MATURE uses least squares regression
producing regression equations in the form Y= a Lb, while RMA fits a linear regression to the data in the form ( Y=
bX+a) where b is the slope and a the intercept.
Morphometric Station Regression MATURE
Y=aXb
RMA
Y=bX+a
Parameter Line a b a b
Appendix masculina 8 Lower 0.0082 1.89 -2.4064 0.2386
Length (Males) Upper 0.5181 0.62 -1.0407 0.1731
102 Lower 0.0096 1.81 -2.217 0.220
Upper 0.2303 0.83 0.284 1.118
Cutter Claw length 8 Lower 0.995 1.160 -10.238 1.942
(Males) Upper 0.244 1.550 -28.471 2.523
102 Lower 0.896 1.150 -9.530 1.876
Upper 0.198 1.590 -41.186 2.810
Table 2: Comparison of estimated size at onset of maturity from the present and previous studies based on a change in
allometry of carapace length and claw length for male Nephrops. In the present study cutter claw length was used;
Tuck et al.(2000) used crusher claw length while Farmer (1974 a) used an average of both claws.
Author Area Estimated Size at onset of Maturity
(mm carapace length)
LSR RMA
Farmer (1974 c) Irish Sea 26.0 -
Present study Irish Sea Station 102 31 29.4
Present study Irish Sea Station 8 28.7 25.9
Tuck et al (2000) Clyde Station 1
Station 2
Station 3
Station 4
Station 5
Station 6
Station 7
-
32.7
29.1
29.0
31.0
34.0
46.3
34.0
-
30.9
29.9
-
32.3
46.3
WGNEPH Report 2004 367

Figure 1: General view of male reproductive system relative to the hepatopancreas and coxopodites of the fifth
periopods (from Farmer, 1974 a).
WGNEPH Report 2004
368

A
B
0. 5 mm
Figure 2: A- Longitudinal section through the vas deferens of a male (19.8mm CL). The spermatophore is stained dark
purple. Plate B shows a magnified portion of Plate A in which the spermatophore can be seen more clearly.
WGNEPH Report 2004 369

1
2
7
8
10
15
17
20
30
35
101
102
103
104
105
106
107
108
109
200
207
208
209
210
6.4W 6.2W 6.0W 5.8W 5.6W 5.4W 5.2W 5.0W 4.8W 4.6W
53.4N
53.6N
53.8N
54.0N
54.2N
54.4N
54.6N
54.8N
36
E4 E5
E3
37
38
35
Figure 3: Irish Sea Nephrops stations for DARD research vessel surveys
WGNEPH Report 2004
370

Figure 4:. The appendix masculina on the second pleopod (adapted from Farmer 1974 b).
propodus
Figure 5: Cutter claw chela of mature male adapted from Farmer (1975).
WGNEPH Report 2004 371

0
10
20
30
40
50
60
70
80
90
100
0 5 10 15 20 25 30
Carapace length categories (mm)
% Mature
Ac tual
Es t i ma t e d
15.1 mm
Figure 6: Maturity ogive of males derived from the presence of spermatophores in the vasa deferentia (n=33 Nephrops).
Solid line fitted using probit analysis. L50 is indicated by the dotted lines and arrow
(b) Station102 (RMA)
0
1
2
3
4
5
6
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Low er
Upper
26.9 mm
6
5
2
1
0
(a) Station 102 (MATURE)
3
4
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Appendix masc. length ( mm)
Low er
Upp e r
25.5 m m
(d) Station 8 (RMA)
0
1
2
3
4
5
6
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Low er
Upper
24.3 m m
(c) Station 8 (MATURE)
0
1
2
3
4
5
6
12 14 16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Appendix masc. length ( mm)
Low er
Upper
26.3 m m
Figure 7 (a-d): Relationship between appendix masculina length and carapace length of Nephrops from two sampling
stations in the western Irish Sea. Arrows indicate inflexion points fitted using MATURE and RMA regression
techniques.
WGNEPH Report 2004
372

10
(a) Station 102 (MATURE 2)
0
10
20
30
40
50
60
70
80
90
0
16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Pr opodus length (mm)
Low er
Upper
31.0 mm
(b) Station 102 (RMA)
0
10
20
30
40
50
60
70
80
90
100
16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Low er
Upper
29.4 mm
(d) Station 8 (RMA)
0
10
20
30
40
50
60
70
80
90
100
16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Low er
Upper
25.9 mm
(c) Station 8 (MATURE)
0
10
20
30
40
50
60
70
80
90
100
16 18 20 22 24 26 28 30 32 34 36 38 40
Carapace length (mm)
Pr opodus length (mm)
Low er
Upp e r
28.7 m m
Figure 8(a-d): Relationship between propodus length of cutter claw and carapace length at two sampling stations in the
western Irish Sea. Arrows indicate inflexion points estimated using least squares regression (MATURE) and reduced
major axis (RMA).
WGNEPH Report 2004 373

APPENDIX 7
Working Document to WGNEPH, March 2004
Developing a length-based population model for Bay of Plenty scampi (MetaNephrops
challengeri).
M. Cryer1
B. Hartill1
A. Dunn2
1NIWA
P.O. Box 109695
Auckland
2NIWA
P.O. Box 14901
Wellington
N.Z. Fisheries Assessment Report 2004/xx. xx p.
March 2004
Executive summary
Cryer, M. Hartill, B, Dunn, A. (2004). Developing a length-based population model for Bay of Plenty scampi
(MetaNephrops challengeri). New Zealand Fisheries Assessment Report 2004/xx. xx p.
This report outlines the initial development of a Bayesian, length-based, two-sex population model for scampi
(MetaNephrops challengeri) in the Bay of Plenty (QMA 1) up to the end of the 2002–03 fishing year. We describe the
available data, data inputs, and parameterisation of the model. Fits, diagnostic plots, and initial model outputs are
presented as a basis for discussion rather than firm conclusions on the current and future stock status; this is the first
attempt at developing a length-based population model for any stock of scampi, and represents a substantially different
approach from stock assessments conducted on related species overseas.
The model is Bayesian and length-based and is implemented using the general-purpose stock assessment program
CASAL v2.04. We discuss aspects of the model implementation, model inadequacies, and provide a preliminary
estimate of current stock status for Bay of Plenty scampi. The model offered as a working model here represents some
of the data reasonably well, but does not faithfully represent commercial or research trawl catch-effort data, nor the
observed changes in sex ratio.
Abundance indices from catch-effort data (both research and commercial trawl) are derived from unstandardised
catch and effort measures and may not track abundance well because of changes in emergence rates of scampi.
Photographic estimates of absolute abundance based on emergent scampi may be similarly affected. Conversely,
photographic estimates of relative abundance based on burrows should not be affected by emergence, and these are
more faithfully reproduced by the model.
The preliminary model estimates suggest that the initial spawning stock biomass of scampi in the Bay of Plenty
was around 1550 t in 1985, and the current (2003) biomass is about 630 t.
WGNEPH Report 2004
374

Introduction
This report outlines the initial development of a Bayesian, length-based, two-sex population model for Bay of Plenty
(QMA 1) scampi up to the end of the 2002–03 fishing year. We describe the available data, data inputs,
parameterisation of the model, and initial model output. This is the first attempt at developing a length-based population
model for any scampi stock. The model has been implemented using the general-purpose stock assessment program
CASAL v2.04 (Bull et al. 2003). We discuss aspects of model implementation and model inadequacies, but provide a
preliminary estimate of current stock status. This report fulfils Objective 3 of Project SCI2003/02 “To carry out stock
assessment of scampi in QMA 1, including estimating biomass and sustainable yields”.
Description of the fishery
Scampi is not managed under the QMS. Access is restricted and, until the 1999–00 fishing year, there were restrictions
on the vessels that could be used in each QMA. Until the 2001–02 fishing year, catches were restrained using a mixture
of competitive and individually allocated catch limits. Since October 2001, all scampi fisheries areas have been
managed by competitive catch limits. The annual limit in QMA 1 is 120 t.
The fishery initially developed in QMA 1 in 1987–88 and is conducted mainly by 20–40 m vessels using light
bottom trawl gear. All vessels use multiple rigs of two or three nets of very low headline height. The main fisheries are
in waters 300–550 m deep in QMA 1 (Bay of Plenty), QMA 2 (Hawke Bay and Wairarapa Coast), QMA 3 (Mernoo
Bank) QMA 4 (western Chatham Rise and Chatham Islands) and QMA 6 (Sub-Antarctic) (Figure 1, Table 1). Some
fishing has been reported on the Challenger Plateau outside the EEZ.
Following a reasonably consistent decline since 1995–96, unstandardised CPUE in QMA 1 has increased by about
40% (Figure 2, after Hartill & Cryer 2004). Depending on the index used, catch rates are now on 70% to 84% of those
recorded in the index year (1988–89; Hartill & Cryer 2004). Between 1988–89 and 1997–98, standardised and
unstandardised indices of CPUE in QMA 1 were very highly correlated (data from Cryer & Coburn 2000, r8 = 0.95, p =
0.0003) suggesting that, unless fishing practice has changed markedly, the unstandardised index is likely to be a reliable
measure of overall catch rate. The depths range fished has remained around 400 m since 1988–89 (although some
shallower tows were made 1991–92 to 1994–95, and again since 2000–01 Figure xx), and the spatial extent of the
fishery has remained reasonably consistent in the western Bay of Plenty (Figure xx). Discussions with fishers suggest
that trawl mesh sizes have remained similar or identical since about 1993, although some fishers used finer meshes in
the early years of the fishery. Thus, fishing practice seems to have been reasonably consistent, at least since 1993.
WGNEPH Report 2004 375

SCI 1
SCI 2
SCI 3 SCI 4 (W ) SCI 4 (E)
SCI 5
SCI 6A
SCI 6B
SCI 7
SCI 8
SCI 9
SCI 10
Figure 1 (after Hartill & Cryer 2004): Fishery management areas and the location of the main fishing areas for scampi,
MetaNephrops challengeri, in New Zealand waters. Dots indicate the start positions of trawl tows targeting scampi on
Ministry of Fisheries catch/effort databases by December 2003. SCI 6A is a separate management area containing all
waters within 50 nautical miles of the Auckland Islands, whereas SCI 4 was informally separated for CPUE analysis
into eastern and western portions at longitude 180 ° (dashed line).
WGNEPH Report 2004
376

0.00
0.50
1.00
1.50
2.00
2.50
Fishing year
Index relative to base year
Raw data Groomed 1 Groom ed 2 Groomed 3
Figure 2 (after Hartill & Cryer 2004): Indices of unstandardised catch rate (total catch divided by total effort, hours) for
all vessels fishing in QMA 1. “Raw data”, all data with no grooming; “Groomed 1”, groomed data with irreconcilable
errors included; “Groomed 2”, groomed data with irreconcilable errors excluded; “Groomed 3”, groomed data with
irreconcilable errors and tows with a zero estimated catch of scampi excluded.
200
300
400
500
600
700
Fishing year
Depth (m )
1988-89
1989-90
1990-91
1991-92
1992-93
1993-94
1994-95
1995-96
1996-97
1997-98
1998-99
1999-00
2000-01
2001-02
2002-03
Figure 3 (after Hartill & Cryer 2004): Depth distribution of trawl tows for scampi by fishing year in QMA 1.
Bold horizontal line denotes the annual average depth fished, and narrow lines denote the median (where
visible) and quartiles.
WGNEPH Report 2004 377

173 174 175 176 177 178 179
-38
-37
-36
-35
-34
1988-89 1989-90 1990-91
1991-92 1992-93 1993-94
1994-95 1995-96 1996-97
1997-98 1998-99
2000-01
1999-00
2001-02 2002-03
Figure 4 (after Hartill & Cryer 2004): Spatial distribution of the QMA 1 scampi trawl fishery since 1988–89. Each dot
shows the start position of a tow reported on TCEPR.
WGNEPH Report 2004
378

Table 1 (after Annala et al. 2003): Estimated commercial landings (t) from the 1986–87 to 2000–01 fishing years and
catch limits (t) by QMA (from TCEPR, MFish catch effort database, as at December 2002, early years may be
incomplete). No limits before 1991–92 fishing year; * no separate catch limits for QMAs 6A and 6B before 1992–93,
total catch limit 300 t; (†), catch limits allocated individually until 30 September 2001. Some values may differ from
those in (groomed) research data sets.
QMA 1 QMA 2 QMA 3 QMA 4 QMA 5
CatchLimit (†) Catch Limit (†) Catch Limit Catch Limit (†) Catch Limit
1986–87 5 – 0 – 0 – 0 – − – −
1987–88 15 – 5 – 0 – 0 – 0 –
1988–89 60 – 17 – 0 – 0 – 0 –
1989–90 104 – 138 – 0 – 0 – 0 –
1990–91 179 – 295 – 0 – 32 – 0 –
1991–92 132 120 221 246 1 60 230 250 0 60
1992–93 114 120 210 246 84 60 223 250 2 60
1993–94 115 120 244 246 64 60 261 250 1 60
1994–95 114 120 226 246 66 60 226 250 0 60
1995–96 117 120 230 246 76 60 230 250 0 60
1996–97 117 120 213 246 72 60 232 250 2 60
1997–98 107 120 224 246 60 60 236 250 0 60
1998–99 110 120 233 246 69 60 251 250 30 60
1999–00 124 120 193 246 77 60 268 250 9 40
2000–01 120 120 146 246 79 60 254 250 7 40
2001–02 124 120 247 246 79 60 255 250 <1 40
Table 1 (after Annala et al. 2003): Estimated commercial landings (contd.):
QMA 6A QMA 6B QMA 7 QMA 8 QMA 9
CatchLimit (†) Catch Limit Catch Limit Catch Limit Catch Limit
1986–87 0 – 0 – 0 – 0 – 0 –
1987–88 0 – 0 – 0 – 0 – 0 –
1988–89 0 – 0 – 0 – 0 – 0 –
1989–90 0 – 0 – 0 – 0 – 0 –
1990–91 2 – 0 – 0 – 0 – 0 –
1991–92 323 *300 2 * 0 75 0 60 0 60
1992–93 198 256 81 50 2 75 0 60 2 60
1993–94 242 256 61 50 0 75 0 60 1 60
1994–95 225 256 14 50 2 75 0 60 0 60
1995–96 220 256 50 50 1 75 0 60 0 60
1996–97 230 256 45 50 0 75 0 60 0 60
1997–98 244 256 35 50 0 75 0 60 0 60
1998–99 273 256 53 50 1 75 0 60 <1 60
1999–00 255 256 73 50 1 75 0 5 0 35
2000–01 227 256 37 50 <1 75 0 5 0 35
2001–02 253 256 19 50 <1 75 0 5 0 35
General biological knowledge
Scampi are widely distributed around the New Zealand coast, principally in depths between 200 and 600 m on the
continental slope. Like other species of MetaNephrops and Nephrops, M. challengeri builds a burrow in the sediment
and may spend a considerable proportion of time within this burrow. From trawl catch rates, it appears that there are
daily, seasonal, and, perhaps, longer-term cycles of emergence from burrows onto the sediment surface.
Scampi moult several times per year in early life and probably about once a year after sexual maturity (at least in
females). Data from trawl surveys in QMAs 1 and 2 suggest that females as small as 30 mm OCL can be sexually
mature in these areas. The peak of moulting and spawning activity seems to occur in spring or early summer (Cryer &
Oliver 2001). Larval development of M. challengeri is probably very short, and may be less than 3 days in the wild
(Wear 1976). The abbreviated larval phase may, in part, explain the low fecundity of M. challengeri compared with N.
norvegicus (some tens to a few hundreds of eggs, compared with a few thousands).
WGNEPH Report 2004 379

The growth rate of MetaNephrops challengeri is not well understood, but inferences have been drawn in the past from
tagging studies, aquarium experiments, and length frequency distributions (Table 2). The maximum age of New
Zealand scampi is not known, although analysis of tag return data and aquarium trials suggest that this species may be
quite long lived. MetaNephrops spp. in Australian waters may grow rather slowly and take up to 6 years to recruit to the
commercial fishery, consistent with early estimates of growth in M. challengeri. N. norvegicus populations in some
northern European populations grow to about 30 mm carapace length after 3–4 years (Figure 5) and achieve a
maximum age of 15–20 years, consistent with the estimates of natural mortality, M, for M. challengeri.
Table 2 (after Annala et al. 2003): Estimates of biological parameters.
Population Estimate Source
1. Weight = a(orbital carapace length)b (weight in g, OCL in mm)
All males: QMA 1 a = 0.000373 b = 3.145 Cryer & Stotter (1997)
Ovigerous females: QMA 1 a = 0.003821 b = 2.533 Cryer & Stotter (1997)
Other females: QMA 1 a = 0.000443 b = 3.092 Cryer & Stotter (1997)
All females: QMA 1 a = 0.000461 b = 3.083 Cryer & Stotter (1997)
2. von Bertalanffy growth parameters
K (yr
-1) L∞ (OCL, mm) t0 (yr)
Females: QMA 1 (tag) 0.11–0.14 48.0–49.0 0.0 Cryer & Stotter (1999)
Females: QMA 2 (aquarium) 0.31 48.8 0.0 Cryer & Oliver (2001)
Males: QMA 2 (aquarium) 0.32 51.2 0.0 Cryer & Oliver (2001)
3. Natural mortality (M)
Females: QMA 1 M = 0.20–0.25 Cryer & Stotter (1999)
Figure 5 (after ICES 2000): Early growth curves for six European populations of Nephrops norvegicus.
Model structure, inputs, and estimation
Model structure
The population model partitions QMA 1 scampi into a two-sex population, with length classes 1–65 mm (orbital
carapace length, OCL), in 1 mm classes, with the last group defined as scampi 66 mm or longer OCL. The stock is
assumed to reside in a single, homogeneous area between North Cape and Cape Runaway. The partition accounts
numbers of males and females by length class within an annual cycle, where movements between length classes are
determined by sex-specific growth parameters. Individuals enter the partition by recruitment and are removed by natural
mortality and fishing mortality. The model’s annual cycle is based on the fishing year and is divided into two steps
(Table 3). Note that model references to “year” within this paper refer to the fishing year, and are labelled as the most
recent calendar year, i.e., the fishing year 1998–99 is referred to as “1999” throughout.
WGNEPH Report 2004
380

Table 3: Annual cycle of the population model, showing the processes taking place at each time step, their sequence
within each time step, and the available observations. Fishing and natural mortality that occur together within a time
step occur after all other processes, with 50% of the natural mortality for that time step occurring before and 50% after
the fishing mortality.
Step Period Process Proportion in time step
1 Oct–Dec Recruitment 1.0
Maturation 1.0
Natural mortality 0.25
Fishing mortality From TCEPR
2 Jan–Sep Natural mortality 0.75
Growth 1.0
Fishing mortality From TCEPR
Catch data are available for the years 1985–86 to 2002–03 (see Table 1). Catches occur in both time steps and we
divided the catch among the two according to the proportion of estimated catches recorded on Trawl catch, Effort, and
Processing Returns (TCEPR). Recreational catch, customary catch, and illegal catch are ignored. Individuals are
assumed to recruit to the model at age 0, according to a Ricker (domed) stock-recruitment relationship with a steepness
of 0.75. Length at recruitment is defined by a normal distribution with mean of 1 mm OCL with a c.v. of 0.4. Relative
year class strengths are assumed to average 1.0. Growth is assumed known, but natural mortality is estimated.
The model uses three length-based selectivity ogives for commercial fishing, research trawl surveys, and
photographic surveys (all assumed constant over both sexes, all years, and all time steps of the fishery). A length-based
maturity ogive is used, and assumed to be identical for males and females (though we have data only for the latter). For
this developmental model, selectivity ogives were all assumed to be logistic (although Hartill & Cryer 2003 found
significant asymmetry in selectivity data from research trawl using a variety of mesh sizes), where the parameterisation
for each length class x was;
()
()
50 95
1119 to
axa
fx −

=+

,
where x is the centre of the length class and estimable parameters are a50 and ato95. Selectivity functions were fitted
within the model. The data are described later. The maximum exploitation rate (i.e., the ratio of the maximum catch to
biomass in any year) was unknown, but constrained to no more than 0.9.
Biological inputs, priors, and assumptions
Recruitment
Little data are available on recruitment. Relative year class strengths area were assumed to average 1.0 over all years of
the model. Lognormal priors on relative year class strengths were assumed, with mean 1.0 and c.v. 0.2. The relationship
between stock size and recruitment for scampi is unknown. However, New Zealand scampi have very low fecundity (in
the order of tens to hundreds of eggs carried by each female), so very high levels of recruitment are likely to be
implausible at periods of low abundance. Conversely, our observations of scampi in aquariums suggests that
cannibalism is commonplace, and mortality of juveniles may be higher at high stock size. Thus, we assume a Ricker
(dome-shaped) stock-recruit relationship with a steepness of 0.75. This assumption probably has little impact on the
model estimates of current status (because biomass does not descends much below half of B0), but may affect any
projections made using the model. Scampi enter the partition at age 0+, prior to growth as 1 year olds. The distribution
was assumed to be normally distributed with mean 1 mm OCL and c.v. of 0.4. These parameters were not estimated but
could be in future iterations.
Growth (tagging and aquarium experiments)
Cryer & Stotter (1997, 1999) and Cryer & Oliver (2001) estimated growth from wild-tagged scampi in QMA 1 and
aquarium-reared scampi from QMA 2, respectively (Figures 6 & 7). Recoveries and measurements of captive animals
were made at a variety of intervals, so growth models were based on a modified length increment von Bertalanffy
growth model, estimated using maximum likelihood, mixed effects models (after Francis 1988). Cryer & Oliver (2001)
estimated g30 (expected annual increments for scampi of 30 mm OCL) at 5.01 mm for males and 5.26 mm for females,
and estimated g50 at 1.05 mm for males and –0.82 mm for females. Because negative growth is disallowed in CASAL,
we interpolated equivalent vales of g20 (6.99 mm for males and 8.30 mm for females) and g40 (3.03 mm for males and
WGNEPH Report 2004 381

2.22 mm for females). Growth variability was specified as 1.5 mm for the working model but this and the values of g20
and g40 could be estimated.
The growth estimates described above and used in the working model have several limitations. They were
generated using a combination of data from tagged animals (in QMA 1) and aquarium-reared animals (from QMA 2 but
maintained at 12 °C). The tag data may suffer from both catching (trawling) and tagging artefacts (which, if present,
would both generally lead to some retardation of average growth), and very few small or medium-sized males were
recaptured. On the plus side, tagged scampi were released in about 400 m depth and would have been exposed to
“normal” temperature of about 10 °C (Figure 8). Aquarium-reared scampi were collected from QMA 2 (again, by
trawl), where average growth may be different than in QMA 1. A wider range of size classes of both males and females
are included in this data set, although relatively few large males. The holding temperature of 12 °C may have resulted in
accelerated growth, but little is known of the artefacts of holding scampi for long periods or of the artificial diet. Thus,
both data sets have their limitations and, in addition, there is no consensus on the most appropriate means of combining
the two.
30
35
40
45
50
55
60
25 30 35 40 45 50 55
Length at release (or start) (OCL, mm)
Female
30
35
40
45
50
55
60
25 30 35 40 45 50 55 60
Male
Length at recapture (or death) (OCL, mm)
Figure 6 (after Cryer & Oliver 2001): Relationship between size at release and recapture for tagged males (top) and
females (bottom) (closed circles, data from Cryer & Stotter 1999) overlaid with comparable data from aquarium trials
(open circles) where the increment was measurable. The line indicates no growth.
WGNEPH Report 2004
382

0
10
20
30
40
50
02468101214
OCL (mm)
Female
0
10
20
30
40
50
02468101214
Age (y)
OCL (mm)
Male
0
10
20
30
40
50
02468101214
OCL (mm)
Female
0
10
20
30
40
50
02468101214
Age (y)
OCL (mm)
Male
Figure 7 (after Cryer & Oliver 2001): Age-based von Bertalanffy growth curves calculated from GROTAG estimates of
growth-at-length for female (top) and male (bottom) scampi assuming t0 = 0 and a linear relationship between length
and mean annual increment Left panels show curves using only captive animals, right panels using captive and wild-
released animals.
6
8
10
12
14
200 300 400 500 600
Depth (m)
Bottom temperature (C)
Figure 8 (after Cryer & Oliver 2001): Bottom temperatures recorded using a calibrated headline monitor on 475 trawl
shots made between 200 and 600 m depth in the Bay of Plenty, Hawke Bay, or Wairarapa coast, 1992–2000. The line is
an ordinary least squares regression.
Maturity
The proportion of females mature at each 1 mm size class have been recorded during all research surveys since 1993.
Cryer & Oliver (2001) pooled the available data for females from QMAs 1 and 2, assuming internal gonad stages 2–5 to
be mature, and stage 1 to be immature (Figure 9). No data are available for the maturity of male scampi, so their
maturity ogive was assumed identical to that of females. Maturity is not considered to be a part of the model partition,
but proportions mature were fitted within the model based on a logistic ogive with a binomial likelihood (Bull et al.
2003).
WGNEPH Report 2004 383

0.00
0.25
0.50
0.75
1.00
10 20 30 40 50 60
Orbital carapace length (mm)
P
immature
developing
early
late
spent
0.00
0.25
0.50
0.75
1.00
10 20 30 40 50 60
Orbital carapace length (mm)
P
immature
developing
early
late
spent
Figure 9 (after Cryer & Oliver 2001): Proportions of female scampi having various developmental stages of internal
ovaries. Left panel show proportions for each stage separately, right panel show combined proportions. Aggregated data
from research voyages in QMAs 1 & 2.
Natural mortality
The instantaneous rate of natural mortality, M, has not been estimated directly for scampi, but Cryer & Stotter (1999)
used a correlative method (after Pauly 1980, Charnov et al. 1993) based on their estimate of the K parameter from a von
Bertalanffy growth curve. Based on this rough-and-ready estimate (Figure 10), we placed a log-normally distributed
prior on M of 0.2 with a c.v. of 0.8 for the working model. This prior has little effect on the behaviour of the model,
though.
0
5
10
15
20
25
30
0.00 0.05 0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50
Value of M (less than)
Number of simulations
Figure 10 (after Cryer & Stotter 1999): Frequency distributions, from 200 bootstrap replicates, of the estimated rate of
natural mortality, M, based on Charnov et al.’s (1993) regression of M on the von Bertalanffy K. Solid lines with solid
circles represent the analysis using Ricker’s (1975) method, while dashed lines and open circles indicate the analysis
using Francis’ (1988) method.
Catch data
Commercial catch
Scampi trawlers have recorded tow-by-tow information on Trawl Catch, Effort, and Processing Returns (TCEPR) since
1988–89. Catch by year was taken from Annala et al. (2003), and apportioned between the early and late seasons
(October to December and January to September) in proportion to the sum of estimated catches on TCEPRs for those
months.
WGNEPH Report 2004
384

Recreational catch
There is no known recreational catch of scampi and any such catch is ignored in the model.
Customary catch
There is no known customary catch of scampi and any such catch is ignored in the model.
Illegal catch
We have no information on illegal catches of scampi and they are ignored in the model.
Incidental mortality
We have no information on the incidental mortality cause by the trawl method or on discard mortality caused by the
exclusion of any damaged and discarded animals from reported landings. Both are assumed to be negligible (based on
our experience of the fishery as well as the lack of quantitative information) and are ignored in the model.
Length frequency of the commercial catch
Length frequency samples from the commercial catch have been taken by scientific observers since 1992 (e.g., Hartill
& Cryer 2000?). Estimates of the length-frequency (with associated c.v.s) of the commercial catch were derived using
the NIWA catch-at-age software (Bull & Dunn 2002), using 1 mm (OCL) length classes by sex, weighting the
proportions at length in each of four general areas (Poor Knights, Aldermens, Mayor Island, and East Cape) by the
amount of catch estimated to have been taken from these areas using the estimated catches reported on TCEPR. Length
frequency distributions were calculated separately for early and late steps in the model.
Resource surveys and other abundance information
Photographic estimates of absolute abundance
Photographic surveys have been conducted in the core area of QMA 1 scampi fishery since 1998 (e.g., Cryer et al
2003?). The estimated abundance of visible scampi and a photographic estimate of their average weight (made using a
length-weight regression), can be used to estimate absolute biomass. We assume this to be a minimum estimate of
absolute biomass because some scampi may be hidden within burrows and not visible. We did not fit these indices of
absolute abundance within the model (partly because of uncertainty over an appropriate likelihood function), but we use
them to assess the reliability of model estimates of biomass and the average emergence rate for scampi of different
sizes.
WGNEPH Report 2004 385

Year
1998 1999 2000 2001 2002 2003
Abundance of scampi (millions)
0
10
20
30
40
Figure 11 (after Cryer et al. 2003): Estimated abundance (± one standard error) of visible scampi in strata 302, 303, 402,
and 403, 1998 to 2003. Closed symbols indicate all visible scampi, open symbols include only those scampi completely
out of their burrows.
Photographic estimates of relative abundance
The photographic surveys of QMA 1 described above (e.g., Cryer et al 2003?) have been used to estimate the
abundance of burrows thought to belong to scampi in 1998, 2000, 2001, 2002, and 2003. We assume this time series to
be an index of relative abundance and fitted to these indices within the model using observed c.v.s (assumed log-
normally distributed error).
Year
1998 1999 2000 2001 2002 2003
Abundance of major openings (millions)
0
50
100
150
200
Figure 12 (after Cryer et al. 2003): Estimated abundance (± one standard error) of major burrow openings in strata 302,
303, 402, and 403, 1998 to 2003.
WGNEPH Report 2004
386

Research trawl indices of relative abundance
Stratified random trawl surveys of scampi in QMAs 1 and 2, 200–600 m depth, were conducted in 1993, 1994, and
1995 (Figure 13). At that time, trawl surveys were discontinued because it was inferred from the results (most
especially the relative proportions of males and females and the rapidly increasing catch rate) that catchability was
varying among surveys. Nevertheless, research trawling has continued in QMA 1 for a variety of other purposes (in
support of a tagging programme to estimate growth in 1995 and 1996, to assess selectivity of research and commercial
mesh sizes in 1996, and in support of photographic surveys since 1998). Identical gear has been used throughout
(30 mm cod-end and 80 mm wings and belly), or we have selected only those tows where the standard gear was used.
We assume this time series to be an index of relative abundance (with the caveat that catchability may vary among
years) and fitted to these indices within the model using observed c.v.s (assumed log-normally distributed).
Year
1992 1994 1996 1998 2000 2002 2004
Catch rate
0
5
10
15
20
25
30
Figure 13: Mean catch rates of research trawling in strata 302, 303, 402, and 403 between 1993 and 2002.
Commercial catch-effort indices of relative abundance
Cryer & Coburn (2000) calculated fully standardised indices for the QMA 1 scampi fishery up to the 1997–98 fishing
year. However, they found that the standardised index was very highly correlated with much simpler unstandardised
indices (total catch divided by total fishing effort), and these simpler indices have been used since (e.g., Hartill & Cryer
2003). We have adopted the “G3” time series of Hartill & Cryer (2003) (groomed data excluding obvious errors and
zero catches of scampi and split between the early and late steps in our model, see Figure 2) as an index of relative
abundance and fitted to these within the model using assumed log-normal c.v.s. of 0.25.
Length frequency estimates
Length frequency samples from research trawling have been taken by scientific staff since 1993. Estimates of the
length-frequency (with associated c.v.s) were derived using the NIWA catch-at-age software (Bull & Dunn 2002), using
1 mm (OCL) length classes by sex. These were calculated separately for early and late steps in the model. All length
frequency distributions are shown in the Appendix, but those for 1995 are shown in Figure 14 to illustrate the
relationship between estimated proportions and their c.v.s.
WGNEPH Report 2004 387

0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
15 20 25 30 35 40 45 50 55 60
Male OCL (mm)
Proportion
0.00
0.50
1.00
1.50
2.00
2.50
CV (as line)
0.000
0.005
0.010
0.015
0.020
0.025
0.030
0.035
0.040
0.045
15 20 25 30 35 40 45 50 55 60
Male OCL (mm)
Proportion
0.00
0.50
1.00
1.50
2.00
2.50
CV (as line)
Figure 14: Proportional length frequency distribution of male and female scampi taken by research trawling in 1994.
CVs for proportions at length were estimated using a bootstrap routine in the NIWA catch-at-age software package.
Length frequency distributions were also estimated for both absolute (visible scampi) and relative photographic
abundance series. For the former (Figure 15), the chelipeds of all visible scampi were measured using Didger 3.0 image
analysis software, and their orbital carapace lengths estimated using pre-existing regressions of OCL on cheliped length
(Figure 16, after Cryer et al. 2002, from measurements on dead animals). For the latter, the widths of a sample of major
burrow openings were measured using Didger 3.0 image analysis software and converted to orbital carapace lengths
using regressions of OCL on major opening width (Figure 17) developed using photographs of scampi clearly
associated with burrows. The sample of burrows for measurement was selected on the basis that the image had been
identified as having at least two probable burrow openings (to speed the process), and that two or more (of three)
readers identified the particular burrow opening as likely to belong to scampi during routine screening to estimate
relative biomass (e.g., Cryer et al. 2003). The relationship between OCL and burrow width seems mildly non-linear, so
a variety of curvilinear regression models was fitted. The power relationship shown in Figure xx reproduced roughly the
right amount of curvilinearity (by eye) and had the highest R2 of the models we applied. However, the estimated length
frequency distributions were not very sensitive to the regression model applied.
WGNEPH Report 2004
388

0.000
0.025
0.050
0.075
0.100
10 15 20 25 30 35 40 45 50 55 60 65 70
P
1998
0.000
0.025
0.050
0.075
0.100
10 15 20 25 30 35 40 45 50 55 60 65 70
Estimated OCL (mm)
P
2000
Figure 15: Estimated proportional length frequency distribution of scampi taken seen in photographs from surveys in
1998 and 2000.
20
25
30
35
40
45
50
55
60
15 25 35 45 55 65
Length of opposable cheliped segment (mm)
OCL (mm)
Figure 16: Relationship between the length of the opposable segment of the cheliped and OCL for QMA 1 scampi.
Least squares regression lines for segment length less and more than 44 mm (lines) are used to estimate OCL for scampi
in photographs.
WGNEPH Report 2004 389

OCL = 1.979 W 0.6755
R2 = 0.756
0
10
20
30
40
50
60
70
0 50 100 150 200
Width of major opening (mm)
Occupant size (OCL, mm)
Figure 17: Predictive relationship used to estimate scampi length frequency distributions from burrow width
distributions.
0.000
0.025
0.050
0.075
0.100
10 20 30 40 50 60
Estimated OCL (mm)
P
2003
1998
0.00
0.10
0.20
0.30
0 50 100 150
Width of major opening (mm)
P
2003
1998
Figure 18: Estimated distribution of burrow widths (top) and proportional length frequency distributions (bottom) of
presumed inhabitant scampi from photographic surveys in 1998 and 2003.
WGNEPH Report 2004
390

Model estimates
Model set-up and priors
Estimates of numbers and biomass of scampi were made using the biological parameters and model input parameters
described above, using a negative log-likelihood objective function (Table 7). First, several exploratory runs were made
using all the data (except the length frequency distributions from photographic surveys which were still being
developed), exploring the fits and diagnostics of each. We manipulated the “process error” for each data set so that plots
of observed against theoretical quartiles (q-q plots) fell close to the 95% confidence envelopes. Next, we ran several
scenarios using different subsets of the data to assess the model’s sensitivity to each data set. Assumed priors and the
treatment of each data set are summarised in Table xx. Priors for selectivity ogives (not shown) were uniform across
wide bounds, deliberately chosen to be non-informative for most runs.
Our exploration led us to accept our “Model 11” as a working model as a starting point for discussion. This
working model includes all data sets available and compatible with the model structure (except length frequency
distributions from photographic surveys), but included substantial process error for all trawl-based length frequency
distributions and for all trawl-based relative biomass indices.
A single Monte-Carlo Markov Chain (MCMC) was run on the working model (model 11), with total length
1.5x106 iterations (including a burn-in of 0.5x106 iterations) and systematic sub-sampling (“thinning”) to 1000 samples.
Convergence diagnostics for the model were not formally investigated, although MCMC traces for B0, M, and the
selectivity parameters are shown in Figures xx and xx. There was little evidence of autocorrelation in all traces (Figure
xx) except that for the selectivity of the photographic survey selectivity, suggesting that the chain length was adequate
for most purposes.
1000
1200
1400
1600
1800
2000
2200
2400
0 500 1000 1500
Recruited biomass (t)
0.15
0.16
0.17
0.18
0.19
0.2
0 500 1000 1500
Iteration (thousands)
Natural mortality (M)
Figure 19: MCMC traces for natural mortality (top) and unfished recruited biomass (bottom) from the working model.
The chain was “burnt in” over the first 500 000 iterations.
WGNEPH Report 2004 391

0
.705354 0.790935 1.05612 0.612525 0.425915 0.825887 0.34738 30.267 7.49562 39.1826 10.6674
0
.830334 0.584734 1.36187 0.28521 0.781367 0.37223 0.055614 30.3004 7.27547 38.5926 10.24
0
.746289 0.527295 1.18409 0.644238 0.429699 0.666139 0.230393 30.1658 7.35068 38.2269 10.5161
0
.603174 0.632396 0.883032 0.321264 0.442152 0.870214 0.218988 30.0988 7.57209 38.873 10.5749
0
.815876 0.67673 0.982273 0.503214 0.26087 1.51764 0.225361 30.2962 7.32571 38.3307 10.3026
1.05992 0.613497 1.25706 0.46981 0.368086 0.97653 0.486144 30.1098 7.46447 38.7555 10.1753
0
.581612 0.743113 0.853723 0.450284 0.589315 1.05103 0.369278 30.296 7.28903 38.2603 9.71533
0
.601865 0.655852 1.01098 0.611879 0.30353 0.622958 0.115347 30.3306 7.21094 37.7827 9.09853
0
.680711 0.510962 1.226 0.32479 0.561571 1.04562 0.099783 30.3077 7.23071 38.9268 10.5302
0
.836923 0.434595 1.06837 0.338344 0.369962 0.875431 0.204384 30.2305 7.32737 39.217 9.89462
0
.752444 0.490586 1.02495 0.937247 0.321589 1.73628 0.034402 30.2032 7.3345 38.3402 9.57744
0
.885885 0.554302 0.813657 0.610243 0.577582 2.1516 0.319557 30.1456 7.35294 38.4528 9.82021
0
.782587 0.809627 0.917349 0.597863 0.486925 1.06374 0.043321 30.3427 7.24654 39.0467 10.2851
0
.470638 0.671963 0.7023 0.616561 0.131027 0.559302 0.289912 30.0878 7.41165 37.9728 10.3962
0
.696479 0.464362 0.692079 0.614029 0.46525 0.737355 0.201999 30.1871 7.28875 37.7647 9.6328
0
.883275 0.433733 1.13968 0.361237 0.351523 1.52101 0.106812 30.1657 7.28764 37.9747 9.87136
0
.597628 0.630505 0.825088 0.563943 0.628162 1.71117 0.356827 30.4245 7.39286 38.2119 9.65826
0
.536855 0.666908 0.999874 0.665531 0.753031 1.42031 0.59936 30.3668 7.35756 38.8629 10.1461
0
.572564 0.686364 1.39354 0.385366 0.91084 1.48361 0.470812 30.2652 7.23971 39.139 10.3733
0
.425546 0.645384 1.21091 0.693737 0.576737 0.944111 0.28992 30.2092 7.19456 38.3986 9.51877
0.49939 0.714832 0.807513 0.347877 0.575236 1.14831 0.388249 30.2647 7.26859 39.1535 10.7259
0
.620555 0.616609 0.825824 0.39078 0.266204 2.22697 0.02343 30.3358 7.30358 38.6634 10.5777
0
.706284 0.631579 0.910653 0.326961 0.669789 1.65351 0.097225 30.3377 7.23218 38.9379 9.94589
0
.547408 0.709214 0.83715 0.621263 0.281209 0.866361 0.075983 30.2463 7.47436 38.2533 9.73724
0.57773 0.698833 0.954036 0.509947 0.321071 1.56847 0.243177 30.1423 7.53783 38.2698 9.65812
0
.686697 0.772289 0.761653 0.504258 0.276485 2.17937 0.087549 30.2391 7.30222 39.4023 10.4992
0
.706647 0.695302 1.23043 0.721818 0.323291 0.804698 0.263884 30.2593 7.29484 38.9397 9.98175
0
.457541 0.494033 0.984141 0.382151 0.351377 2.34528 0.377031 30.2966 7.23208 37.9194 9.69605
0
.792205 0.622912 0.927959 0.539031 0.422971 1.69237 0.138495 30.2177 7.39136 38.155 9.54219
0
.618926 0.628546 0.925914 0.526563 0.512003 0.968097 0.037157 30.0669 7.27925 38.3652 9.8592
0
.603384 0.689164 0.679915 0.362798 0.379332 1.59464 0.033999 30.2239 7.34539 38.7265 9.99554
0 983733
0 884555
1 17147
0 654067
1 07299
0 406567
0 189138
30 0055
7 62725
38 1921
9 68681
5
10
15
20
25
30
35
40
0 500 1000 1500
Iterations (thousands)
Length (OCL, mm) at 50% selection
Commercial
Research
Photographic
Figure 20: MCMC traces for the lengths at 50% selection for commercial fishing, research trawling, and the
photographic survey in the working model. The chain was “burnt in” over the first 500 000 iterations.
-0.25
0.00
0.25
0.50
0.75
1.00
02468
Lag between MCMC samples
Autocorrelation coefficient
Bzero
M
Comm50
Rsch50
Photo50
upper
lower
10
Figure 21: Estimated autocorrelation coefficients for B0, M, and the three L50s within the MCMC chain from the
working model. Critical values at α = 0.01 are shown as heavy dashed lines.
Model estimates
Estimated Bayesian posterior distributions for the unfished recruited biomass (B0) and the rate of natural mortality (M)
were reasonably well-defined and close to normally distributed (Figure 22). Posteriors for the lengths at 50% selectivity
by research and commercial trawling were also good (Figure 23), but that for the length at 50% selectivity by the
photographic method was poorly-defined and had numerous peaks and a wide range. This was not unexpected given the
“rambling” nature of the MCMC trace for this measure.
WGNEPH Report 2004
392

0
20
40
60
80
100
120
140
160
180
200
1200 1400 1600 1800 2000 2200 2400
Unfished spawning biomass (t)
F
0
50
100
150
200
250
0.15 0.16 0.17 0.18 0.19 0.2
0
Natural mortality (M)
F
Figure 22: Estimated Bayesian posterior distributions for un-fished spawning biomass (left) and natural mortality (right)
from the working model.
0
50
100
150
200
250
300
350
400
0 10203040
Length (OCL, mm) at 50% selection
F
Figure 23: Estimated Bayesian posterior distributions for lengths at 50% selection for (left to right) photographic
surveys, research trawling, and commercial trawling from the working model.
The relationship between the length at 50% selection and the selection range (the “steepness” of the selectivity ogive)
was tight for both trawl methods (Figure 24), but very poorly defined for the photographic method. In particular, the
MCMC chain wandered very close to the bounds set for both parameters of the photographic selectivity ogive and
appears to have been constrained by them. This suggests that the selectivity of the photographic approach is very poorly
defined in this particular model, perhaps because no photographic length frequency data were included.
WGNEPH Report 2004 393

0
2
4
6
8
10
12
14
0 10203040
Length (OCL, mm) at 50% selection
Selection range (mm)
Maturity
Figure 24: Relationships between lengths at 50% selection and selection range for (left to right) photographic surveys,
research trawling, and commercial trawling from the working model. The much tighter relationship for length at
maturity is shown for comparison.
The model estimated quite variable, but clearly temporally auto-correlated, relative year class strengths. The model
suggested a series of relatively good recruitment years in the mid to late-1980s, poor recruitment in the early 1990s, and
roughly average recruitment since 1995. Without auxiliary data on historical levels of recruitment, however, these
estimates cannot be validated.
0
1
2
3
4
5
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
Year (1986 = 1985/86 fishing year)
Recruitment index (+/- SD from MCMC)
Figure 25: Estimated recruitment indices for 1986 to 2002 with their estimated standard deviations from the MCMC
chain from the working model.
WGNEPH Report 2004
394

Table 4: Objective function values (negative log-likelihood) for MPD fit (Model 11) to data, priors, and penalties (on
catch not taken and the failure to generate a YCS vector averaging 1.0), and the total objective function (negative log-
likelihood) value.
Data:
CPUE-Commercial-Jan -2.52498
CPUE-Commercial-Oc
t
-0.40936
PhotoSurve
y
-0.58612
TrawlSurve
y
5.45777
TrawlSurve
y
ProportionAtLen
g
th-Jan 437.194
TrawlSurve
y
ProportionAtLen
g
th-Oc
t
46.4588
CommercialCatchLen
g
thJan 1458.68
CommercialCatchLen
g
thOc
t
728.398
Maturit
y
(Cr
y
er&Oliver) 36.1983
Priors:
Prior
_
on
_
initialization.B0 0
-1.5902
Prior
_
on
_
recruitment.YCS 0.24706
Prior
_
on
_
maturit
y_
props.all 0
Prior
_
on
_
selectivit
y
[Fishin
g
Sel].male 0
Prior
_
on
_
selectivit
y
[TrawlSurve
y
Sel].male 0
Prior
_
on
_
selec
t
ivit
y
[PhotoSurve
y
Sel].male 0
Prior
_
on
_
q
_
CPUE-Commercialq -3.35756
Prior
_
on
_
q
_
PhotoSurve
y
q 1.46629
Prior
_
on
_
q
_
TrawlSurve
y
q -4.7495
Penalties:
OctCatchMustBeTaken 0
JanCatchMustBeTaken 0
YCS
_
avera
g
e
_
1 0.035962
Total Ob
j
ective function 2700.92
Prior
_
on
_
natural
_
mortalit
y
.all
Model fits to data
The trajectory of stock biomass shows an initial period of steady or increasing biomass (following the years of good
recruitment), followed by a decline in the recruited biomass (Figure 26). Model estimates suggested that the initial
spawning stock biomass was about 1550 t, and the current size is about 625 t (about 40% of B0). Model fits to both
commercial and research trawl-based abundance indices were generally poor. The model failed to reproduce the
characteristic cycling of catch rates observed by both commercial fishers and research trawling and, in particular, could
not reproduce the low catch rates in about 1992 and the high catch rates peaking in about 1995 and 1996. Conversely,
the model fit to the photographic estimate of relative abundance was quite good.
WGNEPH Report 2004 395

1990 1995 2000
0.00.5 1.01.5
Year
Biomass ('000 t)
(a) SSBs
1990 1995 2000
0 20406080
Year
CPUE
o
ooo
o
oo
o
oo
oooo
eeeeeeeeeeeeee
(b) CPUE-Commercial-Oct
1990 1995 2000
0 20406080
Year
CPUE
oooo
oo
ooo
o
o
ooo
eeeeeeeeeeeeee
(c) CPUE-Commercial-Jan
1990 1995 2000
0.00 0.02 0.04
Year
Biomass ('000 t)
oo
oo
oooo
eeeeeeee
(d) TrawlSurvey
Figure 26: Model trajectory of spawning stock biomass (top left) and fits to trawl-based candidate indices of relative
biomass (o = observed datum, e = fitted value).
Model fits to commercial and research survey length frequency distributions were reasonable in general form, although
the model did not reproduce the systematic variation of relative proportions of males and females in concert with catch
rates. In 1993, the model closely reproduced the sex ratio as well as the form of length frequency distributions (Figure
27) whereas the increasing proportion of males in the observed distributions was not reproduced.
WGNEPH Report 2004
396

10 20 30 40 50 60
0.00 0.04 0. 08
length
(a) Trawl-Jan (M, 1993)
10 20 30 40 50 60
0.00 0.04 0. 08
lengt h
(b) Trawl-Jan (F, 1993)
10 20 30 40 50 60
0.00 0.04 0. 08
length
(c) Trawl-Jan (M, 1994)
10 20 30 40 50 60
0.00 0.04 0. 08
lengt h
(d) Trawl-Jan (F, 1994)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Trawl-Jan (M, 1995)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Trawl-Jan (F, 1995)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Trawl-Jan (M, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Trawl-Jan (F, 1996)
Figure 27: Model fits (dashed lines) to observed (solid lines) research length frequency distributions between 1993 and
1996. Note especially the poor model reproduction of the systematic changes in the relative proportions of males and
females.
MCMC estimates for the median posterior and 95% percentile credible intervals are reported for the key output
parameters (Table 5). In general, the point estimates are close to the medians of the posteriors, and most parameters are
precisely estimated. The main exceptions are the selectivity parameters for the photographic method and the recent
recruitment deviations. None has much effect on the model estimates of unfished recruited biomass or M.
WGNEPH Report 2004 397

Table 5: Point estimates for each of the estimated values in the working model and median values and limits to the 95%
credible range from the MCMC chain. The “CV” is estimated as one-quarter of the 95% credible range divided by the
median.
Estimate Point Median Lower Upper "CV"
Bzero 1552 1628 1424 1990 0.09
M 0.174 0.176 0.167 0.186 0.03
R_1985 1.096 1.116 0.736 1.695 0.21
R_1986 3.637 3.673 2.386 5.055 0.18
R_1987 1.865 1.993 1.127 2.900 0.22
R_1988 1.925 2.015 1.499 2.670 0.15
R_1989 1.826 1.926 1.488 2.436 0.12
R_1990 0.760 0.815 0.576 1.097 0.16
R_1991 0.666 0.700 0.507 0.928 0.15
R_1992 0.491 0.529 0.382 0.696 0.15
R_1993 0.380 0.409 0.288 0.552 0.16
R_1994 0.143 0.161 0.094 0.274 0.28
R_1995 0.907 0.953 0.685 1.312 0.16
R_1996 0.595 0.651 0.440 0.960 0.20
R_1997 0.598 0.640 0.424 0.929 0.20
R_1998 0.900 0.988 0.670 1.366 0.18
R_1999 0.407 0.458 0.259 0.792 0.29
R_2000 0.395 0.477 0.231 0.996 0.40
R_2001 1.060 0.946 0.284 2.200 0.51
R_2002 0.010 0.203 0.015 0.972 1.18
Maturity50 30.22 30.22 30.03 30.41 0.00
Maturity95 7.37 7.37 7.12 7.64 0.02
Comm50 38.41 38.44 37.50 39.55 0.01
Comm95 9.97 9.96 9.27 10.81 0.04
Rsch50 29.49 29.58 28.50 30.80 0.02
Rsch95 8.76 8.86 7.58 10.39 0.08
Photo50 5.00 11.95 5.59 19.53 0.29
Photo95 1.13 3.31 1.11 10.81 0.73
Discussion
General points
The working model is presented as a starting point for discussion on the development of a length-based stock
assessment model(s) for scampi. The stock in QMA 1 was used as the test case because It has been fished for longest
and substantially more information is available from a variety of sources (particularly from photographic surveys that
might be considered fully fishery-independent). However, models for other areas could be developed using the
experience gained with QMA 1.
Comparison of model outputs with independent data
Deepwater species are typically difficult to assess, at least in part because estimates of absolute abundance and biomass
are so difficult to obtain. For scampi, the development of a quantitative photographic approach provides a rare
opportunity to compare model trajectories of total, recruited, or mature (spawning) biomass with independent estimate
of absolute biomass. Cryer et al. (2003) derived estimates of the total biomass of visible scampi (i.e., all visible animals,
so not restricted to recruited or mature scampi) and suggested these could be used as minimum estimates of absolute
biomass (because some scampi might be hidden from view in their burrows, Table 6). Formal comparisons have not
been made at the time of writing, but Cryer et al.’s (2003) estimates of minimum biomass seem very close to the
spawning stock biomass trajectory from the working model. However, this comparison is simplistic because the
minimum biomass estimates include all biomass (not just spawning stock) but, conversely, cover only part of the
QMA 1 stock (albeit the most frequently and heavily fished part). More detailed analyses are required to partition the
minimum biomass estimates and compare them more properly with the model outputs. It may also be possible to
include this data set in the model formally, but this needs discussion.
WGNEPH Report 2004
398

Table 6 (after Cryer et al. 2003): Estimates of the (total) biomass of visible scampi within strata 302, 303, 402, and 403
between 1998 and 2003 made using a mean average weight of 35.4 g. These estimates are probably close to estimates of
“minimum biomass”. Scampi “not in burrows” were defined as those for which the telson was not obscured by a
burrow. The specified c.v.s are underestimates because they do not include variance associated with conversions from
observed cheliped length to individual weight.
All visible scampi Scampi not in burrows
Biomass (t) Min. c.v. Biomass (t) Min. c.v.
1998 988 22.3 393 45.8
2000 644 18.2 287 25.4
2001 435 26.3 71 53.5
2002 591 21.3 85 61.6
2003 509 21.1 62 40.9
Cryer et al. (2003) went further and estimated (total) biomass (Table 7) from the density of burrows and an assumed
mean weight (estimated for visible and measurable scampi). The assumptions in this calculation are much more onerous
than those in the estimate of minimum biomass but, prima facie, the model estimates of biomass are only about one-
quarter of the estimates made by Cryer et al. (2003) using burrow density. Again, much more analysis is required and a
discussion is needed on the approach.
Table 7 (after Cryer et al. 2003): Estimates of (total) biomass (t) of scampi within strata 302, 303, 402, and 403 between
1998 and 2003 made by multiplying the estimated abundance of major burrow openings by a mean average weight of
35.4 g. Counts by each reader within “corrected” estimates have been scaled by the inverse of reader factors estimated
from the linear model. The specified c.v.s are underestimates because they do not include variance associated with
conversions from observed cheliped length to individual weight.
Uncorrected Corrected
Biomass (t) Min. c.v. Biomass (t) Min. c.v.
1998 5 434 14.7 5 491 14.7
2000 3 335 12.5 3 423 12.7
2001 4 673 11.8 4 811 11.8
2002 4 761 8.0 4 538 8.1
2003 3 605 12.2 3 606 12.0
Acknowledgments
We thank the many NIWA staff and observers who have measured many thousands of scampi over the years, and Jim
Drury, Matt Smith, Crispin Middleton, and Helena Armiger who have screened many hundreds of seabed photographs
alongside the authors. Helena also generated the size frequency distributions from seabed photographs. The project was
funded by the Ministry of Fisheries under Objective 3 of project SCI2003/02.
WGNEPH Report 2004 399

References
Annala, J.H.; Sullivan, K.J.; O'Brien, C.J.; Smith, N.W.McL.; Grayling, S.M. (Comps.) (2003). Report from the Fishery
Assessment Plenary, May 2003: stock assessments and yield estimates. 616 p. (Unpublished report held in NIWA
library, Wellington.)
Bull, B.; Dunn, A. (2002). Catch-at-age: User manual v1.06.2002/09/12. NIWA Internal Report 114. 23 p. NIWA.
(Unpublished report held in NIWA library, Wellington.)
Bull, B.; Francis, R.I.C.C.; Dunn, A.; McKenzie, A.; Gilbert, D.J.; Smith, M.H. (2003). CASAL (C++ algorithmic stock
assessment laboratory): CASAL user manual v2.01-2003/08/01. NIWA Technical Report 124. 223 p.
Charnov, E. L., Berrigan, D. & Shine, R. 1993: The M/k ratio is the same for fish and reptiles. American Naturalist
142:707–711.
Cryer, M.; Coburn, R. (2000). Scampi assessment for 1999. New Zealand Fisheries Assessment Report 2000/7. 60 p.
Cryer, M.; Hartill, B.; Drury, J.; Armiger, H.J.; Smith, M.D.; Middleton, C.J. (2003). Indices of relative abundance for
scampi, MetaNephrops challengeri, based on photographic surveys in QMA 1 (1998–2003) and QMA 2 (2003).
Final Research Report for Project SCI2002/01 (Objectives 1–3). 18 p.
Cryer, M.; Oliver, M. (2001). Estimating age and growth in New Zealand scampi, MetaNephrops challengeri. Final
Research Report for Ministry of Fisheries Project SCI9802 (Objective 2).
Cryer, M.; Stotter, D. R (1997). Trawling and tagging of scampi off the Alderman Islands, western Bay of Plenty,
September 1995 (KAH9511). New Zealand Fisheries Data Report 84. 26 p.
Cryer, M.; Stotter, D. R (1999). Movements and growth rates of scampi inferred from tagging, Aldermen Islands,
western Bay of Plenty. NIWA Technical Report 49. 35 p.
Francis, R.I.C.C. (1988). Maximum likelihood estimation of growth and growth variability from tagging data. New
Zealand Journal of Marine and Freshwater Research 22(1): 43–51.
Hartill, B.; Cryer, M. (2000). A review of the adequacy of current observer coverage and practices for scampi. Final
Research Report for Ministry of Fisheries Research Project MOF1999/04J. 46 p.
Hartill, B.; Cryer, M. (2004). Unstandardised scampi CPUE indices update for scampi 1988–2003. Final Research
Report for Ministry of Fisheries Research Project SCI2001/02, Obj. 2. 35p.
I.C.E.S. (2000). Report of the study group on life histories of Nephrops, Reykjavik, Iceland. May 2000. I.C.E.S. CM
2000:G, Living Resources Committee. 184 p.
Pauly, D. 1980: On the interrelationships between natural mortality, growth parameters, and mean environmental
temperature in 175 fish stocks. Journal du Conseil International pour L’exploration de la Mer 39: 175–192.
Ricker, W.E. 1975: Computation and Interpretation of Biological Statistics of Fish Populations. Bulletin 191,
Department of the Environment, Fisheries and Marine Service, Ottawa, Canada. 382 p.
Wear R.G. (1976). Studies on the larval development of MetaNephrops challengeri (Balss, 1914) (Decapoda,
Nephropidae). Crustaceana 30:113–122.
WGNEPH Report 2004
400

Appendix 1.1: Fits and diagnostic plots from Model 11. Model fits to candidate relative abundance indices (top) and q-q
plots (bottom).
1990 1995 2000
0.0 0.5 1. 0 1.5
Year
Biomass ('000 t)
(a) SSBs
1990 1995 2000
0 20406080
Year
CPUE
o
ooo
o
oo
o
oo
oooo
eeeeeeeeeeeeee
(b) CPUE-Commerci al-Oct
1990 1995 2000
020406080
Year
CPUE
oooo
oo
ooo
o
o
ooo
eeeeeeeeeeeeee
(c) CPUE-Commercial-Jan
1990 1995 2000
0.00 0.02 0.04
Year
Biomass ('000 t)
oo
oo
oooo
eeeeeeee
(d) TrawlSurvey
1990 1995 2000
0.0 0.1 0.2 0.3 0.4
Year
Biomass ( '000 t)
o
oooo
eeeee
(e) PhotoSurvey
-4 -2 0 2 4
-4 -2 0 2 4
Quantiles of Standar d Normal
Normalised res iduals
(a) CPUE-Oct
-4 -2 0 2 4
-4 -2 0 2 4
Quantiles of Standard Normal
Normalised res iduals
(b) CPUE-Jan
-4 -2 0 2 4
-4 -2 0 2 4
Quantiles of Standar d Normal
Normalised res iduals
(c) TrawlSurvey
-4 -2 0 2 4
-4 -2 0 2 4
Quantiles of Standard Normal
Normalised res iduals
(d) PhotoSurvey
WGNEPH Report 2004 401

Appendix 1.2: Fits and diagnostic plots from Model 11. Model fits (top to bottom) to selectivity ogives, a pooled
maturity ogive, relative year class strengths, and exploitation rates for steps 1 and 2.
10 20 30 40 50 60
0.0 0.4 0.8
Len
g
th
Selec tivity
(c) Photo survey selectivity
1990 1995 2000
0246810
Relative year class strength
1990 1995 2000
0.00 0.10 0.20
Fishing pres sure
1990 1995 2000
0.00 0.10 0.20
Fishing pres sure
WGNEPH Report 2004
402

Appendix 1.3: Fits and diagnostic plots from Model 11. Observed (solid lines) and fitted (dashed lines) length
frequency distributions from research trawl surveys in step 2 (January to September) of 1993 to 2002. Both sexes are
combined for the q-q plots
.
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Trawl-Jan (M, 1995)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Trawl-Jan (F, 1995)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Trawl-Jan (M, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Trawl-Jan (F, 1996)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Trawl-Jan (M & F, 1995)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Trawl-Jan (M & F, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Trawl-Jan (M, 1993)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Trawl-Jan (F, 1993)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Trawl-Jan (M, 1994)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Trawl-Jan (F, 1994)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Trawl-Jan (M & F, 1993)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Trawl-Jan (M & F, 1994)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Trawl-Jan (M, 1998)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Trawl-Jan (F, 1998)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Trawl-Jan (M, 2000)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Trawl-Jan (F, 2000)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Trawl-Jan (M & F, 1998)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Trawl-Jan (M & F, 2000)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Trawl-Jan (M, 2001)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Trawl-Jan (F, 2001)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Trawl-Jan (M, 2002)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Trawl-Jan (F, 2002)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Trawl-Jan (M & F, 2001)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Trawl-Jan (M & F, 2002)
WGNEPH Report 2004 403

Appendix 1.4: Fits and diagnostic plots from Model 11. Observed (solid lines) and fitted (dashed lines) length
frequency distributions from research trawl surveys in step 1 (October to December) of 1996 and 1997. Both sexes are
combined for the q-q plots.
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Trawl-Oct (M, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Trawl-Oct (F, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Trawl-Oct (M, 1997)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Trawl-Oct (F, 1997)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Trawl-Oct (M & F, 1996)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Trawl-Oct (M & F, 1997)
WGNEPH Report 2004
404

Appendix 1.5: Fits and diagnostic plots from Model 11. Observed (solid lines) and fitted (dashed lines) length
frequency distributions from scientific observers on board scampi trawlers in step 2 (January to September) of 1991 to
2000. Both sexes are combined for the q-q plots.
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Catch (M, 1991)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Catch (F, 1991)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Catch (M, 1992)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Catch (F, 1992)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Catch (M & F, 1991)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Catch (M & F, 1992)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Catch (M, 1994)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Catch (F, 1994)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Catch (M, 1995)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Catch (F, 1995)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Catch (M & F, 1994)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Catch (M & F, 1995)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Catch (M, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Catch (F, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Catch (M, 1997)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Catch (F, 1997)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Catch (M & F, 1996)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Catch (M & F, 1997)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Catch (M, 1999)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Catch (F, 1999)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Catch (M, 2000)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Catch (F, 2000)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Catch (M & F, 1999)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Catch (M & F, 2000)
WGNEPH Report 2004 405

Appendix 1.6: Fits and diagnostic plots from Model 11. Observed (solid lines) and fitted (dashed lines) length
frequency distributions from scientific observers on board scampi trawlers in step 1 (October to December) of 1992 to
2002. Both sexes are combined for the q-q plots.
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Catch (M, 1992)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Catch (F, 1992)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Catch (M, 1993)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Catch (F, 1993)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Catch (M & F, 1992)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Catch (M & F, 1993)
10 20 30 40 50 60
0.00 0.04 0.08
length
(a) Catch (M, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(b) Catch (F, 1996)
10 20 30 40 50 60
0.00 0.04 0.08
length
(c) Catch (M, 2002)
10 20 30 40 50 60
0.00 0.04 0.08
length
(d) Catch (F, 2002)
-4 -2 0 2 4
-4 -2 0 2 4
Theore tical Quantiles
Sample Q uantiles
(e) Catch (M & F, 1996)
-4-2024
-4 -2 0 2 4
Theoretical Quantiles
Sample Q uantiles
(f) Catch (M & F, 2002)
WGNEPH Report 2004
406

APPENDIX 8
Working Document to WGNEPH, March 2004
More thoughts on a length-based approach to the assessment of Firth of Forth Nephrops :
incorporation of auxiliary data.
Helen Dobby
FRS Marine Laboratory
Aberdeen
1. Introduction
Last year an exploratory assessment of Firth of Forth Nephrops was carried out using a length-based population model.
The reasoning behind this alternative approach was that making direct use of the catch-at-length data may be more
appropriate than slicing the distribution into ‘age classes’ and then conducting an age-based assessment which is the
current approach. This process of slicing into age classes does not take account of the variability in growth and hence
the variability in length-at-age, which implies that at larger sizes in particular, individuals of the same length may be
different ages. As a consequence the generated ‘age classes’ are likely to consist of individuals of number of different
actual ages.
The assessment method is a modified catch-at-size analysis (CASA) based on that described in Sullivan et al.
(1990) and uses a size transition matrix approach. It has been used in the assessment of the stock of Northern Shelf
anglerfish (ICES 2003) and a series of a series of working documents describes the model development (Dobby, 2000,
2002). The population is described by a vector of numbers-at-length which is projected forwards in time using a size
transition matrix obtained from a stochastic growth model with known parameters. All population dynamic processes
(e.g. recruitment, fishing mortality) are assumed to depend on length rather than age. Parameter estimates (annual
recruitment, mean and standard deviation of recruitment length distribution, selectivity parameters and time dependent
fishing mortality) are then obtained by fitting the yearly catch-at-length predicted by the model to the observed data.
The parameters can then be used (together with estimates of maturity and individual weight) in yield-per-recruit
analysis and to obtain short-term predictions of catch and biomass. A more detailed description of the model and it’s
implementation as applied to Nephrops can be found in Dobby (2003).
The paper presented last year focused on the development of a model which provided a good fit to the quarterly
commercial catch-at-length distribution data. This year we consider how the resulting estimates of stock biomass,
recruitment, etc might be validated or altered by consideration of auxiliary data.
Data
The commercial fishery data available for use in this method consist of quarterly catch-at-length in numbers by sex
from 1981-2002 plus the associated quarterly effort data.
In addition there are estimates of abundance (in numbers) and stock biomass from a TV survey which began in
1993.
General asssumptions
• Mean growth described by von Bertalanffy growth function with parameters given below
Female Male
Immature Mature Immature Mature
L∞ (mm) 66 58 66 66
k (yr-1) 0.163 0.065 0.163 0.163
• Female maturity at length is assumed to be knife-edged at 26mm
• Variability in growth is modelled using a beta function
• Growth is assumed to be time independent i.e. no seasonal effects
WGNEPH Report 2004 407

• Natural mortality is constant over time, but dependent on sex and maturity: M=0.2yr-1 for mature females and
0.3yr-1 for all other individuals.
• Fishing mortality is assumed independent of sex and separable into a temporal component and length dependent
‘selectivity’ curve which takes the form of a logistic function parameterized by a slope and length at 50%
maximum selectivity
• Equal numbers of males and females recruit to the fishery, with the same length distribution
In the model presented last year the seasonal behavioural patterns which result in intra-annual variations in catch rates
were implemented with the introduction of an ‘availability’ function which is used to model the variation in emergence
of mature female Nephrops during the year. The model works by assuming that a proportion of the mature female
population are available to the fishery i.e. subject to fishing and natural mortality while the remaining proportion are
hidden and undergo only natural mortality. The ‘available’ component of the female population is subject to the same
fishing mortality as the male population. However, to obtain an estimate of the effective fishing mortality on the whole
female population, the following transcendental equation must be solved
()
()
()
(
)
MsF
l
q
y
l
q
y
q
Msf
l
q
y
l
q
yl
q
yl
q
ye
MsF
sF
Ave
Msf
sf +−+− −
+
=−
+11
•
•
•
•
•
•
•
•
•
•
where is the temporal component of the fishing mortality (quarter and year), sl is the length dependent selectivity, M is
the natural mortality and Avq is the quarterly mature female availability. Assuming that we are interested in fully
selected individuals, then the equation can be simplified by substituting sl=1 is substituted into the above. An
alternative, possibly more transparent approach to modelling variable female emergence which avoids the solution of
transcendental equations is considered in a later section.
Baseline model
Assumptions
Fishing mortality estimated for each quarter, year combination i.e. no fixed seasonal distribution
Total annual fishing mortality is (weakly) constrained by annual effort
Population assumed to start from equilibrium with historical fishing mortality estimated by fitting the predicted
historical equilibrium catch to the average observed catch over the previous 10 years
Quarterly availability of females is estimated, male availability is fixed (equal to 1.0)
Results
A summary of the results of a base run (configuration as per Dobby 2003, but using updated catch-at-length data) is
given in Figures 1 & 2. The model gives a relatively good fit the catch-at-length data (not illustrated, but see Dobby
2003 for details) with no obvious trends in the residuals (Figure 2). Figure 1 illustrates a summary of the stock trends
from this model.
Relatively stable estimated stock biomass over 12 year period
Estimated female stock biomass between 4-5 thousand tonnes which is almost twice that of the males
Recruitment trends show a very large year class in 1993
For males, annual F is the sum over quarters of the temporal component of the fishing mortality, that is, the fishing
mortality of the fully selected individuals. For females equation (1) has to be used in the calculation.
Length at 50% selectivity is estimated to be 24.5 mm and the slope of the logistic selectivity curve is 0.56.
Mature female availability is estimated to be (0.16,0.30,0.36,0.17) i.e. lowest in quarters 1 & 4 and highest in
quarter 3, compared to male availability of 1.0 for all quarters. Male availability must be fixed as estimates are
confounded with estimated fishing mortality. For example, assuming a fixed male availability of 0.75 causes
increases in the estimated temporal components of the fishing mortality & decreases in the female availability so
that the effective fishing mortalities are unchanged.
Although there are no obvious trends in the residuals, there are still some year/quarter/sex combinations for which
there is general under or over- prediction e.g. female 1994 quarter 4, male 1999 quarter 3. It may be that emergence in
these particular quarters differs substantially from the estimated quarterly pattern. A possible solution to this problem is
WGNEPH Report 2004
408

to estimate fishing mortality separately (or linked less closely) for males and females. However, this option is not
investigated further here.
Catchability versus Availability
An alternative way of modelling the differences implied by the seasonal changes in availability of mature female
Nephrops is just to assume that fishing mortality on mature females is a fraction of that of males:
() ()
l
q
yq
q
lyq
q
ly sfKmFKfF ==
()
fF q
ly
•
•
where is effective female fishing mortality and Kq is a quarterly dependent parameter (to be estimated) which
represents the catchability of mature females relative to the rest of the stock. This provides a much more transparent
way of modelling differences in male and female fishing mortality.
Results
The fit of the new model to the catch-at-length data is indistinguishable from that of the ‘availability’ model and the
stock summaries illustrated in Figure 3 show only very minor differences.
The estimated ‘catchabilities’ of mature females relative to males are (0.18,0.34,0.38,0.18) which are very similar
to the quarterly availabilities estimated in the previous model run (0.16,0.30,0.36,0.17).
Length at 50% selectivity is estimated to be 24.3 mm and the slope of the logistic selectivity curve is 0.57 (Previous
run 24.5 mm & 0.56).
Before considering how we can make use of TV survey information, the model is run using the full time series of
commercial catch-at-length and effort data (1981-2002). The incorporation of this extra data results in small increases
in the recent estimates of total stock biomass when compared to the shortened time series results and very minor
differences to estimated recruitment and fishing mortality (Figure 4). Since the whole time series of data is being used
in the assessment procedure there is no information how the stock has been exploited prior to this on which to help our
estimates of the initial conditions. However, the sensitivity analysis shown in Figure 5 which makes different
assumptions about the historical equilibrium fishing mortality (F*) shows that estimates of recent stock trends are very
insensitive to the assumed initial conditions. In fact, it is really only the estimated stock biomass and catches in the first
5 years that are sensitive to the initial conditions.
Use of Survey Data (biomass)
Figure 6 gives a comparison of length-based analysis stock trends and those resulting from the XSA assessment
conducted at last year’s working group. Both methods give estimates of fishing mortality and recruitment which show
similar trend, but the LBA estimated recruitment shows much more significant fluctuations while fishing mortalities on
female Nephrops are slightly lower than XSA estimates. Female stock biomass estimates are comparable for both
methods while LBA gives significantly lower estimates of male stock biomass. Neither of these illustrated runs make
use of any fishery independent data.
The LBA is able to make use of auxiliary information in the form of survey length distribution data, indices of
absolute and relative biomass which may be differentiated by sex and maturity, and indices of recruitment. TV survey
data from the Firth of Forth is shown in Table 1. The mid-point of the biomass range is incorporated into the LBA as
an estimate of absolute stock biomass.
Results
The incorporation of the survey data did not substantially worsen the fit of the model to the commercial catch-at-length
data – the residual plots were examined and no systematic errors were apparent (plot not shown). The resulting
estimated stock trends are illustrated in Figure 7. Runs are compared in which the survey data is given a high weight
and low weight in the objective function calculation. The run labelled ‘zero weight’ is our original catchability model
run incorporating no survey information. Incorporation of the survey data has a significant effect on stock summaries.
Trends in recruitment and fishing mortality remain broadly similar although estimates of F in the years prior to survey
are lower when the survey is included and recruitment is estimated to be higher. The most significant effects are on the
estimated stock biomass, both on the actual level and trends:
• In the period prior to the survey, the biomass estimates for both males and females are substantially higher, but
follow a similar trend to the run without survey data
• Large increases in stock biomass in 1993-1994 – first few years of survey, followed by decline to late 1990s.
WGNEPH Report 2004 409

• Towards the end of the time series (last 4 years) the biomass estimates from the 3 runs are more similar.
Other parameter estimates such as those defining the length based selectivity curve (L50% = 24.25, slope=0.61) and
female catchability (0.17,0.32,0.36,0.18) are very similar to previous estimates.
Comments
The survey data and commercial catch presented paint quite different pictures of the historic stock trends. That the
survey biomass estimates are larger than those from the assessment without survey data may not be surprising as the
survey may cover a wider area than the fishery. However, the differences in trend over the period 1993-1997 are
difficult to resolve. Two possible explanations for this mismatch are:
1. Commercial catchability has increased over this period which is not incorporated in the model and therefore even if
the stock biomass decreased, catches have remained stable.
2. The trend in the survey is largely driven by two extreme values - a very high value in 1993 and a very low value in
1998. Was there particularly good/bad weather, different burrow counters in these years?
Use of Survey Data (numbers)
Earlier discussions of TV data (ICES, 1997) have suggested that TV surveys may provide reasonable estimates of
trends in recruiting year class. The estimates of total annual recruitment are unconstrained except by the commercial
catch-at-length distribution data which do not show signals which might indicate when a large year class may be
entering the fishery. The abundance in numbers is incorporated in the LBA as an index of recruitment.
Results
The results are illustrated in Figure 9. The estimated stock trends in the early part of the time series before the survey
data is available are virtually unchanged. The differences which occur in the most recent years are highlighted below
The general trends in the estimated recruitment remain relatively similar with the inclusion of the recruitment index
although there may be some evidence that recruitment has been higher in recent years than estimated by the catch-
at-length data alone.
•
•
•
•
Estimated stock biomass virtually indistinguishable except for most recent years where it is predicted to be higher
than in the run without the recruitment index
Similarly fishing mortality for both males and females is unchanged except for the most recent years in which it is
lower.
Estimates of the selectivity parameters and female catchability are very similar to previous model runs
Comments
Although the addition of the survey recruitment index does not substantially change the view of the stock it does
provide different (hopefully better if we believe the survey!) estimates of recruitment. The recent recruitment is
estimated to be higher when the recruitment index is incorporated and this results in slightly higher stock biomass and
lower fishing mortality.
Round-up
1. It is reassuring that the results from this exploratory assessment show similar trends in stock biomass and fishing
mortality to the XSA assessment conducted last year.
2. Further consideration is required of the differences between biomass as estimated by the survey and that predicted
by the assessment based on only the commercial catch-at-length and effort data.
3. This paper further highlights the difficulties in obtaining good estimates of total recruitment from catch-at-length
data alone when there is no strong signal in the length frequency data. In such cases it is likely that auxiliary
information in the form of a recruitment index will help to provide better estimates.
WGNEPH Report 2004
410

References
Dobby, H. 2000. A length-based population model for anglerfish. Working Document for the Working Group on the
Assessment of Northern Shelf Demersal Stocks 2000.
Dobby, H. 2002. A length-based population model for anglerfish in Division VIa: developments in growth modelling.
Working Document for the Working Group on the Assessment of Northern Shelf Demersal Stocks 2002.
Dobby, H. 2003. Investigating a size-transition matrix approach to the assessment of Nephrops. Working Document
for the Working Group on Nephrops Stocks 2003.
ICES 1997. Report of the Working Group on Nephrops Stock. ICES CM 1997/Assess:11 (mimeo)
ICES 2003. Report of the Working Group on the Assessment of Northern Shelf Demersal Stocks, 2002. ICES CM
2003/ACFM:04.
Sullivan, P. J., H-L. Lai and V. F. Gallucci. 1990. A catch-at-length analysis that incorporates a stochastic model of
growth. Can. J. Fish. Aquat. Sci. 47, 184-198.
WGNEPH Report 2004 411

Table 1. Firth of Forth Nephrops. Results of the 1993-2002 TV surveys.
burrows/m² millions millions '000 tonnes
0.72 655 167 9.9-16.7
0.58 529 92 7.6-10.8
0.48 443 104 5.8-9.3
0.38 345 95 4.2-7.5
0.60 546 92 7.7-10.8
0.57 523 83 7.5-10.3
0.54 494 93 6.8-10.0
0.66 600 140 7.8-12.6
Year
Mean
density Abundanc
e
95%
confidenc
e
Biomass
1993
1994
1995 No survey
1996
1997 No survey
1998
1999
2000
2001
2002
WGNEPH Report 2004
412

Figure 1a. Firth of Forth Nephrops: Females. Summary of results of baseline model run: Trends in catches, total stock
biomass, fishing mortality and recruitment.
catches
Year
'000t
1992 1994 1996 1998 2000 2002
0.0
0.5
1.0
1.5
2.0 model
landings
catch
total stock biomass
Year
'000t
1992 1994 1996 1998 2000 2002
0
1
2
3
4
5
annual F
Year
1992 1994 1996 1998 2000 2002
0.0
0.1
0.2
0.3
0.4
91 92 93 94 95 96 97 98 99 00 01 02
0
100
200
300
400
recruits
millions
catches
Year
'000t
1992 1994 1996 1998 2000 2002
0.0
0.5
1.0
1.5
2.0
2.5
3.0 model
landings
catch
total stock biomass
Year
'000t
1992 1994 1996 1998 2000 2002
0
1
2
3
4
annual F
Year
1992 1994 1996 1998 2000 2002
0.0
0.5
1.0
1.5
2.0
91 92 93 94 95 96 97 98 99 00 01 02
0
100
200
300
400
recruits
millions
Figure 1b. Firth of Forth Nephrops: Males. Summary of results of baseline model run: Trends in catches, total stock
biomass, fishing mortality and recruitment.
WGNEPH Report 2004 413

Female
Quarter 1
1992 1994
0
5
0Female
Quarter 2
Quarter 3
catch-at-length distribution.
-1.0
-0.5
0.0
0.5
1.0
1996 1998 2000 2002
Male
Quarter 1
-1.0
-0.5
0.
0.
1. Male
Quarter 2
Female
-1.0
-0.5
0.0
0.5
1.0
Male
Quarter 3
-1.0
-0.5
0.0
0.5
1.0
1992 1994 1996 1998 2000 2002
Female
Quarter 4
Male
Quarter 4
Year
scaled residual
Firth of Forth Nephrops - LBAv5.2. Residual plots: Estimated-Observed
Figure 2. Firth of Forth Nephrops. Residual plots: Estimated-Observed catch-at-length distribution data by year,
quarter and sex from the baseline run.
WGNEPH Report 2004
414

Figure 3a. Firth of Forth Nephrops: Females. Summary of stock trends comparing catchability and availability model.
catches
Year
'000 t
1992 1994 1996 1998 2000 2002
0.0
0.5
1.0
1.5
2.0
catchability
availability
stock biomass
Year
'000 t
1992 1994 1996 1998 2000 2002
0
1
2
3
4
annual F
Year
1992 1994 1996 1998 2000 2002
0.0
0.5
1.0
1.5
2.0
recruits
Year
millions
1992 1994 1996 1998 2000 2002
0
100
200
300
400
catches
Year
'000 t
1992 1994 1996 1998 2000 2002
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
catchability
availability
stock biomass
Year
'000 t
1992 1994 1996 1998 2000 2002
0
1
2
3
4
5
6
annual F
Year
1992 1994 1996 1998 2000 2002
0.0
0.1
0.2
0.3
0.4
recruits
Year
millions
1992 1994 1996 1998 2000 2002
0
100
200
300
400
Figure 3b. Firth of Forth Nephrops: Males. Summary of stock trends comparing catchability and availability model.
WGNEPH Report 2004 415

Figure 4a. Firth of Forth Nephrops: Females. Summary of stock trends for extended data set. Predicted model catches
are compared to reported landings (o) as well as catch weight calculated as the sum of products of catch-at-length
distribution and weight at length (x).
catches
Year
'000t
1985 1990 1995 2000
0.0
0.5
1.0
1.5
2.0 model 2
model 1
landings
catch
total stock biomass
Year
'000t
1985 1990 1995 2000
0
1
2
3
4
5
6
annual F
Year
1985 1990 1995 2000
0.0
0.1
0.2
0.3
0.4 recruits
millions
81 83 85 87 89 91 93 95 97 99 01
0
100
200
300
400
500
catches total stock biomass
Year
'000t
1985 1990 1995 2000
0.0
0.5
1.0
1.5
2.0
2.5
3.0 model 2
model 1
landings
catch
Year
'000t
1985 1990 1995 2000
0
1
2
3
4
5
annual F
Year
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
recruits
millions
81 83 85 87 89 91 93 95 97 99 01
0
100
200
300
400
500
Figure 4b. Firth of Forth Nephrops: Males.
WGNEPH Report 2004
416

catches
Year
'000 t
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
stock biomass
Year
'000 t
1985 1990 1995 2000
0
1
2
3
4
5
6
annual F
Year
1985 1990 1995 2000
0.0
0.1
0.2
0.3
0.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
Fitted F*
F*=0.1
F*=0.5
F*=1.0
Figure 5a. Firth of Forth Nephrops: Females. Summary of stock trends – sensitivity to initial conditions implied by
alternative values of the historical equilibrium fishing mortality.
catches
Year
'000 t
1985 1990 1995 2000
0.0
0.5
1.0
1.5
2.0
stock biomass
Year
'000 t
1985 1990 1995 2000
0
1
2
3
4
5
6
annual F
Year
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
Fitted F*
F*=0.1
F*=0.5
F*=1.0
Figure 5b. Firth of Forth Nephrops: Males.
WGNEPH Report 2004 417

catches
Year
'000 t
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
stock biomass
Year
'000 t
1985 1990 1995 2000
0
1
2
3
4
5
6
annual F
Year
1985 1990 1995 2000
0.0
0.1
0.2
0.3
0.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
Model 2
XSA
Figure 6a. Firth of Forth Nephrops: Females. Summary of stock trends. Comparison with XSA from last year’s
working group.
catches
Year
'000 t
1985 1990 1995 2000
0.0
0.5
1.0
1.5
2.0
stock biomass
Year
'000 t
1985 1990 1995 2000
0
1
2
3
4
5
6
annual F
Year
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
Model 2
XSA
Figure 6b. Firth of Forth Nephrops: Males.
WGNEPH Report 2004
418

catches
Year
'000 t
1985 1990 1995 2000
0.0
0.5
1.0
1.5
2.0
stock biomass
Year
'000 t
1985 1990 1995 2000
0
2
4
6
8
annual F
Year
1985 1990 1995 2000
0.0
0.1
0.2
0.3
0.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
High Weight
Low Weight
Zero Weight
Figure 7a. Firth of Forth Nephrops: Females. Summary of stock trends. Investigating the effect of incorporating
survey data in the form of an index of absolute stock biomass.
catches
Year
'000 t
1985 1990 1995 2000
0
1
2
3
4
stock biomass
Year
'000 t
1985 1990 1995 2000
0
1
2
3
4
5
6
annual F
Year
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
High Weight
Low Weight
Zero Weight
Figure 7b. Firth of Forth Nephrops: Males.
WGNEPH Report 2004 419

Index :1
Abundance index
Model estimates
0 2000 4000 6000 8000 10000 12000 14000
0 2000 4000 6000 8000 10000 12000 14000
93
94
96
98
99
00
01
02
Figure 8. Comparison of model estimates of total stock biomass (males+females) and values from TV survey (mid-
points).
catches
Year
'000 t
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
stock biomass
Year
'000 t
1985 1990 1995 2000
0
2
4
6
8
annual F
Year
1985 1990 1995 2000
0.0
0.1
0.2
0.3
0.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
High Weight
Low Weight
Zero Weight
Figure 9a. Firth of Forth Nephrops: Females. Summary of stock trends. Investigating the effect of incorporating a
recruitment index.
WGNEPH Report 2004
420

catches
Year
'000 t
1985 1990 1995 2000
0.0
0.5
1.0
1.5
2.0
stock biomass
Year
'000 t
1985 1990 1995 2000
0
1
2
3
4
5
annual F
Year
1985 1990 1995 2000
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
recruits
Year
millions
1985 1990 1995 2000
0
100
200
300
400
500
High Weight
Low Weight
Zero Weight
Figure 9b. Firth of Fort Nephrops: Males.
WGNEPH Report 2004 421

APPENDIX 9
Working Document to WGNEPH, March 2004
Meeting on Data Collection on Nephrops
Lisbon, April 2nd, 2004
1. Participants
Bo Sølgaard Andersen Charlottenlund, Denmark
Mike Bell Lowestoft, UK, England
Jon Elson Lowestoft, UK, England
Celso Fariña La Coruña, Spain
Juan Gil Cadiz, Spain
Francisco Leotte Lisbon, Portugal
Colm Lordan Galway, Ireland
Frank Redant (Chair) Ostend, Belgium
Cristina Silva Lisbon, Portugal
Catherine Talidec Lorient, France
Ian Tuck Aberdeen, UK, Scotland
Mats Ulmestrand Lysekil, Sweden
Adrian Weetman Aberdeen, UK, Scotland
Richard Briggs (Belfast, UK, Northern Ireland) was unable to participate, but provided information on male sexual
maturity studies on Nephrops in advance of the meeting.
2. Background
EC Regulation 1639-2001 (the "Data Regulation") requires regular updates of a number of biological parameters (sex
ratio, sexual maturity, fecundity and growth) for all commercially important fish and shellfish stocks (see Appendix
XVI of the Data Regulation). Sex ratio data on Nephrops are routinely collected in all countries and for all Nephrops
Functional Units (FUs) as part of the ongoing market and discard sampling programmes, while fecundity is not
applicable to Nephrops. This leaves us with the updates of sexual maturity (every 6 years) and growth (also every 6
years). Maturity and growth studies in Nephrops are quite laborious, and therefore it is advisable to schedule them
independently from each other (amongst others meaning that they should best be performed in different years). At its
2002 meeting in Lorient, the members of the ICES Working Group on Nephrops Stocks (WGNEPH) tentatively agreed
to schedule the maturity updates in 2004-2005 and the growth updates in 2006-2007.
At the Lorient meeting, it was also agreed to take on these updates in co-operation between the countries
concerned, i.e. concurrently (whenever feasible) and with the same methodological approach. WGNEPH also agreed to
appoint two international co-ordinators (viz. Frank Redant, Ostend, Belgium, for the sexual maturity studies, and Ian
Tuck, Aberdeen, UK Scotland, for the growth studies), whose major task it would be to (a) initiate the discussion on a
common approach and methodology for the sexual maturity and growth studies in Nephrops, and (b) agree on an
appropriate time scale for the execution of these studies.
Following this rationale, the members of WGNEPH agreed to "hook up" an extra day to the 2004 meeting of the
Working Group in Lisbon, Portugal, to further discuss these issues and to set up joint research programmes for the
updates of sexual maturity and growth. The meeting (from here onwards referred to as the "Lisbon Group") was held on
April 2nd, 2004, in the premises of IPIMAR.
3. Purpose of the meeting
• Agree on a time scale and common methodology for the sexual maturity studies.
• Start the discussion on joint studies on Nephrops growth.
4. Female sexual maturity studies
Essentially, there are two methods to study female sexual maturity in Nephrops: (a) by examination of the maturity
stages of the ovaries, and (b) by examination of the presence/absence of spermatophores. Both methods are well-
documented in the scientific literature, although the approaches taken by different authors to e.g. define ovary maturity
stages are somewhat different.
WGNEPH Report 2004
422

¾ Ovary method
Pros
• The method is fairly easy, particularly if the main purpose of the study is to calculate sexual maturity ogives. In
that case, the distinction between successive maturity stages is less important, since basically only the distinction
between immature (i.e. likely not to participate in reproduction) and mature (i.e. likely to participate in
reproduction) females needs to be made.
Cons
• The approach requires the examination of large numbers of females (in order to achieve sufficient levels of
precision) over a limited period of time (say one or two months). This period should be chosen (a) late enough
relative to the start of the maturation cycle, to make sure that all females which are likely to participate in
reproduction can be detected, but (b) not too late, to make sure that the berried females have not yet disappeared in
their burrows. The optimum period differs between stocks, but for most stocks it seems to be summer or early
autumn.
• The method (which relies on visual examination of the general appearance of the ovaries through the carapace)
requires live or "super-fresh" animals. Practice has shown that it cannot be applied to Nephrops that have been kept
on ice for more than a few days.
Method agreed by the Lisbon Group
• The method agreed by the Lisbon Group is that described in Redant (1994), with the addition of an extra stage for
females showing signs of ovary resorbence. The agreed maturity stages thus are:
Empty: No visible signs of ovary development (corresponding to Farmer's stages 1 and 2).
Maturing: Ovary pale green, visible through the carapace, but not extending into the abdomen (corresponding to
Farmer's stage 3).
Mature: Ovary fully developed, dark green in colour and extending into the abdomen (corresponding to Farmer's
stage 4).
Resorbing: With clear signs of ovary resorbence.
Ovigerous (berried): With recently spawned, dark green eggs under the abdomen.
Hatching: With eggs close to hatching (swollen, transparent eggs, with fully developed larvae clearly visible) or
with remnants of recently hatched eggs under the abdomen.
• Precision level of length measurements: 1 mm carapace length (CL).
• Target numbers to be staged: 50-100 females per mm CL size class in presumed range between 25 % (L25) and
75 % (L75) maturity, and 25-50 females per mm CL size class for all sizes < L25 and > L75. This should give a
sufficient level of precision in the critical part of the maturity ogive on both sides of the L50.
¾ Spermatophore method
Pros
• The method, which relies on the examination of females for the presence/absence of spermatophores, is less
sensitive to timing and therefore can be applied over a longer period of time than the ovary method. This is an
advantage for stocks where the collection of sufficiently large numbers of animals might pose problems.
Cons
• The method is more time-consuming than the ovary method.
Method agreed by the Lisbon Group
• The method agreed by the Lisbon Group is that described in Farmer (1974).
• Precision level of length measurements: 1 mm carapace length (CL).
• Target numbers to be examined: 50-100 females per mm CL size class in presumed range between 25 % (L25) and
75 % (L75) maturity, and 25-50 females per mm CL size class for all sizes < L25 and > L75. This should give a
sufficient level of precision in the critical part of the maturity ogive on both sides of the L50.
WGNEPH Report 2004 423

5. Male sexual maturity studies
Essentially, there are three methods to examine male sexual maturity in Nephrops: (a) by histological examination of
the gonads, (b) by morphometric analysis of the appendix masculina (the copulatory organ on the endopodites of the 2nd
pleopods), and (c) by morphometric analysis of the claws. All three methods are described in Mc Quaid and Briggs
(2004). Of these, only the second was retained by the Lisbon Group. The others were considered to be too laborious
(histological examination of the gonads) or insufficiently discriminative (morphometric analysis of the claws) for the
proposed studies.
¾ Appendix masculina method
Pros
• The method is easier and less time-consuming than histological examination of the gonads, and more
discriminative than morphometric analysis of the claws.
• Since the change in morphometry of the appendix masculina is an irreversible and not a cyclic event (the change in
shape remains once it has occurred), this implies that studies of male sexual maturity based on the appendix
masculina are not bound to a particular period of the year (as is the case for methods based on gonad maturity
stages).
Cons
• The method requires some training and may give different readings when the measurements of the appendix
masculina are made by different readers. To make sure that the different data sets are at least internally consistent,
it is advisable that all measurements pertaining to the same data set are made by the same reader.
Method agreed by the Lisbon Group
• The method agreed by the Lisbon Group is that described in Mc Quaid and Briggs (2004).
• Precision level of measurements: 0.1 mm for carapace length (CL) and 0.1 mm for the appendix masculina (ApM).
• Target numbers to be measured: 10-20 males per mm CL size class, over a sufficiently wide range of size classes,
and as much as possible equally spread on both sides of the presumed inflection point in the relationship between
CL and ApM.
6. Comparative sexual maturity studies
Two types of comparative studies are suggested by the Lisbon Group: (a) comparative studies on the two methods
agreed for female sexual maturity, and (b) comparative studies on both male and female sexual maturity within the
same stock.
¾ Comparative studies on the two methods for female sexual maturity
From the literature, it is known that the ovary method and the spermatophore method may give slightly different
estimates of the L50. Since one of the aims of the proposed sexual maturity studies is the comparison of the L50's
between stocks, it is essential that the two methods can be inter-calibrated. Therefore, the Lisbon Group tentatively
agreed to set up comparative studies between the two methods on the following stocks:
• Fladen and maybe some other stock(s) around Scotland (UK, Scotland).
• Irish Sea West (joint study by Ireland and UK, Northern Ireland).
• SW and S Portugal (Portugal).
Note: The list of stocks to be included in the comparative studies might be complemented with other stocks (e.g.
Kattegat-Skagerrak area), depending on the availability of labour, technical and financial resources.
To avoid contamination of the comparison by local differences in sexual maturity within the same stock (see next
paragraph), it is essential that the samples for such comparative studies originate from the same small geographical area.
WGNEPH Report 2004
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¾ Comparative studies on sexual maturity within the same stock
The onset of sexual maturity is likely to be determined by age, and not by length as such. Since growth rates may differ
within the same stock (amongst others in relation to stock density and size composition) it cannot be excluded that the
L50's too differ from one part of a stock to another.
In order to collect as much information as possible on the "within stock variability" of sexual maturity, the Lisbon
Group suggests that comparative studies are made within as many stocks as possible.
An absolute prerequisite for such comparative studies is that sufficiently large samples can be obtained from relatively
small areas with known differences in stock density or size composition. Blended samples from large areas with
variegated stock densities or size compositions are of no use.
7. Timing of sexual maturity studies
An overview of the stocks that will be covered during the proposed sexual maturity studies is given in the table on page
11. For each Nephrops FU, this table shows in which year the maturity studies (males and females) will be undertaken,
which country will take the lead in these studies, and how the samples will be collected (research vessel surveys,
discard trips or market samples).
8. Growth studies
Methods available ¾
∗
∗
•
The Lisbon Group identified three methods that could be used for field studies on Nephrops growth: tagging with
internal tags, tagging with external tags and polymodal analysis of length frequency distributions.
Tagging with internal tags
The method uses internal binary coded wire tags (or a similar type of tags) which are usually inserted in the basis of the
walking legs. Animals are caught, measured, tagged with unique, individual tags (hence the use of binary coded wire
tags) and then released in the wild. Recovery of the tags on recapture requires the use of special screening equipment,
which examines individuals or batches of individuals (entire fish boxes or fractions thereof) for the presence of tags.
Growth information is then derived from the time-lag and the difference in size between capture and recapture.
Pros
• Internal tags are usually well retained over several successive moults (compared to external tags, which may be lost
during moulting).
• Mortality due to tagging stress can be expected to be lower than with external tags (insertion of internal tags is less
aggressive than that of floy-tags).
• Internal tags do not attract predators.
Cons
• Retrieval of the tags requires expensive screening equipment.
• Screening of large volumes of landings is time-consuming and may cause delays that are unacceptable to fishers.
• Tags in discarded animals are likely to remain unnoticed, unless screening is done onboard (which is highly
unpractical in fisheries with many vessels).
Tagging with external tags
The method uses external, numbered floy-tags (or a similar type of tags) that are inserted in the muscles of the
abdomen, through the soft integument between carapace and first abdominal segment. Animals are caught, measured,
tagged with unique, individual tags (hence the use of numbered tags) and then released in the wild. Recovery of the tags
on recapture depends on retrieval by fishermen, who are rewarded for bringing in the tags. Growth information is then
derived from the time-lag and the difference in size between capture and recapture.
Pros
External tags are cheaper than the internal ones, and do not require expensive screening equipment.
WGNEPH Report 2004 425

External tags give better returns for discards. •
∗
∗
Cons
• External tags might be lost during moulting, and therefore are less likely to survive successive moults.
• Mortality due to tagging can be substantial, unless adequate precautions are taken to minimise tagging stress.
• External tags might attract predators.
Polymodal analysis
The method relies on deconvolution of a time-series of polymodal length frequency distributions in their constituent
cohorts, which are then assumed to represent age classes. Linking the cohorts over time then gives a growth curve for
the different age classes in the population. Several software packages are available which make the process easier (e.g.
Elefan, Multifan, Mix).
Pros
• Polymodal analysis could be better fit for growth studies in juvenile Nephrops than tagging.
Cons
• Logistics for the collection of the length frequency samples are complicated. The method requires that large
numbers of animals are taken from an area with a homogeneous population structure. This means time-series of
(many) short hauls within small areas.
• The method can be very subjective, particularly when the cohorts are very close to each other (as is the case for
slow growing species).
• Growth in Nephrops is generally considered to be too slow to give sufficient segregation between successive
modes. This has made that previous attempts to use the method have never been particularly successful.
Conclusion
The Lisbon Group concluded that external tagging seems to be the most appropriate method for the required growth
studies on Nephrops. Internal tagging could be envisaged under particular circumstances, e.g. for relatively small-scale
fisheries (limited volume of landings to be screened) that land their catches in a small number of ports (limited number
of screening points).
Regardless which tagging technique is eventually chosen for, it is essential that the actual tagging experiments are
preceded by a number of preliminary tests (both in the field and in aquaria), to optimise the catching, handling and
tagging procedures and hence to minimise tagging stress.
¾ Problem areas
• Tagging experiments require a considerable input in terms of manpower, working costs (tags, screening
equipment), ship's time, etc. The number of growth studies that can be performed therefore will forcibly be limited
to a small number of representative stocks. Even then, the costs associated with a tagging study can be beyond the
financial capacities of a single MS. This raises the question of cost sharing: can MS's contribute to a study that is
"physically" conducted by another MS, and if so, how can this best be arranged ? What are the legal possibilities
for cost sharing within the framework of the Data Regulation ? What is the point of view on this of individual MS's
? Of the Commission ?
• The return rates of tagging experiments can be very low (in the worst possible case in the order of 1-2 %). This
means that large numbers of animals need to be tagged to yield sufficient recapture data (approx. 10000 for a trawl
fishery, less in a creel fishery). A possible option would be to spread the actual tagging over several years. This
however, would then mean that the study could not be concluded within the time period set by the Data Regulation
(2007 at the latest). Is this acceptable to the Commission ?
WGNEPH Report 2004
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¾ Suggestions made by the Lisbon Group
∗
∗
Candidate stocks for growth studies
The Lisbon Group has identified a number of candidate Nephrops stocks for the growth studies within the framework of
the Data Regulation. The criteria used while making this choice included: accessibility, differences in geographical
location, differences in state of exploitation, etc.
• ICES Sub-area IIIa: Kattegat-Skagerrak (FUs 3+4) (study conducted by Sweden, preferably in co-operation with
Denmark).
• ICES Sub-area IV: Firth of Forth (FU 8) or Farn Deeps (FU 6) (study conducted by UK, preferably in co-
operation with other North Sea countries).
• ICES Sub-area VI: Ideally one of the stocks on the Scottish West coast (FUs 11, 12 or 13) (in which case the
study could be conducted by UK, Scotland).
• ICES Sub-area VIIa: Irish Sea West (FU 15) (study jointly conducted by Ireland and UK, Northern Ireland).
• ICES Sub-area VIIIa,b: Ideally the Bay of Biscay stock (FUs 23+24) (in which case the study could be conducted
by France).
• ICES Sub-areas VIIIc and IXa: Ideally one of the Iberian stocks (in which case the study could jointly be
conducted by Portugal and Spain). The willingness of the MS's concerned to perform such a study may however be
small, in view of the rapidly decreasing importance of the Nephrops fisheries in the area (nowadays less than
1000 t for all Iberian Nephrops stocks combined, with some stocks yielding less than 100 t per annum).
Sensitivity analysis
In view of the high costs of Nephrops growth studies, the Lisbon Group suggests that a sensitivity analysis be
undertaken on the effects of using different growth parameters to slice the length distributions into age groups on the
outcome of age-based assessment models such as XSA. If the effect is limited, then there is little need to repeat the
growth studies in the longer-term future, and the obligation to regularly update the growth parameters for Nephrops
may well be removed from the Data Regulation.
9. Time table and associated task list for the growth studies
• ASAP: All members of the Lisbon Group to check with the co-ordinators of their National Data Gathering
Programmes whether their country will participate in the proposed growth studies or not, and if so, in which studies
and in which phase(s) (preliminary tests and/or actual tagging experiments).
Deadline: Inform Ian Tuck, i.tuck@marlab.ac.uk, as soon as possible.
• ASAP: All countries that foresee to participate in one of the proposed growth studies should include some
personnel and working costs in their National Programme proposal for 2005 (under Module I, Other Biological
Sampling). Budgeted costs should be sufficient to cover preparatory experiments.
Deadline: May 31st, 2004.
• Mid 2004: All countries that envisage to participate in the actual growth studies should make a final decision on
their commitment before the start of the Regional Planning Groups meetings (RPG) for the North Sea and the
Western Seas. The further elaboration of the growth studies will be discussed at these meetings. It is advisable that
the current co-ordinator of the growth studies (Ian Tuck) be given the opportunity to attend both RPG meetings, to
ensure maximum linkage between the initiatives taken in the two areas.
Deadline: September 2004 for the RPG Western Seas (meeting in Galway, Ireland, date to be communicated).
Deadline: September-October 2004 for the RPG North Sea (meeting in Lowestoft, UK, date to be communicated).
• End 2004: Set up a Task Force for each individual tagging experiment. The role of these Task Forces would be to
ensure the preparation, budgeting and execution of the actual tagging experiments. The Task Forces should report
to the Member States concerned, their Regional Planning Groups and to Ian Tuck (the latter once more to ensure
maximum linkage between the different initiatives).
Deadline: It is advisable that the Task Forces be composed by the end of 2004, to make sure that they are fully
operational by the time the National Programme proposals for 2006 have to be written (see next bullet point).
WGNEPH Report 2004 427

• Early 2005: Preparation and submission of the National Programme proposals for 2006. These should take into
account the tagging experiments (and their costs) that are planned for the year 2006, and give cost estimates for the
associated activities that are planned for the years thereafter (continuation of tagging experiments, if any, payments
to fishermen for recovered tags, etc.).
Deadline: May 31st, 2005.
• 2005: Perform optimisation and survival experiments, in preparation of the actual tagging experiments in 2006-
2007.
Deadline: Preliminary studies to be concluded by the end of 2005 and to be reported in the Technical Reports of
the National Data Gathering Programmes for the year 2005 (the deadline for these Technical Reports is May 31st,
2006).
• Early 2006: Preparation and submission of the National Programme proposals for 2007 (provided that the Data
Regulation is extended for another term of six years or more). These should take into account the tagging
experiments (and their costs) that are planned for the year 2007 (if any), and give cost estimates for the associated
activities that are planned for the years thereafter (payments to fishermen for recovered tags, etc.).
Deadline: May 31st, 2006.
• 2006: Start actual tagging experiments.
• 2007-2008: Continue tagging experiments and report results in Technical Reports of National Data Gathering
Programmes to Regional Planning Groups and WGNEPH (see next section).
10. Final remarks
The Lisbon Group recommends that the results of the sexual maturity and the growth studies be evaluated and analysed
at some point by WGNEPH.
In the absence of Nephrops experts from the Mediterranean countries (particularly Italy and Greece), the Lisbon Group
was not in a position to extend the intended co-operation beyond the ICES area. However, Nephrops experts from the
Mediterranean area are most welcome to participate in this initiative.
The Lisbon Group agreed to send copies of its meeting report to: the participants to the meeting, the co-ordinators of the
National Data Gathering Programmes, the European Commission, and the Chairs of SGRN, STECF and PGCCDBS.
11. References
Farmer, A.S.D. (1974): Reproduction in Nephrops norvegicus (Decapoda, Nephropidae). Journal of Zoology London,
174, 161-183.
Mc Quaid, N. and Briggs, R. (2004): Sexual maturity of male Nephrops norvegicus (L.) in the Irish Sea. Working Paper
presented at the 2004 meeting of the ICES Working Group on Nephrops Stocks, Lisbon, Portugal.
Redant, F. (1994): Sexual maturity in female Norway lobster, Nephrops norvegicus, in the central North Sea. ICES,
Shellfish Committee, C.M. 1994/K:43.
WGNEPH Report 2004
428

Overview of planned maturity studies for Nephrops
Sexual maturity study
planned for …
Nephrops
FU
ICES
Sub-area
None 2004 2005
Country
performing
study
Data source(s)
3 IIIa X Sweden Discard trips
4 IIIa X Sweden Discard trips
9 IVa X UK Scotland R/V surveys
10 IVa 2004 or 2005 (d) UK Scotland R/V surveys
7 IVa X UK Scotland R/V surveys
32 IVa X (a)
6 IVbc X UK England Discard trips
8 IVbc X UK Scotland R/V surveys
5 IVbc X Belgium Discard trips / Market
33 IVbc X (c) Denmark (c) To be decided
11 VIa X UK Scotland R/V surveys
12 VIa X UK Scotland R/V surveys
13 VIa X UK Scotland R/V surveys
14 VIIa X UK Northern Ireland R/V surveys
15 VIIa X UK Northern Ireland R/V surveys
16 VIIbcjk 2004 or 2005 (d) Spain R/V surveys
17 VIIbcjk X Ireland Discard trips
18-19 VIIbcjk 2004 or 2005 (e) Ireland Discard trips
20-22 VIIfgh X France Discard trips
23-24 VIIIab X France Discard trips / Market
25 VIIIc X (b)
31 VIIIc X (b)
26-27 IXa X (b)
28-29 IXa X Portugal R/V surveys / Market
30 IXa 2004 or 2005 (e) Spain Market samples
i
. Stock mostly outside EU Waters
i
. Current landings too small to obtain samples is sufficient quantities
i
. No formal commitment yet
v
. Depending on catch opportunities during research surveys
v
. Depending on sample availability
WGNEPH Report 2004 429

TECHNICAL MINUTES
Review of the WGNEPH report 2004.
Made by correspondence by a review group for ACFM
Group members:
Sergey Bakanev
Mike Bell (Chair, WGNEPH)
Guus Eltink
Dankert W. Skagen (Review group chair)
1. Introduction
The Group has reviewed the report by WGNEPH, that met 29 March to 1 April 2004, as requested by ACFM according
to the ‘Review Group Responsibilities’ issued March 2004. The review group report includes comments to lay-out and
presentation in the WG report, an overview of how the terms of reference have been addressed, evaluation of
assessments and predictions for each individual stock and some general comments to the work done by this group. We
have also included a section with general points of view on methodology for these stocks, where the age of individuals
cannot be determined directly.
The Chair of WGNEPH has taken part in the work, but also has supplied comments on behalf of the WG to the
points made by the review group. These comments are included in the report, in italics. The review group supports the
views expressed in these comments.
2. Presentation
Although voluminous, the report is actually quite concise. For an external reviewer, it is quite easy to understand, both
with respect to the WGs thoughts and ideas, the special features of these stocks and, in broad terms, what has been
done. At some points, the text is too concise, however, so that is not clear exactly what has been done, and why. Some
examples are mentioned under the individual stocks.
The lay-out is logical, but not always practical. It would have been easier if assessment inputs, results, diagnostics
and accompanying figures had been assembled stock by stock, instead of being grouped by management area. As it is, it
happens too often that one is looking at tables for the wrong stock. It helps that everything is properly labelled, though.
Comment by WG chair: Noted. Future reporting format will depend on the regionally-based WGs to which the
assessment tasks will be devolved (see Section 11). So far as is possible within these new formats we will collect text,
figures and tables FU by FU before collecting together the Management Area considerations.
Previously WGNEPH has presented the diagnostic material in a separate data appendix. In response to last year’s
review comments the diagnostics are now included in the main report, taking advantage of the fact that only a few
stocks were assessed this year. Future report structure will depend on the regionally-based WG report formats. The
review group notes that for an external reviewer, diagnostics are just necessary.
The standard procedure is to convert catches at length to catches at age by applying a slicing procedure. This
procedure is not transparent. It is done with standard software, with references to WG reports in 1992 and 2001, but the
length distributions are not presented and although the basic principle is mentioned briefly, it is not possible for an
external reviewer to evaluate how dependent the final results are on this procedure. It is strongly recommended that the
WG in the future gives the catches by length, either as tables (preferable), or as graphs.
Comment by WG chair: Noted. WGNEPH has tended to take the slicing procedure for granted because it has
been standard practice for so many years. We will make sure to tabulate length data in future.
Terms of reference
Tor a requests assessment of some selected, presumably problematic, stocks. This has been done (Section 5), for the
stocks where analytic assessments have been done before. For FU31, no assessment was done due to shortage of data,
as in previous years. For FU30, a provisional length based yield per recruit analysis was presented. This is about as far
as one should go with such sparse data.
Neither the terms of reference nor the WG have classified the assessments as update or benchmark. The character
of the assessments presented is more or less update. However, not the least because the method used as a standard has
its well known short-comings, we have attempted to evaluate the assessments somewhat beyond checking that the right
data are input and the adopted procedures have been followed. This is done stock by stock below.
Comment by WG chair:Until recently, all Nephrops stocks were assessed biennially, as no need was seen to
update the advice more frequently. Since 2001, however, the southern stocks have been assessed annually owing to
evidence of stock declines. Incorporation of the assessments within the frameworks of the regionally-based WGs will
regularise the assessment cycles and definitions as update or benchmark.
WGNEPH Report 2004
430

Tors b, c and d addresses the reliability of landings statistics, and is covered in Section 6. Some of the
background was a proposal from the UK industry to revise their landings statistics. So far, this has not been done,
however. The WG highlights important points about implications of misreporting, and the reviewers agree in the WGs
views. The WG makes the suggestion that where absolute measures of total abundance, notably by TV surveys, are or
become available, the management advice can be based on these instead of on analytical assessments that at best are
problematic. The reviewers support this idea, and encourages further development and testing of such a strategy for
giving advice.
Tor e considers medium term predictions, and is covered in Section 7. A medium term projection with stochastic
recruitments was made for FU 28-29, to show that a progressive reduction in fishing mortality down to F0.1 would lead
to a gradual increase in biomass, with recruitment at the recent level. The WG points out that the lack of a reliable stock
recruitment relation precludes meaningful medium term predictions. This is true, except for studies like the one
presented. Moreover, the crucial question for long term strategies is why recruitment fails, and this may not necessarily
be because the SSB is reduced. The impression is that the Iberian stocks seem to be suffering from a recruitment-stock
relationship rather than the other way round.
Tor f is to continue work on alternative assessment methods. This is covered in Section 8, and is discussed further
below.
Tor g is addressed in Section 9, Tor h in Section 10 and Tor i in Section 11. This is largely drawing on the
expertise on Nephrops in general and local conditions, where the review group has little to contribute. The presentation
looks clear and orderly and the conclusions sound as far as we can judge it.
Technical minutes from last year have been addressed, except that length distributions by sex of discards have
not been included.
Comment by WG chair: Noted. There are effectively no discards for the Iberian stocks. Discards for Bay of Biscay are
estimated from data in only a few years. Future presentations will make sure to include plots of length-distributions for
recent years for which there are data as opposed to estimated discards.
3 General on assessment methodology and strategy
The standard method for assessing the Nephrops stocks is to partition catches at length into catches at age by
deterministic slicing, i.e. by allocating an age to each length class. The catch numbers at ‘age’ as well as CPUE, and
sometimes survey data at age are then analysed with XSA, giving estimates of fishing mortalities and stock numbers at
age.
For an outsider, this appears to be a somewhat artificial way of assessing the stock. It has the advantage that
standard age based software can be used, which also makes the logistics easy in the advisory process, but the
disadvantage that the actual observations are converted into more or less artificial data, that are analysed. At least, this
is intellectually not satisfactory. The more important question is whether this process can generate misleading results.
The WG is fully aware of these problems, and is considering alternative ways of assessing the stock, where the
length data are used directly. Such methods are being explored by the WG, but are not without problems of their own.
Individuals of a given length will have different ages due to individual variations in growth. Thus, year classes will
be ‘smeared out’, as also pointed out by the WG. The assumed yearly length increments, which depend on the K-value,
also translate the disappearance rate by length into disappearance by age, which is the mortality signal. Hence,
mortalities are confounded with the assumed K. This will also be the case in length based dynamic models. As pointed
out by the WG, it is hardly possible to estimate K and F separately unless there are good observation-based age-length
keys. Hence, this problem will not automatically be solved by turning to dynamical length based methods.
For most of the stocks that are considered this year, the catches have gone drastically down in the last years while
the fishing mortality apparently is more or less stable. Hence, the reduced catches are attributed to reduced abundance,
i.e. to reduced recruitment. The alternative would be that a drastic reduction in fishing mortality is concealed because
the slicing leads to a wrong mortality signal. Some simple simulation studies were done by members of the review
group, generating catches at age from a length distribution assuming a K-value and putting the catch numbers into a
VPA. Although by no means comprehensive, there were indications that a reduction in fishing mortality may give a
false impression of reduced recruitment, in particular if the assumed K-value is too low. This is a cause for concern, not
the least when tuning data are sparse and sometimes questionable (see below)
Hence, the review group sees a strong need for a further development of robust methods for assessment and
management advice. Both such methods, and the current procedure, should be explored with artificial data, in order to
reveal possible sources of misleading inferences that are not intuitively clear. Furthermore, as noted above, advice based
directly on measurements of total abundance represent an alternative strategy that deserves further consideration. Future
WGNEPH meetings should include terms of reference for further exploration of alternative assessment methods
integrated with management advice.
Given the lack of methods for direct age-determination, the slicing problems are unlikely to go away – perhaps
some further exploration of the sensitivity of assessment outcomes to slicing artefacts would be appropriate. Also,
some cross-comparison (based on simulated data) between explicitly length-based and sliced-age-based assessments
would be appropriate. The experience with two-stage methods such as CSA is that they tend to give similar results to
XSA for equivalent data, which offers some support that estimated trends are at least qualitatively correct.
WGNEPH Report 2004 431

Another general point is the way effort is calculated. In section 10.1.3 nothing has been mentioned on deficiencies
in effort and LPUE data. As noted below, only trips where a the proportion of Nephrops in the catch exceeds some limit
are considering FU 23-24 The question is whether this is a correct method of calculation, because the calculated effort
appears to be correlated with the Nephrops stock size. This problem, which is a common one in mixed fisheries, might
be the case for other stocks as well.
The effort and CPUE data have a major impact on the assessment, and are to a large extent the key to
understanding the results for the last years. Therefore, both presentation of the effort and CPUE data that go into the
assessment, and clear descriptions on how effort is calculated for all stocks would be useful in the next WG report. In
addition it would be appreciated if at the same time would be explained how sensitive these effort estimates are in
relation to the Nephrops stock size.
Comment by WG chair: This is something that could be addressed by a future WGNEPH meeting. The problem is
one of definition of directed effort. In many cases a gear- and area-based definition of Nephrops-directed effort may be
more appropriate than one based on species composition alone.
Individual assessments (by stock):
FU 23-24
The calculation of effort is done in the following way: Voyages are considered to be Nephrops directed when > 10% of
their revenue is accounted for by Nephrops (or in weight if revenue is missing). The question is whether this is a correct
method of calculation, because the calculated effort appears to be correlated with the Nephrops stock size. At low stock
size effort will be calculated extra low, because there will be relatively more finfish than Nephrops in the catches (less
ships will achieve more than 10% Nephrops in their catches). This implies that the estimated LPUE might be seriously
overestimated at low stock size.
Comment by WG chair: This is a reasonable conclusion, and certainly an argument for deriving better measures
of directed effort. In practice, however, it may be less of a problem than might be feared since genuinely directed
Nephrops fishing is likely to be spatially targeted and thus likely to meet the proportional criterion while a significant
directed fishery exists. It is worth noting that spatial targeting has itself the potential to cause a positive bias in LPUE,
but stock declines severe enough to cause a serious bias for either reason are likely to be apparent from other
indicators such as dwindling effort index values. Use of the Le Guilvinec series, which according to my understanding
did not require the use of the >10% criterion, should in this case provide some guard against wrong conclusions from
biased LPUE data. More work on this topic is clearly needed.
Furthermore, it is confusing that 4 different LPUE series are presented in the report, while two (Le Guilvinec and
that with Le Guilvinec excluded) are used for tuning the XSA. Both show fluctuations in SOP/effort that is not apparent
in the LPUE series as presented, and both have a rising trend over time in the residuals which is reversed in recent
years. Hence, it is at best unclear how the age distribution of the tuning data has been achieved. These data are critical
to the estimate of recent trends in the stock and mortality, hence it is difficult to judge how reliable these estimates can
be. Furthermore, the series with Le Guilvinec excluded is said to be less reliable. Putting both into the XSA on equal
grounds gives them more or less equal weight.
Comment by WG chair: Agreed – presentation of effort and LPUE data is confusing. In future it might be
preferable to present just the best scientific judgement of effort and LPUE trends. The whole issue of tuning data for
Nephrops assessments is problematic, since there are rarely real survey data available. The Bay of Biscay assessments
appear to be, at least qualitatively, fairly robust to the use of different tuning series (e.g. see Figure 5.2.9). Un-
quantified increases in efficiency are likely to be a more important cause of recent bias in estimated stock trends.
Derivation of better indices of directed effort and more refined use of commercial data for tuning is something which
could benefit all Nephrops assessments.
In the prediction, the average recruitment is taken over the period 1990-2001 (GM 609 million). The reviewers
suggest a lower recruitment value because of the decreasing trend in recruitment and taking into account that the last
recruitment estimates (2000-2001) are less reliable. Estimates for 2002 and 2003 (the final two years of the assessment)
have already been excluded. If a recruitment value of 500 million is specified (with appropriate adjustment of numbers
at age 2 at the beginning of 2004) then a slightly more pessimistic prediction is made. This prediction is attached to the
report as an Excel file with graph and table showing prediction outcomes. Recruitment of about 500 million would be
typical of the late 1990s, slightly above the series low point of 474 million in 1998.
The reviewers would have liked a discussion on the explanation for the increase in CL (mm) of the discards over
time in 1987, 1991, 1998 and 2003 (except from increase in mesh size 1990) (see table 5.2.4b). The reviewers assume
that this might be related to recruitment strength. If so, it would imply that the mean size (CL) of discards is low when
the recruitment is strong and high when recruitment is weak. If one might conclude from table 5.2.4b that recruitment is
relatively low in 2003 then this might have been another argument to choose for a lower value of recruitment for the
short-term predictions.
Comment by WG chair: It seems reasonable to suppose that this might be related to recruitment strength. It is
worth noting, however, that the post-1990 increases are fairly small, and we do not know the precision of the estimates.
Compared to last assessment, the present one shows a slightly larger biomass, but by and large the assessments are
rather consistent. The fishing mortality appears to be very high, but that is very sensitive to the assumed K-value. The
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reviewers agree that the assessment is likely to be on the optimistic side, and there does not seem to be any good
arguments for changing the current advice to reduce the effort by 50%. The measures to reduce discards and improve
selection would definitely be helpful.
FU 25
For this stock, both landings and effort have gone down over many years, but the effort reduction has been weaker and
later than the landings reduction. Accordingly, the estimated stock has gone down over many years, and the stock is
regarded to be in a critical state. The assessment indicates a severe recruitment failure.
It is stated that the landings are unreliable in 1998-2001. Tuning data are CPUE from the A Coruña Baca fleet,
which appears to be the main fishery. At least, the age distribution in the tuning data and in the catches is more or less
the same, giving approximately the same mortality signal in both sources of data.
The choice of options for the XSA seems to be adequate by usual standards. In the assessment, the F-values in the
last year are mostly driven by the shrinkage for the youngest ages, and by the tuning data for the older ages. There are
year effects in 1998 and 2000, reflecting the low reported catches in those years, which are somewhat out of proportion
with the effort.
The estimates of recruitment in the last years, which indicate an almost total recruitment failure, come from the
very low catches at youngest age. The low values are less prominent in the CPUE at age, because the effort has gone
down, which seems to be the reason why the shrinkage dominates the estimation of F at those ages. The crucial question
is however, whether the recruitment failure is as bad as it looks. If the strong reduction in catches at young age are due
to changes in the fishery, e.g. because of mesh size regulations, the XSA will not interpret that correctly, because
catchability for the CPUE series is assumed to be constant. The shrinkage will have a similar effect. The retrospective
pattern in recruitment estimates is in line with this reasoning. The picture for both males and females is rather similar.
The mortality of the females is lower, but the trends are the same.
Hence, it seems possible that the recruitment failure may not be as severe as it seems – the retrospective patterns
also tend to suggest revision of recruitment estimates upwards (but see the last two years for females in Figure 5.3.6).
However, it is clear that there are major uncertainties in the assessment, not least because it is based on such low
quantities of landings. The downwards trend in catches over a long time, with less and delayed reduction in effort leaves
no doubt that the stock is deteriorating, the only question is about exactly how low the recent recruitment is. Because of
the doubts about recent recruitment, the value of the short term prediction is limited but does serve to illustrate this
worst case scenario. In conclusion, the present assessment gives no indications that the stock is developing more
favorable than believed previously, and gives no reason to deviate from the previous advice of closing the fishery.
Some technical notes:
It is confusing that landings and effort are tabulated only back to 1994, while they are used back to 1984 and 1986
respectively in the assessment, and the catches in Figure 5.3.1 go back to 1975. Since the trends in catches and effort are
so important for the advice, it would be easier if they were presented in a consistent way. Similar remarks apply to
several other stocks as well.
Comment by WG chair: It has been standard practice for the WG report to tabulate only the last ten years of data,
giving the full series in graphical form only. There would be no problem in tabulating longer series in future, although
this would add to the volume of output.
A more in depth evaluation of the effect of mesh size regulations on the catchability for small Nephrops should be
undertaken, in order to adjust the catchability at young ages in recent years. That might give more realistic estimates of
recruitment, which obviously are important for this stock. The general comment that length distributions should be
presented in the report also applies here.
Comment by WG chair: This would be a topic for the future, although evidence of effects of mesh changes on
Nephrops catchability is scanty – Nephrops tend to entangle with each other in the catch, making changes in mesh size
less effective than they might otherwise be. Rigid grids and other tailored sorting devices would show more effect.
FU 26-27
This stock seems to be in a very poor state. Catches have declined since 1990 to in the order of 10% of what they used
to be. The effort in the Marin fleet has gone down since 1995, while the effort in the Muros fleet has a slight increasing
trend (These data can only be found in the tuning files, which are not in the report). Both series are noisy, in particular
the Muros series. Age 1 in the Marin series is virtually non-informative.
Two CPUE series are used for tuning. It is stated in the report that the XSA was tuned to the effort, presumably
catch per unit of effort is meant. Both series are local, from different areas, and show quite different degrees of decline
in CPUE over time.
The input data evidently shows the decrease in catch in the considered period. In recent years LPUE seems to have
stabilized at low levels. F-shrinkage is used with a rather small error. Obviously, with so small SE the influence of F-
shrinkage on estimation of survivors will be rather strong and population in terminal year with current trends in fishing
WGNEPH Report 2004 433

mortality will be underestimated, and F - overestimated. In this case, it might be better to use F-shrinkage with Min. SE
for Mean F equal to 1 or attempt to do without F-shrinkage.
On the other hand, the most prominent problem with the XSA tuning seems to be the conflict between the two
tuning series, the Marin being the ‘optimist’ and the Muros the ‘pessimist’. The assessment to a large extent becomes a
compromise between these conflicting signals, with the estimates referring to the shrinkage being somewhere between
these two.
Looking at the diagnostics, we noted some things that could deserve further exploration in the future. The
residuals of the first index which are very high for Age 1 in the tuning both for males and females. It could be
considered to leave out this age from the tuning. High residuals are also observed for Age 2 that evidently indicates that
Age 2 could be removed in the tuning. In the residuals of the first index we can observe the year-effect in 1996 when
the residuals are rather high and have the same sign. Perhaps this year should be removed from the model and its effect
on the final results should be assessed. We also suggest to explore power regression for Ages 3 and 4 for males, and P-
shrinkage for calculation of abundance for Ages 1 and 2.
This is also a stock where recruitment seems to fail. The signal is evident in most sources of information, notably
in the catches at age and in the Muros time series. The Marin time series gives a somewhat more optimistic picture, but
even that indicates recruitments no better than in the recent past. Hence, there is no argument about the depleted state
of the stock, just about quite how depleted it is, and we agree with the WG that there is no reason to change the current
advice to stop the fishery.
FU 28-29
In this stock, catches declined to about half the previous level in the mid 1990ies, but have increased gradually since
then. Effort has increased in the last few years. Recruitment dropped to between ½ and 1/3 of the previous level in the
same period, but seems to have stabilized there. The current recommendation is for zero TAC, in order to rebuild the
stock.
Two series of tuning data are used, one is CPUE in the fishery, the other is a relatively short series from a survey
aiming at crustaceans. A very weak F-shrinkage was used, which may be adequate given the recent increase in effort.
More shrinkage would have given higher estimates at the younger ages.
Comment by WG chair: Various shrinkage options were explored for this stock, and the XSA diagnostics were not
very informative about which should be preferred. In the end, the selected options were those which gave slightly better
retrospective patterns, were consistent with the previous assessment and were conservative about current recruitment
levels.
The options used in the XSA seem quite reasonable. Residuals are relatively low, but there are some year effects
in residuals of fleet 2 (e.g. in 2001 and 2003). Log catchability residuals of fleet 2 are generally high at older age. The
two tuning series are rather consistent. Moreover scaled weights of this index are not considerable. Higher weight is
given to P-shrinkage then to survey data at the youngest age, but the F-estimates are very close. Altogether, the XSA
estimates look reasonably well behaved.
The choice of inputs to the short term prediction seems adequate.
The medium term consequences of a gradual reduction in fishing mortality was explored with the CP software,
which is a relatively simple stochastic projection model, written in R. It showed that with the current low recruitment
(arithmetric mean as in 1997 – 2003), a gradual reduction in realized F towards F0.1 can be expected to lead to a gradual
increase in SSB. The WG points out that without a clear understanding of the stock-recruit relationship, medium term
predictions are not very meaningful. The exception may be the present example, where the probability that a given
management regime will have a desired effect despite recruitment at the current low level, is evaluated.
For this stock, both recruitment and SSB seem to have stabilised at about half of what they were in the late 1980ies
and early 1990ies. The reason for the reduced recruitment is not necessarily a reduced SSB. The figure below shows the
history of the R-SSB pairs. A likely interpretation is that recruitment has changed stepwise, and the SSB has followed.
FU 28-29
Stock-recruit e stim ates
0
5000
10000
15000
20000
25000
0 200 400 600 800 1000 1200
SSB
Recruitment
Females
Mal es
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According to the yield per recruit, reducing the effort by something in the order of 50%, leading to somewhere
near F0.1 would ensure a larger biomass without much loss of long term yield. The medium term calculations made,
although they may need to be refined, indicate that a gradual reduction of F over some years can be achieved without
much loss in catch, even with recruitment remaining at the present level.
This is a stock for which the current recommendation is for no fishing. There is no doubt that the stock needs
strong conservation measures, and that it should have the potential to be more productive that it is at present. The
fishery of Nephrops is closely linked to the fishery for hake. Actual catch levels are always likely to be determined by
measures applied to hake rather than Nephrops which is taken alongside hake. The southern hake/Nephrops recovery
plan that was discussed at Lisbon in 2003 provides a management prescription with a progressive reductions in F
towards F0.1 (together with closed areas). If such a management regime could be implemented, it seems likely that it can
serve as a recovery regime also for Nephrops. If such a recovery plan cannot be implemented, both the WG and the
reviewers suggest a continuation of the zero TaC advice to be the most adequate, to maintain the signal that urgent
management action is needed.
Some technical notes on Management Area Q
First page:
Though the reference to description of bottom fisheries in the Northwest Spain is given, it would be better to present the
fishing process in the area (FU 26-27) during the last 2 years (direct and mixed fishery or as by-catch only) in the paper.
Some explanations are only given in Table 5.4.8., but it is not clear how long this fishery has been conducted.
Comment by WG chair: Agreed. A fuller statement should appear in future.
In Table 5.4.1. the total catch (FUs 26-27 combined) does not correspond to the sum of catches by countries.
Perhaps the cause of discrepancy should be determined.
Comment by WG chair: The cause of the apparent discrepancy is that the Portuguese figures for FU27 are given
separately for trawl and creel and then the sum of the two (sub-total). A simple sum across the row thus would count
the Portuguese figures twice. Given that subtotal=trawl+creel, the FU26-27 total is correct.
Second page:
From the description of LPUE it is not clear whether trawlers have equal characteristics and the same fishing gears, in
order to consider Unit Effort as one trip. If they have, it is desirable to point out that vessels are equipped with the same
fishing gears, if not, LPUE (as kg per trip) is not correct.
Comment by WG chair: Clarification will be sought on this issue.
FU 30 – Gulf of Cadiz.
Here, no assessment was done due to sparse and uncertain data. A Jones length cohort analysis was done. Trends in
mortality and recruitment cannot be inferred from this analysis, but there were indications that the males may be
exploited above Fmax. The WG concludes that there is insufficient evidence to claim that current landings can be
sustained in the long term. The reviewers support that conclusion, and agrees that further inferences cannot be made
based on the presently available data.
General comments
It is remarkable that the assessment model explains all changes over time mainly as changes in SSB and recruitment,
while F remains rather stable over time. In this way a large reduction in catch is translated as a decrease in recruitment
and SSB. For the stocks for which an assessment is carried out it would be informative to show in the WG report the
plots of the stock recruitment relationship. However, it is by no means obvious that the reduced recruitment s caused by
a low SSB, it may very well be the other way around, and since both have just been declining in the assessment period,
there is nothing to indicate what comes first.
Comment by WG chair: WGNEPH has been reluctant to present graphs of stock and recruitment data because they
are somewhat misleading for Nephrops and certainly should not be used to derive reference points. The slicing
procedure tends to smear the year-class effects in the assessment, such that recruitment and SSB estimates tend towards
their mean values. The assessments for southern stocks presented in this report are somewhat atypical of the norm for
Nephrops in that they show more variation in recruitment and SSB. Northern stocks tend to show the reverse pattern –
stability of SSB and recruitment (probably somewhat artificial because of the slicing effect) and more variable F. For
the southern stocks the WG believes that, even in the face of uncertainty about quantitative stock levels, the assessments
provide a fair qualitative reflection of recent stock trends. Exploitation levels are probably driven by fishing for
southern hake, and it would not be too unexpected for F to remain relatively stable.
The descriptions in the WG report on how the short-term predictions are carried out is extremely brief. It would be
useful if the calculation of the inputs for the short-term predictions were included in future WG reports for all stocks
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where it is done together with a more extensive description on how the inputs for the short-term prediction were
calculated. This would facilitate the work of the reviewers.
Comment by WG chair: Noted. Short-term predictions are a relatively new activity for WGNEPH, having been
performed only since some stocks declined. Calculations will be made more explicit in future.
There is an inconsistency in the mean stock weights at age. These should represent the weight at spawning time,
which taken as 1st of January. However, the mean stock weights are the same as the mean catch weights, which
represent the mean weight at age in the catch around the middle of the year.
Comment by WG chair: This is a crudity of the slicing process – all the assessment inputs are generated by the
slicing program. All lengths are treated as if they were measured at the same time, and no adjustment is made for time
of year. The stock weights are considered to be identical to the catch weights at age. Undoubtedly this is not
satisfactory, but compared with some other shortcomings and approximations in these assessments it is perhaps not too
important. Since we treat the results mainly in relative terms, it should not matter too much so long as all things are
measured on the same scale.
Only for MA N, length distributions by sex are presented, while they are missing in the other MA’s. We think it is
very informative not only to present the length distributions of the landed Nephrops but also in the same figure the
length distributions of the discards by sex (if there are any).
Comment by WG chair: Noted. Future assessment reports will include these as standard.
As noted above, the WG report is very concise, reflecting the WGs attempt to meet the general problem that WG
reports tend to become very voluminous. For the WGNEPH, which assesses a large number of stocks and often split on
two sexes, the report will grow immensely unless one is very restrictive. The crucial question is then if the right things
are included in a WG report. This is a general problem for ICES. The revision of the review process puts this problem
into a somewhat new perspective, because it now becomes critical that the report contains the information an external
reviewer will need. This may sometimes include things that have been standard practise for a long time, and are obvious
to the WG. Admittedly, the WG chair is supposed to be part of the reviewing team, but the report should not be
designed so that it only can be understood with the chair present.
Comment by WG chair: Agreed. The external review process has turned up a number of issues that have been
treated as standard practice in the past and which have not received close scrutiny. Future reporting of Nephrops
assessments will depend somewhat on integration within the regionally-based WGs.
This question is linked to the quality handbook process, where the specifications of the methods are assembled in
an appendix, and the WG is supposed to follow that procedure. The review can then in principle be restricted to looking
after that the procedure has been followed. From an external reviewers point of view, however, it is hard to avoid asking
if the procedure that is followed is the right one, and if the results really reflect the state and exploitation of the stock.
Some questions of that kind have been asked above. Such questions should not be left to reviewers, but rather be asked
and investigated by the WG, as far as possible. This is not the same as revising the assessment method every year, but
rather confirming that the method is still valid when adding new data, or when taking into account recent developments
in the stock biology and fishery.
For the stocks that were assessed this time, referring to ToR a, the crucial question is whether the recent strong
reduction in landings is due to a dramatic failure of recruitment. The answer by the WG is affirmative except for the
stock in the Bay of Biscay, and as far as we are able to see, this is the right conclusion. What we would have liked to
see, however, is a broader scrutiny of alternative hypotheses. The lack of familiarity with stocks without real age
partitioning, as well as the lack of the primary data, precludes the review group to go much beyond what the WG did
along that line.
Comment by WG chair: Broader scrutiny of alternative hypotheses is something that could be addressed by a
future WGNEPH meeting. Current WG meetings tend to be directed towards producing the required assessment output
within the allotted meeting time, which can on its own be challenging (much shorter meeting time this year). If the
assessment tasks are devolved to other WGs (see Section 11), then a future WGNEPH would profitably direct its efforts
to more exploratory analyses. Nephrops is probably not a special case in this respect, but is certainly the case that
there are many issues to explore to ensure the best scientific basis for assessments. In 2002 WGNEPH (a longer
meeting) examined hypotheses about environmental control of recruitment in southern Nephrops stocks. No evidence
for such control was found (although more recent analyses have been more enlightening), but this is an example of the
type of exploratory work that should be encouraged.
The reviewers agreed with the approach of WGNEPH in drawing on multiple lines of evidence to gain an
appreciation of stock status and the direction of stock trends rather than being based on the quantitative output of
analytical assessments. Given the tentative nature of some of the input data the reviewers consider it inadvisable to treat
the terminal estimates from XSA as an absolute quantitative basis to derive catch options. However catch predictions
were presented for those fisheries requiring urgent management action to halt or reverse adverse stock trends (Bay of
Biscay and Iberian stocks). This was because WGNEPH considered that they provided the best scientific basis from
which to draw conclusions about future stock trends. This approach was endorsed by the reviewers.
Accordingly, we recommend that the advice is given in such a way that it reflects what is considered as robust
inferences, even if the form of the advice then becomes different from the standard one. To this end, we support the
further development of advice based directly on observations of abundance, as is now being explored for some stocks.