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Evidence for an unrecognised blue
whale foraging ground in New Zealand
LG Torres a
a National Institute of Water and Atmospheric Research Ltd ,
Hataitai , Wellington , New Zealand
Published online: 15 May 2013.
To cite this article: LG Torres (2013): Evidence for an unrecognised blue whale foraging
ground in New Zealand, New Zealand Journal of Marine and Freshwater Research,
DOI:10.1080/00288330.2013.773919
To link to this article: http://dx.doi.org/10.1080/00288330.2013.773919
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RESEARCH ARTICLE
Evidence for an unrecognised blue whale foraging ground in New Zealand
LG Torres*
National Institute of Water and Atmospheric Research Ltd, Hataitai, Wellington, New Zealand
(Received 29 November 2012; accepted 25 January 2013)
Blue whale distribution in the Southern Hemisphere is poorly understood. Their survival is
dependent on the ability to reliably encounter large aggregations of euphausiid prey. Therefore,
documenting and protecting blue whale foraging grounds is fundamental to enhancing their
recovery. Various data sources are compiled here to support the hypothesis that the South
Taranaki Bight, between the north and south islands of New Zealand, is used as a foraging
ground by blue whales for a common euphausiid prey that aggregate as a function of a nearby
coastal upwelling system. The distribution of blue whales is compared with ship traffic density
and the distribution of seabed mining activities in the region, and reveals close proximity
between whales and these potential threats. This paper presents evidence that the South
Taranaki Bight is a blue whale foraging habitat and calls for a greater understanding of their
habitat use patterns to manage anthropogenic activities effectively.
Keywords: blue whale; distribution; foraging ground; New Zealand; Nyctiphanes australis;
seabed mineral exploration and extraction; ship traffic
Introduction
Blue whales Balaenoptera musculus were subject
to intensive exploitation by whaling operations
during the 20th century, reducing the Antarctic
blue whale population to less than 1% of its
original population size (Branch et al. 2004).
Despite their massive size and once large
population, the blue whale is fairly elusive
and little is known about its distribution or
habitat use. In fact, only four blue whale
foraging grounds have been documented in
the Southern Hemisphere outside Antarctic
waters: the south and south western coasts of
Australia (Gill 2002; Rennie et al. 2009), near
the fjords of southern Chile (Hucke-Gaete et al.
2004), near the Crozet Islands in the Indian
Ocean (Samaran et al. 2010) and on the
Madagascar Plateau (Best et al. 2003).
In the Southern Hemisphere, two subspecies
of blue whales are recognised based on genetics
and morphology: the Antarctic (or true) blue
whale (Balaenoptera musculus intermedia) and
the pygmy blue whale (Balaenoptera musculus
brevicauda). During the austral summer, the
majority of pygmy blue whales do not migrate
to Antarctica (Branch et al. 2007; Attard et al.
2012), but Antarctic blue whales are generally
found south of 558S (Ichihara 1966; Branch
et al. 2007). However, there is recent evidence
from a number of locations around the world,
including New Zealand (McDonald 2006), that
some Antarctic blue whales do not migrate
*Email: l.torres@niwa.co.nz
Supplementary data available online at www.tandfonline.com/10.1080/00288330.2013.773919
Supplementary file 1: Table S1. Details of incidental, anecdotal and survey sightings of blue whales in the
South Taranaki Bight examined in this study; Supplementary file 2: Table S2. Details of blue whale strandings
in the South Taranaki Bight (STB) and all of New Zealand examined in this study.
New Zealand Journal of Marine and Freshwater Research, 2013
http://dx.doi.org/10.1080/00288330.2013.773919
#2013 The Royal Society of New Zealand
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south every winter (Branch et al. 2007; Samaran
et al. 2010). The IUCN Red List of Threatened
Species currently lists the Antarctic blue whale
as Critically Endangered (Reilly et al. 2008) and
the pygmy blue whale as Data Deficient (Ceta-
cean Specialist Group 1996). The New Zealand
Threat Classification System lists the blue whale
as a Migrant (Baker et al. 2010) and therefore
does not designate a threat status.
Due to their enormous size, fully aquatic
lifestyle and zooplankton diet, blue whales have
the highest prey demands of any predator that
ever existed (Rice 1978; Williams et al. 2001),
but they exhibit relatively short dive durations
because of the high energetic demands of their
lunge-feeding strategy (Acevedo-Gutierrez
et al. 2002). Therefore, a critical life-history
strategy for blue whales is to encounter and
exploit dense aggregations of their preferred
prey, euphausiids, which may be spatially and
temporally ephemeral (Croll et al. 1998; Fiedler
et al. 1998). Aggregations of foraging blue
whales have been reported near cold water
coastal upwelling systems in Australia and the
USA where dense patches of their prey are
concentrated. Along the southern Australian
coast, pygmy blue whales aggregate each aus-
tral summer between the Great Australian
Bight and Bass Strait to feed on the euphausiid
Nyctiphanes australis (Gill 2002). Similarly,
blue whales off California, USA predictably
congregate to feed on dense euphausiid schools
in the Channel Islands (Croll et al. 1998) and in
Monterey Bay (Croll et al. 2005).
No dedicated study of blue whales has ever
been conducted in New Zealand. However,
marine mammal observer records from recent
seismic surveys in the South Taranaki Bight
(STB; Blue Planet Marine 2011) suggested a
potential concentration of blue whales in the
region. This paper presents a compilation of
data from published and unpublished sources
demonstrating the consistent presence of blue
whales in the STB. Also investigated is the
potential for a nearby and prominent cold
water coastal upwelling system off Kahurangi
Point (Bowman et al. 1983; Shirtcliffe et al.
1990) to generate concentrations of blue whale
prey.
Since 1979, the largest offshore natural gas
and oil extraction operation in New Zealand
has been located within the STB. This opera-
tion now includes seven production platforms
and significant sea-floor pipelines. Despite ex-
tensive environmental assessments conducted
in the 1970s and 1980s prior to and during the
development of these extraction facilities, no
consideration was given to potential impacts on
marine mammals or other megafauna (Shell BP
and Todd Oil Services Limited 1974; Kibble-
white et al. 1982; Office of the Parliamentary
Commissioner for the Environment 1988). As a
coastal area near multiple urban centres, ship-
ping traffic is also prevalent throughout the
STB. Both shipping traffic and seabed mining
activities have been shown to impact blue
whales directly, alter their behaviour and de-
grade their habitat (Zacharias & Gregr 2005;
Van Waerebeek et al. 2007; Di lorio & Clark
2010; Melcon et al. 2012). As these activities
continue to intensify in the STB, knowledge
about ecosystem function and biodiversity is
necessary if we are to exploit our marine
environment sustainably and avoid deleterious
impacts.
Materials and methods
The STB encompasses 55,835 km
2
and lies bet-
ween the north and south islands of New
Zealand (38849’S to 40853’S, 171837’E to
175813’E; Fig. 1). Within this region, blue
whale sighting and stranding records were
compiled to examine the frequency, seasonality
and persistence of blue whale presence. Modern
(since 1979) records of blue whale sightings
within the STB from the following sources of
cetacean sighting records were examined: (1) a
database curated by the New Zealand Depart-
ment of Conservation (DOC) in which each
sighting is validated (Department of Conserva-
tion 2012a); (2) sightings recorded by trained
observers aboard transiting ships between New
Zealand and overseas ports collated between
2LG Torres
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Figure 1 Distribution of blue whale sightings and strandings within the South Taranaki Bight (STB), New Zealand relative to regional bathymetry,
the location of the Kahurangi Point upwelling system, and sampled areas of high blue whale prey density. Incidental, survey and anecdotal sightings
are symbolised by source. Inset map shows New Zealand with a black box around the STB that is enlarged; Wellington and the Cook Strait are
denoted. Black lines indicate 50-m bathymetry isobaths. The centre of upwelling off Kahurangi Point is demarcated in grey; tongues of upwelled
water extend as a plume to the north and northeast. The ellipses indicate the approximate areas of increased Nyctiphanes australis density sampled
in March and April 1983 (green ellipses; Bradford & Chapman 1988; James & Wilkinson 1988) and February 1981 (blue ellips; Foster & Battaerd
1985). Note: No zooplankton sampling has been conducted in the STB north of c. 39’508S.
Blue whale foraging ground in New Zealand 3
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1979 and 1999 (Cawthorn 2009); (3) sightings
recorded by scientists and vessel captains at the
National Institute of Water and Atmospheric
Research Ltd (NIWA) and photo verified by
the author (L. Torres unpubl. data); (4) sight-
ings recorded during two recent seismic surveys
with on-board marine mammal observers in the
STB between 9 May and 22 July 2011, which
consisted of 519.7 h of visual surveys (Blue
Planet Marine 2011); and (5) anecdotal sight-
ings by a tugboat captain and a DOC ranger in
October 2007, which were followed-up with
personal conversations. Additionally, the dis-
tribution and density of incidental blue whale
sightings from the DOC and Cawthorn datasets
were compared between the STB and all of
New Zealand. Geographic locations for all
these sightings were recorded on-site by the
observers. Also investigated were stranding
records of blue whales within the STB and all
of New Zealand held in the DOC whale
stranding database (Department of Conserva-
tion 2012b). It is difficult to distinguish between
an Antarctic and pygmy blue whale without
genetic analysis and therefore sightings and
strandings in the STB region were not recorded
to subspecies. Hereafter, the term ‘blue whale’
refers to both subspecies in the Southern Hemi-
sphere unless otherwise described to subspecies.
The temporal distribution of blue whale
sightings and strandings was examined to iden-
tify seasonal trends of blue whale presence in the
STB. In this temporal examination, sightings
recorded during seismic surveys were ignored
due to the sampling bias of observational effort
these data create in May, June and July when
the surveys occurred. Monthly distribution
maps of blue whales in the Southern Hemisphere
based on catches, strandings, acoustic records
and Discovery marks published by Branch et al.
(2007; figs. 11 and 12) were also examined. Due
to the lack of standardised survey effort across
the study region, it is not possible to infer
trends in spatial distribution of blue whales
within the STB.
Additionally, literature on blue whale dis-
tribution within the Southern Hemisphere was
investigated for information on occurrence pat-
terns in the STB. Branch et al. (2007) provided
low resolution maps (28grid cells) that indi-
cated the relative occurrence of blue whales at
global and regional scales, including the dis-
tribution of (1) Soviet whaling effort between
1958 and 1973 and the proportion of which
were blue whales, and (2) Japanese Scouting
Vessels (JSV) survey effort between 1965 and
1987 with the corresponding sighting rate of
blue whales.
In order to assess the potential association
between blue whale distribution and their prey
in the STB, the literature on the Kahurangi
Point upwelling system and related zooplank-
ton studies were explored. Group size data
from the recent blue whale sightings were also
examined as an indication of foraging beha-
viour because blue whales are typically solitary
but are known to aggregate on foraging
grounds (Sears & Perrin 2009; Gill et al.
2011). However, solitary, or pairs of, blue
whales do not necessarily denote non-foraging
behaviour.
To understand possible impacts to blue
whales and their habitat in the STB, overlap
was assessed between recent incidental and sur-
vey sightings of blue whales with two sources of
potential anthropogenic threats: (1) seabed
minerals exploration and extraction activities
and (2) ship traffic density. Spatial data layers
were acquired of production platform locations
(Land Information New Zealand 2012), areas
currently permitted for petroleum or mineral
and coal extraction, and proposed blocks for
oil and gas exploration (Ministry of Economic
Development 2012), and a map of commercial
shipping traffic that represents ship density per
1km
2
grid cells (Halpern et al. 2008). These
shipping traffic data were derived from 12 mon-
ths (October 2004September 2005) of ship
location data, which represents roughly 11%
of merchant ships 1000 gross tonnage at sea,
and does not include fishing vessels. Therefore,
these data likely under-represent ship traffic
density in the STB.
4LG Torres
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Results
The DOC and Cawthorn sighting databases
both have eight blue whale sightings recorded
in the STB (Fig. 1 and Table S1). Additionally,
two blue whale sightings in the STB were
reported by NIWA scientists. In addition to
these 18 incidental sightings of blue whales, two
recent seismic surveys with on-board marine
mammal observers in the STB region (Blue
Planet Marine 2011) recorded 11 blue whale
sightings (n2 in May 2011; n9 in June
2011). (An additional 16 sightings of unidenti-
fied large baleen whales likely to have been blue
whales are also reported, but for this study only
the 11 confirmed blue whale sightings are
considered.) Recently, two anecdotal sightings
of blue whales were described: on 29 October
2007, the captain of the tugboat Rupe en route
to service an oil rig observed a group of
approximately 20 blue whales in 100 m water
depth (B. Govier pers. comm. 2012). The
following day, a DOC ranger followed up this
report and initially observed a single blue whale
at 10:30 h in approximately 120 m of water
(C. Lilley, DOC, pers. comm. 2012). Soon after,
the Rupe captain reported observing an esti-
mated 12 blue whales from the bridge within a
few nautical miles of the sighting on the
previous day. At 11:15 h the DOC ranger
observed five more blue whales in about 100 m
of water near the location of the Rupe.The
DOC ranger notes,
There were possibly more [blue whales], but it was
very difficult to obtain a count as they were
distributed and spending long lengths of time
under water. [The Rupe captain] could probably
see more as he was much more elevated on the
bridge of Rupe compared with us on a smaller
(8 m) vessel. The whales were displaying feeding
behaviour ...They would surface, spout a few
times over a minute or two, then dive again for
about 5 or 6 minutes.
Photos taken at the sighting were provided to
confirm individuals as blue whales.
Scattered incidental sightings of blue whales
have been recorded broadly across New Zealand
waters (Fig. 2), yet two clusters of sightings are
evident: (1) in the STB and (2) off the east coast
of Northland, between the Hauraki Gulf and
the Bay of Islands.
Twenty blue whale strandings have been
recorded in New Zealand since 1893. Six of
these strandings occurred in the STB and
another four were within 45 km of the STB
(Figs. 1 and 2, Table S2). These 10 strandings
are not clustered, but rather are evenly spread
along the coastlines surrounding the STB from
just north of New Plymouth, through to Well-
ington and along the northern coast of South
Island. The other 10 blue whale strandings in
New Zealand are spread around the country’s
coastlines with a cluster of three near the
densely populated city of Auckland (Fig. 2).
Examination of whaling records from So-
viet catches between 1958 and1973 illustrates a
substantial increase in catch density of blue
whales within the STB region and to the
immediate west relative to surrounding ocean
basins (Figs 3a and 3b). Additionally, the STB
is indicated as having high sighting rates of blue
whales from JSV between 1965 and 1987 (Figs
3c and 3d).
The sightings derived from the seismic
surveys indicate the presence of blue whales in
the STB during May and June (Table 1).
Without considering these seismic survey sight-
ings, small peaks of blue whale presence in the
STB are evident in May and OctoberNovem-
ber. The May peak is complemented by five
recent blue whale strandings, which occurred in
May and June (Table S2). One or more
incidental blue whale sighting has been re-
corded in the STB in all months but February
and July when no blue whale sighting has been
reported. Similarly, year-round presence of
blue whales along the west coast of North
Island, New Zealand is indicated by monthly
illustrations presented by Branch et al. (2007)
of blue whale catches by whalers, sightings,
stranding, acoustic recordings and Discovery
marks. These monthly plots also show peaks in
the number of records in the STB region
between December and April, but this pattern
Blue whale foraging ground in New Zealand 5
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Figure 2 Distribution of all blue whale sightings (black dots) and stranding (open stars) records in New
Zealand with the South Taranaki Bight indicated by the black box. The east coast of Northland, between the
Hauraki Gulf and the Bay of Islands, is indicated by the dashed box. City centres of Auckland, New
Plymouth and Wellington are denoted by crosses.
6LG Torres
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could be due to increased observational effort
during summer months.
A cold upwelling plume, driven by prevail-
ing strong westerly winds, is a persistent feature
in the southwestern region of the STB (Bow-
man et al. 1983; Shirtcliffe et al. 1990; grey area
in Fig. 1). Alongshore winds and coastal promi-
nences result in the upwelling of nutrient-rich
water from depths of about 100 m off Kahur-
angi Shoals. Rotating eddies are created that
are transported downstream (north and north-
east) with a life span of 2 weeks (Foster &
Battaerd 1985; Shirtcliffe et al. 1990). Studies
have documented large concentrations of
zooplankton, including elevated biomass of
N.australis, linked to these upwelling plumes
due to enhanced primary productivity (Foster
& Battaerd 1985; Bradford & Chapman 1988;
James & Wilkinson 1988; Bradford-Grieve
et al. 1993). All of these studies found N.australis
concentrations most abundant downstream of
the upwelling area to the north and east (Fig. 1).
Unfortunately, the majority of zooplankton
sampling sites in these studies occurred between
0
1
2−4
5−19
20−99
≥ 100
80°S
60°S
40°S
20°S
0°
20°N
180°W 120°W 60°W 0° 60°E 120°E 180°
80°S
60°S
40°S
20°S
0°
20°N
0
0.02
0.1
0.2
0.5
1
180°W 120°W 60°W 0° 60°E 120°E 180°
80°S
60°S
40°S
20°S
0°
20°N
80°S
60°S
40°S
20°S
0°
20°N
A
B
Figure 3 Increased blue whale presence in the South Taranaki Bight (red boxes in B and D) from Soviet
catches between 195873 in the Southern Hemisphere (A and B) and sightings from Japanese Scouting
Vessels (JSV) between 1965 and 1987 (C and D). A, Number of Soviet catches of all large cetaceans in each 28
grid cell, to be used as a rough measure of effort compared with B, the proportion of large cetacean catches in
each 28grid cell that were blue whales. C, JSV survey effort in km to be compared with D, sightings of blue
whales per unit effort in each 28grid cell (no effort in the northern Indian Ocean). Figures taken from Branch
et al. (2007); reprinted with permission from T. Branch, Mammal Review and John Wiley & Sons Ltd.
Publishing.
Blue whale foraging ground in New Zealand 7
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the upwelling area and south of 39?508S, and no
long-term records of the zooplankton commu-
nity in the STB have been made. Therefore, no
empirical data are available on the variation in
zooplankton composition throughout the entire
STB region or temporally. However, Bradford
& Chapman (1988) found the greatest biomass
of N.australis at the northern and eastern limits
of their sampling area and illustrated increasing
wet weight toward the north. Furthermore, the
STB area has the most extensive zooplankton
biomass of all coastal regions in New Zealand
(Bradford & Roberts 1978) and a study of the
euphausiid community in nearby Cook Strait
found N.australis to be the dominant species
with year-round presence (Bartle 1976). Brad-
ford & Chapman (1988) postulated that a
resident population of N.australis may exist
within the STB region, but this remains un-
proven. Although more comprehensive data on
the spatial and temporal distribution of the
zooplankton community in the STB is needed,
available evidence indicates that a common
prey of the blue whale, N.australis, is abundant
Figure 3 (Continued)
Table 1 Monthly distribution of blue whale sightings in the South Taranaki Bight (STB).
Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Unknown Total
Incidental and
anecdotal sightings
10 1 1 3 10113 6 1 1 20
Seismic survey sightings 0 0 0 0 2 9 0 0 0 0 0 0 0 11
Total 1 0 1 1 5 10 0 1 1 3 6 1 1 31
Notes: Blue whale sighting sources include incidental sightings derived from: (1) the New Zealand Department of
Conservation (2012a); (2) Cawthorn (2009); and (3) the National Institute of Water and Atmospheric research (NIWA)
cetacean sighting databases (see Methods); (4) anecdotal sightings provided by a tugboat captain (pers. comm., Barry
Govier, April 2012, Tug Master, 341 South Road, Omata, New Plymouth, New Zealand) and Department of Conservation
ranger (pers. comm., Callum Lilley, April 2012, Ranger/Technical Support*Marine, Department of Conservation,
Taranaki Area Office, PO Box 462, 55A Rimu Street, New Plymouth 4310, New Zealand); (5) seismic survey sightings
collected by marine mammal observers aboard seismic survey vessels in the STB (Blue Planet Marine 2011).
8LG Torres
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and does concentrate in the STB in response to
upwelling plumes formed off Kahurangi Point.
Another indication that the STB may be a
foraging ground for blue whales is the relatively
large group sizes estimated at incidental sight-
ings (Table S1). Although group size estimates
from these sightings cannot be regarded as
completely accurate, many observations re-
corded multiple animals including eight sight-
ings with more than two individuals present.
These larger groups could represent feeding
aggregations. Furthermore, the anecdotal sight-
ing on 30 October 2007 was reported by a DOC
ranger as five foraging blue whales. Due to the
large group size (20 individuals) reported by the
tug boat captain on the previous day, this is
also assumed to be a feeding aggregation.
Almost the entire northern portion of the
STB (above 408S) and in waters less than 150 m
is permitted for either petroleum exploration
and extraction or mineral and coal mining (Fig. 4).
Twenty-four of the 31 blue whale sightings
examined in this study (77%) occurred within
a permitted seabed mineral extraction area.
Additionally, a few of the incidental blue whale
sightings were recorded from production plat-
forms. Low-level ship traffic covers the entire STB
(not illustrated in Fig. 1 to simplify figure), and a
relatively dense shipping lane extends north
south near the 1738E meridian (Fig. 4). This
shipping lane runs within 10 km of 14 blue whale
sightings examined in this study.
Discussion
Multiple data sources have been examined here
in an effort to understand the occurrence
patterns of blue whales in the STB, New
Zealand and their functional habitat use. This
synthesis of data sources supports the hypoth-
esis that the STB is a blue whale foraging
ground where whales feed on N.australis that
concentrate in response to Kahurangi Point
upwelling plumes. Whaling records indicate
that blue whales were common in this region,
but the STB has never been recognised as a blue
whale foraging ground. This potential oversight
is reinforced by the listing of blue whales as a
Migrant under the New Zealand Threat Classi-
fication System (Baker et al. 2010), which
should be re-evaluated.
Evidence of elevated blue whale presence in
the STB includes increased density of blue
whale sighting records in the STB relative to
other areas around New Zealand. Elevated blue
whale sightings along the east coast of North-
land may indicate that this area is a migration
corridor and may be due to increased observa-
tional effort from relatively extensive fishing
effort and recreational boater activity in the
area. Additionally, examination of the Soviet
whaling and JSV blue whale data demonstrates
increased blue whale presence in the STB region
relative to other areas globally and within New
Zealand, and a persistent use of the STB region
by blue whales over time. The stranding record
also indicates a history of blue whales in the
STB with four of the nine strandings recorded
between 1893 and 1951.
Due to unstandardised observer coverage
across the STB and the various and limited data
sources explored, a seasonal pattern of blue
whale presence in the STB cannot be deter-
mined. This lack of seasonal pattern may be
due to (1) the relatively few available blue
whale sighting (n31) and stranding (n10)
records in the STB, which are temporally
biased due to the lack of standardised survey
effort; (2) blue whales feeding in the STB
during winter months based on evidence that
winter blue whale distribution can be influ-
enced by foraging opportunities (Croll et al.
2005; Branch et al. 2007); (3) a life history
strategy that entails blue whale foraging outside
the Antarctic in summer (e.g., Hucke-Gaete et
al. 2004), which is a typical behaviour for
pygmy blue whales (Gill 2002; Best et al.
2003); (4) different distribution patterns be-
tween blue whale subspecies where the presence
of subspecies in the STB alternates temporally;
or (5) a combination of these factors. Despite a
lack of evidence for a seasonal pattern of sight-
ings, the presence of blue whales in the STB
during summer months (NovemberApril),
Blue whale foraging ground in New Zealand 9
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Figure 4 Distribution of blue whale sightings within the South Taranaki Bight (STB), New Zealand overlaid on the distribution of potential
anthropogenic threats in the region. Locations of production platforms and layers of permitted seabed mineral exploration and extraction areas are
derived from Land Information New Zealand (2012) and the Ministry of Economic Development (2012). Ship traffic density is derived from
Halpern et al. (2008). Grid cells with less than 284 ship tracks per km
2
cover almost the whole STB region and are not displayed here to simplify the
plot. Inset map shows New Zealand with a black box around the STB that is enlarged; Wellington and the Cook Strait are denoted. The centre of
upwelling off Kahurangi Point is demarcated in grey; tongues of upwelled water extend as a plume to the north and northeast.
10 LG Torres
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when the majority of Antarctic blue whales are
expected to be foraging in southern Antarctic
waters, indicates that these sightings may be
pygmy blue whales. However, sympatric blue
whale subspecies on foraging grounds has been
documented, as well as the year round presence
of Antarctic blue whales north of the Polar
Front (Samaran et al. 2010). Therefore, in
order to resolve occupancy patterns in the
STB by blue whale population, individuals
must be identified to subspecies.
Multiple publications on zooplankton com-
position in the STB offer evidence that
N.australis is found in dense concentrations
that could attract foraging blue whales. The
large distances between the Kahurangi Point
upwelling area and the majority of blue whale
sightings presented here (50150 km) does not
weaken this hypothesis. A spatial disconnect
between upwelling centres and locations of
euphausiid blooms with high rates of blue
whale sightings has been documented in studies
of blue whales off southern Australia (Gill et al.
2011), Channel Islands, California (Croll et al.
1998) and Monterey Bay, California (Croll
et al. 2005). All three of these studies reported
increased sightings of foraging blue whales in
association with dense concentrations of eu-
phausiids that formed downstream of cold
water coastal upwelling systems. This spatial
lag is due to wind-forcing, currents and tem-
poral lags in zooplankton growth. Based on
concentrations of a main blue whale prey,
N.australis, toward the distal end of the
Kahurangi Point upwelling system, it is possi-
ble that blue whales use this habitat to feed on
dense aggregations of their prey. Of course, the
paucity of blue whale sightings south of 408S
where high densities of N.australis have been
documented (ellipses in Fig. 1) cannot be
interpreted as a lack of habitat use by blue
whales because all these sightings data were
collected without standardised observer effort
across the region. Therefore, the absence of
sightings does not indicate the absence of blue
whales.
Assessment of spatial overlap between ex-
isting records of blue whale sightings in the
STB and potential threats illustrates close
proximity between whales and seabed mineral
exploration and extraction activities and ship-
ping traffic. This study suggests that a blue
whale foraging ground in the STB has gone
unrecognised for decades amidst these and
other sources of anthropogenic threats. The
impacts of these threats are unknown, but
anthropogenic noise from seismic activity and
shipping traffic has been shown to alter blue
whale acoustic behaviour (Di lorio & Clark
2010; Melcon et al. 2012) and ship strikes of
baleen whales is a growing threat globally (Van
Waerebeek et al. 2007), including in New
Zealand where one reported blue whale strand-
ing death near Auckland was caused by a ship
strike (Table S2). If human activities in the STB
do affect blue whales the impacts could cause
population declines of an endangered species
and ecosystem changes due to the removal of
top-down forcing and subsequent trophic cas-
cades (Estes et al. 2011). Moreover, marine
ecosystems and animals can be simultaneously
under pressure from multiple sources of anthro-
pogenic impacts (Greene & Pershing 2004;
Rosa & Seibel 2008). Therefore, despite appar-
ent low-level impacts from individual sources,
we must be cognisant of cumulative effects and
manage these threats with a coordinated
approach.
To gain a more comprehensive understand-
ing of blue whale distribution throughout the
STB, two complementary methods, aerial sur-
veys and acoustic loggers, can be employed.
Systematic aerial surveys, conducted at regular
temporal intervals (e.g., monthly) can collect
standardised data that will elucidate the spatial
(how big) and temporal (how frequent and
persistent) scale of blue whale distribution in
the region (e.g., Gill et al. 2011). The produc-
tion of high intensity, low frequency and long
duration acoustic calls is a common and
important aspect of blue whale behaviour
worldwide (McDonald et al. 2006). Therefore,
an array of acoustic loggers deployed in the
Blue whale foraging ground in New Zealand 11
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STB would detect the presence of calling blue
whales and clarify temporal patterns of occu-
pancy (e.g., Stafford et al. 2001), and identify
habitat use to sub-species (e.g., Samaran et al.
2010), based on previously described unique
calls (McDonald et al. 2006). Data collected
from these methods should be examined rela-
tive to oceanographic data, either remotely
sensed or collected in situ, to synoptically link
blue whale presence and absence with upwelling
events and plume location dynamics (e.g.,
Rennie et al. 2009). Boat-based surveys can
complement these methods through photo-
identification of individuals, collection of biopsy
samples to genetically distinguish between Ant-
arctic and pygmy blue whale subspecies, and the
collection of continuous hydroacoustic data and
conductivitytemperaturedepth (CTD) casts to
investigate synoptically the links between blue
whales, prey and habitat.
Conclusion
This study presents evidence that the STB is a
blue whale foraging ground and is an example
of how extraction of marine resources can be
sanctioned without a complete understanding
of potential impacts on the environment or
biodiversity. Human activities have already
dramatically reduced blue whale numbers,
leaving only a remnant population (Branch et
al. 2004; Branch 2007). Foraging is a critical life
history component of any animal, and for blue
whales, the ability to encounter reliable, dense
prey aggregations can dramatically impact
survival and reproductive rates. Outside of the
Antarctic there are few documented blue whale
foraging grounds in the Southern Hemisphere.
It is therefore essential that a firm understand-
ing of blue whale distribution and habitat use
patterns within the STB is gained before
anthropogenic activities escalate to levels of
disturbance that could cause displacement of
blue whales from a potentially critical foraging
ground.
Supplementary files
Supplementary file 1: Table S1. Details of
incidental, anecdotal and survey sightings of
blue whales in the South Taranaki Bight
examined in this study.
Supplementary file 2: Table S2. Details of blue
whale strandings in the South Taranaki Bight
(STB) and all of New Zealand examined in this
study.
Acknowledgements
I would like to thank OMV NZ Ltd and NIWA for
funding this research and M. Patrick for facilitating
the project. I thank M. Cawthorn and the New
Zealand Department of Conservation for contribut-
ing incidental blue whale sightings and strandings
data, and C. Lilley for supplying details of blue
whale foraging sightings. Plots of Soviet catch and
JSV sighting data of blue whales are reproduced here
with permission from T. Branch, Mammal Review
and John Wiley & Sons Ltd. Publishing. I am
grateful to J. Bradford-Grieve, R. Constantine,
A. Rowden, D. Thompson and two reviewers for
insightful comments on this manuscript.
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