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An evaluation of different structures to age
freshwater fish from a northeastern US river
M. J. MACEINA & S. M. SAMMONS
Department of Fisheries, Auburn University, Auburn, AL, USA
Abstract Largemouth bass, Micropterus salmoides (Lacepe
`de), smallmouth bass, Micropterus dolomieu Lacepe
`de,
and yellow perch, Perca flavescens (Mitchill), were collected from the Hudson River, New York, USA, to compare
the precision of age estimates derived from scales and otoliths. Similar procedures were used to compare otolith
and spine ages from brown bullhead, Ameiurus nebulosus (Lesueur). Overall percent agreement between readers
ranged from 91% to 98% for otoliths compared with 38% to 67% for scales and spines. Disagreement rates
associated with scales and spines increased as fish grew older. Average percent error between readers was about an
order of magnitude higher for scales and spines than for otoliths. Ages estimated from scales and spines pro-
gressively decreased as age increased based on otolith examination. The use of scales and spines to age largemouth
bass, smallmouth bass, yellow perch and brown bullheads from the northeastern US was less precise and will likely
lead to underestimation of age of larger and older fish.
KEYWORDS: ageing, northeastern US, otoliths, precision, scales, spines.
Introduction
Estimates of fish ages provide important demographic
parameters to analyse and assess fish populations.
Historically, scales have been widely used to age
freshwater fish, although otoliths have been found to
be more accurate and precise structures to age fish
(DeVries & Frie 1996). Ictalurids are routinely aged
using pectoral spines, but recent research (Buckmeier,
Irwin, Betsill & Prentice 2002) has found that otoliths
provide more accurate and precise age estimates for
channel catfish Ictalurus punctatus (Rafinesque).
Ageing fish with otoliths was more accurate, showed
greater precision and provided higher estimates of age
compared with scales for various species in a number
of waterbodies in the southern US (e.g. Boxrucker
1986; Welch, Van Den Avyle, Betsill & Driebe 1993;
Besler 2001). However, in more northern latitudes
(>40N) in North America and Europe, mixed results
were reported when age estimates and precision of
scale and otolith ages were compared (Skurdal,
Vollestad & Qvenild 1985; Barbour & Einarsson
1987; Mosegaard, Appelberg & Nangstroem-Klevbom
1989; Robillard & Marsden 1996; Isermann, Meer-
beek, Scholten & Willis 2003). A comparison of spine
and otolith ages for ictalurids has only been conducted
in southern US waterbodies (Nash & Irwin 1999;
Buckmeier et al. 2002). The objectives of this paper
were to compare age estimates and reader precision
between scales and otoliths of largemouth bass,
Micropterus salmoides (Lacepe
`de), smallmouth bass,
Micropterus dolomieu Lacepe
`de, and yellow perch,
Perca flavescens (Mitchill), and between otoliths and
spines for brown bullhead, Ameiurus nebulosus (Lesu-
eur), collected from the upper Hudson River located in
northeastern USA.
Materials and methods
Fish were collected from the upper Hudson River
north of Albany, New York, USA (4245¢N),
19–80 km north of the confluence with the Mohawk
River using DC electric fishing in June 2002 and 2004.
For largemouth bass, smallmouth bass and yellow
perch, scales were removed from below the lateral line
and behind the pectoral fin (DeVries & Frie 1996).
Pectoral spines were removed from brown bullheads
(Buckmeier et al. 2002). After scale and spine removal,
sagittal otoliths were extracted from the same fish
(Buckmeier et al. 2002). Some additional fish were
Correspondence: Michael J. Maceina, Department of Fisheries, Auburn University, 203 Swingle Hall, Auburn, AL 36849, USA (e-mail:
maceimj@auburn.edu)
Fisheries Management and Ecology, 2006, 13, 237–242
2006 The Authors. Journal compilation 2006 Blackwell Publishing Ltd 237
collected in 2004 and otoliths were obtained, but scale
and spine samples were not taken.
Scale and spine processing and age enumeration
were conducted by experienced readers at Ecologic,
Inc. (Syracuse, NY, USA). Scales were placed between
two microscope slides or impressions were made onto
acetate. Some larger scales were briefly soaked in a 5%
acetic acid solution to facilitate softening and clearing
of the scale. Pectoral spines were sectioned just above
the basal recess using either a Dremel cutting wheel or
jewellers saw and were generally less than 0.5-mm
thick. Spine sections were soaked in a 5% acetic acid
solution for at least 24 h and placed between two
microscope slides.
Scales were magnified and viewed with a microfiche
projector. Spine sections were observed under either a
compound or dissecting microscope. For scale sam-
ples, we assumed that annulus formation was either
complete or was forming in June based on observa-
tions made by Maraldo & MacCrimmon (1979) for
largemouth bass in Canada. Thus, the outer margin
was considered to be the final annulus. Scales and
spines were aged independently by two readers; if
agreement of age assignment did not occur, then these
two readers re-examined the structure together and
reached concurrence. If an age could not be agreed
upon, a third interpreter assisted in making the final
age interpretation.
Otoliths for largemouth bass, smallmouth bass and
yellow perch were processed and aged following the
procedures of Hoyer, Shireman & Maceina (1985),
Maceina & Betsill (1987) and Maceina (1988). For
black bass and yellow perch, whole otoliths were
soaked in a 1:1 solution of ethanol and glycerine for
about 4 weeks. Otoliths were examined independently
by two readers in whole view for fish displaying up to
six or seven annuli. In older fish, or where annuli were
not clearly visible, otoliths were sectioned (Maceina
1988) and annuli were counted by two readers.
Bullhead otoliths were sectioned, processed and viewed
independently by two readers following the procedures
of Buckmeier et al. (2002). Where disagreement in
enumeration of age occurred, an age was assigned after
concurrent viewing without the assistance of a third
reader. The outer edge was considered an annulus as
annulus formation was visible on some otoliths or
would be completed shortly if fish were not collected.
This assignment was consistent among scales, spines
and otoliths.
For scales, spines and otoliths, Pearson correlation
coefficients were computed between the age assign-
ments of the first and second readers. Percent
agreement among the range of ages examined and
total percent agreement were computed, and the
average percent error (APE) between readers was
derived using the formula presented by Beamish &
Fournier (1981):
APE ¼1
RX
R
i¼1
jxij xjj
xj
100;
where x
ij
is the ith age determination of the jth fish, x
j
the average age calculated for the jth fish and Rthe
number of times each fish is aged.
The APE is not only sensitive to age disagreement,
but also to the magnitude in the difference in age
assignment between or among readers (Beamish &
Fournier 1981).
Results
Percent agreement of ages between independent
readers was higher for otoliths than for scales and
spines (Table 1; Fig. 1). Percent agreement ranged
from 91% to 98% for otoliths compared with 40–
67% for scales and spines. For largemouth bass,
smallmouth bass and yellow perch, agreement
between scale age assignment was greater than 80%
for young fish (ages 1 to 3–4), but decreased to less
than 60% for fish older than age 7. Percent agreement
Table 1. Comparison of percent agreement rates, average percent error (APE), the Pearson correlation coefficient (r) between reader age
assignment and agreement rates between scales/spines and otoliths from fish collected from the Hudson River
Species
Percent agreement APE rbetween readers Percent agreement between
scale/spine and otolith
Scale/spine Otolith Scale/spine Otolith Scale/spine Otolith
Smallmouth bass 67 94 4.3 0.5 0.92 >0.99 43
Largemouth bass 57 91 7.3 0.5 0.80 >0.99 20
Yellow perch 65 98 5.4 0.2 0.91 >0.99 47
Brown bullhead 40 92 9.1 0.8 0.68 0.99 18
Largemouth bass, smallmouth bass and yellow perched were aged using scales and otoliths and brown bullhead were aged with spines and
otoliths.
M. J. MACEINA & S. M. SAMMONS238
2006 The Authors. Journal compilation 2006 Blackwell Publishing Ltd
between readers who examined brown bullhead spines
was generally low (<50%) for all ages except for age-
4 fish (Fig. 1). Percent agreement between readers for
otolith ages decreased with fish age, but overall
agreement over the range of ages were typically
greater than 90% (Fig. 1).
Average percent error in reader precision was about
an order of magnitude higher for scales and spines
than for otoliths (Table 1). Similarly, the correlation
coefficients between ages assigned by readers for scales
and spines were much lower than for otoliths
(Table 1).
Average agreed-upon age estimates for scales were
within 1 year of the agreed-upon otolith ages for
smallmouth bass and yellow perch estimated to be up
to 6–7 years old using otoliths (Fig. 2). For fish
estimated to be older than this from otoliths, scale
ages were less than otolith ages and these differences
progressively increased with older fish. For largemouth
bass, scale ages were greater than otolith ages for fish
>7
7
65
43 >8876541–3
>887651–4
Percent agreement
shtilotO
7
6
=n
se
l
ac
S
98=
n
s
e
nipS
36=
n
shtilotO
611=n
selacS
211=n
shtilotO
7
9
2
=n
>8
87654321
sel
a
c
S
4
02=n
shtilotO
412=n
Brown bullhead
Largemouth bass
Smallmouth bass
Yellow perch
Agreed-upon age (years)
0
20
40
60
80
100
0
20
40
60
80
100
0
20
40
60
80
100
0
20
40
60
80
100
Figure 1. Agreement rates between independent readers that assigned ages to scales and otoliths over a range of agreed-upon ages for four species of
fish collected from the Hudson River.
)srae
y(
ega
h
t
i
lo
t
O
8161
4
12
1
01
8
642
Difference in scale age (years)
–8
–6
–4
–2
0
2
4
6
(n = 83)s
s
abhtuomegraL
41210
1
8642
Difference in scale age (years)
–4
–3
–2
–1
0
1
(n = 91)ssabhtuomllamS
210186
4
2
–4
–3
–2
–1
0
1
2
3
(n = 183)hcrepwolleY
8
1
6
1
412
1
01864
Difference in spine age (years)
–10
–8
–6
–4
–2
0
2
(n = 65)daehllubnworB
Figure 2. Differences in mean age and the range in age differences determined from spines and scales compared with otoliths (spine or scale age
minus otolith age) for four species of fish collected from the Hudson River.
COMPARISON OF AGEING STRUCTURES 239
2006 The Authors. Journal compilation 2006 Blackwell Publishing Ltd
that were estimated up to 9 years old with otoliths.
After age 11, average scale ages were lower than otolith
ages. For brown bullheads estimated to be older than
age 3 from otoliths, ages estimated from spines were
progressively less than otolith age as the fish grew
older. Agreement between scale or spine and otolith
ages was low and ranged from 18% to 47% among the
species examined (Table 1). Finally, for fish that were
less than 5 years old (with otoliths), agreement rates
between otolith and scale ages varied among species
and was 79% for smallmouth bass, but was only 52%
and 35% for yellow perch and largemouth bass
respectively.
The maximum ages of fish aged with spines and
scales were 9, 10, 12 and 14 for brown bullhead,
smallmouth bass, yellow perch and largemouth bass
compared with maximum ages of 18, 14, 19 and
13 years old, respectively, estimated from otolith
examination of the same fish.
Discussion
The opaque band formation on otoliths were not
validated as true annuli in fish from the Hudson River,
but otoliths have been verified as accurate ageing
structures for largemouth bass (Taubert & Tranquilli
1982; Hoyer et al. 1985; Buckmeier 2002) and small-
mouth bass (Heidinger & Clodfelter 1987) in locations
south of the Hudson River. Although otolith annulus
formation has not yet been validated for yellow perch
and brown bullhead, otoliths serve as accurate ageing
structures for other percids (Erickson 1983; Heidinger
& Clodfelter 1987) and ictalurids (Buckmeier et al.
2002). Maraldo & MacCrimmon (1979) validated scale
annuli up to 7 years old for largemouth bass in a
Canadian lake (4502¢N), which was near the
Hudson River, but sample size was small (n¼8).
Scales, spines and otoliths have not been validated as
accurate ageing structures for these four species in the
northeastern US. In the nearby Delaware River basin
(4030¢N), percent agreement for scale readings of
American shad Alosa sapidissima (Wilson) ranged
from 34% to 49% for known age 3 to 6-year-old fish
(McBride, Hendricks & Olney 2005). In addition,
accuracy using scales from these fish declined to less
than 13% for known age fish older than 6 years old
and scales over- and underestimated the true age of
young and older fish respectively (McBride et al.
2005).
Age assignment from spines and scales was less
precise than from otoliths for fish collected from the
upper Hudson River, and scale ages were progressively
lower than otolith ages for older fish. Imprecise and
inaccurate age enumeration from scales has been
attributed to reabsorption, deposition of false annuli
due to stress and food limitation, and annuli becoming
obscure because scale growth tends to cease as fish
grow older (Beamish & McFarlane 1987; DeVries &
Frie 1996). Underestimation and lack of precision to
age ictalurids using spines may occur due to expansion
of the central lumen, which may obliterate early
formed annuli, the appearance of multiple growth
rings and poor sectioning techniques (Buckmeier et al.
2002). However, basal recess spine sections examined
for brown bullheads from the Hudson River may have
provided lower age estimates when compared with
sections made from the articulating process of the
spine (Nash & Irwin 1999). Nevertheless, otoliths
continue to grow and form annuli even as body
growth slows and asymptotic length is reached, and
annuli reabsorption does not appear to occur during
periods of food limitation or stress (DeVries & Frie
1996).
Reader agreement for ages compared between scales
and otoliths was high (>80%) for black crappie,
Pomoxis nigromaculatus (Lesueur), and white bass,
Morone chrysops (Rafinesque), less than 6–7 years old
from South Dakota, USA (Kruse, Guy & Willis 1993;
Soupir, Blackwell & Brown 1997). However, Soupir
et al. (1997) found annuli on white bass scales were
difficult to interpret after age 6. For yellow perch in
Pennsylvania, USA, percent agreement between read-
ers was 96% and 83% for otoliths and scales, but scale
age agreement was 59% for fish that were ‡4 years old
(Niewinski & Ferreri 1999), similar to the results in this
study. Also similar to results of this study, yellow perch
from Lake Michigan, USA, had a greater number of
annuli on their otoliths than on scales when more than
seven annuli were visible on otoliths (Robillard &
Marsden 1996). In addition, APE values between
readers were only about 16-25% less for yellow perch
otoliths compared with scales; thus, Robillard &
Marsden (1996) recommended otoliths be used to age
these fish from Lake Michigan.
Age agreement between scale readers was low and
scale ages were less than otoliths in long-lived walleye
Sander vitreus (Mitchill) populations in Canada
(Erickson 1983), similar to the results for black bass
and yellow perch from the Hudson River. For walleye
(<age 10) collected from South Dakota, Isermann
et al. (2003) found 51% age agreement between scale
readers, which was slightly less than that found for the
three species aged from scales in the Hudson River
(57–67%). Age agreement among readers using scales
of various ages of American shad in Pennsylvania,
USA, ranged from 50% to 77% (McBride et al. 2005).
M. J. MACEINA & S. M. SAMMONS240
2006 The Authors. Journal compilation 2006 Blackwell Publishing Ltd
Whole and sectioned otolith age agreement was
87–88% for walleye (Isermann et al. 2003), which
was also slightly less than otolith age agreement rates
for Hudson River fishes.
Reader precision was high for both scales and
otoliths obtained from roach, Rutilus rutilus (L.), in
Sweden, but ages discerned from scales were much
lower than those observed from fish that were >10–
11 years old estimated from otolith examination
(Mosegaard et al. 1989). For brown trout, Salmo
trutta L., arctic charr Salvelinus alpinus (L.) and white
fish Coregonus clupeaformis (Mitchill), scale-age esti-
mates were less than otolith ages for fish estimated to
be greater than 3–5 years old from otoliths (Jonsson
1976; Skurdal et al. 1985; Barbour & Einarsson 1987).
From these comparative studies in northern latitudes
(>40N) and the results collected from the Hudson
River, underestimation of age using scales likely occurs
at mid- to later-life stages of fish.
Spine and otolith age comparisons for precision or
bias have not been made for ictalurids in northern
latitudes, but in Alabama, USA, agreement in age
assignment for basal recess sections of spines was much
lower than for otoliths for flathead catfish, Pylodictis
olivaris (Rafinesque) (Nash & Irwin 1999), and channel
catfish (Buckmeier et al. 2002), which was observed for
brown bullheads from the Hudson River. After age 4,
ages estimated from basal recess spine examination
progressively underestimated age compared with
otolith estimates for a long-lived flathead catfish
population (maximum age 28 years; Nash & Irwin
1999), analogous to long-lived brown bullheads from
the Hudson River.
In conclusion, age determination from scales and
spines of largemouth bass, smallmouth bass, yellow
perch and brown bullheads from the northeastern US
were likely less accurate and will probably lead to
underestimation of age of larger and older fish. Thus,
estimates of growth will be higher for older fish and
survival using catch-curve regression will be lower if
scales and spines are used to age fish from this region.
In addition, age estimates from these structures will
likely be less precise than for otoliths. However,
validation of otoliths as accurate ageing structures
has not been conducted for these species in the
northeastern US and warrants investigation. These
results also suggested that scales, in some instances,
may provide reasonable estimates of age for younger
fish, but validation of this structure using marked or
known-age fish should be conducted. Beamish &
McFarlane (1987) warned that scale ages may be
unreliable structures for ageing fish and these results
confirmed this observation.
Acknowledgments
This project was funded by General Electric Company,
Albany, New York. T. Vandevalk, T. Brooking and
M. Arrigo with Ecologic, Inc. processed and examined
scales and spines.
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