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Comparison of the Precision of Age Estimates Generated from Fin Rays, Scales, and Otoliths of Blue Sucker

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Evaluating the precision of age estimates generated by different readers and different calcified structures is an important part of generating reliable estimations of growth, recruitment, and mortality for fish populations. Understanding the potential loss of precision associated with using structures harvested without sacrificing individuals, such as scales or fin rays, is particularly important when working with imperiled species, such as Blue Sucker Cycleptus elongatus. We collected otoliths (lapilli), scales, and the first fin rays of the dorsal, anal, pelvic, and pectoral fins of nine Blue Sucker. Age estimates were generated from each structure by both experienced (n=5) and novice (n=4) readers. We found that independent of the structure used to generate the age estimates, the mean coefficient of variation (CV) of experienced readers was approximately 29% lower than that of novice readers. Further, the mean CV of age estimates generated from pectoral fin rays, pelvic fin rays, and scales were statistically indistinguishable and less than those of dorsal fin rays, anal fin rays, and otoliths. Anal, dorsal, and pelvic fin rays and scales underestimated age compared to otoliths, but age estimates from pectoral fin rays were comparable to those from otoliths. Skill level, structure, and fish total length were factors influencing reader precision between subsequent reads of the same aging structure from a particular fish. Using structures that can be harvested non-lethally to estimate the age of Blue Sucker can provide reliable and reproducible results, similar to those that would be expected from using of otoliths. Therefore, we recommend the use of pectoral fin rays as a non-lethal method to obtain age estimates for Blue Suckers.
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Comparison of the Precision of Age Estimates Generated from
Fin Rays, Scales, and Otoliths of Blue Sucker
Author(s): Matthew R. Acre, Celeste Alejandrez, Jessica East, Wade A. Massure,
Seiji Miyazono, Jessica E. Pease, Elizabeth L. Roesler, Heather M. Williams and
Timothy B. Grabowski
Source: Southeastern Naturalist, 16(2):215-224.
Published By: Eagle Hill Institute
https://doi.org/10.1656/058.016.0208
URL: http://www.bioone.org/doi/full/10.1656/058.016.0208
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Southeastern Naturalist
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SOUTHEASTERN NATURALIST
2017 16(2):215–224
Comparison of the Precision of Age Estimates Generated
from Fin Rays, Scales, and Otoliths of Blue Sucker
Matthew R. Acre1, Celeste Alejandrez1, Jessica East1, Wade A. Massure1,
Seiji Miyazono1, Jessica E. Pease1, Elizabeth L. Roesler1, Heather M. Williams1,
and Timothy B. Grabowski2,*
Abstract - Evaluating the precision of age estimates generated by different readers and dif-
ferent calcied structures is an important part of generating reliable estimations of growth,
recruitment, and mortality for sh populations. Understanding the potential loss of precision
associated with using structures harvested without sacricing individuals, such as scales or
n rays, is particularly important when working with imperiled species, such as Cycleptus
elongatus (Blue Sucker). We collected otoliths (lapilli), scales, and the rst n rays of the
dorsal, anal, pelvic, and pectoral ns of 9 Blue Suckers. We generated age estimates from
each structure by both experienced (n = 5) and novice (n = 4) readers. We found that, inde-
pendent of the structure used to generate the age estimates, the mean coefcient of variation
(CV) of experienced readers was approximately 29% lower than that of novice readers.
Further, the mean CV of age estimates generated from pectoral-n rays, pelvic-n rays,
and scales were statistically indistinguishable and less than those of dorsal-n rays, anal-n
rays, and otoliths. Anal-, dorsal-, and pelvic-n rays and scales underestimated age com-
pared to otoliths, but age estimates from pectoral-n rays were comparable to those from
otoliths. Skill level, structure, and sh total-length inuenced reader precision between
subsequent reads of the same aging structure from a particular sh. Using structures that
can be harvested non-lethally to estimate the age of Blue Sucker can provide reliable and
reproducible results, similar to those that would be expected from using otoliths. Therefore,
we recommend the use of pectoral-n rays as a non-lethal method to obtain age estimates
for Blue Suckers.
Introduction
Accurate and precise age determinations are vital for generating reliable esti-
mates of demographic parameters, such as recruitment, mortality, and growth, that
are necessary for the effective management and conservation of shes (Campana
2001). There are a number of calcied structures, including various bones, n rays,
and scales, that can be used for age determination, but otoliths have generally been
found to produce the most accurate and precise age estimates for most species
(Buckmeier et al. 2002, Erickson 1983, Hining et al. 2000, Maceina and Sammons
2006, Secor et al. 1995). However, the process of otolith removal results in mortal-
ity to the sh. Given that age and growth studies can require signicant sample sizes
1Texas Cooperative Fish and Wildlife Research Unit, Department of Natural Resources
Management, Texas Tech University, Lubbock, TX 79409-2125. 2US Geological Survey,
Hawaii Cooperative Fishery Research Unit, University of Hawaii at Hilo, Hilo, HI 96720.
*Corresponding author - tgrabowski@usgs.gov.
Manuscript Editor: Nathan Franssen
Southeastern Naturalist
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2017 Vol. 16, No. 2
216
to generate reliable estimates (Campana 2001, Quist et al. 2012) , researchers work-
ing with imperiled species are often left seeking non-lethal alternative structures
to make age determinations. For example, scales can produce reliable estimates of
age (Devries and Frie 1996), but they can also severely underestimate the age of
individuals of long-lived species, such as catostomids (Rupprecht and Jahn 1980,
Spiegel at al. 2010, Sylvester and Berry 2006). The use of n rays and spines for
age estimation can be difcult due to variation in shape, deterioration of early an-
nuli in older sh, and lack of a well-dened centrum (Rupprecht and Jahn 1980,
Weber and Brown 2011). Therefore, a full evaluation of the precision and accuracy
of age estimates generated from calcied structures, particularly those that can be
harvested non-lethally, is important to determine their utility for age estimation in
imperiled species.
Cycleptus elongatus Lesueur (Blue Sucker) is a large-bodied, long-lived river-
ine catostomid that is increasingly becoming of conservation concern throughout
its range. The species is found throughout the Mississippi River drainage and Gulf
Slope drainages in Louisiana and Texas (Gilbert 1980, Harris et al. 2014). Even
though it is widely distributed, Blue Sucker is listed variously as a species of great-
est conservation need, threatened, presumed extirpated, or endangered by 19 of the
23 states it inhabits (Steffensen et al. 2015). However, the status of most popula-
tions is uncertain because relatively little information exists regarding growth,
recruitment, and mortality (Bacula et al. 2009). Although scales have been used
for Blue Sucker age determination (Beal 1967, Labay et al. 2011, Morey and Berry
2003, Rupprecht and Jahn 1980), they have been found to underestimate the age of
older individuals in most populations (Labay et al. 2011, Rupprecht and Jahn 1980).
The rst pectoral-n ray has also been used to determine the age of Blue Sucker
(Bacula et al. 2009, Labay et al. 2011, Rupprecht and Jahn 1980) and seems to yield
more-accurate estimates than those from scales (Labay et al. 2011). However, there
has been no report of a comprehensive comparison of the precision and accuracy of
age estimates from calcied structures that can be non-lethally harvested from Blue
Sucker relative to those from structures, such as otoliths, that typically yield more-
accurate age estimates in other species and that require sacrice of individuals.
Therefore, our objective was to compare precision of age estimates generated from
several calcied structures by readers with different skill levels, and their accuracy
relative to those from lapilli of Blue Sucker.
Study Site and Methods
We captured adult Blue Suckers from the Colorado River in Texas (n = 170) and
Sabine River on the Texas and Louisiana border using a boat-mounted electrosher.
Blue Sucker is a protected species in Texas; thus, our samples were limited to indi-
viduals that did not recover after capture (n = 5, all from the Colorado River) or that
were sacriced for other purposes (n = 4, all from the Sabine). We euthanized Blue
Suckers that were still exhibiting opercular movement but no other sign of recovery
15–20 min post-capture through immersion in a >400-mg/L aqueous solution of
clove oil (eugenol; Leary et al. 2013) and stored them on ice for processing in the
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M.R. Acre, et al.
2017 Vol. 16, No. 2
lab. The Blue Suckers used in this study had a mean (± SD) total length (TL) of
606 ± 86 mm (range = 507–720 mm TL). Lapilli, hereafter referred to as otoliths,
were removed and stored dry. We used lapilli because the sagittae of ostariophysan
shes, such as catostomids, are highly modied and difcult to use for age estima-
tion (Secor et al. 1992). We harvested the rst ray of the dorsal, anal, pectoral, and
pelvic ns, removed tissue from the ns, and stored the samples dry (Bacula et al.
2009, Labay et al. 2011). We also collected and stored dry a sample of 3–5 scales
from between the lateral line and dorsal n just posterior to the origin of the pecto-
ral n as described by Labay et al. (2011).
We embedded the otoliths in epoxy and used a low-speed isomet saw to
cross-section them along the transverse plane through the nucleus (South Bay
Technologies, San Clemente, CA) as described by Quist et al. (2012). We also
embedded the n rays in epoxy and made 0.8-mm sections from the proximal end
of the ray. Multiple sections were taken from each n ray starting at approximately
1.0–1.5 cm from the articulation point of the ray in order to produce sections that
would be comparable to those taken from sh that were released alive (Bacula et
al. 2009, Labay et al. 2011). We cleaned and placed scales between 2 glass slides
to hold them at. We took digital photographs of each calcied-structure section
at 3.0–11.0x magnication using an Olympus SZX16 stereo microscope (Olympus
Corporation, Tokyo, Japan) equipped with an Innity 1-5C 5.0-MP digital camera
(Lumenera Corporation, Ottawa, ON, Canada).
We used ImageJ v. 1.48 image-analysis software (Abramoff et al. 2004) to en-
hance the visibility and clarity of the annuli. We assigned images a random identier
that allowed images of different sections of the same n ray or scales from the same
sh to be grouped together but prevented readers from identifying which structures
came from the same sh. Readers were not provided any information regarding the
individual sh. In addition, we inserted duplicate images from 3 sh into the dataset
to assess the precision within an individual reader. We instructed readers to iden-
tify annuli following published criteria for otoliths, scales, and n rays (Casselman
1983, DeVries and Frie 1996, Quist et al. 2012). Each of the 9 readers was assigned
to a skill level based on whether they had participated as a reader in a previous age
and growth study (experienced; n = 5) or not (novice; n = 4).
We tested hypotheses related to the variability of age estimates among readers,
age estimates generated from otoliths and other structures, and precision of indi-
vidual readers. We calculated the variability of age estimates among readers as the
coefcient of variation (CV), i.e., the standard deviation of the observations divided
by the mean multiplied by 100. We calculated a separate CV for the novice readers
and the experienced readers for each structure from each individual Blue Sucker.
We conducted analysis of covariance (ANCOVA) to test the null hypothesis that
aging structure (xed effect), reader skill level (xed effect), and the TL of the sh
(covariate) did not inuence the CV of age estimates. The difference between the age
estimate generated for a particular sh from its otolith compared to the other aging
structures of that sh was calculated for each reader. We employed a mixed-model
ANCOVA to test the null hypothesis that age estimates from other structures did not
Southeastern Naturalist
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2017 Vol. 16, No. 2
218
differ from those from otoliths. Aging structure, reader skill level, and TL of the sh
were used as xed effects in the model, individual readers were used as a random ef-
fect, and individual sh were treated as a subject effect. We calculated the precision
of individual readers as the difference in the age estimates by a given reader between
repeated reads of the same structure from the same sh. We ran a mixed-model
ANCOVA to assess the effects of aging structure, reader skill level, and TL of the
sh (xed effects) on reader precision. Individual readers were treated as a random
effect and individual sh as a subject effect. We tested all interactions, but removed
them from the nal models if they were not statistically signicant. We assessed
parametric assumptions of independence, normality, and equality of variance and set
α = 0.05 for all tests of statistical signicance. We employed Tukey’s HSD post hoc
test to compare means among structures and 2-tailed t-tests to test the null hypothesis
that mean differences between estimates did not differ from zero. Analyses were per-
formed in SAS 9.4 (SAS Institute, Inc., Cary, NC).
Results
The CV of age estimates varied by aging structure and skill level of the reader
(Table 1; Fig. 1), but no interaction effect was evident, nor did TL inuence the
Table 1. Results from analysis of covariance assessing the inuence of TL, structure used for age
estimation (anal, dorsal, pectoral, and pelvic n rays, lapillar otolith, and scales), and reader skill
level (novice vs. experienced) on the coefcient of variation of age estimates of Blue Sucker (n = 9)
collected from the Colorado River, TX, and the Sabine River, TX–LA, during 2015.
Fixed effect df F-value P-value
TL 1134 0.42 0.52
Structure 5134 5.44 <0.01
Skill 1134 36.52 <0.01
Figure 1. Mean coef-
cient of variation for
age estimates derived
by experienced (n =
5) and novice (n = 4)
readers from the rst
ray of the (A) anal n,
(D) dorsal fin, (P1)
pectoral n, and (P2)
pelvic n, (S) scales,
and (O) lapillar oto-
liths of Blue Sucker (n
= 9) captured from the
Colorado River in TX,
and the Sabine River
in TX–LA. Error bars
represent standard er-
ror.
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M.R. Acre, et al.
2017 Vol. 16, No. 2
CV of the age estimates. Independent of the structure used to generate the age es-
timates, the mean CV of experienced readers was ~29% lower than that of novice
readers. The mean CVs of age estimates from otoliths were greater than those from
pectoral n rays, pelvic ns rays, and scales (P < 0.02). The mean CVs of age
estimates from all structures other than otoliths were statistically indistinguishable
from each other (P > 0.17).
The difference between the age estimated for the same individual from its otolith
and that from other aging structures was inuenced by the structure used to gen-
erate the age estimate (Table 2, Fig. 2) and tended to increase with TL. The skill
level of the reader did not have a detectable effect. Anal, dorsal, and pelvic n rays
underestimated the age compared to otoliths (Table 3; the least-square mean differ-
ences were all less than zero (t441 ≤ -2.37, P 0.02; Fig. 2). However, age estimates
from pectoral n rays (t441 = -1.62, P = 0.11) and scales (t441 = -0.95, P = 0.75) did
not exhibit any bias relative to otoliths.
Skill level, structure, and TL inuenced the readers’ precision between subse-
quent estimates of the same structure of a particular sh (Table 4, Fig. 3). Precision
Table 2. Tests of xed effects from a mixed-model analysis of covariance assessing the inuence of
TL, structure used for age estimation (anal, dorsal, pectoral, and pelvic n rays, and scales), and reader
skill level (novice vs. experienced) on the difference between the age estimated from that structure and
the age estimated from the lapillar otolith of Blue Suckers (n = 9) collected from the Colorado River,
TX, and the Sabine River, TX–LA, during 2015. Individual readers were treated as a random effect
and individual Blue Suckers as a subject effect in this model.
Fixed effect df F-value P-value
TL 1441 19.42 <0.01
Structure 4441 2.44 0.05
Skill 1441 0.16 0.69
TL*Structure 4441 3.78 0.01
Figure 2. Mean dif-
ference between age
estimates generated
from anal (A) fin,
(D) dorsal n, (P1)
pectoral n, and (P2)
pelvic n rays, and
(S) scales of Blue
Sucker, and the age
estimated from the
lapillar otolith of that
individual by expe-
rienced (n = 5) and
novice (n = 4) read-
ers. Error bars rep-
resent one standard
deviation.
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2017 Vol. 16, No. 2
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Table 4. Tests of xed effects from a mixed-model analysis of covariance assessing the inuence of
TL, structure used for age estimation (anal, dorsal, pectoral, and pelvic n rays, and scales), and read-
er skill level (novice vs. experienced) on the within-reader precision of age estimates of Blue Suckers
(n = 9) collected from the Colorado River, TX, and the Sabine River, TX–LA, during 2015. Individual
readers were treated as a random effect and individual Blue Suckers as a subject effect in this model.
Fixed effect df F-value P-value
TL 1120 3.63 0.06
Structure 5120 1.27 0.28
Skill 1120 0.24 0.62
TL* Structure*Skill 11,120 2.16 0.02
Figure 3. Mean differ-
ence between age es-
timates generated by
experienced (n = 5) and
novice (n = 4) readers
during their first and
second readings of (A)
anal n, (D) dorsal n,
(P1) pectoral n, and
(P2) pelvic n rays, (S)
scales, and (O) lapillar
otoliths of Blue Suck-
er collected from the
Colorado River in TX,
and the Sabine River
in TX–LA. Error bars
represent one standard
deviation.
Table 3. Total length (TL) and mean (± SE) age estimates generated by 9 independent readers using
the anal, dorsal, pectoral, and pelvic n rays, lapillar otoliths, and scales of Blue Sucker (n = 9) col-
lected from the Colorado River, TX, and the Sabine River, TX–LA, during 2015.
Anal Dorsal Pectoral Pelvic
River TL (mm) n rays n rays Otoliths n rays n rays Scales
Colorado 596 5.9 ± 0.8 5.4 ± 0.5 9.0 ± 1.0 7.1 ± 0.9 7.3 ± 0.7 6.3 ± 0.7
642 4.4 ± 0.3 7.8 ± 0.7 9.2 ± 1.3 8.8 ± 0.6 6.0 ± 0.6 7.9 ± 0.8
674 7.0 ± 0.8 5.6 ± 0.6 11.2 ± 1.0 7.2 ± 0.7 6.8 ± 0.6 9.0 ± 1.4
691 3.7 ± 0.5 6.6 ± 1.0 10.8 ± 1.5 6.7 ± 0.6 4.1 ± 0.3 8.6 ± 1.1
720 6.7 ± 0.5 6.5 ± 0.5 8.3 ± 0.8 9.2 ± 0.3 6.3 ± 0.5 7.1 ± 0.4
Sabine 507 4.4 ± 0.4 4.2 ± 0.5 5.4 ± 0.5 4.8 ± 0.5 4.2 ± 0.4 5.9 ± 0.3
513 4.1 ± 0.6 6.2 ± 0.7 5.4 ± 1.1 9.0 ± 0.8 3.3 ± 0.4 5.7 ± 0.5
516 4.6 ± 0.6 4.8 ± 0.5 6.2 ± 1.2 5.7 ± 0.7 4.8 ± 0.4 5.8 ± 0.6
538 3.9 ± 0.4 6.3 ± 1.2 5.0 ± 0.7 5.6 ± 0.6 6.3 ± 0.7 6.1 ± 0.6
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M.R. Acre, et al.
2017 Vol. 16, No. 2
tended to decrease with increasing TL and subsequent estimates from the same
structure by experienced readers were overall about 77% more precise than those
of novices, though aging of scales was a notable exception where novices' age
estimates were closer to the actual ages than were those of experienced readers
(Fig. 3). Structure was not identied as an important factor inuencing precision
by itself because only the precision of estimates from anal n rays and otoliths
exhibited an appreciable difference (Fig. 3).
Discussion
Although age estimates from pectoral fin rays for Blue Sucker previously have
been shown to be more precise than those from scales (Labay et al. 2011), our
results represent the first assessment of the accuracy of age estimates generated
from fin rays and scales relative to otoliths. Previous research with Blue Sucker
and other catostomids has shown that age estimates generated from scales tend to
underestimate the age of the fish relative to otoliths (Quist et al. 2007, Sylvester
and Berry 2006). However, age estimates for pectoral fin rays and otoliths have
been shown to be similar in species such as Catostomus discobolus Cope (Blue-
head Sucker) and Catostomus latipinnis S.F. Baird & Girard (Flannelmouth Suck-
er) (Quist et al. 2007). Age estimates from the pectoral fin rays of Catostomus
commersonii Lacépède (White Sucker) generally were in agreement with those
from otoliths, but discrepancies tended to occur in older individuals, particularly
after age 7 (Sylvester and Berry 2006). Our results indicated that not only were
the age estimates of Blue Sucker generated from pectoral fin rays comparable to
those produced from otoliths, but the estimates from pectoral fin rays also had a
lower CV and greater reproducibility than those from otoliths. Furthermore, the
age estimates generated from Blue Sucker scales did not show the expected sig-
nificant negative bias relative to those from otoliths. Finally, our results indicate
that rays from the pelvic, dorsal, and anal fins of Blue Sucker do not produce reli-
able and reproducible age estimates.
The high degree of precision and reproducibility of age estimates generated
from pectoral n rays and scales relative to those from otoliths was unexpected.
Otoliths, particularly the sagittal otoliths, are the preferred structure for age de-
termination for most sh taxa (Campana 2001, Maceina et al. 2007, Secor et al.
1995), specically because they have a higher degree of accuracy and precision
than other structures (Beckman 2002, Boxrucker 1986, Buckmeier et al. 2002).
However, in ostariophysan shes, such as Blue Sucker, the size and morphology
of the sagittal otoliths render them unusable for age estimation (Secor et al. 1992,
Sylvester and Berry 2006). The lapillar otolith is used instead for estimating the age
of ostariophysan shes, but the ease of interpreting annuli can vary among species
(Campana 2001, Phelps et al. 2007). Experienced and novice readers both generally
regarded the annuli from Blue Sucker otoliths examined for this study as difcult to
identify and count. The potential difculties interpreting the otoliths could account
for the relatively low reproducibility and high CV of age estimates from otoliths,
particularly those made by the novice readers. In contrast, the annuli on the pectoral
Southeastern Naturalist
M.R. Acre, et al.
2017 Vol. 16, No. 2
222
n rays and scales were relatively clear and distinct, which would reduce the degree
of subjectivity involved in identifying annuli and lead to higher precision regard-
less of reader-experience level. The unexpectedly high levels of reproducibility and
agreement with otolith age estimates obtained from the scales also was likely due
in part to the relatively young sh (Table 3) used in our study compared with those
from other studies (Bacula et al. 2009, Labay et al. 2011, Morey and Berry 2003,
Rupprecht and Jahn 1980).
In summary, we demonstrate that age estimation using scales and pectoral n
rays is a viable alternative to otoliths for generating information on age structure
of Blue Sucker populations. It is also important to note that although we used the
age estimates generated from otoliths as the “true age” for analysis purposes, our
results suggest lapilli in this species may not very useful. Validating the formation
of annual increments on the calcied structures of Blue Sucker using known-age or
marked individuals is therefore an important next step to identifying the structures
and procedures capable of producing accurate age estimates for this species.
Acknowledgments
We thank P. Bean, G. Cummings, D. Geeslin, S. Magnelia, and K. Mayes for their as-
sistance with collecting Blue Suckers. This manuscript beneted from the comments and
suggestions provided by J. Long. Blue Suckers from the Colorado River were collected un-
der the auspices of the Texas Tech University Institutional Animal Care and Use Committee
(AUP# 14003-02). Blue Suckers from the Sabine River were provided by K. Mayes and Texas
Parks and Wildlife. With the exception of the corresponding author, the authors of this manu-
script are listed in alphabetical order, and order does not reect contributions to this work.
Financial and logistic support was provided by the Texas Cooperative Fish and Wildlife Re-
search Unit and the Hawaii Cooperative Fishery Research Unit (US Geological Survey, Texas
Tech University, the University of Hawaii system, Texas Parks and Wildlife Department,
Hawaii State Department of Land and Natural Resources, Wildlife Management Institute, and
US Fish and Wildlife Service cooperating). Use of product, trade, or rm names is for descrip-
tive purposes only and does not imply endorsement by the US Government.
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... However, accurate estimates of age and growth are imperative in understanding the reasons behind differences in PSD values. Comparable estimates of growth may not currently be available for Blue Suckers because fish have MANAGEMENT BRIEF 203 traditionally been aged using pectoral fin rays (Bednarski and Scarnecchia 2006;LaBay et al. 2011;Acre et al. 2017), but recent studies comparing the use of fin rays versus otoliths to age Blue Suckers have demonstrated that ages that are assigned using otoliths tend to be higher in larger individuals (Carlson et al. 2021;Radford et al. 2021). Although ages that are assigned by using otoliths and fin rays have not been validated for Blue Suckers, validations that have been performed for other species have demonstrated that otoliths provide more accurate age estimates (Buckmeier et al. 2002;Buckmeier and Howells 2003;Lackmann et al. 2019). ...
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Blue Sucker Cycleptus elongatus is a species of concern across much of its native range due to population fragmentation and habitat loss. A key component of managing this species is monitoring various population characteristics including size structure. A common way to quickly index population size structure is to calculate the proportional size distribution (PSD). However, no standard length categories have been established for Blue Suckers, precluding the use of this index. We used databases, literature searches, field guides, and sampling records to find the largest recorded Blue Sucker. The maximum size Blue Sucker on record was 93 cm, so we propose the following standardized length categories: stock = 23 cm, quality = 38 cm, preferred = 51 cm, memorable = 58 cm, and trophy = 74 cm. We estimated mean PSD values using a generalized linear mixed model with a multinomial likelihood for populations of Blue Suckers from six rivers: the James, Big Sioux, Colorado, Red, Wabash, and Missouri. Most of these populations exhibited large size structure except the James River. These PSD length categories should provide an additional tool for evaluating spatial and temporal changes in size structure of Blue Sucker populations when monitoring the status of this species of concern.
... LaBay et al. (2011) reported that, relative to fin rays, scales were less precise and underestimated the ages of individuals >7 years old. Acre et al. (2017) compared Blue Sucker age estimates from scales, anal fin rays, dorsal fin rays, pelvic fin rays, pectoral fin rays, and lapillus otoliths. They did not identify any bias between the ages obtained from scales or pectoral fin rays relative to otoliths. ...
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... However, given that males stop growing in length at sexual maturity, we could not assess the true age of adult males in the wild, and instead used comparisons across life history stages to estimate selection for or against growing faster. In future studies, incorporating more sophisticated methods to assess the true age of wild individuals (Acre et al. 2017) would greatly improve the study of selection on growth rates in this system. ...
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Annuli counts from scales and otoliths are commonly used to estimate the age of rainbow trout Oncorhynchus mykiss in southern Appalachian streams. However, validation of annuli counts from these two structures for rainbow trout has not been reported. Oxytetracycline (OTC) injections (50 mg OTC/kg fish) were used to mark otoliths of visible-implant-tagged rainbow trout in a mark-recapture study. The validation of scales for age estimation was performed by comparing the number of annuli on scales of individual rainbow trout at capture with those collected 12-15 months later upon recapture. Scale accuracy declined from 72% for age-2 fish to 0% for age-4 fish. In contrast, and regardless of age, all fish formed an additional annulus outside the OTC mark on otoliths. We conclude that annuli counts from otoliths will provide accurate age estimates for rainbow trout in the southern Appalachians. The use of otoliths and consequential sacrifice of fish may not be an option in some cases. However, annuli counts obtained from the scales of rainbow trout in southern Appalachian streams may not provide accurate age estimates for fish older than age 2.
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Scales and otoliths (sagittae) were taken from a sample of 137 white crappies (Pomoxis annularis) collected by fyke netting from Ft. Supply Reservoir, Oklahoma, in November 1982. Scales and otoliths from each fish were aged independently by three experienced scale readers, none of whom had prior experience aging otoliths. The average percent error and coefficient of variation of the scale method was approximately seven times greater than for the otolith method, indicating a greater degree of precision for the otolith method. No differences were observed in back-calculated lengths derived from measurements obtained from the right versus left otolith. No significant differences in back-calculated lengths up to age 3 for a given year class sampled in successive years were observed for white crappies aged by the otolith method. These results indicate that age and growth data generated from the otolith method would be sufficiently consistent for biologists to recognize yearly trends in growth variations. Known-age white crappies, needed to verify the accuracy of the otolith technique, were unavailable. However, scales and otoliths were taken from 31 white crappies collected from the James River arm of Table Rock Lake, Missouri, in spring 1984. The scale method for aging white crappies in Missouri is considered to be accurate by the Missouri Department of Conservation. The ages of these fish, as determined by scales read in Missouri and otoliths aged in Oklahoma, were in agreement for 30 of the 31 fish sampled. The use of the otolith method for aging white crappies in Oklahoma is recommended over the scale method. Once field personnel become efficient in extracting otoliths, processing time in the field is only slightly greater than when taking scale samples. No elaborate preparation procedures are required because ages can be obtained from whole otoliths.