Relationship of Trout Growth to Frequent Electroﬁshing and Diet
Collection in a Headwater Stream
Niall G. Clancy*
Wyoming Cooperative Fish & Wildlife Research Unit, University of Wyoming, 1000 East University Avenue, Department
3166, Laramie, Wyoming 82071, USA
James L. Dunnigan
Montana Fish, Wildlife & Parks, 385 Fish Hatchery Road, Libby, Montana 59923, USA
U.S. Geological Survey, Utah Cooperative Fish and Wildlife Research Unit, Department of Watershed Sciences, Utah
State University, 5210 Old Main Hill, Logan, Utah 84322, USA
Research on ﬁshes sometimes requires that individual ﬁsh be
captured and subjected to invasive procedures multiple times over
a relatively short time span. Electroﬁshing is one of the most com-
mon techniques used to capture ﬁsh, and it is known to cause
injury to ﬁsh under certain circumstances. We evaluated the rela-
tionship of growth rates in Columbia River Redband Trout Oncor-
hynchus mykiss gairdneri to the number of times that they were
captured via electroﬁshing and gastrically lavaged during the sum-
mer of 2018 in a mountainous, headwater stream. We captured
ﬁsh between two and seven times over the course of 86 d using
continuous (smooth) DC backpack electroﬁshing. We observed no
relationship between the growth rate of Columbia River Redband
Trout and the number of times that they were captured or gastri-
cally lavaged. Although these ﬁndings contrast with hatchery elec-
troﬁshing experiments, they may represent the greater resiliency of
wild ﬁsh. It appears that researchers can use electroﬁshing and
gastric lavage in cold waters at least once per month, and poten-
tially up to twice per month, without greatly affecting the growth
of wild Columbia River Redband Trout.
Since the development of electricity as a gear for sam-
pling stream ﬁshes (Haskell 1940), there has been concern
about its propensity to cause injury and mortality of
aquatic species (Hauck 1949). Efﬁciency and safety of
electroﬁshing has increased over time, with contemporary
practice calling for continuous or pulsed, direct-current
(DC) electroﬁshing with frequency (pulses) and voltage
adjusted so as to maximize ﬁsh capture while minimizing
injury (Fredenberg 1992; Curry et al. 2009). Continuous
DC electroﬁshing tends to be the least damaging to ﬁsh
(reviewed in Snyder 2003). Yet despite technological and
methodological advances, injury and death of ﬁsh still
occurs and remains a topic of investigation (e.g., Miranda
and Kidwell 2010; Panek and Densmore 2013; Simpson et
al. 2016). Furthermore, the sublethal, indirect effects of
electroﬁshing remain poorly understood even though they
can be diverse and signiﬁcant (e.g. Dalbey et al. 1996;
In coldwater streams, trout of the family Salmonidae
are simultaneously the most sought-after gameﬁsh and
one of the most imperiled taxa (Muhlfeld et al. 2020).
Trout are therefore one of the groups most likely to be
subjected to sampling via electroﬁshing. Previous studies
have indicated that trout are among the most susceptible
taxa to spinal fractures, hemorrhaging, and mortality
when they are electroﬁshed (Snyder 2003). Although
reported mortalities of juvenile and adult salmonids that
are subjected to continuous DC (300–400 V) are low
(<1.5%), spinal injuries that are caused by electroﬁshing
(which are more common when using pulsed DC) have
been shown to result in decreased growth (Dalbey et al.
*Corresponding author: firstname.lastname@example.org
Received March 2, 2021; accepted November 6, 2021
North American Journal of Fisheries Management 42:109–114, 2022
©2021 American Fisheries Society
ISSN: 0275-5947 print / 1548-8675 online
1996; Ainslie et al. 1998), which often leads to decreased
survival (Ware 1975). Hatchery electroﬁshing experiments
have shown that Rainbow Trout Oncorhynchus mykiss,
Cutthroat Trout O. clarkii, and Arctic Grayling Thymallus
arcticus all appear to exhibit decreased growth when they
are electroﬁshed, whether with low-frequency (30–60 Hz)
pulsed DC or continuous DC (75–300 V; Dwyer and
White 1997; Ainslie et al. 1998; Dwyer et al. 2001). How-
ever, a similar study examining repeated electroﬁshing of
Atlantic Salmon Salmo salar parr with continuous DC
(Gregg Horton, personal communication) at 300–500 V
found no signiﬁcant growth effects (Sigourney et al. 2005).
Gastric lavage has been demonstrated to be an efﬁcient
method of collecting salmonid diets with little to no mor-
tality (Bowen 1983; Light et al. 1983). However, few stud-
ies have examined its potential effects on ﬁsh growth (but
see Hafs et al. 2011). It is plausible that gastric lavage
could affect growth through handling stress, loss of food
items, or even injury.
In ﬁsheries research, some study designs may require
that ﬁsh be captured multiple times within a relatively
short period. This is especially true for multiple capture
studies estimating vital rates or trophic studies where a
single capture event only provides a snapshot of diet com-
position. However, no study has examined the appropriate
time interval between electroﬁshing captures necessary for
little or no effect on ﬁsh growth, another parameter of
interest in trophic research. Moreover, invasive procedures
are sometimes required once the ﬁsh have been captured
in order to collect necessary data. Therefore, our objective
was to determine whether frequent capture and use of
invasive procedures in trophic studies affect ﬁsh growth.
Due to the paucity of research on electroﬁshing and han-
dling effects on ﬁsh over short time frames, we examined
the growth of Columbia River Redband Trout O. mykiss
gairdneri that were subjected to electroﬁshing and gastric
lavage up to seven times during the summer of 2018 (once
every 2 weeks).
This study was completed as part of a larger project
that examined the inﬂuence of benthic algae on ﬁsh food
webs (Clancy et al. 2021). Bear and Ramsey creeks are
tributaries to Libby Creek in the Kootenai River basin of
northwestern Montana (Figure 1). The Libby Creek water-
shed drains the east side of the rugged Cabinet Mountains
and is located within the globally rare inland temperate
rainforest biome (DellaSala et al. 2011). The estimated
mean June–August discharge at the Bear Creek site is
/s (0.85 m
/s), and 30.2 ft
/s (0.86 m
/s) at the Ram-
sey Creek site (McCarthy et al. 2016). The mean summer
water temperature at both study sites during 2018 was
9.79°C (Clancy et al. 2021). The ﬁsh assemblage was
dominated by native Columbia River Redband Trout
(hereafter, “Redband Trout”) and federally threatened
Bull Trout Salvelinus conﬂuentus. Ramsey Creek also con-
tained a small number of Columbia Slimy Sculpin Urani-
We chose a 300-m-long study site on both streams and
sampled seven times from June to September 2018 at an
interval of once every 2 weeks. We collected the ﬁsh via
single-pass backpack electroﬁshing with a model LR-24
Electroﬁsher (Smith-Root, Vancouver, Washington) set
for continuous (smooth) DC output and equipped with a
two-tailed cathode. We used the minimum voltage set-
tings that effectively captured the ﬁsh—typically 200 to
500 V in Bear Creek and 700 to 990 V in Ramsey Creek,
with lower voltages being required later in the summer.
This discrepancy in required voltages was explained by
large differences in the speciﬁc conductance between
streams: 110.2 μS/cm in Bear Creek and only 27.7 μS/cm
in Ramsey Creek. Upon initial capture (during the ﬁrst
three sampling events), we anesthetized each trout that
was larger than 100 mm with clove oil, implanted each
with a 12-mm passive integrated transponder (PIT) tag
(Model HDX12, Biomark, Boise, Idaho), and marked
them by clipping a small piece of the caudal ﬁn. We mea-
sured the total length and wet weights of the trout at
each capture, recorded the PIT tag number, and gastri-
cally lavaged a large proportion (91%) to obtain diets for
a separate study (Clancy et al. 2021). We made multiple
passes during the ﬁnal sampling event to maximize the
recapture of tagged ﬁsh. Following the method of Shoup
and Michaletz (2017), growth for the individual trout
was calculated as
¼final weight initial weight
days between first and last capture:
We analyzed the growth data via multiple linear regres-
sion as a function of the initial weights of the trout and
the number of times that they were handled. We then
completed the same analysis using initial weights and
number of times gastrically lavaged because not all of the
ﬁsh that were handled were lavaged. Initial weight was
included as a covariate because ﬁsh size is an important
intrinsic factor that inﬂuences ﬁsh growth rate (von Berta-
lanffy 1938; Beauchamp 2009). We chose to assess ﬁsh
weight over ﬁsh length because weight changes are more
readily observed over short periods due to the cubic rela-
tionship of length and weight (Busacker et al. 1990). Start-
ing with a global model that included all of the covariates
(number of times handled or lavaged, initial weight, and
an interaction between handled or lavaged and initial
weight), we used the “MuMIn”package in R (Barton
110 CLANCY ET AL.
2020; R Core Team 2020) with corrected Akaike informa-
tion criterion (AIC
) to compare all possible combinations
of the covariates (Burnham and Anderson 2002). We used
at-test to assess differences in growth rates between the
two streams. All of the graphs were completed using the
“ggplot2”package in R (Wickham 2016).
We recaptured PIT-tagged Redband Trout in greater
numbers in Bear Creek (n=50) than in Ramsey Creek (n
=20), and combined, the Redband Trout grew an average
of 0.00185 (gg
)0.00238 (mean 1 SD). The
growth rates for Redband Trout (length range: 103–241
mm) were highly variable and demonstrated little relation-
ship to the number of times that they were handled (R
0.03, P=0.19; Figure 2A). Given that most of the ﬁsh
(91%) were gastrically lavaged upon handling, the rela-
tionship of growth to number of times lavaged was similar
to the growth relationship with number of times handled
=0.03, P=0.15; Figure 2B). The mean growth rate
was similar in both creeks (t-test: t=−0.307, df =38.05, P
=0.76; Figure 2C). Growth rate was negatively correlated
with initial ﬁsh weight (Figure 2D). Multiple regression
analyses using AIC
model selection indicated that the
models using only initial weight were equally parsimoni-
ous to those including number of times handled or num-
ber of times lavaged (Table 1). Additionally, times
handled or lavaged was not statistically signiﬁcant (P≤
0.05) in any model (Table 1). The covariate interactions
between Redband Trout weight and handling pressure or
lavages were also insigniﬁcant.
Some experimental designs in ﬁsheries science require
recapturing ﬁsh over a relatively short period. Electroﬁsh-
ing is one of the most widespread and effective methods
of capture (Bonar et al. 2009) but is sometimes associated
with ﬁsh injury and death (Vincent 1971; Snyder 2003).
Many growth studies also incorporate diet collection, so
determining “how often is too often”for ﬁsh to be both
electroﬁshed and gastrically lavaged is useful to future ﬁsh
We found little observable relationship between sum-
mer growth rate in Redband Trout and the number of
FIGURE 1. Study area in the Kootenai River basin of northwestern Montana near the Cabinet Mountains Wilderness. The bullseyes indicate the
sample sites on Bear and Ramsey creeks.
MANAGEMENT BRIEF 111
electroﬁshing captures or gastric lavage events. However,
it is important to note that only four Redband Trout were
captured more than ﬁve times and three of those four had
below-average growth rates. This low sample size makes it
difﬁcult for us to determine whether ﬁsh that were cap-
tured more than ﬁve times experienced decreased growth
rates due to handling pressure.
Broadly speaking, our results support those of Sigour-
ney et al. (2005), who observed no signiﬁcant growth
effects of continuous DC electroﬁshing on hatchery-reared
Atlantic Salmon at an interval of once every 2 months.
Despite using considerably larger ﬁsh, our results demon-
strate few observable effects on Redband Trout growth at
even shorter intervals, where ﬁsh were also subjected to
Our results similarly support the ﬁndings of Hafs
et al. (2011), who observed no statistical relationship
between gastric lavage and growth of Brook Trout S.
fontinalis. Again, our results demonstrated no observable
effects, even when the ﬁsh were subjected to repeated
lavage. Wild trout in poor condition are known to com-
pensate by increasing their growth rate to offset harsh
environmental conditions (Al-Chokhachy et al. 2019).
Thus, it is possible that the wild Redband Trout in our
study were able to repeatedly offset any negative effects
of gastric lavage, such as stress or food loss, by altering
FIGURE 2. Growth (gg
) of PIT-tagged Redband Trout in Bear Creek (pink circles) and Ramsey Creek (dark green triangles) versus (A) the
number of times captured via electroﬁshing, (B) the number of times gastrically lavaged, (C) between the two streams, and (D) starting length of the
individual ﬁsh. The dashed, light-gray lines indicate a growth value of 0. The black lines with gray clouds indicate linear regressions and associated
standard errors. The period of measurement was from June 10 to September 4, 2018.
112 CLANCY ET AL.
their behavior to increase growth (e.g., increase foraging
However, our results differ from the ﬁndings of
decreased growth in a series of hatchery experiments on
Arctic Grayling, Cutthroat Trout, and Rainbow Trout
that were subjected to only a single electroﬁshing event
(Dwyer and White 1997; Dwyer et al. 2001). Although
those experiments were conducted at temperatures near or
below those in our study, the ﬁsh that exhibited the great-
est decreases in growth were subjected to pulsed DC cur-
rent, which tends to cause higher injury rates than
continuous current (Dalbey et al. 1996). In addition,
hatchery ﬁsh generally have lower resilience relative to
wild ﬁsh (Wales 1954; Pinter et al. 2018) and may not
respond to electroﬁshing in a manner similar to that of
wild ﬁsh. Our study is the ﬁrst of which we know to
examine frequent electroﬁshing effects on the growth of
wild trout in a natural stream.
Electricity is known to affect ﬁsh differently at high
temperatures (Reynolds 1983). The streams in our study
were very cold, with a mean August water temperature of
9.79°C. Similar studies should be conducted in higher tem-
perature streams to determine the broader applicability of
our results. There is also the possibility that ﬁsh that were
not captured during a given sampling event were still
inﬂuenced by electroﬁshing, so the number of times han-
dled may not truly represent the number of times electrof-
ished. Nonetheless, we cannot rule out the possibility that
Redband Trout that we captured a limited number of
times were actually shocked up to seven times but avoided
capture. Yet we still observed little effect on growth.
Additionally, all of the ﬁsh in our study were captured at
least twice. A nonelectroﬁshing control group may beneﬁt
future studies. Future research on the effects of frequent
electroﬁshing and invasive sampling techniques could also
include other vital rate statistics such as behavior, sur-
vival, and reproductive success—all known to be sensitive
to electroﬁshing in some cases (Keefe et al. 2000; Siepker
et al. 2006; Fraser et al. 2017).
Electroﬁshing and gastric lavage are both common
techniques used in ﬁsheries research. We found no
observable effect of either technique on the growth rate
of Redband Trout despite repetition at a shorter interval
than previously reported. Although ﬁsh in warmer tem-
peratures and in hatchery studies may respond to electro-
ﬁshing differently, it is likely that researchers who
conduct trout growth studies in cold, headwater streams
can capture ﬁsh at least once per month and potentially
up to twice per month (using continuous DC), as well as
doing gastric lavage without having a negative effect on
Discussions with Tom McMahon and Chris Clancy
served as the impetus to collect and analyze these data.
Thank you to Jon McFarland, Jay DeShazer, Ryan Sylve-
ster, Jared Lampton, Jordan Frye, Brian Stephens, Monty
Benner, and Mike Hensler for their help at the Libby
Field Ofﬁce of Montana Fish Wildlife & Parks. Janice
Brahney was instrumental in making this ﬁeld season hap-
pen, and Gary P. Thiede provided logistical assistance
with ﬁeld equipment. Dan Dauwalter and two anonymous
reviewers provided comments that greatly improved the
manuscript. This work was supported by the U.S. Geolog-
ical Survey—Utah Cooperative Fish and Wildlife
Research Unit (in-kind); the Utah State University,
Department of Watershed Sciences and Ecology Center;
and Montana Fish, Wildlife & Parks (in-kind). This study
was conducted under the auspices of USU IACUC proto-
col 10006 and Montana scientiﬁc collector’s permit 07-
2018. Any use of trade, ﬁrm, or product names is for
descriptive purposes only and does not imply endorsement
by the U.S. Government. There is no conﬂict of interest
declared in this article.
Niall G. Clancy https://orcid.org/0000-0001-9223-6843
TABLE 1. Multiple linear regression results predicting weight growth
rates of Columbia River Redband Trout in two Cabinet Mountains
streams, 2018. The explanatory variables are trout starting weight
), number of times handled (Handled), and number of times
gastrically lavaged (Lavaged). The *symbol indicates covariates with a
P≤0.05; the corrected Akaike information criterion (AIC
) scores and
difference in AIC from the top regression (ΔAIC
) are included.
Regressions for Growth (gg
Growth ~Handled +Weight
Growth ~Handled +Weight
Growth ~0*(Null Model) −643.8 15.5
Growth ~Handled −643.4 15.9
Growth ~Handled +Weight
Growth ~Handled +Weight
Growth ~0*(Null Model) −643.8 15.5
Growth ~Handled −643.8 15.5
MANAGEMENT BRIEF 113
Ainslie, B. J., J. R. Post, and A. J. Paul. 1998. Effects of pulsed and con-
tinuous DC electroﬁshing on juvenile Rainbow Trout. North Ameri-
can Journal of Fisheries Management 18:905–918.
Al-Chokhachy, R., R. P. Kovach, A. Sepulveda, J. Strait, B. B. Shepard,
and C. C. Muhlfeld. 2019. Compensatory growth offsets poor condi-
tion in native trout populations. Freshwater Biology 64:2120–2130.
Barton, K. 2020. MuMIn: multi-model inference. R package version
1.43.17. R Foundation for Statistical Computing, Vienna.
Beauchamp, D. A. 2009. Bioenergetic ontogeny: linking climate and
mass-speciﬁc feeding to life-cycle growth and survival of salmon.
Pages 53–72 in C. C. Krueger and C. E. Zimmerman, editors. Paciﬁc
salmon: ecology and management of western Alaska’s populations.
American Fisheries Society, Symposium 70, Bethesda, Maryland.
Bonar, S. A., W. A. Hubert, and D. W. Willis, editors. 2009. Standard
methods for sampling North American freshwater ﬁshes. American
Fisheries Society, Bethesda, Maryland.
Bowen, S. H. 1983. Quantitative description of the diet. Pages 325–336 in
L. A. Nielsen and D. L. Johnson, editors. Fisheries techniques. Amer-
ican Fisheries Society, Bethesda, Maryland.
Burnham, K. P., and D. R. Anderson. 2002. Model selection and multi-
model inference: a practical information–theoretic approach, 2nd edi-
tion. Springer-Verlag, New York.
Busacker, G. P., I. R. Adelman, and E. M. Goolish. 1990. Growth.
Pages 363–387 in C. B. Schreck and P. B. Moyle, editors. Methods
for ﬁsh biology. American Fisheries Society, Bethesda, Maryland.
Clancy, N. G., J. Brahney, J. Dunnigan, and P. Budy. 2021. Effects of a
diatom ecosystem engineer, Didymosphenia geminata, on stream food
webs: implications for native ﬁshes. Canadian Journal of Fisheries
and Aquatic Sciences 78:154–164.
Coldwater ﬁsh in rivers. Pages 139–158 in S. A. Bonar, W. A. Hubert,
and D. W. Willis, editors. Standard methods for sampling North Ameri-
can freshwater ﬁshes. American Fisheries Society, Bethesda, Maryland.
Dalbey, S. R., T. E. McMahon, and W. Fredenberg. 1996. Effect of elec-
troﬁshing pulse shape and electroﬁshing-induced spinal injury on
long-term growth and survival of wild Rainbow Trout. North Ameri-
can Journal of Fisheries Management 16:560–569.
DellaSala, D. A., P. Alaback, L. Craighead, T. Goward, P. Paquet, and
T. Spribille. 2011. Temperate and boreal rainforests of inland north-
western North American. Pages 82–110 in D. A. DellaSala, editor.
Temperate and boreal rainforests of the world: ecology and conserva-
tion. Island Press, Washington, D.C.
Dwyer, W. P., B. B. Shepard, and R. G. White. 2001. Effect of backpack
electroshock on Westslope Cutthroat Trout injury and growth 110
and 250 days posttreatment. North American Journal of Fisheries
Dwyer, W. P., and R. G. White. 1997. Effect of electroshock on juvenile
Arctic Grayling and Yellowstone Cutthroat Trout growth, 100 days
after treatment. North American Journal of Fisheries Management
Fraser, G. S., D. L. Winkelman, K. R. Bestgen, and K. G. Thompson.
2017. Tributary use by imperiled Flannelmouth and Bluehead suckers
in the upper Colorado River basin. Transactions of the American
Fisheries Society 146:858–870.
Fredenberg, W. 1992. Evaluation of electroﬁshing-induced spinal injuries
resulting from ﬁeld electroﬁshing surveys in Montana. Montana Fish,
Wildlife and Parks, Helena.
Hafs, A. W., J. M. Niles, and K. J. Hartman. 2011. Efﬁciency of gastric
lavage on age-0 Brook Trout and the inﬂuence on growth and sur-
vival. North American Journal of Fisheries Management 31:530–534.
Haskell, D. C. 1940. Stunning ﬁsh by electricity: electric shock provides
method of anesthetizing ﬁsh in laboratory. Progressive Fish-Culturist
Hauck, F. R. 1949. Some harmful effects of the electric shocker on large Rain-
bow Trout. Transactions of the American Fisheries Society 77:61–64.
Keefe, M. L., T. A. Whitesel, and P. Angelone. 2000. Induced mortality
and sublethal injuries in embryonic Brook Trout from pulsed DC
electroshocking. North American Journal of Fisheries Management
Light, R. W., P. H. Adler, and D. E. Arnold. 1983. Evaluation of gastric
lavage for stomach analyses. North American Journal of Fisheries
McCarthy, P. M., R. Sando, S. K. Sando, and D. M. Dutton. 2016.
Methods for estimating streamﬂow characteristics at ungaged sites in
western Montana based on data through water year 2009. U.S. Geo-
logical Survey, Investigations Report 2015-5019-G, Reston, Virginia.
Miranda, L. E., and R. H. Kidwell. 2010. Unintended effects of electro-
ﬁshing on nongame ﬁshes. Transactions of the American Fisheries
Muhlfeld,C.C.,D.C.Dauwalter,V.S.D’Angelo, A. Ferguson, J. J. Giersch,
D. Impson, R. Itsuro Koizumi, P. Kovach, J. McGinnity, J. E. Schoeff-
mann, and L. A. Vollestad. 2020. Global status of trout and char: conserva-
tion challenges in the twenty-ﬁrst century. Pages 717–760 in J. L. Kershner,
J. E. Williams, R. E. Gresswell, and J. Lobon-Cervia, editors. Trout and
char of the world. American Fisheries Society, Bethesda, Maryland.
Nielsen, J. L. 1998. Electroﬁshing California’s endangered ﬁsh popula-
tions. Fisheries 23(12):6–12.
Panek, F. M., and C. L. Densmore. 2013. Frequency and severity of
trauma in ﬁshes subjected to multiple-pass depletion electroﬁshing.
North American Journal of Fisheries Management 33:178–185.
Pinter, K., S. Weiss, E. Lautsch, and G. Unfer. 2018. Survival and growth
of hatchery and wild Brown Trout (Salmo trutta)parrinthreeAus-
trian headwater streams. Ecology of Freshwater Fish 27:146–157.
R Core Team. 2021. R: a language and environment for statistical com-
puting. R Foundation for Statistical Computing, Vienna.
Reynolds, J. B. 1983. Electroﬁshing. Pages 147–163 in L. A. Nielson and
D. L. Johnson, editors. Fisheries techniques. American Fisheries Soci-
ety, Bethesda, Maryland.
Shoup, D. E., and P. H. Michaletz. 2017. Growth estimation: summari-
zation. Pages 233–264 in M. C. Quist and D. A. Isermann, editors.
Age and growth of ﬁshes: principles and techniques. American Fisher-
ies Society, Bethesda, Maryland.
Siepker, M. J., D. H. Wahl, D. P. Philipp, and K. G. Ostrand. 2006.
Evidence of reduced reproductive success of nesting Largemouth Bass
sampled with standard electroﬁshing procedures. North American
Journal of Fisheries Management 26:631–635.
Sigourney, D. B., G. E. Horton, T. L. Dubreuil, A. M. Varaday, and B.
H. Letcher. 2005. Electroshocking and PIT tagging of juvenile Atlan-
tic Salmon: are there interactive effects on growth and survival?
North American Journal of Fisheries Management 25:1016–1021.
voltage gradient on the survival of electroshocked steelhead embryos and
larvae. North American Journal of Fisheries Management 36:1149–1155.
Snyder, D. E. 2003. Invited overview: conclusion from a review of elec-
troﬁshing and its harmful effects on ﬁsh. Reviews in Fish Biology and
Vincent, R. 1971. River electroﬁshing and ﬁsh population estimates. Pro-
gressive Fish-Culturist 33:163–169.
von Bertalanffy, L. 1938. A quantitative theory of organic growth (inqui-
ries on growth laws II). Human Biology 10:181–213.
Wales, J. H. 1954. Relative survival of hatchery and wild trout. Progres-
sive Fish-Culturist 16:125–127.
Ware, D. M. 1975. Relation between egg size, growth, and natural mor-
tality of larval ﬁsh. Journal of the Fisheries Research Board of Can-
Wickham, H. 2016. ggplot2: elegant graphics for data analysis. Springer-
Verlag, New York.
114 CLANCY ET AL.