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Relationship of Trout Growth to Frequent Electrofishing and Diet Collection in a Headwater Stream



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 common techniques used to capture fish, and it is known to cause injury to fish under certain circumstances. We evaluated the relationship of growth rates in Columbia River Redband Trout Oncorhynchus mykiss gairdneri to the number of times that they were captured via electrofishing and gastrically lavaged during the summer 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 gastrically lavaged. Although these findings contrast with hatchery electrofishing 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 potentially up to twice per month, without greatly affecting the growth of wild Columbia River Redband Trout.
Relationship of Trout Growth to Frequent Electroshing 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
Phaedra Budy
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 shes sometimes requires that individual sh be
captured and subjected to invasive procedures multiple times over
a relatively short time span. Electroshing is one of the most com-
mon techniques used to capture sh, and it is known to cause
injury to sh 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 electroshing and gastrically lavaged during the sum-
mer of 2018 in a mountainous, headwater stream. We captured
sh between two and seven times over the course of 86 d using
continuous (smooth) DC backpack electroshing. 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 ndings contrast with hatchery elec-
troshing experiments, they may represent the greater resiliency of
wild sh. It appears that researchers can use electroshing 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 shes (Haskell 1940), there has been concern
about its propensity to cause injury and mortality of
aquatic species (Hauck 1949). Efciency and safety of
electroshing has increased over time, with contemporary
practice calling for continuous or pulsed, direct-current
(DC) electroshing with frequency (pulses) and voltage
adjusted so as to maximize sh capture while minimizing
injury (Fredenberg 1992; Curry et al. 2009). Continuous
DC electroshing tends to be the least damaging to sh
(reviewed in Snyder 2003). Yet despite technological and
methodological advances, injury and death of sh 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
electroshing remain poorly understood even though they
can be diverse and signicant (e.g. Dalbey et al. 1996;
Nielsen 1998).
In coldwater streams, trout of the family Salmonidae
are simultaneously the most sought-after gamesh 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 electroshing. Previous studies
have indicated that trout are among the most susceptible
taxa to spinal fractures, hemorrhaging, and mortality
when they are electroshed (Snyder 2003). Although
reported mortalities of juvenile and adult salmonids that
are subjected to continuous DC (300400 V) are low
(<1.5%), spinal injuries that are caused by electroshing
(which are more common when using pulsed DC) have
been shown to result in decreased growth (Dalbey et al.
*Corresponding author:
Received March 2, 2021; accepted November 6, 2021
North American Journal of Fisheries Management 42:109114, 2022
©2021 American Fisheries Society
ISSN: 0275-5947 print / 1548-8675 online
DOI: 10.1002/nafm.10728
1996; Ainslie et al. 1998), which often leads to decreased
survival (Ware 1975). Hatchery electroshing 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 electroshed, whether with low-frequency (3060 Hz)
pulsed DC or continuous DC (75300 V; Dwyer and
White 1997; Ainslie et al. 1998; Dwyer et al. 2001). How-
ever, a similar study examining repeated electroshing of
Atlantic Salmon Salmo salar parr with continuous DC
(Gregg Horton, personal communication) at 300500 V
found no signicant growth effects (Sigourney et al. 2005).
Gastric lavage has been demonstrated to be an efcient
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 sh 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 sheries research, some study designs may require
that sh 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 electroshing captures necessary for
little or no effect on sh growth, another parameter of
interest in trophic research. Moreover, invasive procedures
are sometimes required once the sh 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 sh growth.
Due to the paucity of research on electroshing and han-
dling effects on sh over short time frames, we examined
the growth of Columbia River Redband Trout O. mykiss
gairdneri that were subjected to electroshing 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 inuence of benthic algae on sh 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 JuneAugust discharge at the Bear Creek site is
30.1 ft
/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 sh assemblage was
dominated by native Columbia River Redband Trout
(hereafter, Redband Trout) and federally threatened
Bull Trout Salvelinus conuentus. Ramsey Creek also con-
tained a small number of Columbia Slimy Sculpin Urani-
dea cognata.
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 sh via
single-pass backpack electroshing with a model LR-24
Electrosher (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 shtypically 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 specic conductance between
streams: 110.2 μS/cm in Bear Creek and only 27.7 μS/cm
in Ramsey Creek. Upon initial capture (during the rst
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 n. 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 nal sampling event to maximize the
recapture of tagged sh. Following the method of Shoup
and Michaletz (2017), growth for the individual trout
was calculated as
Growth gg1d1
¼final weight initial 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
sh that were handled were lavaged. Initial weight was
included as a covariate because sh size is an important
intrinsic factor that inuences sh growth rate (von Berta-
lanffy 1938; Beauchamp 2009). We chose to assess sh
weight over sh 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 MuMInpackage in R (Barton
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
ggplot2package 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: 103241
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 sh
(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 sh 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 signicant (P
0.05) in any model (Table 1). The covariate interactions
between Redband Trout weight and handling pressure or
lavages were also insignicant.
Some experimental designs in sheries science require
recapturing sh over a relatively short period. Electrosh-
ing is one of the most widespread and effective methods
of capture (Bonar et al. 2009) but is sometimes associated
with sh injury and death (Vincent 1971; Snyder 2003).
Many growth studies also incorporate diet collection, so
determining how often is too oftenfor sh to be both
electroshed and gastrically lavaged is useful to future sh
biology studies.
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.
electroshing captures or gastric lavage events. However,
it is important to note that only four Redband Trout were
captured more than ve times and three of those four had
below-average growth rates. This low sample size makes it
difcult for us to determine whether sh that were cap-
tured more than ve times experienced decreased growth
rates due to handling pressure.
Broadly speaking, our results support those of Sigour-
ney et al. (2005), who observed no signicant growth
effects of continuous DC electroshing on hatchery-reared
Atlantic Salmon at an interval of once every 2 months.
Despite using considerably larger sh, our results demon-
strate few observable effects on Redband Trout growth at
even shorter intervals, where sh were also subjected to
gastric lavage.
Our results similarly support the ndings 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 sh 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 electroshing, (B) the number of times gastrically lavaged, (C) between the two streams, and (D) starting length of the
individual sh. 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.
their behavior to increase growth (e.g., increase foraging
However, our results differ from the ndings of
decreased growth in a series of hatchery experiments on
Arctic Grayling, Cutthroat Trout, and Rainbow Trout
that were subjected to only a single electroshing event
(Dwyer and White 1997; Dwyer et al. 2001). Although
those experiments were conducted at temperatures near or
below those in our study, the sh 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 sh generally have lower resilience relative to
wild sh (Wales 1954; Pinter et al. 2018) and may not
respond to electroshing in a manner similar to that of
wild sh. Our study is the rst of which we know to
examine frequent electroshing effects on the growth of
wild trout in a natural stream.
Electricity is known to affect sh 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 sh that were
not captured during a given sampling event were still
inuenced by electroshing, 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 sh in our study were captured at
least twice. A nonelectroshing control group may benet
future studies. Future research on the effects of frequent
electroshing and invasive sampling techniques could also
include other vital rate statistics such as behavior, sur-
vival, and reproductive successall known to be sensitive
to electroshing in some cases (Keefe et al. 2000; Siepker
et al. 2006; Fraser et al. 2017).
Sampling Implications
Electroshing and gastric lavage are both common
techniques used in sheries 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 sh in warmer tem-
peratures and in hatchery studies may respond to electro-
shing differently, it is likely that researchers who
conduct trout growth studies in cold, headwater streams
can capture sh 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 Ofce of Montana Fish Wildlife & Parks. Janice
Brahney was instrumental in making this eld season hap-
pen, and Gary P. Thiede provided logistical assistance
with eld equipment. Dan Dauwalter and two anonymous
reviewers provided comments that greatly improved the
manuscript. This work was supported by the U.S. Geolog-
ical SurveyUtah 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 scientic collectors permit 07-
2018. Any use of trade, rm, or product names is for
descriptive purposes only and does not imply endorsement
by the U.S. Government. There is no conict of interest
declared in this article.
Niall G. Clancy
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
P0.05; the corrected Akaike information criterion (AIC
) scores and
difference in AIC from the top regression (ΔAIC
) are included.
Regressions for Growth (gg
Covariates AIC
Handling Pressure
Growth ~Weight
*659.3 0.0
Growth ~Handled +Weight
*657.7 1.6
Growth ~Handled +Weight
+Handled ×Weight
655.5 3.9
Growth ~0*(Null Model) 643.8 15.5
Growth ~Handled 643.4 15.9
Gastric Lavage
Growth ~Weight
*659.3 0.0
Growth ~Handled +Weight
*659.2 0.1
Growth ~Handled +Weight
+Handled ×Weight
657.0 2.4
Growth ~0*(Null Model) 643.8 15.5
Growth ~Handled 643.8 15.5
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Compensatory growth—when individuals in poor condition grow rapidly to catch up to conspecifics—may be a mechanism that allows individuals to tolerate stressful environmental conditions, both abiotic and biotic. This phenomenon has been documented fairly widely in laboratory and field experiments, but evidence for compensatory growth in the wild is scarce. Cutthroat trout (Oncorhynchus clarkii subsp.) are cold‐water specialists that inhabit montane streams in western North America where seasonal conditions can be harsh and growth rates vary greatly among seasons. Understanding if individuals compensate for periods of reduced growth and body condition will improve understanding of the requirements of fish throughout their life‐cycle and across freshwater habitats. We quantified compensatory growth of juvenile cutthroat trout using extensive mark–recapture data from 11 stream populations (1,125 individuals) and two subspecies inhabiting a wide range of ecological settings in the northern Rocky Mountains, U.S.A. Our objectives were to determine how growth was linked across seasons and whether individuals behaviourally compensated for depressed body condition via emigration. Fish in relatively poor condition consistently demonstrated compensatory growth in mass during subsequent seasons. In contrast, fish in relatively better condition responded with positive growth in length during the summer signalling these fish may be better suited to headwater environments; no compensatory growth in length was found during the winter. Furthermore, there was no evidence that individual condition mediated migration tendencies of fish to seek more favourable habitat. Across a wide range of environmental conditions, we found consistent empirical support for compensatory growth in mass in the wild. A critical next step is to quantify how changing abiotic and biotic conditions influence the ability of stream fishes to compensate for locally or seasonally challenging conditions, thereby affecting long‐term resiliency, viability, and adaptation in the face of changing environmental conditions.
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Habitat alterations and establishment of nonnative fishes have reduced the distributions of Flannelmouth Sucker Catostomus latipinnis and Bluehead Sucker C. discobolus to less than 50% of their historical ranges in the Colorado River basin. Tributaries are sometimes less altered than main-stem habitat in the basin and may be important to support various life history processes, but their role in the maintenance of Flannelmouth Sucker and Bluehead Sucker populations is poorly understood. Using mark-recapture techniques, we show tributaries are important habitat for native suckers in the upper Colorado River basin and report three main findings. First, both Flannelmouth and Bluehead suckers likely respond to a thermal cue that initiates spawning movement patterns. Suckers moved into Coal Creek from the White River beginning in mid-May of 2012 and 2013 to spawn. The majority of sucker spawning movements occurred when water temperatures inWhite River exceeded 11-14°C and those in Coal Creek were 2.5-4°C warmer, while flows varied between years. Second, based on PIT tag detection arrays, 13-45%of suckers showed spawning site fidelity. Sampling only with fyke nets would have resulted in the conclusion that site fidelity by native suckers was only 1-17%, because nets were less efficient at detecting marked fish. Third, most suckers of both species emigrated from Coal Creek within 48 h after being captured while suckers that were detected only via arrays remained resident for 10-12 d. The posthandling flight response we observed was not anticipated and to our knowledge has not been previously reported for these species.Remote PIT tag antenna arrays allowed for a stronger inference regarding movement and tributary use by these species than what could be achieved using just fyke nets. Tributaries are an important part of Flannelmouth Sucker and Bluehead Sucker life history and thus important to conservation strategies for these species.
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Electrofishing is commonly used to monitor fish populations and to control nuisance or invasive fishes. These applications typically focus on juvenile and adult fish, and comparatively less is known about how early developmental stages of fish are affected by electroshock. We examined the survival of hatchery steelhead Oncorhynchus mykiss embryos and larvae exposed to three waveforms often emitted by commercially available electrofishing equipment—AC, square pulsed DC (PDC), and half-sine-wave PDC—at different voltage gradients across six developmental stages. There was a strong negative relationship between voltage gradient and survival of steelhead embryos and larvae. Fish were most resistant to electroshock after embryonic pigmentation had occurred (93% mean survival at 4.5 V/cm) until their sensitivity again increased at the swim-up larval stage (32% mean survival at 2.5 V/cm). The greater survival of embryonic and alevin steelhead exposed to half-sine-wave PDC (42% mean survival at a peak voltage gradient of 2.5 V/cm) compared with square PDC and AC (8% mean embryonic survival at 2.5 V/cm) suggested that root mean square voltage gradient is a stronger determinant of mortality than are peak voltage gradient or alternating polarity. The AC waveforms were more deadly to swim-up larvae than were other waveforms, so the mechanism by which electroshock kills this life stage is probably different than the mechanism that kills steelhead during earlier developmental stages. The results of this study have direct implications to electrofishing in environments where some sympatrically occurring species and developmental stages are not the intended target for electroshock. Accordingly, we offer some simple suggestions for how waveforms can be manipulated to limit, or increase, the mortality of fishes where electrofishing is used as a management or conservation tool. Received December 17, 2015; accepted April 25, 2016
This new edition to the classic book by ggplot2 creator Hadley Wickham highlights compatibility with knitr and RStudio. ggplot2 is a data visualization package for R that helps users create data graphics, including those that are multi-layered, with ease. With ggplot2, it's easy to: • produce handsome, publication-quality plots with automatic legends created from the plot specification • superimpose multiple layers (points, lines, maps, tiles, box plots) from different data sources with automatically adjusted common scales • add customizable smoothers that use powerful modeling capabilities of R, such as loess, linear models, generalized additive models, and robust regression • save any ggplot2 plot (or part thereof) for later modification or reuse • create custom themes that capture in-house or journal style requirements and that can easily be applied to multiple plots • approach a graph from a visual perspective, thinking about how each component of the data is represented on the final plot This book will be useful to everyone who has struggled with displaying data in an informative and attractive way. Some basic knowledge of R is necessary (e.g., importing data into R). ggplot2 is a mini-language specifically tailored for producing graphics, and you'll learn everything you need in the book. After reading this book you'll be able to produce graphics customized precisely for your problems, and you'll find it easy to get graphics out of your head and on to the screen or page. New to this edition:< • Brings the book up-to-date with ggplot2 1.0, including major updates to the theme system • New scales, stats and geoms added throughout • Additional practice exercises • A revised introduction that focuses on ggplot() instead of qplot() • Updated chapters on data and modeling using tidyr, dplyr and broom
A set of density-dependent growth and survivorship equations is derived from evidence that the instantaneous death rate in the sea is inversely proportional to particle size. The survivorship equation reproduces several well-known phenomena observed in fish populations. It predicts: 1) that winter and spring spawning species ought to produce larger eggs than summer spawners, 2) that it is advantageous for species that spawn in batches to produce progressively smaller eggs in spring and summer, and 3) that the death rate of a cohort of fish should decrease continuously as the survivors grow and approach the critical size.The biological basis for the observed variation in the size of pelagic fish eggs and larvae is thought to be due primarily to trophic relations within the pelagic community. It is suggested from what is known of the relative abundance and foraging capabilities of different sized particles, that the survival rates of larval and juvenile fish should increase as they grow and occupy a progressively higher position in the food chain.