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Comparing two methods for sampling and estimating abundance of mottled sculpin in the Logan River, Utah
Nathan C. Malmborg1, Gary P. Thiede1, and Phaedra Budy1,2,3
1Quinney
College of Natural Resources, Department of Watershed Sciences, Utah State University, Logan, Utah, 84322
2US Geological Survey, Utah Cooperative Fish and Wildlife Research Unit. 3Ecology Center.
INTRODUCTION 120
16
surber
100
OBJECTIVES
Above. Electrofishing at Twin Bridges
80
10
60
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2
40
20
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250
electrofishing
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150
0
1.2
0
(unable to use surber)
electrofishing
1.0
0.8
50
0.0
0
20
0
40
60
80
0
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0
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0
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0
16
Above. Dismounting trap net at rear of sampler
Above. Sculpin receive a light dose of MS-222
0
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Figure 1. Length frequencies of sculpin
captured using the sculpin surber (top
panel) and via electrofishing (bottom
panel) in the Logan River, summer 2014.
Sculpin < 30 mm are age-0. Note
changes in y-axis scales.
R2 = 0.54, p = 0.47
Surber density
(sculpin / m2)
12
10
8
6
4
2
0
RESULTS
Lengths of sculpin we captured varied greatly between the two sampling methods;
most sculpin captured using the surber sampler were age-0, whereas electrofishing
captured all age classes of sculpin except age-0 (Figure 1). Using electrofishing
depletion methods, we estimated sculpin abundance to range from 0.09 – 0.8
sculpin/m2; likely underestimating the abundance of small, age-0 sculpin (Figure 2).
Because of bias in the sizes of fish captured by the two methods, surber abundance
estimates were skewed toward small fish; up to 8.8 sculpin/m2 at the Third Dam 2014
site (Figure 2). In general, densities of sculpin captured using the surber sampler
were 4 to 10-times higher than electrofishing density estimates, although our
comparison sample size was low (Figure 3).
0.2
0.4
0.6
0.8
1.0
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Sample site
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Above. Recording lengths, weights, and counts
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Total length (mm)
Above. Sorting through trapped contents
Electrofishing
We used both backpack-mounted and
canoe mounted electro-fishing units to
collect sculpin. When 3-pass surveys
attained true depletions, we computed
estimates of sculpin abundance using
the Huggins closed-population
estimator in Program MARK. In cases
where we did not attain true depletions,
we combined catches in pass 1 and 2
then used a modified Zippin two-pass
depletion formula (Budy et al. 2014). 2
0.2
STUDY SITES
Surber sampling
In the summer of 2014, we used a
modified 0.5 m2 benthic ‘surber-like’
sampler at five different sites
previously surveyed by electrofishing.
We modeled the sampler and methods
of use after a study performed by
Steinmetz and Soluk (2001). We
randomly placed the surber sampler 20
times throughout each reach, and then
manually disturbed the substrate and
fish for capture. We then counted,
measured, and released all sculpin. 4
0.4
14
METHODS 6
0.6
100
•  Compare and contrast two different sampling methods to collect sculpin, estimate
sculpin abundance, and understand sampling bias
•  Compare and contrast demographics of sculpin captured by the two methods Map 1. Location of longterm electrofishing index
sites (gray circles) and
sculpin-surber sampling
sites (red circles) on the
Logan River, Utah.
Generally, mainstem
sample reaches were 200m long and tributary
reaches were 100-m long.
We captured no sculpin in
the Temple Fork or Right
Hand Fork tributaries.
Density (sculpin / m )
Above. Surber sampling at Beaver Creek
Number of sculpin captured
12
Mottled sculpin (Cottus bairdii) are an important but very understudied component of
many native fish communities of the Intermountain West. Three-pass depletions are
one of the most commonly used abundance estimation techniques in stream fisheries
science; however, resulting estimates can be biased low and underestimate fish
abundance differentially across both species and size classes (Peterson et al. 2004).
Past efforts to quantify mottled sculpin densities in the Logan River, Utah have proven
to be inaccurate and imprecise.
Having the ability to accurately monitor sculpin abundance in the Logan River could
potentially increase our understanding of the trophic dynamics between sculpin and
non-native, piscivorous brown trout (Salmo trutta). Although recent evidence suggests
sculpin abundance and distributions are not controlled by piscivory, but rather abiotic
factors, brown trout were shown to consume significantly more sculpin than the native
Bonneville cutthroat trout (Oncorhynchus clarkii utah; Meredith et al. 2014). These
findings suggest there is a need to more accurately and precisely monitor sculpin
populations in order to understand their role in the native fish community and the
ecosystem. Therefore, we used and completed a novel sampling technique to
estimate sculpin abundance and determine bias in depletion-based abundance
estimates.
surber
14
1.2
1.4
Electrofishing density (sculpin / m2)
Figure 2. Density estimates of sculpin
from five surber sampler sites (mean ± 2
SE; CI; top panel) and six electrofishing
survey sites (mean ± 95% CI) on the
Logan River, summer 2014. We
captured no sculpin using the surber
sampler at the Beaver Creek; however,
we slightly modified the sampler on
subsequent sampling events. Surber
sampling was not possible at all sites,
and asterisks indicate sites where we
did not electrofish in 2014. Figure 3. Relationship between mean
sculpin density estimates in the Logan
River at three sites where we conducted
3-pass electrofishing (± 95% CI) and
sculpin-surber sampling (± 2 SE),
summer 2014. Regression line, R2, and
p value are shown.
CONCLUSIONS
•  The surber sampler is fast and easy to use; however, while electrofishing is
biased toward larger sculpin, the surber sampler is biased toward smaller sculpin.
•  Abundance estimates via 3-pass electrofishing are much lower; however, they
may be a more valid estimate of ecologically-relevant population abundance.
•  Pairing results between the two methods may be the most accurate means to
quantify demographics and abundance of mottled sculpin in the Logan River.
•  Our sculpin surber sampler is ineffective in fast moving, deep water.
•  Information about sculpin populations could have management implications for
both non-native brown trout and the preservation of the native fish community of
the Logan River. LITERATURE CITED: For reference list or study details, contact [email protected]
ACKNOWLEDGEMENTS
Funding and support was provided by the US Forest Service, the USGS Utah Cooperative Fish and
Wildlife Research Unit (in kind), and a travel grant from the Quinney CNR Undergraduate Research
Committee. Thanks to Chantel Rasmussen, Harrison Mohn, Brett Roper, and Jamie Reynolds. Thanks
to the UDWR Dedicated Hunter Program for field assistance.
Above. An age-0 sculpin caught using the
surber sampler
Above. A 153 mm sculpin caught while
electrofishing