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Effects of Environmental Factors on Crayfish Abundance
in the Boundary Water Canoe Area Wilderness
Nathan Servey, Brennan Dow, Brittany Burant and Mason Loden
Department of Biology  University of Wisconsin-Eau Claire
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r2 = 0.55
p = 0.046
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Crayfish Weight (g)
The objective of this study was to investigate how crayfish in the Boundary
Water Canoe Area Wilderness (BWCA) responded to lake productivity and
water depth. Both are important aspects of crayfish habitat and may
determine food availability, predation risk and other factors (Weinlaender &
Fuereder 2012, Ficetola et al. 2012). We estimated lake productivity using
a Secchi disk, a simple but reliable measure of lake trophic state, and
surveyed crayfish populations in five BWCA lakes using two methods (Dorn
2005). Five commercial crayfish traps were set at depths ranging 1-5 m,
baited and left overnight. Trapped crayfish were then identified, counted,
sexed and weighed, and their carapace length was measured. Active
sampling involved doing a visual count of crayfish along lake shorelines for
5-min intervals to obtain an average number crayfish observed per minute.
Results Cont.
Results
Crayfish Weight (g)
Background
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7
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Total Crayfish Captured
120
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Secchi Depth (m)
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Carapace Length (mm)
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Figure 3. Orconectus obscurus crayfish weight as a function of carapace
length. O. obscurus was the most abundant crayfish species in our traps,
comprising 89% of all individuals captured. We found that the length-weight
relationship did not vary across lakes, despite differences in O. obscurus
weight among lakes (Fig. 1). The data suggest these corresponding traits
show little plasticity.
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Discussion
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 The data did not support our hypothesis; in fact, we observed the
opposite of what had been predicted. Rather than crayfish being more
abundant in productive lakes, less productive lakes had more and larger
crayfish (Fig. 1).
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Secchi Depth (m)
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Figure 1. Mean crayfish weight (± 1 SE) and total crayfish captured in
each lake as a function of average Secchi depth. Five Secchi readings
were taken per lake. Low lake productivity correspond to higher Secchi
readings.
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Mean Proportion of
Crayfish Captured
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• Lake perimeter and maximum depth
Passive sampling
• Lakes sampled using 5 baited
minnow traps set at 1 m intervals
along 1-5 m depth gradient.
• Traps set in the afternoon and
recovered the following day.
Captured crayfish were identified,
sexed, weighed and had carapace
length measured.
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r2 = 0.53
p = 0.05
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• Productivity (with Secchi disk)
Active sampling
• Each lake visually surveyed 5 times using
successive 5-min sampling periods.
• If no crayfish sighted, sampling interval
continued until crayfish sighted or 15 min.
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Environmental factors measured:
• Trap sampling depth
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Lake selection based on:
1.) Accessibility
2.) Rocky substrate
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Hypothesis:
We predict that lakes showing higher levels of productivity will
correlate with increased crayfish abundance and biomass.
Methods
r2 = 0.86
p < 0.001
r2 = 0.98
 This raises the possibility that, rather than responding to lake productivity,
non-native Orconectus obscurus crayfish may be negatively affecting lake
productivity. Invasive species abundance often corresponds to declines in
native crayfish and primary producers (Weinlaender & Fuereder, 2012), with
detrimental implications for aquatic ecosystems (Ficetola et al., 2012).
 Most crayfish occurred in depths ranging 2-4 m (Fig. 2), suggesting that
shallow and deep water present less favorable habitat. We speculate that
shallow water presents greater risk of predation from shore predators (e.g.,
herons, raccoons and otters) whereas deep water has less abundant food
(i.e., fewer aquatic plants and invertebrates).
 Little is known about how non-native O. obscurus affects native crayfish
populations and aquatic ecosystems, much less those in the Boundary
Waters. Further studies examining the spread, competitiveness, and
abundance of O. obscurus are warranted.
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 This study will guide future BWCA crayfish research in Summer 2013.
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Acknowledgements: Funding and support for this research project was provided by the UWEC
Biology Department and individual course fees. We would also like to thank Todd Wellnitz, our
mentor and professor, and our BWCA outfitter, Williams and Hall.
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Literature Cited:
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Trap Depth (m)
Figure 2. The proportion of crayfish trapped at different depths were
calculated as a proportion of the crayfish captured for a given lake, and
then the mean (± 1 SE) for each depth was calculated across the 5 lakes
sampled. Crayfish were proportionally more abundant at intermediate
depths.
Crocker, D.W. & D.W. Barr. 1968. Handbook of the crayfishes of Ontario. Royal Ontario Museum
of Life Sciences, miscellaneous publications.
Dorn, N.J., R. Urgelles & J.C. Trexler. 2005. Evaluating active and passive sampling methods to
quantify crayfish density in a freshwater wetland. Journal of the North American Benthological
Society 24:346-356.
Ficetola, G.F., M E. Siesa, F. De Bernardi, & E. Padoa-Schioppa. 2012. Complex impact of an
invasive crayfish on freshwater food webs. Biodiversity and Conservation 21:2641-2651.
Minnesota DNR, Lake Information Report, http://www.dnr.state.mn.us/lakefind/index.html
(accessed November, 11, 2012).
Weinlaender, M. & L. Fuereder. 2012. Associations between stream habitat characteristics and
native and alien crayfish occurrence. Hydrobiologia 693:237-249.