Running head: GROWTH AND POPULATION SIZE OF PACIFASTACUS LENIUSCULUS TITLE PAGE
Growth and Population Size of Signal Crayfish (pacifastacus Leniusculus)
Sara K Anderegg
University of Idaho
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ABSTRACT
Crayfish(order Decapoda) are a species that are threatened in many parts of North America.
Threats to Crayfish include loss of habitat, urban development, and invasive species, among others. The
direct result of these threats, however, is somewhat uncertain because of the lack of current research
regarding certain species of North American Crayfish. The purpose of this study was to survey the local
crayfish populations within the streams surrounding the McCall area of the Idaho Batholith region and
examine the relationship between the pH of the water and the size of the Crayfish. Sampling at six sites in
the Upper Payette River watershed during October of 2012 showed that Pacifastacus Leniusculus and
Procambarus Clarkii were the species of crayfish present in the McCall area. P. Leniusculus seemed to be
the dominant species in these waters, with only 1 specimen of the P. Clarkii identified during the
investigation.
Synthesis.There was not a statistically significant difference between the size of the crayfishes found in
more acidic water compared with the size of the crayfishes found in less acidic water, although there were
more found at a higher pH than at a lower pH. With the constraint of a limited amount of time to complete
the investigation, there was not enough evidence to conclude that these results are an accurate
representation of the population.
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INTRODUCTION
Crayfish play an important role in our ecosystems as predators, bioprocessors of vegetation and
carrion, and as a critical food resource for fishes and numerous other terrestrial and aquatic
organisms(Taylor et al. 2007). Because of their role as a bioprocessor, Crayfishes serve as an important
link between primary energy sources and aquatic and terrestrial predators. Consequently, the addition or
subtraction of a crayfish species can have far-reaching consequences for communities and
ecosystems(Larson & Olden 2011).
In relation to the role of Crayfish in a community, there are many areas in which little is known.
Data such as the distribution, life history, species identification, and relation to habitat, are a necessary
and missing part of our understanding of this species(Riggert et al. 1999). One reason for this is because
studies on specific characteristics such as distribution have historically not been well funded (Riggert et
al. 1999). Master(1990) found a disproportionate number of aquatic organisms in need of conservation
attention when compared to their terrestrial counterparts (Taylor et al. 2007). The lack of attention given
to Crayfish only furthers our misunderstandings and mismanagement of this aquatic organism.
In addition to the deficit of research on Crayfish there are issues in the acknowledgement of
Crayfish in the Pacific Northwest specifically. There is a striking regional disparity in the attention given
crayfishes by fisheries biologists. Researchers in the Southeastern US are increasing efforts to conserve
the region’s endemic crayfish diversity while researchers in the Great lakes region and California have
made important contributions quantifying the economic and ecological costs associated with crayfish
invasions. By contrast, few recent studies on distributions, ecology, or management of crayfish have been
conducted in the Pacific Northwest region of the US and Canada(Larson & Olden 2011).
One of the major concerns is the effect of introduced species on their native counterparts. The
native species P. Leniusculus, often referred to as the “Signal Crayfish” is said to be one of the most
widely distributed and best known of the crayfishes native to the Pacific Northwest, although it has been
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better studied as an invasive species in California, Europe, and Japan(Larson & Olden 2011). Compared
to other North American Crayfish, however, very little is known about the factors influencing dispersal
and movements of Signal Crayfish(Bubb, Thom, & Lucas 2004). This presented a challenge in preparing
the investigation and selecting appropriate sample sites. Another challenge was the fact that previous
studies of movement and colonization by Signal crayfish have been predominantly concerned with
populations in lakes and lowland rivers. Their movement behavior under the more variable and rapidly
changing conditions in upland rivers is mostly unreported (Bubb et al. 2004). Of the literature concerning
P. Leniusculus, it is noted that these Crayfish generally prefer fast flowing water and can tolerate a wide
range of low temperatures, depending on gravel and boulder substrates, woody debris, and vegetation for
refuge from predators(Stein 1977)(Taylor et al. 2007).
Of the threats to Crayfish populations, one of the more controversial issues is the effect of the
acidification of streams on associated populations. Based on the assumption that acidification results in a
reduction in species diversity in aquatic systems, Crayfish were thought to suffer as a result of an increase
in the acid level of their habitat. The population-level effect of an environmental change like acidification
may not be predictable from individual-level studies because although such environmental stress may
have a direct negative effect on individuals, stress may have an indirect positive effect on a population
with relatively high tolerance by reducing predation or competition(Seiler & Turner 2004). A study
conducted by Seiler and Turner(2004) found that acidification of headwater streams has contrasting effect
on individuals and populations. Acidification had a negative effect on the growth of individual crayfish,
and these effects persisted even when crayfish were transplanted into circumneutral reaches. Despite the
negative effects of acidification on individuals, crayfish population sizes were more than sixfold larger in
acid streams relative to neutral streams, perhaps due to modification of food web interactions(Seiler &
Turner 2004).
In this study I chose to study the size of the Crayfish found during sampling and see if there was a
statistically significant difference between the size of the Crayfish found in water with a lower pH
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compared with those found in water with a higher pH. I chose two areas with different substrate matter,
and therefore different water pH to sample Crayfish. I hypothesized that the Crayfish found in the water
with the lower pH would be smaller in size, but may be more abundant than those found in the water with
the higher pH.
METHODS AND MATERIALS
A Benthic-Macroinvertebrate survey of wadeable streams in the McCall area of central Idaho was
completed in an effort to identify the species of crayfish present in the North Fork of the Payette river
watershed. Streams were chosen based on the bedrock substrate, suitability for crayfish habitat, and
accessibility to investigators. Sampling was carried out using an Environmental Protection Agency(EPA)
Rapid Bioassessment protocol, following the single habitat approach. Following the protocol, a 1 meter
kick net was used as the primary collection tool. At each sample site, a 100 m reach was established along
the stream, making sure that no bridge or disturbance was upstream of the sampling site. The reach at
each sampling site consisted of a variety of habitats including a combination of riffles, runs, and pools.
Starting downstream and proceeding upstream, samples were taken approximately every 10m.
Each sample was taken by positioning the net and disturbing one square meter upstream of the net. Larger
substrate particles were picked up and examined by hand, dislodging any attached organisms.
Supplemental sampling methods such as dip nets were used to collect organisms not otherwise captured
by the kick net. Collected samples were measured and identified using a dichotomous key and then
released back into the stream. Physical habitat assessments were completed for all sampling sites. The
individual habitats were evaluated based on visual observations of the physical characteristics of the
stream, in relation to substrate, location, riparian vegetation, etc.
Water Temperature, Dissolved Oxygen, water pH, and turbidity were measured at each sampling
site within the 100m reach. Water pH was the main focus for water characteristic data, being the purpose
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of this study to identify whether there was a relationship between the pH of the water and the size of the
crayfish. Basic descriptive statistics were generated to determine what the relationship was between size
and the pH of the stream.
RESULTS
Crayfish were collected in three of the six total sites sampled. The data shown in this report
reflect the results from the three sampling sites in which Crayfish were found. The water quality and other
data from the remaining three sites are not included in this report.
The sizes of the Crayfishes ranged from 3.8 to 6.3 cm. The mean size was 5.36cm. Using basic
data analysis, I concluded that there was not a statistically significant difference between the sizes of
Crayfish in the water with the lower pH compared with those found in the water with the higher pH.
DISCUSSION
My data did not support the hypothesis that the Crayfish would be impacted negatively on an
individual scale and positively on a population scale. Due to the constraints of time and materials, the data
found during the investigation needs to be increased in order to ensure that the data is true to the
population. The sample size in this investigation is too small to draw any major conclusions, and due to
the constraints of time and materials the investigation was completed before more evidence could be
collected.
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Bubb, D.H., Thom, T.J. & Lucas, M.C. (2004) Movement and dispersal of the invasive signal crayfish
Pacifastacus leniusculus in upland rivers. Freshwater Biology, 49, 357–368.
Larson, E.R. & Olden, J.D. (2011) The State of Crayfish in the Pacific Northwest. Fisheries, 36, 60–73.
Master, L. (1990) The imperiled status of North American aquatic animals. Biodiversity Network News, 3,
1-2, 7-8.
Riggert, C., Distefano, R. & Noltie, D. (1999) selected aspects of the life histories and habitat associations
of the crayfishes Orconectes peruncus (Creaser, 1931) and O. quadruncus (Creaser, 1933) in
Missouri. The American midland naturalist, 348–362.
Seiler, S.M. & Turner, A.M. (2004) Growth and population size of crayfish in headwater streams:
individual- and higher-level consequences of acidification. Freshwater Biology, 49, 870–881.
Taylor, C.A., Schuster, G.A., Cooper, J.E., Distefano, R.J., Eversole, A.G., Hamr, P., Iii, H.H.H.,
Robison, H.W., Skelton, E., Thoma, R.F. & Skelton, C.E. (2007) A Reassessment of the
Conservation Status of Crayfishes of the United States and Canada after 10 + Years of Increased
Awareness. Fisheries, 32, 372–389.