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NCER Grantee Research Project Results

Measuring the Extent and Impact of Biotic Invasions: Case Study of Signal Crayfish in Sierra Nevada (CA) Streams

EPA Grant Number: U915147
Title: Measuring the Extent and Impact of Biotic Invasions: Case Study of Signal Crayfish in Sierra Nevada (CA) Streams
Investigators: Light, Theo
Institution: University of California - Davis
EPA Project Officer: Smith, Bernice
Project Period: October 1, 1997 through October 1, 2000
Project Amount: $102,000
RFA: STAR Graduate Fellowships (1997)
Research Category: Academic Fellowships , Ecological Indicators/Assessment/Restoration , Fellowship - Ecology and Ecosystems



The objective of this research project is to examines the distribution and impacts of the introduced signal crayfish (Pacifastacus leniusculus) in streams of the Truckee River drainage in the eastern Sierra Nevada, California. My major questions are:

1. Is the extent of this invasion limited by the naturally variable flow regime of California streams, or conversely, facilitated by the many small reservoirs and regulated stream reaches in this system?

2. What are the community impacts of signal crayfish on native benthic organisms, particularly Paiute sculpin (Cottus beldingi), and on food web processes in Sagehen Creek?


(1) Extent of invasion: In summers of 1994 and 1998, I surveyed most streams of the Truckee River basin for signal crayfish. For each stream section sampled, I measured flow and average stream width and depth in the field, and determined gradient, elevation, stream order, and distance to the nearest impoundment from topographic maps. I will analyze these variables using multivariate techniques in order to identify factors associated with crayfish presence and abundance. Three streams (two with natural hydrographs, one regulated) have been sampled quantitatively for crayfish and sculpins each year of my study (1994-1998); all three of these streams have hydrologic (flow) data available from the U.S. Geological Survey. Using time-series analysis, I will examine the association of winter high flow events (timing and severity) with the distribution and abundance of crayfish in the following season. Initial results suggest that crayfish are associated with a number of (intercorrelated) factors: higher stream order, lower elevation, proximity to reservoirs, and flow regulation. Crayfish abundance was reduced after winter high flow events in 1995-1997.

(2) Community effects of crayfish: I am examining crayfish effects on native Paiute sculpins and benthic food webs using a combination of field cage experiments, field removals, and behavioral experiments in a semi-natural observation stream. In addition, I will use data from field surveys of crayfish and sculpins to examine associations between the two species and winter flood effects on sculpins. Cage experiments manipulating densities of crayfish and sculpins were completed in 1995 and 1996. I measured growth rates of both species in sympatry and allopatry, and assessed their impacts on algal and invertebrate biomass and diversity on artificial substrates. Behavioral experiments in 1996 and 1998 assessed the impacts of crayfish presence on sculpin shelter use, feeding rate, velocity microhabitat selection, and overall activity level. Field removal experiments involved crayfish removal from randomly- selected pools in an area of high crayfish density in Sagehen Creek. I examined the effects of crayfish removal on invertebrate abundance and diversity, algal biomass, and sculpin abundance and position in pools. Preliminary results of cage and behavioral experiments suggest that crayfish reduce sculpin growth rates and shelter use, increase their overall activity levels, and lead to their use of higher- velocity habitats.

Supplemental Keywords:

fellowship, biotic invasions, Sierra Nevada, California, CA, signal crayfish, Pacifastacus leniusculus, Truckee River, Cottus beldingi, time-series analysis, benthic food webs, Sagehen Creek., RFA, Scientific Discipline, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, State, Monitoring/Modeling, Habitat, Environmental Monitoring, Biology, habitat dynamics, biodiversity, food web, community composition, benthic food web, ecological consequences, crayfish, invasive species

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The perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.

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