Muskrat Predation on Endangered Freshwater Mussels in Virginia

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Abstract
We assessed foraging by muskrats (Ondatra zibethicus) on freshwater mussels at North Holston Ford (NHF), North Fork Holston River (NFHR), by comparing the mussel assemblage in fall 1981 to shell middens collected seasonally between 1980 and 1981. Nearly 30,000 adult mussels of 16 species occupied NHF in 1981. Abundance of most prey species in shell middens was generally related to the relative abundance of that species at the site, although 2 mid-size species were selected and the smallest species was not consumed in proportion to availability. From 1979 to 1986, 28% of endangered shiny pigtoes (Fusconaia cor) were consumed; other species lost 8.6-24.3% of their demes to muskrat predation. Shell middens collected quarterly at 12 sites in the NFHR and Clinch River for 1 year (1984-85) contained 623 (13%) endangered mussels. Muskrats appeared to prey on mussels and Asiatic clams (Corbicula fluminea) during most of the year, with the greatest consumption at sites with the largest mollusk assemblages. The Asiatic clam is the dominant molluscan prey of muskrats in the Clinch River. Muskrat predation appears to be inhibiting the recovery of endangered mussel species, and likely placing some demes of endangered pigtoe mussle species in further jeopardy of extirpation from sites in both rivers.