Assessing muskrat predation on a freshwater mussel assemblage in a southeastern United States river

Abstract

Many freshwater mussel species are experiencing significant declines across the United States, particularly in the Southeast where most of the diversity in this animal group occurs. In this study, we evaluated the impact of muskrat (Ondatra zibethicus) predation on the mussel assemblage at Kyles Ford, a well-studied reach of the Clinch River, Tennessee. We compared quantitative estimates of abundance and size structure of live populations with shells that accumulated in muskrat middens between September and December 2023. We used a sampling approach that censused all shells deposited by muskrats at this site during the study and allowed us to quantify predation rates and size-and species-selectivity of muskrat predation. In total, we documented the predation of 2370 individual mussels of 26 species, including 14 federally listed species and one candidate species. The mean predation rate was 20 mussels per day, and muskrats exhibited preference for larger individuals. The Chesson's index confirmed significant species selectivity coinciding with endangered species and size-selectivity was observed in four species. These findings underscore the need for further research into the seasonal and environmental variability of muskrat predation and its long-term effects on mussel populations. Additionally, our results suggest that muskrat middens may serve as a valuable tool for monitoring mussel species occurrences.