Propagation and Release of Freshwater Mussels (Bivalvia: Unionidae) for Two Natural Resource Damage Assessment and Restoration Cases in the Clinch and Powell Rivers in Virginia and Tennessee

Two Natural Resource Damage Assessment and Restoration cases in the upper Tennessee River basin are among the first and largest cases in the United States involving injury to freshwater mussels due to the release of hazardous substances. The Certus, Inc. spill of a rubber accelerant occurred in 1998 in the upper Clinch River in Virginia, killing an estimated 18,621 mussels, including individuals of three endangered species. The Lone Mountain Processing, Inc. spill of coal slurry occurred in 1996 in the Powell River in Virginia, affecting mussels over a 105-miles river section. Settlement money was used to propagate and release mussels at multiple sites in both rivers. We compiled the number of mussels produced from 2003 to 2018 on host fishes and the number of mussels released from 2004 to 2019 at population restoration sites by the Virginia Department of Wildlife Resources' Aquatic Wildlife Conservation Center (AWCC) and Virginia Tech's Freshwater Mollusk Conservation Center (FMCC). A total of 8,456,191 juvenile mussels of 34 species was produced by AWCC and FMCC, with 861,845 mussels of 26 species released at sites in Virginia and Tennessee. Of the released mussels, 150,680 were 20–40 mm long and 1–3 yr old. The remaining mussels (711,165) were typically a few weeks old and <1 mm long and were released from 2004 to 2008. By 2010, both facilities were growing mussels to larger sizes before release, which allows mussels to settle into substrate more quickly and thus improves their chances of survival. Of the mussels produced from 2010 to 2019, mean survival to a stockable size (20–40 mm) was 4.8% for AWCC and 6.1% for FMCC, with no species experiencing survival >22%. Our data show that production must be much higher than the target number of mussels to be released, and they allow researchers to better estimate the amount of production necessary to reach restoration goals.