Restoration and colonization of freshwater mussels and fish in a southeastern United States tailwater

Abstract

The French Broad River originates in North Carolina, flows west into Tennessee and at its confluence with the Holston River forms the Tennessee River. Douglas Dam, located on the French Broad River 52 km above its mouth, is operated primarily for peaking hydroelectric power and flood control. Prior to completion of the dam in 1943, the lower French Broad River contained about 53 species of freshwater mussels and 100 species of fish. By 1977, the fauna in the 52-km-long tailwater was reduced to 12 species of mussels and 42 native species of fish. Improvements in tailwater conditions occurred following initiation of minimum flows in 1987, and consistent reaeration of discharge in 1993. From 1988 to 2002, we sampled three sites (4, 28, and 39 km downstream of the dam) to monitor the fish assemblage. Each year since 1988, we have collected one or more additional species, indicating continued immigration. We collected 82 native and 9 exotic species of fish overall, but the maximum of 67 species in 1 year suggests that some species reside in the tailwater at low densities or all immigrants may not successfully colonize the tailwater. There is limited potential for most extirpated species of mussels to naturally recolonize the tailwater because source populations are isolated. Consequently, 19 754 adult mussels of 19 species were introduced between 1997 and 2000. Survival of translocated mussels has been high, and successful reproduction of at least one translocated species has occurred. Additionally, four mussel species are naturally colonizing the tailwater. Colonization and recruitment of additional mussel species is expected as populations of their host fishes increase. We believe that the improved conditions of the tailwater may allow for the re-establishment of sustaining populations of 30 mussel species of historic occurrence, but the continued operation of Douglas Dam as a peaking hydroelectric project will reduce the probability of successfully reintroducing some species.