RECENT CATASTROPHIC DECLINE OF MUSSELS (BIVALVIA, UNIONIDAE) IN THE LITTLE SOUTH FORK CUMBERLAND RIVER, KENTUCKY

During 1987, we sampled 16 sites in the Little South Fork Cumberland River to assess the status of mussel populations. We found 21 species, of which 12 were alive. Mean densities in the lower one-third of the stream had declined from 2.9 to 7.5 mussels/m2 in 1981 to 0 to 1.1 mussels/m2 in 1987. Moreover, we found few live mussels at six other stations in this section of stream. Between 1981 and 1987, two species (Villosa trabilis and Pegias fabula), listed as federally endangered, appeared to have been extirpated from the lower one-third of the stream. Viable populations of most mussel species are now restricted to the middle section of the Little South Fork. Surface mining of coal has increased in the lower watershed of the Little South Fork in recent years and may be responsible for the mussel decline. Unlike the unionid mussel fauna, the density of the exotic Corbicula fluminea has increased nearly ninefold since 1981. This increase appears to be related to the general population expansion of C. fluminea in the Cumberland River system.