Native Fishes Below Dams: Working With What We Have

Mary C. Freeman
USGS Patuxent Wildlife Research Center, University of Georgia, Athens, GA 30602 (706-542-5181, FAX 706-542-1235, mary_freeman@usgs.gov)

Elise R. Irwin
USGS Alabama Cooperative Fish and Wildlife Research Unit, Auburn University, AL 36849

Byron J. Freeman
Institute of Ecology, University of Georgia, Athens, GA 30602

A century of improvements for efficient barge travel and electricity production has transformed the physical and biological character of southeastern rivers. Remnants of native riverine communities now persist in headwaters and tributaries of impounded river systems and, importantly, in unimpounded river fragments flowing between an upstream dam and the next downstream reservoir. Our research in the eastern Mobile River basin has shown large differences in relative diversity and abundance of native fishes among regulated river fragments. For example, regulated segments of the Tallapoosa River support substantial populations of as much as 70% of the native non-anadromous fauna. In contrast, regulated segments of the Etowah River and lower Coosa River support a smaller fraction of their native fish faunas, at low abundances. Differences in integrity among regulated segments partly correspond to differences in dam operations, hydrologic regimes and instream habitat, especially with respect to short-term flow stability and availability of shallow-water riffle habitats. Applying adaptive management to these regulated segments, by integrating management with research designed to test hypothesized mechanisms of species survival, could enhance conservation of native fauna and improve our understanding of relations between river fishes and hydrologic regimes.