PARENT SESSION
Symposium 7: When the Rivers Run Dry: Cross-Disciplinary Perspectives on Societal Responses to Drought and Ecosystem Impacts
Organized by: A Covich and C Pringle
Tuesday, August 5. 1:30 PM to 5:00 PM, SITCC Oglethorpe Auditorium.

Effects of drought and policy on fish assemblages in the southeastern United States.

Freeman, Mary^*,1, ¹ U.S. Geological Survey, Athens, GA, US

ABSTRACT- The southeastern United States is a globally significant center of aquatic biodiversity, the great majority of which evolved in flowing-water ecosystems. Over the past century, hydropower development has fragmented and extensively inundated this stream habitat, and native faunal assemblages have persisted primarily in the undammed tributaries of major river systems. These tributaries are coming under increasing pressure from water supply development. Present policy focuses almost entirely on provision of minimum flow levels at withdrawal points and downstream from reservoirs. Research conducted on the effects of municipal withdrawals in six river systems across the Piedmont province of Georgia during the drought of 2000 and 2001 has shown declining integrity of fish assemblages coincident with increasing relative withdrawal size. In contrast, reference streams (having relatively unaltered flow regimes) have sustained high Index of Biotic Integrity scores despite drought flows. Additionally, fish assemblages downstream from water supply reservoirs exhibit declines in a suite of native fishes relative to reference-stream assemblages. Fishes persisting and dominating assemblages downstream from reservoirs are species common in lentic and lotic habitats, including sunfishes (Centrarchidae) and mosquitofish (Poeciliidae). Assemblages downstream from water withdrawals (i.e., without instream impoundments) are more similar to reference conditions, generally supporting larger diversity and abundances of minnow (Cyprinidae), darter (Percidae), and sucker (Catostomidae) species, as well as in selected catfish (Ictaluridae) and lotic bass (Centrarchidae) species. The differences in fish assemblages downstream from water supply reservoirs compared to other sites are not strongly related to differences in local habitat, catchment landuse, or minimum flow requirements. Understanding the biological consequences of alternative water supply strategies will require quantifying the cumulative effects of reservoir proliferation and flow alteration at a landscape scale, issues that extend beyond consideration of provision of minimum flows during drought or low-flow periods.

Key words: stream fishes, water supply, minimum flow, drought