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REGULATED RIVERS: RESEARCH & MANAGEMENT, VOL. 11, 263-274 (1995) BIOLOGICAL MONITORING OF FISH ASSEMBLAGES IN TENNESSEE VALLEY RESERVOIRS MARTIN J. JENNINGS*, LESKA S. FORE AND JAMES R. KARR University of Washington, Institute for Environmental Studies, Engineering Annex, FM-12, Seattle, WA 98195 USA ABSTRACT Reservoirs comprise an expanding proportion of global freshwater resources. New multimetric approaches to biological monitoring, such as the index of biological integrity, have been useful in streams; similar approaches in reservoirs might aid managers concerned about the reservoirs they manage. Electrofishing data from Tennessee Valley Authority reservoirs were used to evaluate the applicability of biomonitoring to those reservoirs. Individual metrics and overall index scores exhibited substantial annual variation. Within-year variation in scores from a supplemental data set suggests that annual changes in scores may not represent real fluctuations in resource condition. Species accumulation curves demonstrate that standard samples consisting of ten timed runs were not adequate; the sample error was high. Some metrics are useful, but they require more testing; other metrics are clearly not appropriate for use in a integrative multimetric index. Finally, the reservoirs included in this study may be similarly degraded; independent data from separate regions and watersheds are needed to resolve this and other issues. Although attaching qualitative judgements (e.g. excellent to poor) is premature, the concept of a reservoir biomonitoring index deserves more study, especially the development of more comprehensive and systematic sampling programmes designed to resolve sample adequacy and sources of variation in sample data. KEY WORDS: biomonitoring; biotic integrity; electrofishing; fish assemblages; reservoirs; Tennessee River INTRODUCTION Concern about the condition of aquatic ecosystems has expanded in the past two decades with a recognition that chemical standards have not protected aquatic resources (Adler et al., 1993). Biological monitoring provides an effective supplement to the chemical approach because it provides direct information on an important societal endpoint-the condition of the aquatic biota (Angermeier and Karr, 1994)-and it is sensitive to chemical contamination as well as other human influences (Karr, 1991). Multimetric indexes, such as the index of biotic integrity (IBI) originally developed for use in Midwestern streams (Karr, 1981), provide an integrative approach to the assessment of aquatic resource condition (Davis and Simon, 1995). The IBI framework has been successfully applied to biomonitoring programmes in other geographical regions and aquatic systems (Miller et al., 1988; Oberdorff and Hughes 1992). The IBI is an integration of selected fish or insect assemblage attributes, referred to as metrics, such as species richness, proportional abundances of trophic guilds, abundance and individual condition. Use of the IBI to evaluate stream condition relies on a knowledge of conditions at relatively undisturbed reference sites, from which regional expectations for a healthy biota can be derived. Reservoirs present significant challenges to water resource managers because reservoirs are created by human actions, and, thus, natural reference sites do not exist. Reservoirs, however, make up an increasing proportion of freshwater resources, and workable approaches to biomonitoring are needed to identify and track threats to the biology of reservoirs. The development of an assessment tool for reservoirs may incorporate the ecological principles on which the IBI is based, but its development must also acknowledge important aspects of water bodies created by impounding rivers (Dionne and Karr, 1992). *Present address: Wisconsin Department of Natural Resources, Bureau of Research, Box 309, Spooner, WI 54801 USA. CCC 0886-9375/95/070263-12 Received 15 July 1994 © 1995 by John Wiley & Sons, Ltd. Accepted 18 January 1995