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266 M. J. JENNINGS, L. S. FORE AND J. R. KARR dominant taxa in warm water streams throughout much of North America but represented by few species in reservoirs. We used the proportion of individuals as invertivores (PINV) as a substitute metric to measure similar ecological stresses or system responses (Karr et al., 1986; Miller et al., 1988; Steedman, 1988). All proportional metrics excluded shad. Although shad are an important component of these systems, variation in shad abundance among littoral zone samples prevented the detection of differences in other components of the fish assemblage when shad were included. Two metrics are based on reproductive guilds (number of migratory spawning species-TMIG; and num- ber of lithophilic, broadcast-spawning species-TLIT). The TMIG detects the population status of species that typically move large distances to spawn; they may also be affected by human-made structures that block movements. Thus a variety of human actions may contribute to a decline in migratory spawning species. The TLIT is modified from a similar metric (substrate spawning species) evaluated for rotenone data (Dionne and Karr, 1992). Lithophilic spawners comprise a group that may be sensitive to siltation, a common impact known to have deleterious effects on reproduction of some freshwater fishes (Berkman and Rabeni, 1987). For this metric we included only those species that spawn over rocky substrates and do not provide subsequent parental care to their offspring. The RFAI contains two metrics that evaluate the condition of individual fish. The first, also found in IBI, is that proportion of individuals with diseases, parasites or anomalies (PDIS). We hypothesize that this metric reflects the presence of environmental factors that either directly cause abnormalities, or produce stress sufficient to increase the susceptibility of fish to diseases or parasites. We also evaluated the fish health assessment index (FHAI) for its utility as a metric. This composite index of several internal and external indicators of individual health (Goede and Barton, 1990) is calculated by TVA biologists with a sample of 15 largemouth bass taken at each collection site. The FHAI is designed to detect subtle differences in over- all condition, compared with the binary classification of the PDIS metric. Although restricted to a few indi- viduals of a single species, this procedure may provide a comprehensive evaluation of fish condition in an abundant, easily captured top-carnivore. METHODS Fish data set Development of the RFAI is based on electrofishing samples taken by TVA biologists in 10 reservoirs during 1989-1992 in each of three longitudinal zones designated as inflow (upstream end), transition (located in areas where suspended sediments begin to settle out of water column) and forebay (above dam). Two relatively small reservoirs (Wilson and Nickajack) were only sampled in inflows and forebays. An electrofishing sample consisted of a series of 10 timed (10 minutes) runs taken downstream along the bank. The 10 runs were selected to be representative of habitats roughly in proportion to their occur- rence. Field crews attempted to collect all individual fish (except for easily identifiable, large individuals, which were counted from the boat) and large concentrations of young shad or bluegill, for which numbers were estimated. Individuals of important recreational species were identified, measured and counted. Metric values were calculated from cumulative totals of all 10 electrofishing runs because the probability of sampling uncommon species in a single run is low. Because several metrics are based on species counts and the presence of rare species can potentially differentiate sites, combining runs was considered the best approach to define a representative sample. This represents a methodological departure from existing stream versions of the IBI, in which an entire reach, including all representative habitats, can be effectively sampled with a single collection. Metric scoring criteria Ideally, scoring criteria are based on an analysis of pattern along a gradient of human influence. Efforts to define unambiguously such gradients among TVA reservoirs were unsuccessful; therefore, we used an alternative approach. We assumed that the relationship between human actions and the relevant biological variables was similar to those in earlier studies of ecologically equivalent metrics (Karr et al., 1986; Miller et al., 1988; Steedman 1988; Kerans and Karr, 1994). Scoring criteria were based on best (maximum or