EVALUATION OF GENERALIZED HABITAT CRITERIA FOR ASSESSING IMPACTS OF ALTERED FLOW REGIMES ON WARMWATER FISHES

Assessing potential effects of flow regulation on southeastern warmwat er fish assemblages is problematic because of high species richness an d poor knowledge of habitat requirements for most species. Our study i nvestigated relationships between availability and temporal persistenc e of key habitats and fish assemblage structure at regulated and unreg ulated sites in the Tallapoosa River system. Fish assemblage character istics at seven sites were quantified based on 1,400 electrofishing sa mples collected during 1994 and 1995. Physical Habitat Simulation (PHA BSIM) programs were used to model availability and persistence of key habitats at regulated and unregulated sites. Associations between fish assemblages and availability or persistence of key habitats were iden tified via regression and analysis of variance. We found that hydropea king dam operation reduced the average length of time that shallow-wat er habitats persisted and also reduced year-to-year variation in the p ersistence of shallow-water habitats compared with unregulated sites. Across sites and years, proportional representation of catostomids was positively correlated with persistence of shallow and slow-water habi tats during spring. Proportion of individuals as cyprinids was positiv ely correlated with median availability of deep-fast habitat whereas p roportion of percids was inversely related to median availability of d eep-fast habitat. Mean fish density was positively correlated with the persistence of shallow and slow-water habitats. Comparisons of key-ha bitat measures and fish abundances between 1994 and 1995 at each site indicated that higher abundances of percids, catostomids, and cyprinid s were associated with increased availability and persistence of shall ow and slow-water habitats in 1995. These findings demonstrate that th e temporal and spatial availability of key habitats could serve as use ful measures of the potential effects of flow alteration on lotic fish assemblages and suggest that both short-term persistence of key habit ats as well as annual variation in key-habitat availability are import ant for maintaining diverse fish assemblages.