Fish were collected from riffles, runs, pools and woody habitats in the Vermillion River, South Dakota, to examine the temporal dynamics of habitat use during non-flood summer months. The densities of small fishes (30-75 mm; cyprinids and young-of-the-year individuals) were greatest in riffles and woody habitats during periods of moderate discharge (1.14 and 1.44 m(3)/s); however, their densities were greater in riffles than other habitats during late summer low now (0.49 m(3)/s). Large fishes (> 75 mm; juvenile and adult individuals of several species) were distributed evenly among habitats across flow levels. During moderate stream flows, 89% and 95% of the individual species and size classes exhibited random use of habitats. In contrast, 35% of the individual species collected during late summer low stream flows exhibited preferences for two or three habitats, but only one species (central stoneroller Campostoma anomalum) exhibited a preference for a single habitat type (riffles). We found Little evidence for the existence of discrete habitat guilds of fish because neither individual species nor groups of species consistently associated with a single habitat type. We suggest a community-level approach based on the combined densities of small and young-of-the-year fishes, rather than an individual species or guild approach, be used to define fish associations with habitat in hydrologically variable prairie streams because discrete patterns of habitat use exist at the community level.
