The Influence of Habitat Structure and Environmental Variability on Habitat Use by Fish in the Vermillion River, South Dakota

This study was initiated to 1) examine the associations of fish with meso- and microhabitat in the Vermillion River, South Dakota, and 2) quantify fish communities in Vermillion River tributaries. Fish were collected from four mesohabitats (riffles, pools, runs, stream areas with woody debris) in natural and channelized regions of the river during July and August 1991, and May 1992 with an electric seine. Fish collected were categorized as small (\u3c76 mm) or large(\u3e 75 mm). Density (number/100 m2) and biomass (grams/100 m2) were calculated in each habitat for the entire community (all species combined), and density was also determined for individual species in each habitat. Densities of small fish were highest in riffles and woody habitats, but small fish were most concentrated in riffles during low flow conditions (August) when younq-of -the- year fish were recruited to the community. Patterns of habitat use by large fish were unaffected by flow and densities of large fish were evenly distributed among woody habitats, riffles, and pools. Densities of both small and larqe fish were linearly dependent on microhabitat conditions (depth, velocity, substrate) within individual mesohabitats. Biomass patterns closely resembled patterns of habitat use by large fish. Mesohabitats in natural and channelized areas of the river supported similar fish density and biomass, but channelized runs had higher densities than natural runs, and natural pools supported higher fish biomass than channelized pools. Most species were generalized in their habitat use patterns during moderate flow conditions (May and July), but several species (i.e., sand shiner Notropis stramineus, central stoneroller campostoma anomalum, red shiner Cyprinella lutrensis, channel catfish Ictalurus punctatus) constricted their habitat use to one or two habitats during low flow conditions. Tributary fish communities were dominated by fathead minnows Pimephales promelas, brassy minnows Hvboqnathus hankinsoni, oranqespotted sunfish Lepomis humilis, and black bullheads Ameiurus melas, but seasonal changes in species composition and abundance were evident and may have been induced through predator-prey interactions. Topeka shiners Notropis tristis, a candidate for federal threatened and endangered status, was locally abundant in some tributary pools. The results of this study emphasize that habitat complexity strongly influences fish distribution and abundance in the Vermillion River, but season, temporal changes in stream flow, and juvenile recruitment affect habitat utilization patterns. Protection of complex habitats and tributary streams is essential for the wellbeing of Vermillion River fishery resource