Integrating biological realism into habitat restoration and conservation strategies for small streams

Successful habitat conservation or restoration must be biologically based, which requires an understanding of habitat variables most influencing fish; the relative influence of each habitat variable and the spatial scale over which each operates. Determining necessary habitat conditions requires examination from several perspectives, including observation of individual fish during all seasons and population analysis over a range of spatial scales. There is a definite spatial hierarchy of influences that must be addressed to separate those habitat conditions responsible for presence and abundance from those habitat conditions responsible for within-stream distribution. A case study of habitat factors influencing smallmouth bass (Micropterus dolomieu) in Missouri streams indicates that examination at the smallest spatial scales allows one to determine the influence of habitat conditions (depths, velocities, cover factors) relating mainly to the fish's distribution in a stream reach. Evaluation of populations at the stream-system level allows an understanding of how individual fish preferences relate to amounts of habitat as determined by geomorphic and fluvial dynamic forces and how this influences standing stocks throughout a stream system. Evaluation at the ecoregion level shows the overriding influence of physiographic variables on both the presence and abundance of fish across stream systems, as well as the importance of land use.