摘要：The Devils River is a spring-fed river that drains desert landscape in southern Texas and provides essential habitat for several endemic and threatened fish species. To evaluate potential effects of seasonal changes in physical habitat on fish distribution and abundance, we examined species-habitat associations in two reaches separated by 1.5 km. A distinct assemblage pattern existed in each of three mesohabitat types (pool, riffle, run). At the scale of stream reach, species distribution and abundance were associated more with factors related to geomorphology than physicochemistry. Similar mesohabitats had similar fish assemblages, irrespective of reach. Reaches and mesohabitats displayed seasonal variation in physicochemistry and fish assemblage structure. Assemblages associated with runs were least variable across seasons, however no species was strongly associated with runs. Because runs had comparatively little structural complexity and provided little protection from piscivorous smallmouth bass (Micropterus dolomieu), species probably use these areas primarily as migration corridors. Densities of two threatened species, Etheostoma grahami and Cyprinella proserpina, were negatively correlated with smallmouth bass density.
