Structure and habitat associations of Devils River fish assemblages
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Spatial variation in the structure of fish assemblages at eight sites in the Devils River was examined seasonally over one year. Data were analyzed to explore natural variation at the mesohabitat scale. The local fish fauna was dominated by four minnows (Cyprinidae) and one mosquitofish (Poeciliidae). Overall assemblage composition in this study was similar to that reported previously, but three species were not reported before, and nine species previously reported were not observed during our study. Four threatened species ranked among the most abundant fishes encountered during our survey. Species diversity (H') and fish abundances showed relatively large variation between mesohabitats as well as between scions within most mesohabitats. The most species-rich mesohabitats were pools, channels, channel edges, and riffles, whereas the least species occurred in shallow, isolated pools dominated by Cyprinodon eximius. Spatiotemporal patterns of taxonomic composition were examined using principal components analysis. Seasonal shifts in assemblage structure were associated primarily with an axis that contrasted domination by Moxostoma congestum, Etheostoma grahami, Cyprinodon eximius, and Dionda diaboli versus domination by Micropterus dolomieu, Cyprinella proserpina, Cyprinella venusta, and Cichlasoma cyanoguttatum. Canonical correlation analysis was performed using assemblage data in combination with a set of environmental parameters. The first pair of canonical axes described a pattern in which fishes occupied a wide range of sites during summer, and in which during winter, most species were associated with shallow, channel mesohabitats with high dissolved oxygen. The Devils River is dominated by small fishes that have extended spawning periods and that scatter their eggs over open substrates.