Composition, structure, and habitat associations of fish assemblages of the Dolan Falls Preserve

Abstract

The composition and stability of fish assemblages at eight stations of the Devil's River at the Texas Nature Conservancy Preserve were quantified in four surveys over a one-year period. Data were analyzed to explore natural variation at the mesohabitat scale in the system. The local fish fauna was dominated by four minnows (Cyprinidae) and one mosquito fish (Poecilidae). Species composition in this study was similar to that reported previously. Three species were found that have not been reported before, and nine species previously reported were not observed during this study. Four species listed as threatened by Texas Parks and Wildlife Department were among the most abundant species during this survey. Species diversity (H') and fish abundances showed relatively large variation between mesohabitats and between seasons within mesohabitats. The most diverse mesohabitats were pool, channel, channel edge, and riffle, whereas the least diverse were the shallow isolated pools dominated by Cyprinodon eximius. Spatiotemporal patterns of taxonomic composition were examined using principal component analysis (PCA). Seasonal shifts in assemblage structure were primarily with respect to an axis contrasting domination by Moxostoma congestum, Etheostoma grahami, Cyprinodon eximius, and Dionda diaboli versus domination by Micropterus dolomieu, Cyprinalla Proserpina, Cyprinella venusta, and Cichlasoma cyanoguttatum. In addition to the PCA, canonical correspondence analysis (CANCOR) was performed using assemblage composition in combination with a set of environmental parameters. The first three axes of the CANCOR, for both community variables and environmental variables, accounted for 90.7% of the total variance. The first pair of canonical axes described a pattern in which seasonal variation in assemblages was associated with the convergence of many species on a subset of mesohabitats during colder periods. Diverse reproductive strategies are represented in the fish community of the Devil's River, but small opportunistic species with extended spawning periods dominated.