Spatial and Temporal Variation in Fish Assemblage Structure in Village Creek, Hardin County, Texas

-Fish assemblages were sampled seasonally at Village Creek, a blackwater tributary of the Neches River in Hardin County, Texas. Forty-four fish species were captured from aquatic mesohabitats that included backwater pools, deep channel pools, sloping sandbanks, sandy riffles, and shallow channel margins. Associations between fish assemblage structure and mesohabitats were strong, yet also affected by seasons and discharge fluctuations. Principal components analysis (PCA based on faunal composition at sample sites across four seasons) was performed on a dataset containing the 10 species with highest site occurrence. The first PC axis identified an assemblage gradient that contrasted deep pool and backwater habitats versus shallow riffle and sandbank habitats, and the second PC axis identified a gradient between backwaters versus channel habitats. Relationships between assemblage composition and mesohabitat attributes were examined using canonical correlation analysis (CCA) based on the 10 species with the highest site occurrences and six physical parameters at each site. The first canonical correlation gradient modeled 75% of the total variation and was primarily a water temperature gradient secondarily influenced by dissolved oxygen. Seasonal variation in species relative abundances and length frequency distributions were examined according to mesohabitats. Seven fishes, including the dominant species, Cyprinella venusta, revealed size distribution patterns consistent with protracted spawning seasons. During winter and spring, stream disharge was high and many species increased the range of habitats occupied. Juveniles of many species tended to occupy shallower mesohabitats than adults, with backwaters being particularly important for several channel pool-dwelling species. Seasonal variation in fish relative abundances and mesohabitat associations poses problems for indices of biotic integrity, however, following Karr's index, the Village Creek fish community is classified as excellent to good. This study examines spatiotemporal patterns of fish assemblages in Village Creek, a relatively pristine stream in the Big Thicket region of east Texas, and contributes species assemblage and population structure data useful for ecological assessment. Patterns in community structure and the perceived degree of assemblage stability are influenced by the spatial scale of observations. Matthews et al. (1994) contended that stream investigators should select spatial scales that reflect biologically meaningful units, in contrast to a priori selection of linear distances for study. In a large stream, neither the watershed nor the entire stream