Effects of Spatial and Temporal Variability of Shoal Habitat on Stream Fish Assemblages in Chattahoochee Tributaries, Alabama

Abstract

Abiotic factors associated with habitat quality may have profound effects on fish assemblage structure. Variability in physical habitat parameters as well as temporal fluctuation in characteristics such as water depth and flow often dictate species persistance in stream mesohabitats. Few studies have extended the study of abiotic factors to habitat patch size or spatial relationship, however. Linkages between fish assemblages and the temporal and spatial variation of shoal habitats in three streams (Little Uchee, Wacoochee, and Halawakee) of the Chattahoochee River basin in east

Alabama were investigated. Richness, composition, and density of fishes were quantified to determine their relationship with habitat type, size, physical parameters and spatial distribution. Tributaries of the Chattahoochee River in Alabama were found to have unique shoal fish assemblages. Comparison of adjacent pool/shoal fish assemblages revealed higher richness in shoals than pools and also showed low similarity between the two habitats, demonstrating the uniqueness of these habitat types. Many fishes were habitat specialists, species found in shoal samples > 75% of species occurrence included: shoal bass, Micropterus cataractae; bluefin stoneroller, Campostoma pauciradii; blackbanded darter, Percina nigrofasciata. These species showed variability with size, quality, and position of shoal habitats. Drought conditions were evident in 2006, causing a significant change in the size of shoal habitat patches sampled in both 2005 and 2006. Richness and density of fishes increased in 2006 across all shoals of all sizes. Fish assemblages varied annually and were best predicted by shoal volume, substrate composition, and CV of depth and flow. Spatial distribution of shoals in watersheds predicted composition and density of fishes. Results from this study suggest that shoal size may be a better predictor of species richness than spatial position. Shoals acted as islands providing structure and resources for stream fishes. Stream fish from all families were present in shoal habitats. For this reason, reaches of streams that contain shoal habitat should be the focus of managers charged with conserving stream fishes.