| Scope and method of study. Our study was initiated to evaluate potential effects of rainbow trout Oncorhynchus mykiss introduction on native fishes in Brush Creek, a small Ozark stream, with an emphasis on effects of trout introduction on smallmouth bass Micropterus dolomieu populations, which support an active recreational fishery. We sampled native fishes using electrofishing methods from February 2000 to October 2002, and experimentally stocked rainbow trout into the stream from November 2000 to March 2001 and November 2001 to March 2002. We used abundance and mark-recapture data to evaluate performance of hatchery trout, evaluate native fish assemblage structure before and after rainbow trout introduction, and evaluate population characteristics of smallmouth bass and shadow bass Ambloplites ariommus after rainbow trout introduction.; Findings and conclusions. Apparent survival of stocked rainbow trout was negligible over the course of our study, and is likely due to an inability to survive summer temperatures. Stocked trout generally lost weight and lipid content after stocking, and movement of stocked rainbow trout within the stream increased as stream discharge increased. Native fish assemblage structure differed significantly among mesohabitat types, but we did not detect an effect of season. We did not detect any changes in assemblage structure in glide or riffle habitats among years. Species relative abundance in pool habitats before trout introduction differed from assemblage structure in both the first and second year of stocking. Declines in seven species, including smallmouth bass, contributed to assemblage dissimilarity in pool habitats between pre-stocking conditions and the second year of stocking. Our results indicate that stocking rainbow trout may cause local disruption in assemblage structure in pool habitats. Abundance of smallmouth and shadow bass was correlated negatively with high densities of rainbow trout at the stocking site, but we did not detect similar relationships at other pools. Presence of rainbow trout in Brush Creek did not appear to influence movement patterns of smallmouth or shadow bass, and we documented recruitment by both species during our study, indicating that rainbow trout introduction did not inhibit spawning. We did not detect differences in smallmouth bass relative weight among pre-stocking, the first year of stocking, and the second year of stocking. |
