Fish assemblage changes in relation to watershed landuse disturbance

Abstract

Fish assemblage collections were assessed in sub-watersheds containing various land use types to relate overall biotic condition to patterns of watershed disturbance and to the influence of introduced fishes. Four hundred historical and contemporary fish collections were analyzed in conjunction with land use and land cover data among 200, first- through fourth-order sub-watersheds across Pennsylvania. A high degree of collinearity among several land use types and the presence of non-indigenous fishes was determined, indicating multiple anthropogenic influences. Significant relationships were found between various land use types and the Jaccard coefficient of similarity, the primary index used to evaluate changes between fish collections, across all major drainages. In general, the Jaccard coefficient of similarity increased to a value of one as the percentage of forested land increased, while the Jaccard coefficient of similarity decreased as percentages of agricultural and urban land increased. Sub- watersheds that showed declines in species richness had significantly higher percentages of agricultural and developed land, while those sub-watersheds with higher amounts of forested land appeared relatively stable. Seventy-percent of those species that experienced declines were either insectivores or benthic insectivores. The largest increases among the fish guilds occurred within the insectivore-piscivore group. We conclude that land use influences at the sub-watershed scale and the introduction of non-indigenous fishes have had a significant influence on fish community composition.