An index of biotic integrity based on fish assemblages for subtropical streams in southern Brazil

Several methods for calculating indices of biological integrity (IBIs) have been developed for different ecogeographic regions of the world. All of them calculate IBI scores by comparing against reference sites or historical data on fish assemblage composition. Because of intensive agriculture and urbanization in our study area, we located no reference sites, and historical information about fish assemblage composition did not exist. Instead, we developed hypothetical reference scores based on seasonal electrofishing surveys at six study sites in adjacent but geomorphologically different watersheds. Our IBI included 10 metrics that varied with degree of degradation. We found that Shannon - Wiener indices varied significantly between seasons, indicating significant changes in species composition. Therefore, we calculated seasonal IBI scores also, but these did not significantly differ from each stream's general IBI score, which was calculated on the basis of four samples per site. General stream IBI scores reflected differing levels of anthropogenic disturbance.