Relationship between river surface level and fish assemblage in the Ocklawaha River, Florida

Understanding the relationship between river flows and levels and fish communities is important to setting minimum flow and level regulations designed to prevent ecological harm. We reviewed a long-term Florida Fish and Wildlife Conservation Commission data set from the Ocklawaha River, Florida, to evaluate trends in fish abundance and fish communities relative to historical river levels. Fish data were collected using electrofishing at the Ocklawaha River, Florida, during 1983–1994. Electrofishing data were used to estimate catch per minute and biomass per minute of selected species, fish diversity, richness and evenness. Catch rate variables were compared among years and significant differences in abundance and community indices were related to historical water levels using multiple regression models. Results indicated that differences in abundance and community indices among years were more common at the site with increased river level variability. Regression models indicated that fish abundance and species richness were positively related to river levels, and species diversity was negatively related to variability in river level during the two years prior to sampling. Spotted sunfish Lepomis punctatus exhibited the most variability in species-specific catch per effort and spotted sunfish abundance was positively related to river levels. Low river levels negatively influenced fish abundance and fish communities, and minimum flows in Florida should manage for the periodicity of low flow events to prevent sequential years of adverse effects on fish populations. Copyright © 2005 John Wiley & Sons, Ltd.