Evaluating Effects of Pump-storage Water Withdrawals Using an Individual-based Metapopulation Model of a Benthic Fish Species

As demand on freshwater resources increases, managers are increasingly tasked with identifying water withdrawal, storage, and management strategies that minimize impacts on aquatic species. Identifying critical features of the flow regime that sustain particular ecological processes can be difficult due to site and speciesspecific characteristics. Our goal was to simulate tradeoffs between differing water withdrawal strategies for an off-channel, pump-storage reservoir and the ecologicalflow requirements of flow-dependent taxa. Using a case study of a 30-km reach of the Middle Oconee River near Athens, we evaluated multiple demographic models for selecting a flow management strategy for maintaining abundance of a native fish species, the Turquoise darter (Etheostoma inscriptum). We developed and applied an individual-based metapopulation model to assess the relative influence of five alternative flow management strategies. Each strategy differed based on the magnitude and timing of water withdrawals. We explicitly incorporated uncertainty in the analysis by applying two alternative flow-survival relationships and stochastic variation in recruitment and survival. The influence of each flow management strategy on fish populations was evaluated based on the mean and standard deviation of darter abundance following a 20-year period of simulated water withdrawals. This evaluation demonstrates the utility of individualbased population models to inform a common freshwater flow management problem, balancing economic and ecological flow requirements.