Thurmond Reservoir Fishes

Assessment of Population-Level Threat from Entrainment at Russell Dam on Thurmond Reservoir Fishes

Karen V. Root and Scott Ferson

funded by Army Corp of Engineers and Electric Power Research Institute

Summary

        This project evaluates entrainment impacts on five fish species in the J. Strom Thurmond Reservoir (JSTR) on the border between South Carolina and Georgia.  Two species, threadfin shad and blueback herring, are both short-lived and their growth is strongly regulated by density.  Each has a robust reproductive potential and appear to rebound quickly from impacts.  The third and fourth fishes, striped bass and hybrid bass, are long-lived species.  They do not reproduce in the reservoir and instead are annually stocked.  Little is known about the black crappie, the fifth species, in this reservoir.

        To predict the long-term population-level consequences of the mortality induced by the pump storage operation at the Richard B. Russell Dam, we developed a stochastic demographic model that captures the essential population dynamics of the species.  Using data supplied by U.S. Army Corps of Engineers Waterways Experiment Station, the Georgia Cooperative Fisheries and Wildlife Research Unit, and Aquacoustics, Inc., we parameterized baseline models for the five fish species.  These models were then modified to reflect the impacts of entrainment and impingement predicted from pumpback operations.  Specifically, the modified models incorporated two different entrainment scenarios: Scenario A models are based on entrainment data collected from August 31, 1993 to October 31, 1996.  They depict the long-term effects of the mean water year entrainment using the mean entrainment rate as well as higher rates specified by both the Army Corps and state fisheries groups.  For each fish species, a single Scenario B model is presented, representing the effects of mean water year entrainment based on a 12-month expansion of Phase III entrainment data.  With these baseline and entrainment models, we used Monte Carlo simulation to make separate probabilistic forecasts for the risks of population decline, assuming that these conditions persist 50 years into the future.

        Simulation outputs suggest that entrainment affects the five species to varying degrees.  For threadfin shad the maximum increase in risk is 5% above background. Entrainment increases the risk of decline for blueback herring a maximum of 33%.  For the hybrid bass and striped bass and increase in stocking rates of 20% and 28% respectively, essentially mitigate any increase in decline due to entrainment.  Therefore, the model provides guidelines on the level of risk for various degrees of entrainment and potential management actions to mitigate the possible negative effects.

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