Passage Method, Turbine Mortality, and Migratory Delay of Silver American Eels (Anguilla rostrata) at Five Hydroelectric Dams on the Shenandoah River

Hydroelectric dams can impact downstream migrations of silver American Eels (Anguilla rostrata) through migratory delays and turbine mortality. A radio-telemetry study on American Eel was conducted to determine impacts of five hydroelectric dams located over a 195km stretch of the Shenandoah River in Virginia and West Virginia. American Eels migrated downstream during all months of the year except July, with most individuals migrating during fall through spring and at night. The median time to pass all five dams was 18 days. Migratory delays at dams were generally less than 1 hour and nearly all individuals passed downstream within 10 d of first detection at a dam. Turbine mortality occurred at all five dams. Implementation of a seasonal nighttime turbine shutdown period reduced cumulative mortality for eels passing all five dams from 63% during regular operation to 7% during shutdowns. Nighttime shutdowns were an effective method to protect downstream migrants, and the seasonal timing for implementation for the shutdowns in the Shenandoah River encompassed 67% of the total downstream passage events in the study. Turbine mortality of downstream migrants could be reduced by extending the three month nighttime shutdown period, particularly by inclusion of spring months.