Environmental Variables Associated with American Eel (Anguilla rostrata) Downstream Migrations in the Shenandoah River

The timing of downstream migrations of silver American Eel (Anguilla rostrata) have been associated with environmental variables. To determine if environmental variables were associated with dam passage events on the Shenandoah River, a total of 96 American Eels were radio-tagged and monitored while migrating downstream past five hydroelectric dams. Over the three-year study, 292 dam passage events were recorded. A logistic regression model was developed to determine which environmental variables were associated with dam passage events. The model was able to properly assign 85% of passage and non-passage days during the study. The model also determined that passage was more likely to occur during high river discharge and when the proportion of current day’s discharge was higher than the previous 5-day average of discharge (i.e. increase in discharge). Passage occurred most frequently when water temperatures were between 5 and 12^oC. Similar to other rivers where out-migration of American Eel has been studied, river discharge and water temperature were the environmental variables most closely associated with downstream migration events of American Eels in the Shenandoah River.