Generalizing Trends in Upstream American Eel Movements at Four East Coast Hydropower Projects

Dams impede the upstream migration of juvenile American eel Anguilla rostrata, limiting their access to freshwater habitat and potentially contributing to population declines across their range. The implementation of fishways at large hydropower dams help restore access to upstream habitat, and represents a long-term dataset of American eel captures. We analyzed the relationships between eel captures and select environmental variables (river discharge, water temperature, and lunar illumination) at four hydropower projects on east coast rivers with a comparable decade of data and sampling techniques; Roanoke Rapids Dam on the Roanoke River in North Carolina, Conowingo Dam, on the Susquehanna River in Maryland, Holyoke Dam, on the Connecticut River in Massachusetts, and the Moses-Saunders Dam on St. Lawrence River in New York and Canada. The number of eels captured varied among projects, from year to year, and seasonally. American Eel are opportunistic in their upstream movements, with peak movement events associated with high flows, increased water temperature, and low lunar illumination. Our results suggest that systems altered by hydropower dams offer unique challenges to American eel migrants, and that a multitude of factors play a role in the timing of upstream movements.