An approach to identify dam passage performance standards for American Shad in four Maine rivers

Abstract Objective Diadromous fishes make crucial connections across ecosystems and require adequate habitat connectivity to complete their life history, a necessity that has become more difficult in many river systems with the construction of dams. We assessed the fish passage performance standards at Federal Energy Regulatory Commission-licensed dams required to meet two hypothetical restoration scenarios for American Shad Alosa sapidissima on the Penobscot, Kennebec, Androscoggin, and Saco rivers in Maine. Methods We modified an existing stochastic life-history-based model to estimate the impact of poor dam passage on American Shad abundance and to identify the upstream and downstream performance standards required to achieve two hypothetical restoration scenarios, which were based on achieving target abundances in historic American Shad habitat above the upstreammost dam in each river. Results A range of performance standards were required to meet both hypothetical restoration scenarios, but in general, high upstream passage (>80%) and downstream survival (>75%) was required. Conclusion Incorporation of performance standards required to meet identified management objectives into decision-making processes at hydroelectric dams may promote recovery of American Shad in Maine rivers, potentially leading to the restoration of a wide suite of ecosystem services.