Quantitative Decision-Support Tools for Dam Passage Performance Standards in the Northeast US

Poor passage and delay at dams can affect population structure and abundance of anadromous fishes, and has contributed to range-wide declines in Alosine stocks. Recovery actions commonly involve increasing passage performance and reducing delay at dams during upstream and downstream migration; however, quantitative approaches incorporating uncertainty in life-history and migration characteristics is often absent when setting passage performance standards. We describe a stochastic, life history-based simulation model for Alosines that can be used to estimate effects of dam passage and migratory delay on vital rates and demographic structuring of populations through space and time to support quantitative-based decisions. We examine projected American Shad (Alosa sapidissima) population responses to changes in dam passage performance in the Penobscot River, Maine in relation to recovery objectives. Recovery was achieved under high rates (90%) of upstream and downstream passage. Demographic tradeoffs, including reduced spawner abundance, resulted when downstream passage was less than 100% even at high rates of upstream passage. These results underscore the importance of providing adequate downstream passage for adult and juvenile migrants in addition to upstream passage for adults. Tradeoffs in recovery metrics resulting from interactive effects of upstream and downstream passage warrant consideration during decision-making processes at regulated hydropower dams.