An American Eel Egg-Per-Recruit Model To Evaluate The Effects Of Fish Passage: A Case Study On The Susquehanna River

Dams and their associated effects on American eel (Anguilla rostrata) migration and mortality have been implicated as a significant factor in the current depleted status of the species along the Atlantic coast of North America.  Female American eels that mature in areas below dams may be smaller and have lower fecundity compared to their counterparts that mature in more upstream reaches of a river system.  However, increased mortality associated with downstream migration through hydroelectric turbines upon maturity may negate any reproductive advantage afforded to American eels occupying areas upstream of hydroelectric facilities.  We developed an American eel egg-per-recruit (EPR) model and applied it to the Susquehanna River to investigate how various levels of upstream and downstream passage may affect the reproductive output from a river with hydroelectric facilities.   Results from our American eel EPR model applied to the Susquehanna River suggest that if American eels are going to be passed upstream of the first dam on the river, cumulative downstream passage survival must be ≥33% otherwise upstream passage is likely to result in an EPR deficit compared to not passing American eels upstream and allowing them to mature below dams.   Cumulative downstream passage survival would need to increase substantially above these levels to have a high probability of making any restoration gains in terms of EPR.  Our EPR modeling framework can be adapted to other systems and used to make recommendations for necessary upstream and downstream passage for conservation of American eels in rivers impacted by hydroelectric facilities.