An Egg-Per-Recruit Model to Evaluate the Effects of Upstream Transport and Downstream Passage Mortality of American Eel in the Susquehanna River

Abstract

Dams and their associated effects on the migration and mortality of the American Eel Anguilla rostrata 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 than individuals that mature in more upstream reaches of a river system. However, increased mortality associated with downstream migration through hydroelectric turbines 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 to investigate how various levels of upstream and downstream passage may affect the reproductive output from rivers with hydroelectric facilities. We applied our model to the Susquehanna River and found that if American Eels are passed upstream of multiple dams on the river, cumulative downstream passage survival must be ≥33% for the upstream passage to be beneficial; otherwise, upstream passage is likely to result in an EPR deficit when compared with no passage. Cumulative downstream passage survival would need to increase substantially above 33% to have a high probability of making any 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 the conservation of American Eels in rivers impacted by hydroelectric facilities.

Received December 24, 2013; accepted March 28, 2014

ACKNOWLEDGMENTS

We would like to thank Alex Hoar, David Sutherland, Steve Minkkinen (U.S. Fish and Wildlife Service), Andrew Titler (U.S. Department of the Interior), and Sean McDermott (National Marine Fisheries Service) for the impetus to develop this model and Keith Whiteford (Maryland Department of Natural Resources) for providing data on American Eel sex ratio in the Susquehanna River. We would also like to thank David Smith (U.S. Geological Survey), Joe Hightower (U.S. Geological Survey), and three anonymous reviewers for their helpful comments on an earlier version of the model and manuscript. The findings and conclusions in this article are those of the authors and do not necessarily represent the views of the U.S. Fish and Wildlife Service.