Effects of Upstream and Downstream Fish Passage On Post-Spawning Survival of American Shad

American shad historically conveyed millions of metric tons of biomass annually between rivers and the continental shelf.  Whether the net nutrient flux was toward freshwater or toward the marine environment is unclear, and depends largely on the freshwater mortality of adults.  Bioenergetics models suggest that mortality may be largely driven by delays incurred at barriers such as dams, and that delays to downstream passage coupled with mortality associated with passage at dams might have shifted the nutrient balance from the marine to the freshwater environment.  A 2-year telemetry study of American shad migration on the Connecticut River documented passage rates at 3 dams, including cumulative effects of delays on migration success and survival.  These results confirm that migratory delay in both upstream and downstream directions has important effects on migration range and survival.