Turbine Passage Survival of Late Running Adult American Shad and Its Potential Effect on Population Restoration
Paul G. Heisey, Dilip Mathur, Joanne L. Fulmer, and Enn Kotkas
Abstract.—The results of our study contradict the current view that postspawned or late running adult American shad Alosa sapidissima suffer higher turbine-related mortality, particularly at water temperatures ≥ 20.0°C, than prespawned upstream migrants. The reported difficulty in successfully tagging postspawned American shad led us to fabricate a specialized stress reduction device to minimize handling and tagging related mortality; such losses were essentially zero in our turbine passage survival experiment. Our methodology may be broadly applicable to other large-sized fish (>350 mm) or fragile species for estimating postpassage in-river survival. We successfully noted the postpassage condition and injury type of virtually all recaptured fish, removed balloon tags, and released shad with radio tags attached to estimate postpassage in-river survival. The estimated 24–48 h, post-passage, inriver survival through Kaplan and mixed-flow turbines was 88.2% (90% confidence interval [CI] = 82.5–94.0%) and 84.3% (90% CI = 77.9–90.6%), respectively. These estimates are higher than the only two literature citations (53% and 75.8%) found for healthy prespawned shad passed through similar type turbines. Mathematical projections of potential American shad population responses show that a reduction in repeat spawners of the magnitude estimated herein has a minor effect on the time to achieve a self-sustaining population in the upper Susquehanna River relative to the effects of reductions in fishway passage efficiency (<80%) at each dam and low reproductive rates (indexed by returning adults after accounting for mortality from all sources). However, it appears that the American shad population can increase downstream of the first dam on the river.