TURBINE-PASSAGE MORTALITY OF JUVENILE AMERICAN SHAD AT A LOW-HEAD HYDROELECTRIC DAM

The immediate (l-h) turbine-related mortality of juvenile American sha d Alosa sapidissima at the Hadley Falls Hydroelectric Station on the C onnecticut River, Holyoke, Massachusetts, was estimated to be 0% +/- 1 4.5% (95% confidence interval) at the 35% wicket gate opening and 2.7% +/- 16.2% at the 100% opening. We used the HI-Z Turb'N tag-recapture technique, which helped minimize control mortality and maximize recapt ure rates. Earlier literature estimates of turbine-related mortality ( up to 82%) of juvenile alosids in passage through Kaplan turbines, in our view, were substantially overstated due to either low recapture ra te, high control mortality, or both.