A RELIABLE TAG RECAPTURE TECHNIQUE FOR ESTIMATING TURBINE PASSAGE SURVIVAL - APPLICATION TO YOUNG-OF-THE-YEAR AMERICAN SHAD (ALOSA-SAPIDISSIMA)

A new technique (HI-Z Turb'N Tag, U.S. Patent No. 4,970,988) for estimating turbine passage survival was applied to juvenile American shad (Alosa sapidissima) under three operating conditions at a hydroelectric project. Fish are fitted externally with the Turb'N tag and introduced into turbine penstocks. The Turb'N Tag inflates after turbine passage and buoys fish to the surface for recapture and examination; after removal of tags, fish are held to assess long-term effects. Almost all (96%) test (299) and control (300) fish were recovered; average recovery time was less than 9 min. The overall short-term (1 h) survival of test fish, adjusted for control, was 97%; 24-and 48-h survivals were 98 and 94%, respectively. The 48-h survival of test fish was 98-100% for mixed flow and Kaplan turbines and 66.8% for the mixed flow unit in the vented mode. Acute control mortality was negligible (<5%). Our technique offers several significant advantages over traditional net recapture methods: applicable to wide range of species and size; allows predetermination of statistically valid sample size, level of significance, and power of the test to determine need for mitigation measures; and estimation of cumulative effects of multiple turbine exposure.