Thumbnail Image

Estimation of Turbine passage survival of juvenile American shad, Alosa sapidissima, by different methods for practical application

The impetus for our presentation is primarily three-fold: (1) present survival estimate of juvenile American shad, Alosa sapidissima recaptured and examined after passage through a relatively large Francis turbine (hydraulic capacity > 6,000 cfs) at Conowingo Hydroelectric Station, MD and its implications on restoration of the species to the Susquehanna River, (2) compare fish survival derived from a blade-strike equation, and (3) applicability of using literature based survival estimates for multiple fish size and species without conducting a field study at a hydroelectric project. Limited published data exist on passage survival of juvenile American shad through relatively large Francis units. Survival probability of juvenile American shad (106 to 142 mm total length, average 119 mm) was estimated while passing through an aerated Francis turbine using the HI-Z Tag recapture technique. The experiment utilized 138 hatchery reared juveniles released into the turbine and 76 fish released downstream of the turbine discharge as controls. The turbine passage survival was estimated at 89.9% with 90% (α = 0.10) confidence intervals of ± 5.5%. This estimated survival is within the range (83.5-94.7%) of empirically determined (HI-Z Tag) estimates for similar sized Francis units (runner diameter >110 in, buckets 13-17). While blade-strike derived survival estimates generally show a close correspondence, particularly for salmonids, with empirically determined estimates for Kaplan type turbines, it appears that some differences between the two estimates may occur for clupeid passage through Francis turbines. For the tested Francis turbine at Conowingo, the survival estimate from the blade-strike equation was approximately 5% higher than the empirically determined estimate of 89.9%. Blade-strike equation generated survival estimates maybe higher than empirical estimates because they do not account for potentially higher mortality due to the sensitivity of juvenile shad. Across all Francis type turbines, EPRI field estimated survival of small sized fish was 92%, relatively similar to that estimated herein. While the application of published and/or mathematically derived survival estimates to non-studied sites is encouraged and is useful, caution should be exercised to include only field studies with acceptable control mortality (handling, tagging, and recapture). We suggest control mortality be ~20% for clupeids and ~10% for other species. The life stage and sensitivity of a given species also needs to be considered when using mathematically derived estimates.