Mortality of Juvenile American Shad and Striped Bass Passed through Ossberger Crossflow Turbines at a Smallscale Hydroeljktric Site

-A full-recovery technique was used in mortality experiments conducted with juveniles of American shad Alosa sapidissima and striped bass Morone saxatilis passed through Ossberger crossflow turbines to obtain antecedent information about their fish passage characteristics. Immediate turbine-induced mortality was 66% for 85-mm-long (total length) American shad. Turbineinduced mortality of striped bass was significantly related to the total length of the fish and ranged from l6Y0 for 67-83-mm-long fish to 39% for 136-mm-long fish immediately after passage; after 24 h, turbine-induced mortalities of these two size-groups were 61 and 72%, respectively. The mortality of striped bass was not affected by power output (320-600 kW) of the turbine or by turbine size (650 versus 850 kW). Because of high mortality of control fish, the full-recovery technique was not fully adequate for obtaining reliable delayed-mortality estimates for these fragile fish species. Recent concerted efforts to rehabilitate runs of anadromous fishes in rivers of eastern North America have, by chance, coincided with a resurgent interest in small-scale hydropower development in this region (Gloss and Wahl 1983). Fish passage facilities at many hydroelectric sites are allowing movement of anadromous fish migrants to upper-river spawning areas, but few sites have downstream bypass capabilities to protect migrating juveniles, subadults, and postspawn adults from entrainment. Total mortality probable for fish passed through turbines, particularly juvenile migrants, has consequently become an important consideration in regional fisheries management planning and environmental impact assessment. Populations of American shad Alosa sapidissima are being successfully restored with increasing frequency in U.S. east-coast river systems where hydropower obstacles must be negotiated (Howey 198 1; Moffitt et al. 1982). Migrations of subadults of striped bass Morone saxatilis into both natal and nonnatal rivers (and through fishways) have Present address: Department of Natural Resources, Bureau of Research, Post Office Box 125, Brule, Wisconsin 54820, USA. Present address: Wyoming Water Research Center, / ,i Post Office Box 3067, University Station, University of Wyoming, Laramie, Wyoming 8207 1, USA. The New York Cooperative Fishery Research Unit is jointly sponsored by the New York State Department of Environmental Conservation, Cornell University, the U.S. Fish and Wildlife Service, and the Wildlife Management Institute. -.. been fiequently documented (Raney et al. 1954; Nicholas and Miller 1967; Kynard and Warner 1 987). Whereas reasonable mortality estimates are available for several salmonid species passed through any of various turbine types (Turbak et al. 1981; Gloss and Wahl 1983), such data are scarce for nonsalmonids, as is information on the suitability of associated-mortality testing procedures. Taylor and Kynard (1985) estimated immediate turbine-induced mortality of juvenile American shad passed through a 17-MW Kaplan turbine at three levels of power generation. Stokesbury and Dadswell (199 1) estimated the immediate mortality of several clupeid species passing through a STRAFLO turbine at a low-head tidalpower dam. However, in neither case were shad held for determination of delayed mortality; hence, it is likely that these results underestimate total turbine-induced mortality. No published documentation exists for turbine-induced mortality of subadult striped bass. Estimates of mortality resulting from passage of fish through hydraulic turbines have been based on various recovery techniques. These have included using returns of adult fish that were marked as juveniles before turbine passage and the partialrecovery techniques of Schoeneman et al. (1 96 l), as well as full-recovery methods in which all fish are recovered in nets immediately after they pass through turbines (Cramer and Donaldson 1964). If returns of adult fish are monitored, several years are required to evaluate results, and there are inherent, potentially severe, problems related to sta-