Mortality of Fish Passing through Tidal, Low-head Hydropower Turbines and Possible Mitigation Strategies

Lowhead hydroelectric turbines driven by the ocean tides are now in operation at sites in Canada, France, the Soviet Union, and China. These electrical generation facilities are of the gated barrage design. Exploitation of power present in ocean tides will invariably result in conflicts with fisheries resources. Studies conducted on a 7.6-m STRAFLO turbine at the Annapolis Tidal Generating Station in Nova Scotia indicated that mortality was observed for all sizes of fish. Smaller fish have a lower strike rate but greater mortality caused by pressure, shear, and cavitation. For adult American shad tested using sonic tags, mean mortality was 46.3% %. Juvenile alosids monitored during natural downstream passage showed an average mortality of 54.4%. Mitigation studies are in progress at Annapolis Royal. Some form of bypass mechanism coupled with mechanical or biological behavior modifiers may have the greatest potential in reducing mortality. Although still on the drawing board, alternative tidal power designs look promising for reducing impacts on fish stocks.