Catch-related fish injury and catch efficiency of stow-net-based fish recovery installations for fish-monitoring at hydropower plants

Hydropower-related damage to fish remains a great challenge, making objective monitoring of turbine-related fish injury a necessity. The catch of fish at turbine outlets is currently realised by net fishing, but potential catch-related injuries are largely unknown. Catch efficiency and fish-friendliness in relation to fish handling, exposure time, floating debris and fish biomass of four fish recovery installations were assessed using seven species. Highly species-specific lethal and sublethal effects were observed. Exposure time had the strongest effects on catch-related damage, being up to 150-fold increase after 12 hr compared to 1 hr. Up to 84% mortality occurred in the most sensitive species Thymallus thymallus L. Besides exposure time, higher current speed and biomass within the net resulted in greater fish damage. To minimise catch-related effects, keeping emptying periods <1–2 hr and considering the effects of current speed, fish and debris biomass are crucial to increase data comparability among studies.