Evaluating technical improvements for downstream migrating diadromous fish at a hydroelectric plant

Technicalimprovements to ameliorate downstream passage for diadromousfish have rarely been evaluated in regulated rivers in northern Europe. The current study evaluated rehabilitative measures for downstreammigrating Atlantic salmon, brown trout and European eel at ahydroelectricplant in southern Sweden. Smolts (N = 66), kelts (N = 20) and silver eels (N = 55) were caught, radio-tagged and tracked whilst passing the facilities in spring (salmonids) and fall (eels) of 2007. A surface gate in combination with a 90 mm-spaced turbine intake rack had afish guidance efficiency ranging from no effect for eels and trout smolts to 50% for trout kelts. A siphon discharging water from the bottom of the same 90 mm rack did not bypass any tagged fish, and only a few untagged eels. The poor function of the measures was attributed to the failure of the rack to stop smolts and eels from entering the turbines. The kelts, on the other hand, could not pass through the rack, and instead took a long time to locate the surface bypass entrance. The conditions for downstreammigratingfish have improved at the hydroelectricplant, but the total losses remain quite high for the studied groups (10–67%), and there is a need for a new rehabilitative measure that effectively allows all fish to bypass the turbines.