Devices to aid downstream salmonid migration: Behavioral barriers

Two behavioral guidance devices, one electric screen and one sonic screen, were tested in the intake canal of the Halsou hydropower plant on the River Nive (France). The purpose of such devices is to guide the salmon smelts ( Salmo salar) towards a bypass before they pass through the turbines. This s tudy was conducted from 1995 to 1997 on a wild salmon population. The effic iency of the devices was evaluated by mark-recapture techniques and double trapping. Smelt behavior was studied by direct observations, video recordin g and radiotracking. The influence of the electric parameters of the screen , of water velocity, bypass shape and lighting of the bypass was studied. T he guidance effect of the electric screen was observed, but this effect is frequently no more than partial and is not effective. for all fish. Complem entarity between the screen and the bypass did not prove satisfactory: many smelts are guided by the screen but do not want to enter into the bypass. The maximum efficiency of the electric screen, obtained with the adjustment "130 V - 10 electric pulses" varied from 5 to 28%. Under the same experime ntal conditions, the sonic screen was found to have no effect on smelt beha vior. Lighting of the bypass entrance with a mercury vapor lamp during the night resulted in a spectacular rise in its efficiency, which can reach 70% .