Strobe lights as a fish deterrent

Underwater strobe lights were evaluated as a deterrent for presence of rainbow trout, cutthroat trout and Dolly Varden at the John Hart Reservoir penstock intakes during early summer of 2007. Five trials were conducted using underwater strobes cycled on/off at a frequency of 360 times/minute and a light intensity of 450 candela. Operation of strobes was highly effective in deterring fish (80% average reduction) at night, in both the short term and longer term tests. Mixed results were observed during daylight hours; however, the shorter duration tests did not provide evidence of an effect of strobe operation on averting fish from the critical zone, probably as a result of the high background ambient light. Fish aversion response to strobe light operation did not appear to vary across different size classes of fish.