Evaluation of an Electric Gradient to Deter Seal Predation on Salmon Caught in Gill-Net Test Fisheries

Abstract

An electric deterrent system was tested as an effective and safe method of deterring predation by Pacific harbor seals Phoca vitulina richardsi on sockeye salmon Oncorhynchus nerka and pink salmon Oncorhynchus gorbuscha caught in a Fraser River gill-net test fishery. Seals were deterred from foraging in a test fishing gill net in the Fraser River by using a pulsed, low-voltage DC electric gradient. Salmon catch per unit effort (CPUE) was significantly greater for the treated (electric) section of the gill net than for the nontreated section (marginal mean CPUE = 4.0/1,000 m · min versus 1.0/1,000 m · min), and there was no overlap in the 95% confidence intervals for the two treatments. There were no apparent injuries to any animals during the study. This previously undocumented nonlethal technology demonstrates the potential to reduce pinniped predation on salmon, with meaningful implications for fisheries management agencies that rely on gill-net test fisheries in freshwater rivers frequented by pinnipeds.