Evaluation of an Electrical Gradient to Deter Seal Predation on Salmon Caught in Gillnet Test Fisheries
Keith W. Forrest1; Jim D. Cave1; Catherine G.J. Michielsens1; Martin Haulena2; David V. Smith3
An electrical deterrent system was tested for minimum effective dosage required to deter captive Pacific harbour seals (Phoca vitulina richardsi), from entering a section of pool at the Vancouver Aquarium. Based on this information, a system was installed and tested as an effective and safe method to deter harbour seals and their predation on sockeye (Oncorhynchus nerka), and pink salmon (Oncorhynchus gorbuscha), caught in Fraser River gillnet test fisheries. Seals were deterred from foraging from a test fishing gillnet in the Fraser River by using a pulsed, low-voltage DC electrical gradient. Salmon catch-per-unit-effort (CPUE) was significantly greater for the treated (electric) section of a gillnet compared to the non-treated (non-electric) section, (electrical section: marginal mean CPUE = 4.0·(103m·min-1)-1 versus non-electrical section: marginal mean CPUE = 1.0·(103m·min-1)-1, and there was no overlap between the 95% confidence intervals for the two treatments. There were no apparent injuries to any animals throughout the study. This previously undocumented non-lethal technology demonstrates the potential to reduce pinniped predation on salmon, with meaningful implications for fisheries management agencies that rely on gillnet test fisheries in freshwater rivers frequented by pinnipeds.
We are grateful for the collaborative efforts of numerous people from various agencies. We especially thank L. Carstenson, L. Harlan, K. Smith and C. Burger from Smith-Root Inc., B. Sheehan from the Vancouver Aquarium, C. Beggs, B. Munro and staff from the Puntledge River Hatchery, M. Lapointe from the Pacific Salmon Commission and M. Joyce and A. Greene from Fisheries and Oceans Canada. We thank Fisheries and Oceans Canada and Vancouver Aquarium Animal Care Committees for their contributions and approvals of animal use protocols. Finally, we thank four anonymous reviewers for their invaluable comments and improvements to the manuscript. Funding was provided by the Pacific Salmon Commission, Southern Restoration and Endowment Fund.