Research Document 2017/074

Summary of Fraser River Sockeye Salmon (Oncorhynchus nerka) ecology to inform pathogen transfer risk assessments in the Discovery Islands, BC

By Grant, S.C.H., Holt, C., Wade, J., Mimeault, C., Burgetz, I. J., Johnson, S. and Trudel, M.

Abstract

This paper describes the biology and ecology of the Fraser River Sockeye Salmon (Oncorhynchus nerka) relevant to assessments of the risks to wild salmon due to pathogen transfer from salmon farms located in the Discovery Islands area of British Columbia. The spatial and temporal presence of the Fraser River Sockeye Salmon in the Discovery Islands area for out-migrating juveniles is based on data from the timing when they exit the Fraser River from mid-April to late-May, the estimated 20 to 59 days spent migrating through the Strait of Georgia, and catch data from the Discovery Islands. Juvenile lake-type Fraser River Sockeye Salmon tend to migrate through the Discovery Islands from mid-May to mid-July, with peak catches in early-to-mid June. The residence time for juvenile Fraser River Sockeye Salmon in the Discovery Islands is estimated to range between 5 to 14 days. Adult Sockeye Salmon return to the Fraser River via either the northern or southern route, with 52% diverting through Johnstone Strait in recent years. In-season test fishery data shows that adult Sockeye Salmon are present in the Discovery Islands from at least mid-July to the beginning of September. Back calculations based on swimming speed and arrival time at Mission estimate that adult Sockeye Salmon could be in the Discovery Islands from late-June to early-October assuming no residence time in the Strait of Georgia. Based on these same estimates, Fraser River Sockeye Salmon could spend approximately three days swimming through the Discovery Islands.

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