Exposure Time of Wild, Juvenile Sockeye Salmon to Open‐Net‐Pen Atlantic Salmon Farms in British Columbia, Canada

Abstract

AbstractThe role that open‐net‐pen farms for Atlantic Salmon Salmo salar play in the global decline of stocks of wild salmonids (Salmo spp. and Oncorhynchus spp.) is contentious; Canada’s west coast is no exception. We identified the proportion of acoustic‐tagged juvenile Sockeye Salmon Oncorhynchus nerka migrating through the main migration routes of the Discovery Islands region of British Columbia and measured both residence time in a major waterway hosting several Atlantic Salmon farms and exposure times to individual farms. One‐third of tagged fish migrated through this channel, with median residence times of 32.6 h in 2017 and 46.0 h in 2018. The median time near individual farms was 4.4 min in 2017 when farms were fallow and 10.9 min in 2018 when farms were stocked. The increase in 2018 was probably not caused by farm activity because the proportion of total time spent in the channel was the same across years. Sockeye Salmon used all major migration pathways, but the lack of farms and rapid migration speeds in the westernmost passage offers the lowest potential exposure to fish farms. These are the first individual‐level data available to inform assessments of the transmission risk of infectious agents from farms to wild salmonids.