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Research Document 2019/036

Assessment of the risk to Fraser River Sockeye Salmon due to piscine orthoreovirus (PRV) transfer from Atlantic Salmon farms in the Discovery Islands area, British Columbia

By Mimeault, C., Polinski, M., Garver, K.A., Jones, S.R.M., Johnson, S., Boily, F., Malcolm, G., Holt, K., Burgetz, I.J. and Parsons, G.J.

Abstract

Fisheries and Oceans Canada, under the Aquaculture Science Environmental Risk Assessment Initiative, is conducting a series of assessments to determine risks to Fraser River Sockeye Salmon due to pathogens on marine Atlantic Salmon farms located in the Discovery Islands area in British Columbia.

This document is the assessment of the risk to Fraser River Sockeye Salmon due to piscine orthoreovirus (PRV) on Atlantic Salmon farms in the Discovery Islands area of British Columbia (BC) under current farm practices which was conducted in three main steps: first, a Likelihood Assessment which is the outcome of four consecutive steps (a farm infection assessment; a release assessment; an exposure assessment; and an overall infection assessment); second, a Consequence Assessment; and third, a Risk Estimation.

PRV, of which only the PRV-1 genogroup is found in the Eastern Pacific, is endemic to BC where it has been detected both in wild and farmed salmon. PRV infections are ubiquitous, highly prevalent and persistent on Atlantic Salmon farms in BC, it is therefore extremely likely with high certainty, that farmed Atlantic Salmon infected with PRV would be present on one or more Atlantic Salmon farm(s) in the Discovery Islands area in given year. Shedding rates from PRV-infected Atlantic Salmon have not yet been quantified; however, laboratory studies provide evidence that infected Atlantic Salmon can shed the virus. It is therefore extremely likely, with high certainty, that PRV could be released from an Atlantic Salmon farm through infected fish. PRV stability in seawater has not been characterized; however, given evidence of temporal overlap between PRV on Atlantic Salmon farms and migration timing of Fraser River Sockeye Salmon in the Discovery Islands area, it is extremely likely, with reasonable certainty, that at least one juvenile and adult Fraser River Sockeye Salmon would be exposed to PRV released from Atlantic Salmon farms in any given year. Finally, under such exposure, given evidence of infection in cohabitation studies, it was concluded that it would be very likely, with high uncertainty, that at least one Fraser River Sockeye Salmon would become infected. Overall, it was concluded that it is very likely that at least one Fraser River Sockeye Salmon would become infected with PRV released from Atlantic Salmon farms in the Discovery Islands area under current farm practices.

The potential magnitude of consequences to the abundance and diversity of Fraser River Sockeye Salmon was considered to be negligible given that current evidence cannot support the conclusion that PRV-1 causes disease or mortality in Sockeye Salmon. This conclusion was made with reasonable certainty and reasonable uncertainty for potential consequences resulting from juvenile and adult infection, respectively.

Overall, the assessment concluded that PRV attributable to Atlantic Salmon farms in the Discovery Islands area poses minimal risk to Fraser River Sockeye Salmon abundance and diversity under the current farm practices. Conclusions have been reached based on a series of rankings estimated with a range of uncertainties. Conclusions should be reviewed as new research findings fill knowledge gaps.

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