Research Document 2019/023
Assessment of the risk to Fraser River Sockeye Salmon due to Yersinia ruckeri transfer from Atlantic Salmon farms in the Discovery Islands area, British Columbia
By Mimeault, C., Wade, J., Boily, F., Johnson, S., Jones, S.R.M., Aubry, P., Foreman, M.G.G., Garver, K.A., Holt, C., Burgetz, I.J. and Parsons, G.J.
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 (Oncorhynchus nerka) due to pathogens on marine Atlantic Salmon (Salmo salar) 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 Yersinia ruckeri on Atlantic Salmon farms in the Discovery Islands area of British Columbia (BC) under current farm practices. The risk assessment was conducted in three main steps: first, a likelihood assessment that includes four consecutive assessment steps (farm infection, pathogen release, exposure of Fraser River Sockeye Salmon, and infection of Fraser River Sockeye Salmon); second, a consequence assessment; and third, a risk estimation.
Yersinia ruckeri is the causative agent of enteric redmouth (ERM) and is endemic to British Columbia, Canada where it has been detected both in wild and farmed salmon. Based on the evidence of infection and disease that has been reported on Atlantic Salmon farms between 2002 and 2017, it is very unlikely, with reasonable certainty, that farmed Atlantic Salmon in the Discovery Islands area will become infected with Y. ruckeri in any given year under the current farm practices. Although the shedding rates from Y. ruckeri-infected Atlantic Salmon have not been quantified, it is extremely likely, with high certainty, that the bacterium would be released from infected Atlantic Salmon into the marine environment given rearing practices in net pens. Given the limited temporal overlap of Y. ruckeri infections on farms and juvenile Fraser River Sockeye Salmon migration through the Discovery Islands area, it is very unlikely, with reasonable certainty, that at least one juvenile will be exposed in a given year. Exposure for adults is extremely unlikely given the lack of temporal overlap between their migration window and infections on farms. Assuming exposure, the likelihood for Fraser River Sockeye Salmon to become infected with Y. ruckeri attributable to Atlantic Salmon farms is extremely unlikely, with reasonable certainty, given that Atlantic Salmon farms are considered to represent a negligible infection pressure. Overall, it was concluded that it is extremely unlikely that Fraser River Sockeye Salmon would become infected with Y. ruckeri 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 determined to be negligible, with high certainty. This conclusion was made with high certainty given that ERM is primarily a freshwater trout disease.
Overall, the assessment concluded that Y. ruckeri 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. This risk assessment should be reviewed as new research findings fill knowledge gaps.
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