Research Document 2019/019
Assessment of the risk to Fraser River Sockeye Salmon due to Renibacterium salmoninarum 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., Malcolm, G., Foreman, M.G.G., Chandler, P.C., Wan, D., 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 (BC).
This document is the assessment of the risk to Fraser River Sockeye Salmon due to Renibacterium salmoninarum on Atlantic Salmon farms in the Discovery Islands area of BC under current farm practices. The risk assessment was conducted in three main steps: first, a likelihood assessment which includes four consecutive assessment steps (farm infection, pathogen release, exposure of susceptible fish, and infection of susceptible fish); second, a consequence assessment; and third, a risk estimation which combines the first two steps.
Renibacterium salmoninarum, the causative agent of bacterial kidney disease, is endemic to BC where it has been detected both in wild and farmed salmon. Based on evidence of infection and disease reported on Atlantic Salmon farms between 2002 and 2017, it is very likely, with reasonable certainty, that farmed Atlantic Salmon in the Discovery Islands area will become infected with R. salmoninarum in any given year under the current farm practices. Although the shedding rates from R. salmoninarum-infected Atlantic Salmon have not been quantified, it is extremely likely, with high certainty, that R. salmoninarum would be released from infected Atlantic Salmon because it is naturally shed from the body into the surrounding environment. Given temporal overlap of R. salmoninarum infections on farms and Fraser River Sockeye Salmon migration through the Discovery Islands area, it is very likely, with reasonable certainty, that at least one juvenile and returning adult will be exposed in any given year. Under such exposure, however, it is extremely unlikely, with reasonable uncertainty, that juveniles or adults would get infected, as the estimated waterborne concentration of R. salmoninarum on Atlantic Salmon farms is approximately 1/125th of the lowest dose reported to cause infection in Chinook Salmon (O. tshawytscha). Overall, it was concluded that it is extremely unlikely that Fraser River Sockeye Salmon would become infected with R. salmoninarum 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 reasonable uncertainty, for both juveniles and adults given that an infection acquired at the juvenile stage would be not expected to spread and an infection acquired at the adult stage would not be expected to develop before reaching spawning grounds.
Overall, the assessment concluded that R. salmoninarum 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. The risk assessment should be reviewed as new research findings fill knowledge gaps.
- Date modified: