Research Document 2019/021
Assessment of the risk to Fraser River Sockeye Salmon due to Piscirickettsia salmonis transfer from Atlantic Salmon farms in the Discovery Islands area, British Columbia
By Mimeault. C., Jones, S.R.M., Wade, J., Aubry, P., Johnson, S., Foreman, M.G.G., Garver, K.A., Holt, C., Boily, F., 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 Piscirickettsia salmonis on Atlantic Salmon farms in the Discovery Islands area, BC under current farm practices. This risk assessment was conducted in three main steps: (i) the likelihood assessment which includes four consecutive steps (a farm infection assessment, a release assessment, an exposure assessment, and an overall infection assessment; (ii) the consequence assessment; and, (iii) the risk estimation which combines the outcomes of the first two steps.
Piscirickettsia salmonis is the causative agent of salmonid rickettsial septicaemia (SRS), a disease of marine fish. Based on evidence of infection and disease on Atlantic Salmon farms between 2002 and 2017, it is unlikely, with reasonable certainty, that farmed Atlantic Salmon in the Discovery Islands area will become infected with P. salmonis in any given year under the current farm practices. However, when infected, the bacterium is extremely likely, with high certainty, to be released from farmed Atlantic Salmon into the marine environment. Considering the migration window of Fraser River Sockeye Salmon through the Discovery Islands area and the timing of P. salmonis infection on farms, it is unlikely that at least one juvenile, but very likely that at least one adult, both with reasonable certainty, would be exposed to the bacterium released from infected farms in any given year. Under such exposure, it is very unlikely that Fraser River Sockeye Salmon would get infected with P. salmonis attributable to Atlantic Salmon farms located in the Discovery Islands area. Overall, it was concluded that the likelihood that Fraser River Sockeye Salmon would become infected with P. salmonis attributable to Atlantic Salmon farms in the Discovery Islands area is very unlikely under the current fish health management practices.
In the event of a very unlikely infection of Fraser River Sockeye Salmon with P. salmonis attributable to Atlantic Salmon farms in the Discovery Islands area, the potential magnitude of consequences to Fraser River Sockeye Salmon abundance and diversity resulting from an infection was determined to be negligible given that: (i) an infection acquired at the juvenile stage would not be expected to spread within the population, and (ii) an infection acquired at the adult stage would not have time to spread before reaching spawning grounds. Those conclusions were reached with reasonable to high uncertainty given significant knowledge gaps.
Overall, the assessment concluded that P. salmonis 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. This risk assessment should be reviewed as new research findings fill knowledge gaps.
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