Research Document 2019/017
Assessment of the risk to Fraser River Sockeye Salmon due to Aeromonas salmonicida transfer from Atlantic Salmon farms in the Discovery Islands area, British Columbia
By Mimeault, C., Aubry, P., Wan, D., Wade, J., Boily, F., Jones, S.R.M., Johnson, S., Foreman, M.G.G., Chandler, P.C., Garver, K.A., Holt, C., 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 (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 Aeromonas salmonicida 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 wild fish, and infection of susceptible wild fish); second, a consequence assessment; and third, a risk estimation which combines the first two steps.
Aeromonas salmonicida is the causative agent of furunculosis, and is endemic to BC where it has been detected both in wild and farmed salmon. 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 A. salmonicida 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 given evidence that infected Atlantic Salmon in seawater can shed the bacterium. Considering the migration window of Fraser River Sockeye Salmon through the Discovery Islands area and the timing of A. salmonicida infections on farms, it is likely that at least one juvenile and 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 A. salmonicida attributable to Atlantic Salmon farms located in the Discovery Islands area given the infection pressure. Overall, it was concluded that the likelihood that Fraser River Sockeye Salmon would become infected with A. salmonicida 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 A. salmonicida 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 an infection acquired at the juvenile stage would not be expected to spread within the population at sea, and that an infection acquired at the adult stage would not have time to spread before reaching spawning grounds. These conclusions were reached with reasonable to high uncertainty given significant knowledge gaps.
Overall, the assessment concluded that A. salmonicida 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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