Research Document 2020/058
Assessment of the risk to Fraser River Sockeye Salmon due to Moritella viscosa transfer from Atlantic Salmon farms in the Discovery Islands area, British Columbia
By Mimeault, C., Nekouei, O., Garver, K.A., Jones, S.R.M., Johnson, S., Holt, K., Aubry, P., Weber, L., 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.
This document is the assessment of the risk to Fraser River Sockeye Salmon due to Moritella viscosa on Atlantic Salmon farms in the Discovery Islands area of BC under current farm practices which was conducted in three main steps: first, a likelihood assessment which is the outcome of 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.
Moritella viscosa and winter ulcer have been reported on Atlantic Salmon farms in BC. Based on detections and/or winter ulcer diagnoses since 2012, it is very likely, with reasonable certainty, that farmed Atlantic Salmon infected with M. viscosa will be present on one or more Atlantic Salmon farm(s) in the Discovery Islands area in a given year. Shedding rates from Atlantic Salmon infected with M. viscosa have not yet been quantified; however, the bacterium has been isolated from skin lesions. It is therefore extremely likely, with reasonable certainty, that M. viscosa could be released from an infected Atlantic Salmon on a farm. M. viscosa detections and/or winter ulcer diagnoses have been reported on Atlantic Salmon farms during the months of December to February, while the migration timing of Fraser River Sockeye Salmon in the Discovery Islands area occurs from May to October. Given the lack of temporal overlap between M. viscosa occurrence and the Fraser River Sockeye Salmon migration, it is extremely unlikely, with reasonable certainty, that at least one juvenile or adult Fraser River Sockeye Salmon would be exposed to M. viscosa released from the Atlantic Salmon farms in the Discovery Islands area in any given year. The infection assessment was not performed given the outcome of the exposure assessment.
The likelihood assessment concluded that it is extremely unlikely that an infection with M. viscosa attributable to Atlantic Salmon farms in the Discovery Islands area will occur in Fraser River Sockeye Salmon. Given the lack of temporal overlap resulting in the likelihood assessment concluding that it is extremely unlikely that Fraser River Sockeye Salmon would become infected with M. viscosa released from Atlantic Salmon farms in the Discovery Islands area, the consequence assessment was not performed.
Overall, the assessment concluded that M. viscosa 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 of this risk assessment should be revised if winter ulcer on Atlantic Salmon farms in the Discovery Islands area were to occur between May and October.
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