Research Document 2020/065
Assessment of the risk to Fraser River Sockeye Salmon due to viral haemorrhagic septicaemia virus IVa (VHSV-IVa) transfer from Atlantic Salmon farms in the Discovery Islands area, British Columbia
By Parsons, G.J., Burgetz, I.J., Weber, L., Garver, K.A., Jones, S.R.M., Johnson, S., Hawley, L.M., Davis, B., Aubry, P., Wade, J. and Mimeault, C.
Abstract
Fisheries and Oceans Canada (DFO), under the Aquaculture Science Environmental Risk Assessment Initiative, is conducting a series of assessments to determine potential 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 potential risk to Fraser River Sockeye Salmon due to viral haemorrhagic septicaemia virus IVa (VHSV-IVa) on Atlantic Salmon farms in the Discovery Islands area of BC under current farm practices. All the VHSV detected in BC belong to the genotype IVa, therefore, this risk assessment focuses only on the risk associated with genotype IVa. The assessment was conducted in three main steps: (1) likelihood assessment which includes four consecutive steps (farm infection, release, exposure, and infection assessments); (2) consequence assessment; and (3) risk estimation.
Viral haemorrhagic septicaemia virus has occasionally been reported on Atlantic Salmon farms in BC between 2002 and 2019, it is therefore unlikely, with reasonable certainty, that Atlantic Salmon infected with VHSV would be present on one or more Atlantic Salmon farm(s) in the Discovery Islands area in any given year. Despite knowledge gaps around the infection dynamics and shedding rates of VHSV in Atlantic Salmon, it was concluded that the release of the virus from infected farms was extremely likely, with high certainty, given evidence of horizontal transmission of the virus in cohabitation trials. However, the release of the virus through vectors or fomites is unlikely, with reasonable certainty, under the current farm practices given that effective biocontainment measures are in place.
It was concluded that the likelihood of juvenile Fraser River Sockeye Salmon to be exposed to VHSV through seawater during migration was unlikely, with a reasonable certainty, given the limited temporal overlap between Fraser River Sockeye Salmon and occurrence of VHSV on farms. Of the five years (out of 18; 2002-2019) in which VHSV was reported, only one year had evidence of VHSV during the time period that juveniles migrate through the Discovery Islands area. For adult Fraser River Sockeye Salmon, it was concluded that the likelihood of exposure to VHSV through seawater during migration was extremely unlikely, with a high certainty, given there was no temporal overlap between the migrating adults and the occurrence of VHSV on Atlantic Salmon farms in the Discovery Island area.
It was concluded that the likelihood of juvenile and adult Fraser River Sockeye Salmon to become infected with VHSVis extremely unlikely with reasonable certainty given that Sockeye Salmon are not susceptible to VHSV infections.
As the consequences are dependent on the susceptibility of Sockeye Salmon, the magnitude of consequences to the abundance and diversity of Fraser River Sockeye Salmon are both estimated as negligible. As Sockeye Salmon are not susceptible to VHSV infections, without infection, there will be no consequence (which is captured in the negligible consequence category) to the abundance and diversity of Fraser River Sockeye Salmon attributable to Atlantic Salmon farms in the Discovery Islands area.
Overall, the assessment concluded that VHSV 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.
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