Science Advisory Report 2017/048

Advice from the assessment of the risk to Fraser River Sockeye Salmon due to Infectious Hematopoietic Necrosis Virus (IHNV) transfer from Atlantic salmon farms in the Discovery Islands area, British Columbia

Summary

• The assessment concluded that the risk posed to Fraser River Sockeye Salmon abundance and diversity by IHNV infection attributable to Atlantic Salmon farms in the Discovery Islands is minimal under the current fish health management practices
• Two main factors contributed to the resulting minimal risk:
  • the likelihood of an IHN disease outbreak on Atlantic Salmon farms in the Discovery Islands is estimated to be very unlikely with reasonable certainty given current health management practices including vaccination against IHN disease; and
  • the likelihood for juvenile Fraser River Sockeye Salmon to be infected and become diseased due to IHNV released from Atlantic Salmon farms is estimated to be extremely unlikely with reasonable uncertainty given current health management practices (i.e., vaccination, surveillance for early detection and depopulation) that limit the amount of potential IHNV shed into the environment from infected farms.
• The overall likelihood assessment, including separate disease, release, exposure, and infection assessments, was supported by the following key information:
  • regulatory requirements and farm level practices (i.e., vaccination, rapid detection, and depopulation upon confirmation of IHNV);
  • juveniles and adult Sockeye Salmon migrate through the Discovery Islands;
  • once Atlantic Salmon develop IHN disease, virus is shed into the environment;
  • oceanographic processes will transport water away from farms;
  • juvenile Sockeye Salmon are the most IHNV susceptible Sockeye Salmon life stage; and
  • all estimated maximum IHNV waterborne concentrations in net pens and plumes were below the laboratory based estimates of IHNV minimum lethal dose for juvenile Sockeye Salmon.
• Uncertainty in this assessment is driven by the lack of knowledge of:
  • the precise residence time of both juvenile and adult Sockeye Salmon in the Discovery Islands, local migration routes and occurrence around Atlantic Salmon farms (i.e., what proportion of migrating Sockeye Salmon are exposed to farms, how close, and for how long);
  • IHNV mortality rates for post-smolt Sockeye Salmon; and
  • other potential impacts of an exposure of Sockeye Salmon to IHNV at marine life stages (e.g., sub-lethal and cumulative effects).For the purpose of the assessment, a number of key assumptions were made including, for example:
  • current management practices are followed and will be maintained, including IHN vaccination of all farmed Atlantic Salmon, surveillance for early detection, and eradication of infected fish within 14 days of confirmation of positive samples;
  • the APEX-IHN® vaccine has a 95% efficacy in farmed Atlantic Salmon;
  • exposure to a minimum concentration of 108 pfu/m3 (plaque forming units per cubic metre) for an hour or more is required to cause infection and disease in juvenile Sockeye Salmon;
  • juvenile Sockeye Salmon had not developed immunity to IHNV (i.e., are naïve) upon exposure to IHNV released from Atlantic Salmon farms; and
  • all IHNV infections in susceptible Sockeye Salmon results in disease and direct mortality.
  • The risk assessment framework and conceptual model used to assess risk of pathogen transfer was accepted and suggestions were made for improvements to future risk assessments.
• For the purpose of the assessment, a number of key assumptions were made including, for example:
  • current management practices are followed and will be maintained, including IHN vaccination of all farmed Atlantic Salmon, surveillance for early detection, and eradication of infected fish within 14 days of confirmation of positive samples;
  • the APEX-IHN® vaccine has a 95% efficacy in farmed Atlantic Salmon;
  • exposure to a minimum concentration of 108 pfu/m3 (plaque forming units per cubic metre) for an hour or more is required to cause infection and disease in juvenile Sockeye Salmon;
  • juvenile Sockeye Salmon had not developed immunity to IHNV (i.e., are naïve) upon exposure to IHNV released from Atlantic Salmon farms; and
  • all IHNV infections in susceptible Sockeye Salmon results in disease and direct mortality.
• The risk assessment framework and conceptual model used to assess risk of pathogen transfer was accepted and suggestions were made for improvements to future risk assessments.

This Science Advisory Report is from the December 5-8, 2016 national advisory meeting on Assessment of the risk to Fraser River Sockeye Salmon due to Infectious Hematopoietic Necrosis Virus transfer from Atlantic Salmon farms located in the Discovery Islands, British Columbia. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

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