Science Advisory Report 2019/020

Advice from the 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

Summary

Piscirickettsia salmonis Transfer risk assessment

• The assessment was conducted using farm-related and environmental data from 2002-2017, based on the current fish health management practices, and considering relevant scientific information.
• The assessment concluded that P. salmonis attributable to Atlantic Salmon (Salmo salar) farms operating in the Discovery Islands area poses minimal risk to Fraser River Sockeye Salmon (Oncorhynchus nerka) abundance and diversity. During this assessment uncertainties were evaluated at each step and ranged from high uncertainty to high certainty (see bullets below and Table 1).
• Two main factors influenced the attribution of minimal risk:
• in the likelihood steps, it was determined that it is extremely unlikely that Fraser River Sockeye Salmon would become infected with P. salmonis released from an Atlantic Salmon farm in the Discovery Islands area. The uncertainties for the different steps ranged from high certainty to reasonable uncertainty; and
• in the consequence steps, it was determined in the very unlikely event that Fraser River Sockeye Salmon would become infected with P. salmonis due to Atlantic Salmon farms in the Discovery Islands area, the infection would not be expected to spread within wild populations, hence the magnitude of consequences to both Fraser River Sockeye Salmon abundance and diversity would be negligible. The associated uncertainties ranged from reasonable uncertainty to high uncertainty.
• The overall likelihood assessment, including separate farm infection, release, exposure, and infection assessments, was supported by the following key findings:
• Piscirickettsia salmonis and/or salmonid rickettsial septicaemia (SRS) has been detected on Atlantic Salmon farms in the Discovery Islands area;
• there is temporal overlap of migrating juvenile and adult Fraser River Sockeye Salmon with reports of P. salmonis on farms in the Discovery Islands area; and
• although there is no vaccine available for SRS in BC, there has been limited spread of P. salmonis between Atlantic Salmon net pens.
• Uncertainty: Certainty in this assessment is limited by the lack of knowledge about:
• how long and how close populations of wild juvenile and adult Pacific salmon are in the vicinity of Atlantic Salmon farms;
• shedding rates in P. salmonis-infected salmon;
• susceptibility and pathogenesis of P. salmonis in Sockeye Salmon;
• the survival of P. salmonis in the marine environment;
• the minimum infectious and lethal dose of P. salmonis for any of the susceptible salmonid species (Chinook (Oncorhynchus tshawytscha), Coho (Oncorhynchus kisutch), Pink (Oncorhynchus gorbuscha), Sockeye (Oncorhynchus nerka), Chum (Oncorhynchus keta), Atlantic salmon (Salmo salar) or Rainbow Trout (Oncorhynchus mykiss));
• SRS mortality in wild Sockeye Salmon and other susceptible wild fish; and
• the consequences to abundance and diversity of Fraser River Sockeye Salmon resulting from sub-lethal effects of P. salmonis infection.
• For the purpose of the assessment, a number of key assumptions were made:
• positive detection of the pathogen on an Atlantic Salmon farm in the Discovery Islands area is evidence of R. salmoninarum infection on that farm;
• Sockeye Salmon are susceptible to P. salmonis infections and SRS;
• infected Atlantic Salmon shed P. salmonis into the surrounding environment; and
• susceptible fish in wild populations could become infected and die at similar rates to farmed Atlantic Salmon.

Characterization of Piscirickettsia salmonis and salmonid rickettsial septicaemia (SRS)

• Infection with P. salmonis can lead to the development of SRS in a broad range of host-species including several salmonid and non-salmonid species.
• Sockeye Salmon susceptibility to P. salmonis infection and SRS remains to be determined. Laboratory data suggests that Coho Salmon are more susceptible than Rainbow Trout and Atlantic Salmon. There are insufficient data to assign different susceptibilities to different life history stages of salmonids.
• Piscirickettsia salmonis is transmitted horizontally, therefore, susceptible fish can become infected through contact with infected fish, contaminated water and/or contaminated equipment. There is little evidence of vertical transmission.
• The incubation period of P. salmonis ranges from 10 to 20 days and is dependent on environmental conditions, dose, strain of P. salmonis, and the condition of the susceptible host species.
• Disease associated with P. salmonis infection is strongly influenced by environmental factors and other stressful events.
• There are no morbidity or mortality data associated with P. salmonis infection in wild fish.
• There are no data on shedding rates or minimum infectious dose in any species.
• There is limited information about the survival of P. salmonis in the marine environment.

This Science Advisory Report is from the November 6–8, 2018 national advisory meeting on Assessment of the risk to Fraser River sockeye salmon due to bacteria causing systemic infections transferred from Atlantic salmon farms located in the Discovery Islands area, British Columbia. Additional publications from this meeting will be posted on the Fisheries and Oceans Canada (DFO) Science Advisory Schedule as they become available.

Science Advisory Report 2019/020 (PDF, 730 KB)

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