Salish Sea Marine Survival Project

69 In the SSHI, farmed salmon (live- and dead/dying) were collected over one entire production cycle on four farms in Johnstone Strait. The first documented case of HSMI in BC was described as lasting almost a year on one of these farms. A second study has revealed the infective agents most closely associated with dead/dying salmon. The bacterium Tenacibaculum maratimum, the causative agent of mouth rot, was consistently associated with dead/dying salmon across all four farms. What is as important as the identification of pathogens that have been detected are those NOT detected. Most of the agents reportable to the World Organization of Animal Health (OIE) and/or the Canadian Food Inspec- tion Agency (CFIA) that are highly virulent and can impact trade were not detected in over 12,000 salmon surveyed. These include Infectious salmon anemia virus, Oncorhynchus masou virus, Infectious pancreatic necrosis virus, and the parasite Myxobolus cerebralis. Moreover, the two emerging viruses causative of heart diseases other than HSMI, salmon alphavirus (reportable) and piscine myocarditis virus, were also not detected. Figure 4. Salmon Fit-Chips include a panel of genes (biomarkers) co-activated in distressed fish that will die naturally within 72 hours (right cluster). Graph from Aimee Lee Houde. NEXT STEPS Cumulative effects: An overarching need for the SSMSP syntheses is an understanding of cumulative stressors (e.g., do harmful algal blooms and low dissolved oxygen act synergistically with disease development to ultimately cause mortality?) A new molecular tool, salmon Fit-Chips, is poised to address this need, as it uses validated biomarker panels of host genes to identify specific stressor and disease states in individual fish, all based on a gill biopsy sample. Included in this tool are genes predictive of imminent mortality (Figure 4). Application of Fit-Chips to the same juvenile salmon surveyed in the SSHI will not only reveal the cumulative and synergistic interplay between stress and disease, but will identify the environments where salmon are the most compromised and likely to die. Risks from salmon farms: Models are currently under development to evaluate the risks to migratory salmon of pathogen transmission from high density salmon farms. Even with the unprecedented large dataset on wild and farmed salmon, this is perhaps the most difficult question to answer. Early models have explored whether agents found in Chinook salmon were more frequently detected within 30 km of active farms. Future models will apply the full weight of data from all salmon species to tackle this question. Undeniably, two agents showing pathogenic potential in wild salmon and observed more prevalently on farms have come to the fore; piscine orthoreovirus and Tenacibaculum maratimum, but whether these pose the greatest risk of farm to wild transmission is still to be validated. Challenge studies: SSHI will host a workshop of leading world experts to utilize SSHI data and published information to rank infective agents by their potential to cause disease in wild salmon. It was the intent that the highest ranked, most understudied agents would be followed up with infection challenge studies (whereby naïve fish are exposed in the laboratory to pure cultures or concentrations of an agent) in the next phase of SSHI. Some of the newly characterized viruses are certainly in line for follow-up challenge research. Figure 3. Model estimates of probability of infection with parasite Paranucleospora theridion under an average sea surface temperature (left) and a 3 o C rise (right). Lighter color=higher probability. Credit: Art Bass. Longitude (UTM) 2014 Conditions Modelled Latitude (UTM) 5600 5500 5400 500 600 700 800 900 Probability of infection 0.75 0.50 0.25 2014 Conditions with 3 o C Increase 500 600 700 800 900

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