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Campbell River, B.C. – On May 25, a study entitled Aquaculture mediates global transmission of a viral pathogen to wild salmon was published in the journal, Science Advances. This study was part of the Strategic Salmon Health Initiative (SSHI) – and highlights yet again the long-standing concerns of the BC salmon farming industry regarding the credibility of research supported by the SSHI.

The SSHI was established 8 years ago to investigate potential relationships between variability in the survival of juvenile salmon during early ocean migration and the microbes they carry. As presented on the Fisheries and Oceans Canada website, the initiative was to consist of four phases. The first two phases of this initiative were to focus on the identification of microbes currently carried by BC’s wild and farmed salmon – while the latter phases were to investigate the potential effects of identified microbes on the wild and farmed fish. However, the final two phases were never completed.

As a result of the researchers’ inability to complete their stated task, their publications have largely focused on viral discovery; they have failed to publish any scientific studies that investigate whether the viruses they discovered are actually threatening wild or farmed stocks. Therefore, rather than contributing to a greater understanding of the factors actually impacting the health of BC’s wild salmon populations, the SSHI research team leading this 10-million-dollar program (64% of which came from the federal government) has simply succeeded in generating alarm and uncertainty.

The authors of the Science Advances study rely heavily on speculation to draw conclusions. This speculation is clearly evident in the following claims made by the authors:

  1. The development of Atlantic salmon aquaculture facilitated the spread of Piscine orthoreovirus-1 (PRV-1) from Europe to the North and South East Pacific

This claim is based upon the authors’ determination that PRV-1a in the NE Pacific diverged from PRV-1a in the Atlantic Ocean between 1981 – 1997. The authors emphasize that this timing is consistent with the timing of Atlantic salmon egg imports from Europe for salmon farms in the NE Pacific.

In their determination of the timing of PRV-1 introduction, the authors dismiss the fact that a wild-source steelhead trout sampled in 1977 tested positive for PRV by PCR analysis. The authors defend their dismissal of the 1977 positive test by stating that it has not been verified by genetic sequencing. However, in May 2020, researchers at Fisheries and Oceans Canada repeated the positive PRV test in the 1977 sample through sequencing (GenBank). Given that one of the lead authors of the Science Advances study also works at Fisheries and Oceans Canada, it is surprising that this researcher was not aware that the positive test had in fact been repeated.

If this sequenced positive test result is a true positive, then PRV was in BC waters prior to the introduction of Atlantic salmon farming. As such, we recommend that the authors submit a correction to Science Advances that would be appended to the online version of the study. This correction should consider the impact of the presence of PRV in the 1977 sample on their estimates of the arrival of PRV in the NE Pacific.

  1. Evidence strongly supports Atlantic salmon aquaculture as a source of infection in wild Pacific salmon.

To indirectly assess transmission from farmed to wild salmon, the authors state that they investigated the probability of PRV infection for wild Chinook salmon in relation to distance from active aquaculture facilities – and found that PRV-1 infection was closely tied to farm proximity. However, by their own admission, the authors did not take account of other factors that might influence PRV-1 prevalence (e.g. different environmental conditions or differences in host condition between regions). Without accounting for the significance of these factors, how could the authors arrive at their conclusion?

The authors strive to provide support for their conclusion by citing three studies which they say also implicate PRV-1 transmission from farmed Atlantic salmon to wild salmon. However, one of the three cited studies has since been corrected – and these corrections make its original conclusions invalid. Another of the studies considered farm-to-farm transmission (i.e. not farmed-to-wild transmission), while the third was unable to establish a clear line of transmission from farmed to wild salmon. In an effort to bolster their own questionable conclusion, the authors of the Science Advances study thus appear to have adopted rather lax citation standards.

Furthermore, any study considering the transmission dynamics between farmed and wild salmon should recognize that all young farmed Atlantic salmon entering the marine environment have been verified PRV-free. In other words, farmed Atlantic salmon do not introduce PRV to the marine environment. Rather, they acquire it during their ocean residency.

Even when the young Atlantic salmon acquire PRV, it is unlikely that they become a significant source of infection in wild Pacific salmon. The potential for farmed-to-wild transmission is limited by the brief period that migrating salmon spend in proximity to a farm. For example, Reshisky et al., 2021, found that sockeye salmon migrating through the main migration routes of the Discovery Islands only remain within ~200-800 metres of a farm for approximately 4-11 minutes. This limited contact between farmed and wild salmon may be one of the factors contributing to the finding of Marty et al., 2015; this study found the prevalence of PRV was not different between fresh samples from wild Coho salmon collected from Alaska (where there are no salmon farms) and BC.

  1. PRV-1 is now an important infectious agent in critically endangered wild Pacific salmon populations, fueled by aquacultural transmission.

In making the above statement, the authors of the Science Advances study fail to recognize that BC farmed salmon are healthy. Evidence presented from fish farm data (through DFO reporting) indicates that “mortality events” are overwhelmingly due to environmental and mechanical (handling) incidents (nearly 100% in 2019), rather than infectious disease; and about 80% of “fish health events” (where disease is known to be a factor) were due to the prevalence of three infectious diseases historically common and managed in populations of BC farm-raised salmon.

Given that there have been no major die-offs, or significantly high numbers of uncontrollable fish health events on farms, it does not stand to reason that BC farmed salmon are spreading highly infectious and harmful diseases to wild populations. In perhaps a clear example of the impact of social distancing, high density populations, such as those in a farm setting, would be the first to display problems due to a contagion event.

The authors also fail to acknowledge that pathogen detection does not equate to disease. Pathogen detection alone is insufficient to allow inferences of the overall health status of wild fish populations and requires the context of host susceptibility, virulence of pathogen strains, and environmental conditions (Jia et al., 2019). Therefore, it is inaccurate to assume that the detection of pathogens or their DNA in proximity to a salmon farm is an indicator they are causing disease issues for wild salmon swimming near a farm. This has been a common assumption of SSHI work – yet further research has never been conducted to verify assumptions that pathogen presence is causing disease.

There is, however, a weight of evidence that indicates that the PRV isolate found in BC does not cause disease in wild or farmed salmon in the Pacific (Garver et al., 2016; Polinski et al., 2019; Zhang et al., 2019; Purcell et al., 2018) – and Heart and Skeletal Muscle Inflammation (HSMI) (associated with PRV elsewhere) has not been diagnosed by licenced veterinarians caring for fish in British Columbia. Moreover, infection with high loads of PRV does not impede the physiological capacity, biological performance, or the migratory lifecycle of wild Pacific salmon (Purcell et al., 2018; Zhang et al., 2019).

Importantly, Wessel et al., 2020, conducted a lab study to compare the onset of PRV infection between different isolates – and confirmed that high virulent (Norwegian) PRV isolates induced cardiac lesions consistent with HSMI. However, the low virulent isolates (three historical Norwegian isolates and one Canadian (BC) isolate) induced only mild cardiac lesions. According to Dr. Gary Marty, BC Provincial Fish Pathologist, such mild microscopic lesions would not be a threat to wild salmon populations.  Rather, mild lesions are part of the normal inflammatory response to infectious agents that wild fish encounter during their migrations.

A Disturbing Pattern in Publications

The Science Advances study is the latest in a series of publications that base conclusions on speculation.

In a 2017 study, a research group, with clear connections to anti-salmon farming activists, suggested that wild stocks exposed to marine aquaculture sites have much higher rates of PRV infection. Response to this study by their scientific peers required that they post a correction that rendered the claims made in the original report invalid.

Moreover, in 2011, this same activist-linked research group published a report entitled Lethal Atlantic virus found in Pacific salmon. Following this report, Canadian federal and provincial authorities undertook a broad virus surveillance program – and were unable to confirm the report’s claims. Subsequently, a US surveillance program was undertaken using an even broader suite of diagnostic methods and again could not confirm the group’s findings.

In the aftermath of this issue, Minister of Fisheries and Oceans Canada, Keith Ashfield, stated “because some have chosen to draw conclusions based on unconfirmed information, this has resulted in British Columbia’s fishing industry and Canada’s reputation being put at risk needlessly.” The research group was also warned by both the BC Government and Fisheries and Oceans Canada that reckless allegations based on incomplete science can be devastating and unfair to the families that make a living from the sea.

After reviewing the reports published by the research groups discussed in this press release, their scientific peers have concluded the following:

  • Ian Gardner, former Canada Excellence Research Chair in Aquatic Epidemiology, who was part of the Strategic Salmon Health Initiative (SSHI) has described the group’s PRV studies as making “broad sweeping statements not supported by strong evidence.”
  • Hugh Mitchell, an internationally recognised fish health expert, stated that “to speculate that PRV-1 is a danger to salmon is without any foundation. There is scant evidence that PRV-1 is of any clinical significance to wild Pacific salmon.”
  • Kenneth Warheit, fish health and genetic specialist for the Washington Department of Fish and Wildlife has said the group failed to find a single study to support the claim that PRV from open-water pens will harm wild fish.
  • Kyle Garver, a research scientist for Fisheries and Oceans Canada and a PRV expert, has also concluded that PRV has been ubiquitous in the Pacific Northwest for many decades, and that it is not linked to any fish disease or mortality.

 Media Contact:

Michelle Franze

Manager of Communications, Partnerships and Community