A virus is being transmitted between net-pen salmon farms and wild juvenile Chinook salmon in British Columbia waters, according to new findings published Wednesday in Science Advances.
The study traces the origins of piscine orthoreovirus, or PRV, to Atlantic salmon farms in Norway, and found that the virus is now almost ubiquitous in salmon farms in B.C. The virus has been shown to sicken fish.
The collaborative, peer-reviewed study was done by the University of British Columbia and the Strategic Salmon Health Initiative — a partnership between Fisheries and Oceans Canada, Genome BC and the Pacific Salmon Foundation.
The research also showed that wild Chinook salmon are more likely to be infected with PRV the closer they are to salmon farms, which suggests farms transfer the virus to wild salmon.
"Both our genomic and epidemiological methods independently came to the same conclusion, that salmon farms act as a source and amplifier of PRV transmission," said Gideon Mordecai, a viral ecologist and Liber Ero fellow with UBC Science and researcher with UBC Medicine, who led the study.
The finding that PRV is transmitted between farmed and wild salmon stops short of showing that it also causes disease in wild salmon, said Ken Warheit, director of fish health for the state Department of Fish and Wildlife, who provided some of the data used in the study.
Warheit praised the scientists for their research, but said more work is needed to show what the findings mean for wild Pacific Chinook. "This proves transmission. It doesn't prove disease," Warheit said.
Some celebrated the findings. "I'm so glad this paper was finally published," said Kurt Beardslee, executive director of the Wild Fish Conservancy, a nonprofit that opposes open net-pen aquaculture in part because of concerns about pollution and disease.
"This is an amazing paper with grave implications for the fishing industry, tribal food security and wild salmon and killer whale recovery," Beardslee said. "The true test now is if managers will have the same bravery to apply this science to fisheries policy and management."
Some Atlantic salmon farms already are being shut down in B.C., in part because of the objections of First Nations to the farms in waters they never ceded and because of concern for the salmon their cultures depend on.
Atlantic salmon net-pen farming is being phased out in Washington state per a law passed by the Legislature in 2018, following a net-pen escape in north Puget Sound.
Mordecai said it was genomics that enabled the team to advance what is understood about the virus.
"Before I wrote this paper I had been in meetings where people said, 'There is no evidence this virus is transmitted from farms to wild fish,' and I thought well, I use genomic technologies that can get to this answer," he said in an interview.
The team also learned that free-swimming Chinook salmon from the Columbia River system were carrying a different type of the virus.
The study affirms the need to transition away from open net-pen aquaculture to protect wild fish from disease, Mordecai said.
"What does this all mean? My conclusion is that this calls for minimizing interaction between salmon farming and wild fish," Mordecai said.
"This is just another piece of the puzzle that says there could be a problem here."
Alexandra Morton, a B.C. scientist who also has researched virus transmission from fish farms, praised the paper.
"I applaud the publication of this work. It is going to be extremely important to restoring wild salmon, in particular Chinook salmon," Morton wrote in an email.
"It has been devastating to watch this virus spread," Morton said, adding that she hopes the findings will lead to regulation of the virus as a disease agent.