Atlantic salmon from Cooke Aquaculture’s Cypress Island escape tested positive for fish virus that can spread to wild Pacific salmon, though it isn’t known to cause harm to fish in Washington waters.

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An independent Canadian lab that studied 19 Atlantic salmon escaped from Cooke Aquaculture’s Cypress Island net pen last August found they all were infected with a virus that can be spread to wild Pacific salmon.

The results were not a surprise to the Washington Department of Fish and Wildlife, which announced last month that its own tests on four Atlantic salmon from Cooke’s escape found all were infected with the virus, called Piscine orthoreovirus (PRV).

“PRV seems to be ubiquitous in farmed Atlantic salmon, and probably everywhere,” said Ken Warheit, supervisor of the fish-health and genetics lab at the Washington Department of Fish and Wildlife.

“We assumed their fish had PRV,” he said of Cooke’s Atlantic salmon.

Kurt Beardslee, executive director of the Wild Fish Conservancy, a nonprofit that has sued Cooke over the August escape and wants its farms shut down, had the 19 fish tested in the lab of Frederick Kibenge at the University of Prince Edward Island.

The lab found the heart, gill and kidney-tissue samples from the salmon to be infected with PRV.

Beardslee called Cooke’s net-pen farms a “petri dish” that put Pacific salmon at risk of catching disease.

The virus has bedeviled fish farms in Norway.

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In Canadian Atlantic salmon farms, the virus has been associated with an inflammatory disease, called HSMI, that has killed Atlantic salmon. And in Norway, the virus has been shown to cause HSMI.

However, no Pacific salmon have been known to be sickened by HSMI, though they, too, have the virus.

Beardslee said the trouble elsewhere shows the virus can be dangerous. “We should learn from history,” Beardslee said.

But in Washington waters, PRV has been a nonissue so far, Warheit said. It is unknown why the virus does not seem to cause disease here — either in farmed fish or free-swimming native fish.

Even when injected into Pacific salmon in lab experiments, the virus, while it does infect them, does not make them sick, a paper published in January 2016 in the Journal Plos One reported.

Warheit pushed back at the conservancy with a white paper distributed by the Washington Department of Fish and Wildlife (WDFW) to news outlets Friday.

Among the objections, Warheit wrote that the conservancy “misuses the scientific literature to exaggerate risks to native salmon, and fails to find a single study to support the claim that PRV from open-water pens will harm wild fish.”

Warheit also said that PRV occurs naturally and was first confirmed in the Salish Sea from fish samples taken in 1987. The conservancy stated the virus found in the escaped fish originated in Norway, but the conservancy “provides no data or scientific research to support its claim,” Warheit said.

That, however, does not mean the department has no concern about PRV, Warheit said.

“We know that the threat of disease transmission has not materialized in any way that we can recognize affecting native salmon. But I can be concerned about PRV based on the information I have right now. I am not overly concerned, but the risks are never zero,” Warheit said.

Before Cooke’s Atlantic salmon escape, the department already was working on new guidance for testing of farmed Atlantic salmon, to include checking for PRV, Warheit said. That guidance would allow department staff to inspect Atlantic salmon in the net pens and to make decisions, based on those results, about whether they pose a risk to Puget Sound’s Pacific salmon.

The requirements, still in draft form, would require a biosecurity check by WDFW staff taking samples for pathogens twice a year.

Today the state has more limited statutory authority that requires an accredited third- party lab to test for regulated pathogens — five specific viruses — in the Atlantic salmon eggs Cooke receives from Iceland and also to test to ensure that the young salmon Cooke hatches are free of those viruses before they are released to net pens in Puget Sound.

Joel Richardson, vice president for public affairs for Cooke, distributed the department’s white paper to news agencies Saturday along with an email stating, “Cooke Aquaculture Pacific takes great offense to the Wild Fish Conservancy group issuing false and misleading claims.”

Cooke also claimed in a recent news release that its operations “do no damage to wild salmon.” The company has repeatedly stated that science shows Atlantic salmon farming is safe for the region’s native fish.

However, it is not true that farmed Atlantic salmon pose no risk to Pacific salmon, Warheit said.

“When both sides are saying the science is rock solid, they are both not telling the truth,” Warheit said. “Science is a matter of trying to understand a collection of data. Science is only as robust as the last study.

“The science is never rock solid. My approach to this entire thing is there is risk to native salmon from the presence of Atlantic salmon. The biggest risk I can think of is chronic leakage of Atlantic salmon that no one notices, and suddenly 30 years from now we have a population of Atlantic salmon. That risk is not zero.”

It would be smaller, Warheit added, if only female or sterile farmed fish were stocked — a recommendation made by the Pollution Control Hearings board in 1998 when it classified farmed Atlantics as a pollutant in Washington waters.

A bill to require single-sex stocking in Atlantic fish farms was introduced in the House this session but never got out of committee.