Will escaped Atlantic salmon survive — and thrive — in B.C. waters?

The question isn't why did the salmon leave the net, but what happens now that thousands of fish have escaped a Washington state salmon farm and swum off into the Pacific Ocean.

Nets containing an estimated 305,000 Atlantic salmon, which are not native to the region, were damaged at a U.S. fish farm run by Cooke Aquaculture in the San Juan Islands last Saturday, releasing an unknown number of fish.

There is no consensus about what the impact will be.

There is long-standing concern that foreign, farmed fish — and Atlantic salmon is the species that's farmed around the world — could do damage to native fish stocks.

But history hasn't shown any negative impacts or invasiveness of Atlantic salmon in the natural territory of Pacific salmon, says Jeremy Dunn, executive director of the B.C. Salmon Farmers Association.

He pointed to an experiment in the mid-20th century where the Department of Fisheries and Oceans (DFO) introduced hundreds of thousands of Atlantic salmon into British Columbia's waters in hopes they'd colonize and be available for sport fishers.

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"They were out-competed by Pacific salmon for food and weren't able to take in this environment," Dunn said.

And that would be the case again today, Dunn said, at least in part because farmed salmon are fed food pellets, so once in the wild, "they're going to have a hard time eating if the pellets aren't readily available."

Escapes like the one in Washington were more common 10-15 years ago in B.C., he said, but changes in Canadian regulations and improvements in technology mean they don't happen as often as they once did.

"The farms that our members have in British Columbia are highly engineered, able to withstand very fast currents and very rough seas," he said.  

Even with past escapes, he says, there are no Atlantic salmon in the waters of B.C.

'These fish won't adapt': DFO

The DFO's Atlantic Salmon Watch Program substantiates that. The agency has had no reports of Atlantic salmon in B.C. for about three years, according to its website.

The DFO's website also states that its recent research has shown no signs of Atlantic salmon at any life stage in B.C.'s waters.

Minister of Fisheries and Oceans Dominic LeBlanc issued a statement to CBC News Wednesday evening saying the government takes the incident "very seriously."

"We will be working to understand the potential impacts of this incident and prevent any damage to Canada's marine ecosystems," LeBlanc said. 

Another spokesperson for the department said the DFO's science "shows that there is an extremely low likelihood" of Atlantic salmon becoming established in B.C. waters.

"DFO will conduct stream surveys in areas closest to the U.S. border to monitor for any escaped Atlantic salmon," Terry Beech, parliamentary secretary to LeBlanc, said.

"The fish aren't expected to enter into rivers and streams until they mature in the fall. Past research suggests that many of these fish won't adapt to natural feeding practices and that most would either be caught or predated upon."

Interbreeding 'impossible'

Dunn says there is no risk of Atlantic and Pacific salmon mating with each other because they're different species. 

"It's impossible," Dunn said.

That doesn't mean he's ignoring possible risks to the native salmon populations in B.C., he said.

"Any activity or any issue that might be seen to be affecting or potentially affecting Pacific salmon, people are concerned about," Dunn said. "I think B.C.'s concern for Pacific salmon is a good thing and is why we're going to have Pacific salmon here for generations to come."

Breeding could damage hearing in fish: research

A recent study out of the University of Melbourne provides another possible explanation for why escaped farmed salmon may not thrive in a natural environment.    

The study found many farmed salmon are partially deaf, a possible side-effect of their accelerated growth.

The study notes that fish in the wild use their hearing to find prey and avoid predators and as a way to navigate to and from breeding grounds. Without it, their chances for survival are poor.

Ecologist John Volpe at the University of Victoria, however, is concerned about the introduction of thousands of Atlantic salmon.

Survival happens: ecologist

Volpe told CBC News that there have been attempts to colonize Atlantic salmon in B.C. as far back as the early 1900s for fishing, and it hasn't worked. But, he says, there's a big difference between then and now.

"Back in the day, we were introducing fry — young fish prone to predation that themselves were not in peak physical condition," he said.

Salmon that escape from farms these day are more likely to be "physically fit adult fish," which in large numbers could have an environmental impact.

Volpe said escaped salmon do survive and will go on to breed.

He published research in 2000 showing evidence of breeding, but said academic research on the topic has come to a halt since then.

Without research, Volpe said, there's no way of knowing what the impact of this recent salmon escape will be.

"The scope of risk and the magnitude of impact spans a huge gradient," he said.

But some experts warn that regardless of whether the farmed fish survive and breed, they still pose other risks to wild fish. 

Neville Crabbe, a spokesperson for the Atlantic Salmon Federation, a group that researches and advocates for wild salmon populations, told CBC News that the "bigger concern" is that the crowded conditions at fish farms are often breeding grounds for diseases and parasites.

He added in an email that there are now thousands of "possibly diseased fish mingling with wild species across a huge geographic range. No matter how people try to downplay this, it is a disaster."