Escape of Atlantic salmon raises concerns

Impacts of some 21,000 farmed Atlantic salmon that fled a damaged British Columbia net pen in late December remain an unknown, but concerns remain over the risk of them competing with wild fish for habitat or food and spreading parasites and other pathogens.

While it’s tough to track escaped farmed fish, there are concerns over an escape of this magnitude, said Stan Proboszcz, science and campaign advisor for the Watershed Watch Salmon Society, in Vancouver, British Columbia.

Proboszcz cited research done by University of Victoria ecologist John Volpe that concluded that Atlantic salmon can outcompete species like steelhead trout for habitat. Volpe’s research suggests that if Atlantic salmon colonize in coastal British Columbia river systems utilized by native species that they may chase wild fish from that habitat, he said. The other risk is that farmed fish can actually eat wild fish, he said.

A spokesman for the Upper Skagit Indian Tribe in Washington state told The Seattle Times in April 2018 about catching a live Atlantic salmon with bones in its stomach that indicated it had eaten some kind of fish. That fish was believed to have been one of more than 300,000 Atlantic salmon that escaped from Cooke Aquaculture’s Atlantic salmon net that collapsed at Cypress Island eight months earlier.

According to Ted Meyers, a pathologist with the Alaska Department of Fish and Game, Atlantic salmon are highly domesticated and are accustomed to feeding on pelleted food in their net pens. Meyers said that to his knowledge these farmed salmon are unlikely to introduce new diseases that would be infecting Pacific salmon.

Proboszcz meanwhile cited research concerning the spread of pathogens, which showed that when wild fish had to migrate near net pen fish farms, researchers found a higher incidence of the piscine reovirus (PRV) in the wild salmon.

PRV is a highly contagious virus strongly linked to a heart disease in salmon called Heart and Skeletal Muscle Inflammation (HSMI), which has swept through fish farms in Norway. Canadian American marine biologist Alexandra Morton of Raincoast Research, and a resident of British Columbia, co-published the first scientific paper on PRV in British Columbia, reporting that its genetic sequence appears to have originated from northern Norway and arrived in British Columbia in about 2007.

In March of 2019, the science journal Nature reported that PRV is ubiquitous in farmed Atlantic salmon and sometimes associated with HSMI, but that PRV is also widespread in non-diseased fish, particularly in the Canadian Pacific region, where few cases of severe heart inflammation have been documented.