Farmed Atlantic salmon threaten Pacific cousins

Canadian biologist John Volpe looks for stray Atlantic salmon, escapees from fish farms, to study their effect on wild native salmon

June 7, 2000
Web posted at: 12:52 p.m. EDT (1652 GMT)

By Environmental News Network staff

John Volpe, a biologist at the University of Victoria in British Columbia, is an accomplished swimmer and a rare researcher. To study the ecological effects of farmed Atlantic salmon in the wild, Volpe strokes and floats right alongside them.

"I cover lots of ground that way," Volpe said in an interview. "Its kind of like white-water rafting without the raft."

Volpe is uncovering as much as he is covering. He and other researchers have come up with evidence that farmed Atlantic salmon are breeding in the Pacific Northwest, creating more problems for their already beleaguered Pacific cousins.

His findings are published in the June Issue of Conservation Biology.

Cultured in marine-net pens off British Columbia and Washington state, Atlantic salmon can escape when nets are torn due to stormy weather, predators or human error. A release of 300,000 fish into the wild is not unusual, Volpe said.

Less than two decades old, the finfish aquaculture industry is the leading agricultural export in British Columbia.

Confronted with the issue of salmon escapees, the Canadian government maintains that the farmed fish are too domesticated to spawn in the wild, adding that if any were able to spawn, their offspring would not be able to compete with native juvenile salmon.

"I know of no one that has any evidence that Atlantic salmon are reproducing in the wild," said Brian Gorman, a spokesperson for the National Marine Fisheries Service on Monday.

"The science is so immature that those types of statements are easily accepted," Volpe responded. "There is no real way of monitoring how many fish escape. Most farmers do not report them."

Farmed Atlantic salmon have been spotted throughout the Pacific Northwest, even in Alaska where aquaculture is illegal. But despite numerous reports of adult Atlantic salmon in freshwater and marine coastal environments, there were no documented cases of successful reproduction of Atlantic salmon in the North Pacific — until Volpe stepped in.

Above, a 1-year-old Atlantic salmon reared in the wild; below, an adult Atlantic salmon with typical marine coloration

Volpe and his colleagues captured 12 juvenile Atlantic salmon, confirmed by DNA analysis, in British Columbia's Tsitika River, where there are eight species of native salmonids including summer steelhead trout and resident rainbow trout.

Based on two lines of evidence, the researchers maintain that the Atlantic salmon were born in the wild.

First, scale analysis revealed the juveniles had the growth pattern of salmon reared in the wild: scale rings that are far apart during the warm summers but clustered tightly during the cold winters, forming a characteristic dark "winter check."

Second, the juveniles could not have been escapees from aquaculture net pens that made their way to the Tsitika River, in part because there are no such pens in the river's drainage. The nearest aquaculture farm is 26 miles away.

The successful spawning of Atlantic salmon in British Columbia has raised concern that these fish may further jeopardize the continued persistence of already fragile native Pacific salmonids through competition for food and occupation of underutilized habitat.

Eighteen salmon stocks in the Pacific Northwest are listed as threatened or endangered under the Endangered Species Act. The National Marine Fisheries Service recognizes 49 evolutionary significant salmon populations on the West Coast, including Canada.

"Atlantic salmon may constitute an invading species," Volpe suggested.

Steelhead trout, a West Coast version of salmon, could be at the greatest risk, he added.

"A crucial step toward establishment of any prospective invader is successful reproduction in the recipient habitat," Volpe notes in his report.

"Steelhead are in great danger already," Volpe said. "Any river that has available habitat by a weakened steelhead population, is a prime candidate for Atlantic salmon colonization."

"Atlantic salmon grow more quickly than steelhead and they spawn two months earlier," he explained.

Yet both species depend on the same food sources.

Volpe's previous research showed that juvenile Atlantic salmon can defend territory against native steelhead. "They can become competitively superior after just three days," he said.

"At this point, dry land production is the only sure way to eliminate the threat," said Volpe, adding that the U.S. legislature is considering a petition to declare Atlantic salmon "industrial pollution."

"With the exception of our own ongoing research there are no empirical data available upon which confident predictions can be made regarding the performance (and potential effects) of aquaculture escaped Atlantic salmon in the Pacific," Volpe said. "All statements and predictions to date have reflected the agenda of the various speakers and have not been based on valid scientific arguments. Therefore, the biggest problem facing Pacific salmonid stocks is our own ignorance and continuing acceptance of its prominent role in defining natural resource policy."

Copyright 1999, Environmental News Network, All Rights Reserved

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John Volpe
Conservation Biology
National Marine Fisheries Service
   •Eighteen salmon stocks
Marine biology invasions
salmon's life cycle
Stream Net

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