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Salmon farms are having a negative impact on wild stocks globally, in many cases causing survival rates to drop by more than 50 per cent per generation, according to a new study being released today.

The research by Jennifer Ford and the late Ransom Myers, both of Dalhousie University in Halifax, is the first to examine the impact of salmon farming on such a wide scale.

It compared the marine survival of wild salmon in areas with salmon farming to adjacent areas that didn't have farms - and it found wild stocks are suffering wherever they are in contact with salmon farms.

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"We show a reduction in survival or abundance of Atlantic salmon, sea trout and pink, chum, and coho salmon in association with increased production of farmed salmon. In many cases, these reductions in survival or abundance are greater than 50 per cent," the researchers say.

The paper describes the overall impact of salmon farming as "significant and negative."

In order to determine the collective effects of aquaculture on wild fish, the researchers studied five species of wild salmon and trout in five regions of Europe and Canada, including areas in British Columbia, New Brunswick, Nova Scotia and Newfoundland.

The peer-reviewed paper, published by the Public Library of Science, states that generally Atlantic salmon populations were depressed more than Pacific salmon populations, possibly because Atlantics are more susceptible to genetic effects. "The impact of salmon farming on wild salmon and trout is a hotly debated issue in all countries where salmon farms and wild salmon coexist," the researchers say.

"Studies have clearly shown that escaped farm salmon breed with wild populations to the detriment of the wild stocks, and that diseases and parasites are passed from farm to wild salmon. An understanding of the importance of these impacts at the population level, however, has been lacking.

"In this study, we used existing data on salmon populations to compare survival of salmon and trout that swim past salmon farms early in their life cycle with the survival of nearby populations that are not exposed to salmon farms," the study says.

"Many of the salmon populations we investigated are at dramatically reduced abundance, and reducing threats to them is necessary for their survival.

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Reducing impacts of salmon farming on wild salmon should be a high priority."

The researchers state that it is "very unlikely" that factors other than salmon farming could explain the widespread declines.

"It's very significant research. It's basically the first time anybody has put the global data together," John Reynolds, who holds a chair in salmon conservation at B.C.'s Simon Fraser University, said yesterday in commenting on the paper, called "A Global Assessment of Salmon Aquaculture Impacts on Wild Salmonids."

Prof. Reynolds said the study by Ms. Ford and Dr. Myers (who died last year) makes it clear that changes need to be made in the way salmon farms operate.

"Frankly, it's surprising to me," Prof. Reynolds said of the study's conclusions.

"It's a stronger result than I would have anticipated."

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Prof. Reynolds, who serves as a scientific adviser to the provincially funded B.C. Pacific Salmon Forum, which is researching the impact of salmon farming in the province's Broughton Archipelago, said the study clearly shows aquaculture is having an impact. "It tells me we really are going to have to think about the way we are doing salmon farming," he said.

"I don't think we have to give it up. But people will have to make some choices."

Recent data released by the Department of Fisheries and Oceans show that the numbers of wild pink salmon in the Broughton Archipelago this year are similar to last year's.

But Prof. Reynolds said wild salmon populations fluctuate from one year to the next, and the important thing is the overall trend in areas with farms.

"The strength of this study is that it puts everything together," he said.

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