The research, conducted by two Canadian marine biologists, claims to show dramatic declines in the abundance of wild salmon populations whose migration takes them past salmon farms in Canada, Ireland and Scotland.

Since the late 1970s, salmon aquaculture has grown into a global industry, producing over one million tonnes of salmon per year. However, this solution to globally declining fish stocks continues to face criticism from a number of environmental organisations and scientists.

A global survey of wild salmon and trout populations by Jennifer Ford and Ransom Myers, published yesterday in the Public Library of Science Biology Journal, claims to provide the first evidence on a global scale illustrating "systematic declines" in wild salmon populations that come into contact with farmed salmon.

According to the authors, previous 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. However, until now, they say, there has been no assessment of the importance of these impacts at the population level and across the globe. Ford & Myers say they compared the survival of salmon and trout that swim past salmon farms to the survival of those fish that never pass a salmon farm.

In five regions around the world, Ford and Myers claimed that they found a "significant decline" in the survival of wild salmon populations that are exposed to salmon farms. They say this decline took place as farmed salmon production increased in each region. Combining these regional estimates, the authors say they found that wild populations suffer a reduction in survival or abundance of more than 50% when associated with farmed salmon.

"These new results suggest that salmon farming could seriously compromise the persistence of the world’s salmonid populations," a statement issued by the Public Library of Science contended.

According to the Canadian media, Trevor Swerdfager, director general of aquaculture management for the federal Fisheries Department, said he will take a close look at the new research. But he added he has so far not seen any proof that salmon farms harm wild populations.

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