An explosion in commercial fish farming has caused a huge fall in the population of wild salmon, with 15 per cent of salmon rivers in Europe and North America found to be barren in a survey by the World Wide Fund for Nature.
Marine conservation experts from Canada, Norway, the United States and Britain claim that fish farming – rather than preserving stocks of wild salmon, as was predicted 30 years ago – is one of the most damaging threats to the species. The conservation groups are calling for a crackdown on the practice, the establishment of aquaculture-free zones and a stop to commercial fisheries.
"Research shows that farmed fish negatively affect wild Atlantic salmon," said Bill Taylor, president of the Atlantic Salmon Federation.
"Escaped farmed fish interbreed with the wild salmon, which weakens the wild gene pools, and compete for food and habitat. Confinement of fish in cages also contributes to the spread of disease and parasites," he said.
Next week a multinational summit on salmon preservation will be held in the Faeroe Islands to draw up a programme of action.
Research by the World Wide Fund for Nature (WWF) on 2,000 salmon rivers found the wild salmon was already extinct in 15 per cent of them. Only 43 per cent of the rivers surveyed were considered to be "healthy" – with sustainable stocks – but of those 90 per cent were in only four countries – Norway, Iceland, Scotland and the Republic of Ireland.
In Scotland records from the 18th century show that salmon fisheries on the rivers, Tay, Spey, Tweed, Don and Dee regularly produced colossal catches. While supplies of wild salmon remained plentiful for the best part of the 19th century there was a gradual but steady decline throughout the 20th century, partly due to over-fishing and netting.
In the late Sixties, with the advent of commercial fish farming, the hope was that pressure would be taken off the wild population.
But the very explosion of these fish farms is what conservationists now fear has accelerated rather than prevented the demise of the wild salmon. The escape of thousands of genetically inferior farmed fish over the years has enabled them to breed into the native stocks of wild salmon, with disastrous international consequences.
In addition, stocks of wild salmon have been devastated by over-fishing, climatic changes and pollution.
Mr Taylor said: "In the United States there are at least eight rivers which were previously abundant in wild salmon which now have less than 150 of the fish returning to spawn.
"This is an international problem, which requires international legislation."
A coalition of environmental groups is now pressing for the North Atlantic Salmon Organisation, an international body of salmon fishing nations, to take immediate action or risk seeing the species wiped out in the wild.
Tom Grasso, the US director of the WWF's marine conservation programme, said: "With wild Atlantic salmon stocks fading fast in countries including Germany, France and Spain and disappearing completely in some rivers on the other side of the Atlantic, it is time to act to prevent further declines."
George Baxter, of WWF Scotland, said: "We would like to see fish-farm-free zones at the mouth of rivers or bays and other places where their presence could detrimentally affect wild salmon."
If farms are allowed to occupy the mouth of rivers then any wild salmon returning to spawn are put at a serious disadvantage.
"In the UK salmon farms sited near the mouth of wild salmon rivers and in many sea lochs are risking a spread of parasites and damage to wild populations," Mr Baxter said. "The wild salmon needs protection. If we do not see a moratorium on further expansion or any serious consideration that some farms may have to move, then we will fail in safeguarding these magnificent fish."
The coalition would also like to see governments buy back the licences from drift net fisheries, which operate on the coasts of Ireland and England and on the wild salmon's migratory feeding grounds off the Faeroe Islands and west Greenland.