The breakout of around 10,000 salmon Friday from a farm on islands off the north coast of Scotland would introduce extra competition for food, dilute wild salmon genes through mating, and possibly spread disease, they said.

"When farmed salmon escape they not only compete with wild fish for precious food resources but can also spread parasites such as sea lice and act as carriers for diseases," said Don Staniford, a salmon farming researcher. "Wild salmon numbers are in steep decline while, coincidentally, the salmon farming industry has expanded," he said, adding that in some areas of Scotland wild salmon were now extinct.

Willie Baxter, owner of Orkney Sea Farms, said around 10,000 fish had escaped and 200,000 were killed after the strongest and fastest tide of the year Friday broke their cages.

Richard Dixon of Friends of the Earth said farmers should invest in stronger cages since Scotland is famous for bad weather.

The breeding of farmed salmon with their wild cousins polluted the genes of the wild fish, he explained. "Farm salmon have been selectively bred to forget the species' habits in the wild. That means they forget when and where to migrate in order to breed," he said.

A spokesman for the Scottish Executive said it would soon introduce legislation making it a legal requirement for fish farmers to notify the executive of any break-outs.

Hundreds of fishers flocked to the coast over the weekend to hook the escaped salmon, said Mark Hirst, spokesman for Orkney Islands Council. But the council had warned people not to eat dead or dying salmon found on the coast because they could pose a health risk, he added.