Mass escapes from the Orkney Islands' salmon farms may overwhelm the wild salmon gene pool, breaking the link between the genes which tell the fish when to breed and the genes which tell them how to find food. In some rivers 80% of the fish are now of farmed origin.

Research by Ian Fleming at Oregon State University found that 30% less salmon made it back to the ocean when wild and farmed salmon interbred. As well as the above genetic damage, which can take two generations to appear, scientists cited a general weakening of the species by the lice and disease rampant in salmon farms.