With potential young wild salmon instead being converted into hybrids because of the presence of cultivated fish, the study suggests the resulting decline in adult survival could eventually wipe out a population.
Ferguson says the influence of escapee salmon also removes significant genetic differences between wild populations. For instance, this may affect their ability to home in on native breeding rivers when returning as adults to spawn.
He added: "Maintaining genetic variation is important for any species to continue to adapt to changing environmental conditions such as global warming. However, even if all wild populations were genetically the same there would still be a reduction in fitness due to interaction with domesticated salmon."
This is because farm salmon have been bred selectively to grow quickly. The ability to hunt at sea, jump waterfalls and locate a specific river aren't attributes fish farmers look for.
"It can be concluded that genetic changes leading to reduced survival in the wild is a feature of all domesticated salmon and consequently hybrids between farm and wild fish also have reduced survival," Ferguson said.
Conservationists say measures that would reduce or even halt harmful genetic impacts caused by fish farm escapes include closed-contained marine farms (instead of sea cages) and the use of sterile fish known as triploids for salmon aquaculture.
Richie Flynn, of the Irish Salmon Growers Association (ISGA), responded to the study by saying, "The industry will take note of the report in adhering to the strict protocols agreed by ISGA members to prevent farm escapes."
He added: "It is hoped that those who manage river systems will also take note of the consequences of their actions in restocking those systems."
Flynn refers here to another conclusion of the Burrishoole studythat deliberate stocking of young cultivated salmon to boost depleted wild populations is likely have the opposite effect to that intended.
While monitoring farm salmon parr in the river, Ferguson and his team found that these larger, more aggressive juveniles chased away 57 percent of native parr. Ferguson adds that deliberate stocking means large numbers of pure farm juveniles are introduced in the first generation, causing even lower overall survival than hybrid fish.
He added: "Some have argued that stocking does good by introducing new genetic variation. Our study and similar studies on salmonids in North America shows this to be completely false."
There are also those who thought farming of Atlantic salmon would help reduce pressure on overfished wild stocks. Now it seems the industry has set the species on a very different course. Not on that incredible migration from ocean to river, but one that puts its very survival in doubt.
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