WILD Atlantic salmon stocks will be wiped out within decades because of interbreeding with escaped farmed stocks, leading scientists have warned.
New research has revealed that the unique genetic identity of the king of fish is rapidly being eroded by escaped fish from farms around the Scottish coast.
The world's most influential salmon conservation organisation fears that in as little as
50 years the ability of the fish to navigate thousands of miles across the ocean and then back to their home rivers may be damaged by constant interbreeding.
In light of new research which suggests stocks will disappear within 10 generations, the North Atlantic Salmon Conservation Organisation (Nasco) is campaigning for marine farmers to breed a new sterile species to guarantee the genetic make-up responsible for the fish's finely tuned navigational skills will not be eroded.
This safeguard will ensure that even if farmed salmon do escape from their cages and mix with wild salmon during migration, they will not genetically 'pollute' their wild cousins.
Malcolm Windsor, secretary of Nasco, which was formed in 1983 to save the wild salmon, has warned that interbreeding between the two stocks will result initially in an increased population, but one which will soon decline, as the hybrid fish are less able to deal with their environment and weaker for breeding.
Windsor fears that if wild salmon are phased out in this way, the genetically weak hybrids will become increasingly prone to disease or genetic mutation, leaving a dangerously vulnerable population and no original gene pool to fall back on. He believes people will support the sterilisation of farmed salmon when they see what is at stake.
He said: "People are comforted by the fact that there are still wild salmon living in rivers like the Thames and the Clyde. It shows us that we are still maintaining a balanced environment. If this were to be over within 50 years I think people would be disconcerted. It is strange to think a meat that we will continue to buy in the supermarkets will be extinct from the wild."
However, the move is meeting with fierce resistance from the industry, which insists sterile salmon cannot be farmed commercially and that the public would not buy it.
Salmon farming is a hugely successful £350m-a-year industry that produces around 150,000 tonnes of the fish for human consumption. Scotland is one of the main producers, and a worldwide glut means prices at around £10 a kilo are now less than white fish species such as cod.
Although the industry says the number of escapes is falling, winter storms can dramatically change the picture. In January last year, more than 670,000 farmed salmon escaped from cages in sea lochs on the west coast of Scotland - at least six times more than the year before.
Nasco has now opened talks with the industry about trials on using sterile fish.
The current crop of farmed fish are bred from specially selected stock that grow fast and mature early. They are artificially nurtured in hatcheries before being released into cages. If they escape, they remain fertile fish, capable of breeding.
Sterile fish are produced by blasting fish eggs with a high-pressure water jet which prevents them shedding the third female chromosome they carry, in a process called triploidisation. So-called triploid fish are unable to reach maturity and so are unable to breed.
Windsor explained: "This is a simple way of producing sterile fish which, at a stroke, would solve the genetic pollution problem. We have talked to the industry about it and they fear a consumer reaction.
"We don't think that would be a problem as sterile fish are not genetically manipulated. Our view is that the public would accept it if they were told this would help wild salmon."
But the Scottish Salmon Producers' Organisation (SSPO) said the industry was at this stage unlikely to agree to a request to farm sterile fish. John Webster, the SSPO's scientific adviser, said: "We cannot farm fish that way. Keeping the fish in the cages where they belong is what we have to do.
"Escapes are reducing, although there was a blip last year because of winter storms. Nothing is foolproof, but the industry is working very hard to keep fish in their cages."
Webster added that triploid fish do not produce the uniform fish that retailers wanted.
"In a farming situation they can develop abnormal shapes and they are less resistant to certain diseases," he said. "They also do not grow as well."
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Farmed salmon reared in cages have been selectively bred by the industry from originally natural stocks which are known to grow fast.
To produce sterile salmon, marine scientists harvest eggs known to be all-female.
After fertilisation, they are subjected to high water pressure for 10 minutes. This prevents the third female chromosome inside the egg from splitting off.
The fertilised eggs can be reared in a hatchery and then released into cages. If these fish escape, they cannot interbreed with wild salmon.
