Salmon which have escaped from fish farms are breeding with wild salmon and reducing their chances of survival, according to new research.

The findings will be presented to a conference organised by the Atlantic Salmon Trust in Edinburgh.

The results of the 10-year research project comparing survival rates at sea appear to confirm some expert's worst suspicions.

They suggest that the escapees breed with the wild fish - and make it less likely that they will return to the rivers to spawn.

The industry says the situation is improving

Dick Shelton, of the Atlantic Salmon Trust, said: "The worry has always been that if a lot of farmed fish end up inter-breeding with these stable, local populations then there will be very serious consequences for the later life of the hybrids and indeed the progeny of the farmed fish."

Scientists who carried out the research are due to release a summary of it at a conference in Edinburgh with full details to be published in a scientific journal.

To make matters worse, the young farmed salmon grow more quickly and displace their wild counterparts.

Mr Shelton said: "The most worrying thing of all was the finding that the larger progeny of the farmed fish were often able to out-compete the local 'lads' in their river and then fail at sea and that of course would be the worst of all possible outcomes."

Hundreds of thousands of salmon are estimated to have escaped from fish farms.

These break-outs included a mass escape from cages off Kirkwall, in Orkney, this spring.

Quality of cages

Earlier this year conservation groups said the numbers of wild Atlantic salmon had declined by two-thirds in the past 30 years.

They argued that the rapid growth of salmon farming was one of the main threats.

The industry disputes reports that salmon may be extinct in some rivers on the west coast because of the problem but said it accepts that escapes must be halted.

Dr John Webster, of Scottish Quality Salmon, said: "The quality of the cages is improving.

"When the industry began 30 years ago most of the cages were wooden structures and they are now built from galvanised steel with very substantial moorings and nets.

"The key is to use equipment that's suitable for the purpose and also to inspect and maintain them properly so that they remain intact."