PRIZED by conservationists, anglers and diners, wild salmon is one of Scotland's most iconic species and biggest exports.
But a first-of-its-kind study by Scottish Government scientists reveals how some Scottish Atlantic salmon populations are increasingly Norwegian.
That's after DNA from fish farm escapees entered native groups through breeding.
Samples were taken from juvenile fish in more 250 sites between 2018 and 2019. Signs of "introgression" of genetic material were found at almost one quarter of the sites. While most were rated as good (almost 77%), 8% were graded as poor and 6% as very poor, with researchers confirming that these were present in areas where fish firms are operating in sea lochs.
They span from the Shetlands to the Clyde. It's understood the health of wild fish salmon stocks may now be at risk.
The report states: "The genetic integrity of populations observed across the country was not uniform. Rather, signs of introgression were concentrated in areas of marine aquaculture production and freshwater smolt rearing. Outside these areas, little to no genetic changes were detected."
READ MORE: Skye: Both sides of the story of an industry which has changed island life
It goes on: "The available evidence indicates that introgression of genetic material from Norwegian farm salmon strains has altered the genetic composition of some populations within rivers near marine aquaculture production. The Shetland Isles, Hebrides and mainland west coast as far south as the Clyde were all notably affected."
And it said interbreeding between escaped farmed Atlantic salmon and wild indigenous salmon creates a "disruption of the adaptive genetic composition of individuals and populations" which "can impact their fitness, resulting in a significant negative pressure on the viability of wild populations".
Genetic changes were found around the Clyde, Argyll, Lochaber, Wester Ross, West Sutherland, the Inner and Outer Hebrides, and the River Shin and the River Ness.
The Marine Scotland paper was published earlier this month.
The charity Salmon and Trout Conservation Scotland, whose patron is Prince Charles, has called the results "a damning indictment" of the impact of salmon farming.
Its director, Andrew Graham-Stewart, said: "Farmed salmon, the great majority of Norwegian origin, are essentially domesticated animals, bred for the table. When they interbreed with our wild salmon, the offspring are inevitably unsuited and unfit to survive in the wild. The future viability of wild salmon is dependent on their genetic integrity not being compromised by domesticated strains."
While there is no commercial fishing of wild salmon, more than 200 fish farms operate around Scotland. Together they produce in excess of 150,000 tonnes of the product every year. High demand has seen the industry boom over the last 50 years and taken its value to more than £1billion, and there are ambitious plans for future growth. Industry leaders, who have also had to tackle the hit from Brexit and Covid disruption, say this will be sustainable.
READ MORE: Loch Long Salmon: Plans to develop Scotland’s first semi-closed fish farm
However, there have also been a string of controversies around the use of imported ova and the escape of farmed fish, which are kept in pens for around two years before being "harvested" for consumption, as well as damaging outbreaks of parasitic lice which have, in the worst occasions, led to the dumping of large numbers of salmon.
Critics have pointed to the loss of around 9.5m farmed salmon per year – around 20% of the total stocks – from causes including lice, disease and the chemicals used to treat the problems, as well as the release of effluent into waters.
The Scottish Salmon Producers Organisation says the sector is "world-leading in its use of cleaner fish such as wrasse and lumpfish" to "live among farmed salmon and pick off and eat any sea lice", while pens are fitted with tough high-tension with "lice skirts" and other features to protect stocks.
This week a representative of the body said told The Ferret it expects "nine out of every ten salmon farms are meeting" the "tough environmental standards" set down by the Scottish Environment Protection Agency on pollution.
Why are you making commenting on The National only available to subscribers?
We know there are thousands of National readers who want to debate, argue and go back and forth in the comments section of our stories. We’ve got the most informed readers in Scotland, asking each other the big questions about the future of our country.
Unfortunately, though, these important debates are being spoiled by a vocal minority of trolls who aren’t really interested in the issues, try to derail the conversations, register under fake names, and post vile abuse.
So that’s why we’ve decided to make the ability to comment only available to our paying subscribers. That way, all the trolls who post abuse on our website will have to pay if they want to join the debate – and risk a permanent ban from the account that they subscribe with.
The conversation will go back to what it should be about – people who care passionately about the issues, but disagree constructively on what we should do about them. Let’s get that debate started!
Callum Baird, Editor of The National
Comments: Our rules
We want our comments to be a lively and valuable part of our community - a place where readers can debate and engage with the most important local issues. The ability to comment on our stories is a privilege, not a right, however, and that privilege may be withdrawn if it is abused or misused.
Please report any comments that break our rules.
Read the rules here