A storm caused tens of thousands of fish to flee the farms where they lived in northern Europe. There are possible complications for all fish consumers.
When Storm Amy hit the Scottish Highlands in early October, it ripped through the sea nets of a salmon farm, releasing around 75,000 fish into the open waters of Loch Linnhe.
The size of this leak is alarming and comes at a time when the Wild Atlantic salmon — already classified as “endangered” in the UK — continues to decline.
For an animal so central to the UK’s ecology, culture and economy, the incident has serious implications.
At first glance, it may even seem like good news: thousands of fish freed from captivity, perhaps even helping to reinforce wild populations. But the reality is far from comforting.
These fish are not wild salmon in any meaningful sense. They are highly domesticated animalsselected over decades for characteristics that make them profitable in captivity — but ill-prepared to survive in the natural environment.
From wild fish to aquatic livestock
Aquaculture — the farming of fish and other aquatic species — has become one of the fastest-growing forms of food production in the world.
The highest valued marine species is Atlantic salmon, which represented 18% of the total value of global marine aquaculture production in 2022. The UK is the world’s third largest producer, with almost all production concentrated off the coast of Scotland.
Modern salmon fish farming generally involves raising fry in freshwater hatcheries, before being transferred to cages or cages at sea.
Each farm can have six to ten large nets, with up to 200,000 fish in each.
The nets are open to tidal currents, allowing clean, oxygenated water to enter and waste to exit. However, this also makes them vulnerable to adverse weather conditions.
To reduce the risk, nurseries are installed in more sheltered coastal regions, such as fjords or lochs, but this protection is limited.
Storm Amy clearly showed this vulnerability.
Domesticated as sheep or dogs
Atlantic salmon farming began in the 1970s. Since then, the species has been subjected to intense artificial selection, just as happened with sheep, dogs or chickens.
The fish were chosen for faster growth, late sexual maturation, disease resistance and other commercially desirable characteristics.
After 15 generations of selection, these farmed salmon are among the most domesticated fish species in the world, already very different from their wild relatives. They are generally larger, mature differently and they feed on pelleted food instead of hunting live prey — changes that make them more vulnerable to predators.
Some even have characteristics that make them less attractive to wild salmon as breeding partners. Many would not survive long in the natural environment.
The real danger: interbreeding with wild populations
The problem isn’t just that farmed salmon die after escaping — but what happens when some don’t die. Studies show that in certain rivers in Scotland and Norwaymore than 10% of salmon caught are of farmed origin, with higher numbers near intensive fish farming areas.
Although these fish are poorly adapted to the natural environment, some manage to survive long enough to reach rivers and try to reproduce.
When they are crossed with wild salmon, their offspring inherit a mixture of characteristics — neither completely wild nor completely domesticated — making them less suitable for the natural environment. This process, called genetic introgression, gradually deteriorates the genetic integrity of wild populations.
The timing makes this incident even more worrying: now is the time when wild salmon are returning to Scottish rivers to spawn. The sudden influx of tens of thousands of farmed fish increases the risk of crossbreeding and long-term genetic damage.
A threat that could affect the entire species
The scale of this escape is extraordinary. The estimated total population of wild salmon returning to Scotland annually is around 300,000 fish. The release of 75,000 farmed salmon is equivalent to approximately a quarter of that number.
Even if just 1% of escapees survive and reproduce, that would represent about 750 fish entering rivers and potentially mixing with wild populations.
A report by Marine Scotland (2021) concluded that rivers near nurseries are in a “very poor condition”, with evidence of significant genetic changes.
Worryingly, other neighboring rivers, previously classified as being in “good condition”, may now be at risk.
Wild Atlantic salmon already face multiple human-caused threats: climate change, habitat loss, pollution and invasive species.
Genetic pollution caused by escaped farmed fish is yet another blow — and further reduces the species’ ability to withstand other environmental pressures.
Storm Amy’s runaway may have been a single incident, but It is symptomatic of a broader problem. As storms become more intense due to climate changethe probability of future leaks will only increase.
Without stricter regulation, better containment measures and effective genetic monitoring of wild populations, these events could continue to destroy what is left of wild salmon in the UK.
