Wild trout in Scottish lochs are growing to unprecedented sizes, up to 20 times their typical weight, due to a practice known as 'cage-grazing,' according to environmental activists. These unusually large trout, dubbed 'Franken-trout' by some, are reportedly consuming leaked food pellets from salmon farms, leading to concerns about ecosystem disruption.
Activists claim that multinational aquaculture company Cooke Aquaculture, which operates salmon farms in Scotland, is allowing fish food to escape its cages. Wild trout are then consuming these high-energy pellets, allowing them to grow to sizes of up to 20 pounds (9kg), a significant increase from the average Scottish loch trout weight of around 1 pound (0.45kg).
Dale Vince, founder of the Green Britain Foundation, stated that factory farms in wild lochs create an uncontrollable situation where feed, chemicals, and waste enter the water. He described the oversized trout as a direct result of this leakage, gorging on food intended for farmed salmon. This phenomenon is particularly noted in areas like the Loch of Cliff in Shetland.
Nick Underdown, Scotland director at WildFish, characterized the situation as a symptom of an inadequately regulated industry. He warned that artificially fattening wild trout on industrial salmon feed can alter their natural behavior and predatory role within lochs. Furthermore, he raised concerns about wild fish ingesting antibiotics, which are sometimes used in salmon farms to manage disease outbreaks and are typically administered through feed.
Cooke Aquaculture has stated that its sites are subject to strict environmental regulations and ongoing monitoring. A spokesperson for the company indicated that antibiotics had not been used at the Loch of Cliff facility for many years. The company supplies fish to major retailers including Waitrose, M&S, and Tesco.
Beyond the issue of oversized trout, campaigners are raising broader concerns about the salmon farming industry. These include the role of salmon farms as breeding grounds for sea lice, which can affect wild salmon populations, and the potential for escaped farmed salmon to interbreed with native fish, potentially impacting genetic diversity. The impact of large volumes of fish faeces released from farms is also a contentious issue, with some scientists suggesting it can reduce water quality, a claim disputed by the industry.
A Scottish government spokesperson acknowledged that some wild brown trout may grow larger by feeding on uneaten fish farm pellets. However, the government stated there is no evidence to suggest that this localized excess food affects the overall viability of brown trout populations. This assessment contrasts with the concerns voiced by activists and some local guides who have observed a significant increase in the size of trout in areas near fish farms.
The demand for farmed salmon has seen a notable increase, with sales rising by 7.3 percent in the year leading up to April, according to Salmon Scotland. This surge in demand is partly attributed to health-conscious consumers.