Our wild salmon and sea trout are a vital part of Scotland’s heritage and are genetically adapted to life in the wild. Farmed salmon are domesticated strains of salmon which are bred to grow quickly in farms. Escapes of farmed salmon can have negative impacts on wild salmon populations through genetic impacts arising from interbreeding.
When farmed salmon escape, it can lead to ecological interactions with wild salmon populations resulting in increased competition for resources, and genetic interbreeding between wild and farmed fish populations (known as genetic introgression).
Genetic introgression can change the genetic makeup of salmon populations, creating hybrid individuals which can have reduced survival and reproductive capability. For wild salmonid populations in Scotland already below their conservation limits, even a small number of farmed fish interbreeding with the wild population can have a huge impact. These impacts are particularly important in the current context of wild fish populations adapting to rapid climate change.
Marine Scotland have published a report which gives a national assessment of the influence of farmed salmon escapes on the genetic integrity of wild Scottish Atlantic salmon populations, which has shown that escapes have altered the genetic composition of a number of populations within rivers near marine and freshwater aquaculture production.
As a signatory to the North Atlantic Salmon Conservation Organisation (NASCO), Scotland has committed to the international obligation to meet the following NASCO goal: “100% farmed fish to be retained in all production facilities”. Despite this, there are significant numbers of farmed salmon and trout which escape, both in sea water and freshwater. In 2020 alone, nearly 140,000 farmed salmon and rainbow trout have escaped into the wild.
Fisheries Management Scotland have issued guidance which provides details on how to identify a farmed fish, and what to do should you catch one. If you suspect you have caught a fish of farm origin, please use our reporting tool to document the occurrence, and also report the catch to the Marine Scotland Fish Health Inspectorate (firstname.lastname@example.org). If a farmed fish is caught, it should be humanely killed and if possible, a sample of scales should be taken.
Case Study: North Carradale Escape
In August 2020, Mowi Scotland’s North Carradale salmon farm shifted position after its seabed anchors became dislodged during Storm Ellen. The farm contained a total of 550,000 salmon of approximately 4.2kgs in weight. Four pens were damaged, two of which experienced torn netting, and Mowi have confirmed that the cause of the escape was abrasion between the feed barge mooring lines and the pen grid mooring lines during the storm. A total of 48,834 farmed fish escaped.
Fisheries Management Scotland, alongside our members, Marine Scotland and Mowi, conducted a genetic survey to monitor the impact and extent of the escape in the rivers draining into the Firth of Clyde. Marine Scotland Science published the final report in December 2022, and an interim project report was written in March 2021. The catch locations of salmon of farm derived origin have been mapped and can be viewed below, or in full screen here.