Mowi funds three-year monitoring project after escape of 75,000 fish
Salmon farmer Mowi Scotland and local wild fishery management body the River Lochy Association have agreed a long term and wide-ranging scientific study to examine the potential impacts of the fish escape from Mowi’s Gorsten farm in Loch Linnhe in October.
The study, funded by Mowi, will also utilise the genetic expertise of the Institute for Biodiversity and Freshwater Conservation at UHI (University of the Highlands and Islands) Inverness, and will enable Mowi and the River Lochy Association to monitor and mitigate any adverse impacts on wild salmonid biology within the catchment area.
An estimated 75,000 salmon with an average weight of 860g escaped from the Gorsten site in Upper Loch Linnhe on October 5, 2025 as a result of the extreme weather conditions experienced during Storm Amy.
The fish were sexually immature and were raised in a recirculating aquacuture system (RAS), which Mowi said meant that a very low level of survival in the wild was expected.
The immediate post-escape actions taken by Mowi, in consultation and coordination with the River Lochy Association, were as follows:
- Immediate recapture of fish that entered local and more distant rivers. Due to the timing of the escape so close to the salmon and trout spawning season, and the height of the rivers at the time, it was decided not to use nets but to rod catch as many fish as possible.
- Over 100 anglers deployed throughout the region and beyond. All captures were reported on the Fisheries Management Scotland escapes reporting app. As of today, 440 captures (all immature and weighing 0.5 to 2.5kg) have been reported, with the vast majority in the lower reaches of the Rivers Lochy and Leven.
Long-term study
Mowi and the River Lochy Association have now agreed the scope of a long-term study which will include the following:
- Scale samples will be taken from the majority of rod-caught adult returning salmon in both the Lochy and Leven rivers in 2026 and 2027. These samples will be genetically screened against the farm stock to ascertain the level (if any) of farmed fish from this escape in the returning adult fish from the ocean.
- In 2026 local teams of fisheries biologists will undertake timed electro-fishing surveys on all major salmon catchments in the Upper Linnhe region and take samples of fry for genetic screening. This will form the baseline ‘pre-incident’ survey. Fifty eight known fry sampling sites will be used with a wide geographic spread of sites in each catchment. A minimum of 20 and a maximum of 30 fry will be sampled at each site using non-lethal caudal fin clips taken from anaesthetised fish.
- In 2027 and 2028 the above fry sampling will be repeated, and these years will be used to detect the genetic impact (if any) in the wild population from this escape event.
Commenting on the plan, Jon Gibb, manager of the River Lochy Association and director of the Lochaber District Salmon Fishery Board, said: “Obviously an escape of farmed salmon into the wild is something that nobody wants to see. But I am confident that between Mowi and the River Lochy Association, we have designed a comprehensive three-year genetic monitoring plan that will definitively identify whether there will be any impact whatsoever from this unfortunate incident on the local wild salmon population.”
Stephen MacIntyre, head of environment at Mowi Scotland, said: “While we are disappointed this incident occurred, we acknowledge our responsibility to monitor and assess the potential for any adverse impacts on local wild salmon populations.
“Using this scientific approach, the monitoring study will determine whether there is evidence of any changes in the genetic composition of wild salmon arising from the escape incident. We look forward to supporting the delivery of the study with the River Lochy Association over the next three years.”
Little impact on wild fish
Speaking a couple of weeks after the Gorsten escape, Mowi Scotland chief operating officer Ben Hadfield told Fish Farming Expert that he believed the incident would have little effect on wild salmon.
He said that when 48,000 fish escaped from a farm at Carradale during another named weather event, Storm Ellen, in 2020, Mowi funded work to discover whether the fish had interbred with the wild population, and found the escape had almost no detectable impact.
“There were 5,300 wild fish that were analysed in the rivers after that event, and only one of them had any kind of link to aquaculture ancestry,” said Hadfield.
He said he expects the project on the River Lochy to show that most of the escaped fish succumbed to predation from birds, which he said was also a massive problem for wild fish on the river.
