A large proportion of the salmon captured after a fish farm escape of up to 8,000 fish at Killary Harbour, northern Connemara, last summer were sexually mature enough to breed with wild populations, an investigation by Inland Fisheries Ireland (IFI) has found.
This represented a significant threat to wild salmon populations “through genetic contamination, impacting the overall ability of future salmon generations to survive in the wild”.
Responding to the findings, the environmental group Galway Bay Against Salmon Cages said they indicate the scale of the threat to wild salmon populations throughout the west of Ireland that would remain until “salmon farms are taken out of bays along the coast”.
IFI scientists confirm the upriver migration of farmed fish from was over a large area; “well over 100km in both north and south directions from the presumed source of the incident”.
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The fish farm operated by the Mannin Bay Salmon Company and licensed to Docon Ltd of Mulranny, Co Mayo, estimated that between 7,000 and 8,000 fish escaped before a damaged net was repaired and then replaced.
The State environmental agency report shows 20 per cent of the male farm-reared fish were sexually mature and could breed with wild Atlantic salmon during the 2024/2025 spawning season.
Escaped salmon were confirmed in 12 rivers in Galway and Mayo between August 17th and September 30th but 30 rivers were potentially exposed – 26 of these were special areas of conservation for the species.
A minimum of 450 salmon were estimated to have entered rivers after the escape event. Some 50 recovered salmon underwent a full biological examination, and were subsequently verified as being of farm-origin by genetic analyses.
Dr Seán Kelly, IFI’s research officer and lead author, said: “The substantial geographical spread over which escaped farmed salmon were confirmed – in a critical region for wild Irish Atlantic salmon populations – is particularly concerning.”
Salmon suspected to be of farmed origin were caught by anglers in August and September 2024 in Mayo and Galway, and also at IFI’s fish-trapping facility at the National Salmonid Index Catchment, Co Mayo. Salmon specimens caught by anglers were sent to IFI’s river Erriff research station nearby for verification. Escaped farmed salmon were initially identifiable by having an out-of-season silver appearance.
“The potential presence of sexually-mature farmed salmon in wild Irish salmon rivers during the spawning period poses a risk of interbreeding with wild salmon,” said Dr Cathal Gallagher, head of research and development at IFI. “They can pose a significant threat to wild salmon populations through genetic contamination, impacting the overall ability of future salmon generations to survive in the wild.”
The investigation of a single relatively small escape in terms of reported numbers “highlights the potentially large-scale ecological implications that can arise more generally from marine salmon aquaculture escape events”, Dr Gallagher said.
Galway Bay Against Salmon Cages spokesman Billy Smyth said the report confirmed the threat from escapees, especially when there was “no mitigation available to net the fish as soon as they escaped”.
He reiterated the belief many more fish escaped than indicated and in turn entered rivers. “Once salmon enter fresh water they stop feeding. They’re very hard to catch without netting; that was not allowed.”
He said to protect wild populations of Atlantic salmon and sea trout the Department of Agriculture, Food and the Marine (as licensee and regulator) should take out salmon farms from coastal bays. “Salmon farmers should be bought out like the drift-netters were in 2007.”
Mannin Bay Salmon Farm and the department were asked to respond to the findings but have yet to do so.
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