IFI publishes scientific report on escaped fish farm salmon in Mayo

A new study has revealed that a proportion of the salmon captured after a fish farm escape at Killary Harbour last year were sexually mature enough to breed with wild populations.

Inland Fisheries Ireland (IFI) scientists have completed an analysis of salmon believed to have escaped from a fish farm in Killary Fjord in Co. Mayo in August 2024.

They note the upriver migration of farmed fish was well over 100km in both north and south directions from the presumed source of the incident.

The State environmental agency has today published a new scientific report on the escapees, which showed that:

* 20% of the male farm-reared fish were sexually mature and could breed with wild Atlantic salmon during the 24/25 spawning season;

* Escaped salmon were confirmed in 12 rivers in Galway and Mayo between August 17 and September 30 - but 30 rivers were potentially exposed;

* 26 of these 30 rivers comprise Special Areas of Conservation;

* A minimum of 450 salmon were estimated to have entered rivers after the escape event;

* 50 salmon underwent a full biological examination and were subsequently verified as being of farm-origin by genetic analyses;

* There was a 60:40 female-to-male ratio in the captured farmed fish.

Dr. Seán Kelly, IFI research officer and lead author of the study, 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.

Dr. Cathal Gallagher, head of research and development at IFI, commented: “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.

“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.

“Overall, this documentation 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.”

Escaped farmed salmon were initially identifiable by having an out-of-season silver appearance.

IFI have thanked all anglers who presented suspected farmed salmon specimens to staff for verification at IFI’s River Erriff research station in Mayo.