Salmon farms result in sea lice increase

Salmon farms have a negative impact on wild sea trout, a new definitive scientific paper has concluded.

The study, which reviews over 300 scientific publications on the subject, confirms evidence collated since the early 1990s in Ireland regarding the impact of sea lice on wild sea trout stocks, particularly in relation to the collapse of Connemara’s sea trout stocks.

Inland Fisheries Ireland and Galway Bay Against Salmon Cages (GBASC) have both welcomed the report entitled ‘Effects of salmon lice Lepeophtheirus salmonis on wild sea trout Salmo trutta—a literature review’.

They argue the conclusions of the report cast doubt over plans for a massive fish farm in Galway Bay.

The project was funded by the Norwegian Seafood Research Fund which provides investment in Norwegian seafood industry-based research and development. A team of top international scientists from Norway, Scotland and Ireland reviewed all available published studies on the effects of sea lice and have concluded that sea lice have negatively impacted wild sea trout stocks in salmon farming areas in Ireland, Scotland and Norway.

The study also examined the potential effect of sea lice on salmon and concluded that sea lice have a potential significant and detrimental effect on marine survival of Atlantic salmon with potentially between 12% and 29% fewer salmon spawning in salmon farming areas.

These conclusions concur with previously published Inland Fisheries Ireland (IFI) research on the potential impact of sea lice from marine salmon farms on salmon survival. The studies reviewed indicate that salmon farming increases the abundance of lice in marine habitats and that sea lice in intensively farmed areas have negatively impacted wild sea trout populations. The effects of sea lice on sea trout are increased marine mortality and reduced marine growth.

IFI, who welcomed the study, said it has consistently called for marine salmon farms to maintain sea lice levels close to zero prior to and during the wild sea trout and salmon smolt migration period in spring. It also raised concerns regarding the location of salmon farms in the estuaries of salmon and sea trout rivers.

The Board of Inland Fisheries Ireland in a statement said: “This new scientific review paper confirms the need for very tight regulation of sea lice levels on salmon farms and raises legitimate concerns with regard to the potential impact of new large scale salmon farms proposed along Ireland’s west coast on salmon and sea trout stocks.

“Regulators will now need to consider the results of this comprehensive review when making decisions on the sustainability and approval of future marine salmon aquaculture licences and the regulation of sea lice at existing sites so as to ensure no negative impact on salmon and sea trout stocks.”

GBASC also welcomed the report and said it ‘blows out of the water’ previous research which said that sea lice cause just 1% of mortality in wild salmon.

“In light of the results of this new study we also call on Minister Simon Coveney not to grant any licence large or small for a salmon farm in Galway Bay. This new study proves that if a licence is granted for Galway Bay, it will have disastrous consequences for the wild salmon and sea trout in the Corrib and other rivers surrounding Galway Bay,” the lobby group said.