Sea lice. (Photo: Friends of the Irish Environment)

Sea lice kill 1pc of salmon at sea: study

REPUBLIC OF IRELAND
Tuesday, February 05, 2013, 02:50 (GMT + 9)

Sea lice infestation is not one of the factors most likely to influence the conservation status of salmon stocks, according to a study by the Marine Institute and the National University of Ireland Galway (NUIG).

This definitive long-term study, told the Irish Sea Fisheries Board (BIM), involved more than 350,000 fish released into eight different rivers in 28 separate experiments over a nine-year period. The study analysed the impact of sea lice on the marine mortality of Irish salmon smolts and assessed to what extent Irish Atlantic salmon stocks are facing sea lice-induced mortality.

The findings were published in the latest edition of Journal of Fish Diseases.

The researchers treated one group of salmon smolts with a commercial agent that shields them against sea lice infestation for eight weeks after going to sea. The return rates of control or unprotected mirror groups of fish were set against those of the treated fish to check for any additional sea lice induced mortality following their release. 

The research considered the results of a similar but much smaller study done by Inland Fisheries Ireland.

Researchers determined that the level of marine mortality attributable to sea lice infestation was approximately 1 per cent in absolute terms. 

“At these levels, it is unlikely to influence the conservation status of stocks and is not a significant driver of marine mortality,” the article reads. 

Further, the paper suggests that some researchers have reached different conclusions, but that it is only because their experimental design contained serious flaws.

The article notes the powerful trend in climbing marine mortality up to 2008.

“[But] there is no evidence to suggest that this trend is influenced by sea lice infestation levels of outwardly migrating smolts as treated and control fish are equally affected,” the study concludes.

Donal Maguire Director of Aquaculture Development Services of BIM, welcomed the study. 

“This is confirmation of the validity of the approach that we have taken with regard to the development of this industry. The scare stories in relation to sea lice being a threat to wild salmon put out by the opponents of salmon farming have no basis in scientific fact,” he stated. 

“Ireland is uniquely blessed in having an environment naturally suited to salmon farming and all stakeholders should now unite to realise the opportunities this represents and to deliver the much needed economic and employment benefits to coastal communities around Ireland,” Maguire declared.

Professor Phil Thomas, Chairman of Scottish Salmon Producers’ Organisation (SSPO), called the findings “rigorous, definitive and unequivocal.”

“They scientifically expose those who would use speculation and advocacy-based arguments as if they were facts. It is important now for salmon conservation to focus research on the true causes of mortality and the practical ways that they may be addressed or avoided,” he added.

Related article:

- Lice kill large numbers of salmon in Northeast Atlantic Ocean: study 

By Natalia Real
editorial@fis.com
www.fis.com

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