SCOTTISH fish farms are spreading a deadly parasite that now kills more than a third of wild salmon in the north-east Atlantic, experts warn today.
A new international study has found “unexpectedly large” numbers of wild salmon are dying in European waters every year, with 39 per cent killed by the flesh-eating lice.
A leading academic at the University of St Andrews, who took part in the research, said it showed Scotland’s multi-million-pound salmon farming industry needed to do more to prevent sea lice from destroying wild fish stocks – as well as protecting the sector.
The study, disputed by the industry, comes as campaigners renewed warnings that a range of parasitic diseases were spreading through Scotland’s fishing industry “like cancer”.
The sea lice paper, published today in the Proceedings of the Royal Society B journal, stated that “the parasitic crustaceans were probably acquired during early marine migration in areas that host large aquaculture populations of domesticated salmon, which elevate local abundances of ectoparasitic copepods (sea lice).”
Co-author Professor Christopher Todd, specialist in marine ecology at the St Andrews Scottish Oceans Institute, warned: “This high-percent mortality attributable to sea lice was unexpected. The salmon aquaculture industry has long placed a high priority on controlling sea lice on their captive salmon – but these results do emphasise the need for the industry to not only maintain the health of their own stocks, but also to minimise the risk of cross-infection of wild fish.”
He added: “For the first time, we can effectively place a reliable value on the predicted mortality loss of free-ranging salmon subject to infection from this parasite.”
Environmentalists renewed calls for the Scottish Government to toughen legislation in the forthcoming Aquaculture and Fisheries Bill and force the industry to provide more information about the extent of diseases.
Alex Kinninmonth, of the Scottish Wildlife Trust, said: “Sea lice are naturally occurring, but fish farms provide ideal breeding conditions which create unnaturally high populations which juvenile wild salmon are very susceptible to when they migrate to sea.
“There is a voluntary code of conduct on measures like synchronised fallow periods to break the life cycle of the lice. The government suggested publishing sea lice data farm by farm, but that has now been dropped from the bill.”
The Association of Salmon Fishery Boards and the Rivers and Fisheries Trusts of Scotland said the research confirmed that sea lice from farmed fish could have a “highly significant impact on wild stocks”.
“Over the last 20 years there has been no substantive evidence to counter the hypothesis that sea lice arising from aquaculture cages harm wild salmonids,” a spokesman said.
However, the Scottish Salmon Producers’ Organisation (SSPO) chairman, Professor Phil Thomas, said the study appeared “at odds with a number of substantial scientific studies” demonstrating that sea lice were “not a significant factor influencing wild salmon conservation”.
He added: “The report is consistent with the numerous other international studies that show the overwhelming majority of wild salmon, 95 per cent and above of total populations, die at sea during their oceanic migration.” That figure was also noted in the latest study, but authors believe their results are statistically valid.
A Scottish Government spokesman said it wanted reporting of sea lice data to improve, but remain voluntary.Yesterday, Don Staniford, of the Global Alliance Against Industrial Aquaculture, said diseases were rife in the Scottish salmon farming industry.
The SSPO refused to respond to the activist, whose views were branded “prejudiced and unreliable” by a Canadian judge in a recent defamation case.