Sea lice killing ‘large numbers’ of salmon

Sea LiceSCOTTISH fish farms are spreading a deadly parasite that now kills more than a third of wild salmon in the north-east Atlantic, experts warned today.

• Farmed salmon in Scotland are ravaged with disease, say anti-aquaculture campaigners

• FoI request reveals amoebic gill disease, prliferative gill inflammation and chlamydia are ‘rife’ among stocks

A new international study 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 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-per-cent 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.”
The Scotsman
Published on Tuesday 6 November 2012 22:10

Sea lice killing ‘large numbers’ of salmon – BBC

Large numbers of free ranging salmon are being killed by parasitic sea lice in European waters every year, an international study has suggested.

The research involved the release of 280,000 tagged salmon smolts into 10 rivers in Ireland and Norway.

Sea lice were responsible for 39% of deaths among the young fish, according to the study’s newly-published results.

Scientists from University of St Andrews’ Scottish Oceans Institute worked on the research.

Also involved were the Department of Zoology at the University of Otago in New Zealand; Atlantic Veterinary College at the University of Prince Edward Island in Canada; Inland Fisheries in Ireland; the Institute of Marine Research in Norway; and the Norwegian Institute for Nature Research.

The scientists said natural mortality of wild salmon during their ocean migration could be as high as 90-95%, with deaths caused by a variety of factors including sea lice.

Prof Martin Krkosek from the University of Otago stated that “We have learned that parasites are taking a very large share of the catch”

The creatures are a naturally occurring parasite.

The pest also affects the salmon farming industry. Its efforts to control sea lice include the introduction of ballan wrasse, a so-called “cleaner-fish” that prey on the pest, to a farm in the Western Isles.

Prof Christopher Todd, of the Scottish Oceans Institute, said it was important the that industry continued to give control measures high priority.

Angling organisations the Association of Salmon Fishery Boards (ASFB) and Rivers and Fisheries Trusts of Scotland (Rafts) said the study confirmed that, in some circumstances, fish farming was having “highly significant impact” on the health of wild salmon.

Fish farmers said there were many possible causes for the loss of wild fish at sea, including seals, fishing and a lack of food.

‘Major drivers’
The sea lice research team analysed the rates of survival of salmon when they returned to freshwater as mature adults.

The data analysed included 24 trials carried out between 1996 and 2008 which involved the 280,000 individually tagged smolts that were released into rivers.

In each trial half the fish were treated chemically before their release to protect them from sea lice infection during their first one to two months at sea.

The remainder in each trial were untreated control fish.

A proportion of each group were then recovered as adults on their return to coastal waters a year later.

By comparing the tags recaptured from both the treated and control groups in each trial, the researchers showed that sea lice were responsible for an average 39% of the total mortality losses of salmon at sea.

Prof Martin Krkosek, of the University of Otago and who led the study, said the research was similar to clinical studies in medicine but with fish instead of human patients.

He added: “Usually we think of food, climate, predators and fishing as the major drivers of fish abundance, but we have learned that parasites are taking a very large share of the catch.”

In a joint statement, the ASFB and Rafts welcomed the research.

The statement added: “In some circumstances and in some locations, sea lice arising from farmed fish can have a highly significant impact on wild salmon.

“Indeed, over the last 20 years there has been no substantive evidence to counter the hypothesis that sea lice arising from aquaculture cages harm wild salmon.”

Scott Landsburgh, chief executive of Scottish Salmon Producers’ Organisation, said suggestions that the primary origin of sea lice on wild fish came from farms did not “stand up”, adding that the parasite was endemic in the marine environment.

He added: “The consensus amongst the scientific community is that the overwhelming majority of wild salmon, 95% of total populations according to this paper and higher according to other published papers, die at sea – this has nothing to do with salmon farming.

“Major international organisations and projects are in total agreement that the largest problems for the survival of wild salmon are the conditions at sea – this is where further research should be undertaken.”
Published 7 November 2012

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