A report by the Marine Institute shows infestations of sea lice on salmon
farms in Ireland are higher than limits set by the government. Some farmed
salmon were found to be contaminated with up to 71 sea lice each, more than
five times the acceptable threshold.
Conservationists say wild salmon are slowly becoming extinct as a result of
sea lice infestations caused by fish farms, where high levels of the marine
parasites are found.
Wild juvenile salmon and sea trout, which are vulnerable to “clouds” of sea
lice in their free-swimming larval stage, can become heavily infected with
the parasites as they swim past fish farms while leaving estuaries.
Sea lice pose little threat to adult fish, but can kill juveniles whose
scales are softer and cannot protect vital organs against attack.
Among the farms identified by the Marine Institute as having “elevated lice
levels” during September and October were those run by Mannin Bay Salmon
Company in Co Galway and a Marine Harvest fish farm in Lough Swilly, Co
Damien O’Brien, a spokesman for No Salmon Farms at Sea, a campaign
organisation, said sea lice were having a detrimental effect on wildlife
“There are surveys that show that up to 39% of young salmon smolts are
killed after being infected by sea lice while swimming past salmon farms.
“High concentrations of salmon in confined spaces attract the parasites. It
takes 11 sea lice to kill a smolt. Some wild salmon caught by anglers close
to salmon farms around Ireland have been found to be carrying more than 50
parasites,” said O’Brien.
In the wild, salmon generally become infected with small numbers of the
tadpole-like sea louse, Lepeophtheirus salmonis, as adults. Farmed fish are
far more vulnerable.
“The government is promoting fish farming at a cost to the environment and
wild salmon populations. They recently identified 30 sites around the
coastline where they hope to build fish farms. If constructed, they will
have far-reaching consequences for stocks of salmon and the angling
industry,” he said.
Ireland is an important breeding habitat for Atlantic salmon, Salmo salar.
The species spawn each year in rivers around the country and produce
approximately 4m smolts, that migrate out to sea.
Ireland once had a healthy population of wild salmon. In the 1980s, up to
20% of smolts returned as adult fish to spawn in Irish rivers.
In recent years, that figure has dropped to between 8% and 10%, which
suggests that the species is affected by factors that have still not been
identified by scientists.
Conservationists blame the decline in wild populations on fish farms,
over-fishing, pollution and unknown factors.
Gerry O’Donohue, of Mannin Bay Salmon, said sea lice were a problem for all
fish farms. “We are very careful to ensure that we do everything possible to
reduce the prevalence of sea lice in our salmon stocks.
“We have learnt how to deal with sea lice. When high levels of sea lice are
detected, we harvest the fish, as we are an organic farm and do not use
chemicals,” he said.
Marine Harvest Ireland said its Irish operations were audited 14 times a
year by officials from the Marine Institute.
“We note that the control protocols in respect of sea lice operated by the
Marine Institute on behalf of the state are more advanced than those
operated in other jurisdictions, as the inspection regime is independent of
the industry,” the company said.
“Data obtained as a result of inspections is published and treatment trigger
levels are set at a low level. These controls are widely accepted as
representing best practice internationally. Marine Harvest Ireland conforms
fully with this leading pest control strategy.
“We implement tried-and- tested operational procedures to control sea lice.
On occasion, given certain climatic conditions, lice can be more prevalent
and this has occurred this year as the reports clearly illustrate.”
The Marine Institute declined to comment.
16 December 2012
The Sunday Times