By VANCOUVER -- A team of research scientists says it has conclusively linked the transmission of lethal sea lice from farmed to wild salmon, a finding that raises questions about the future of B.C.'s $400-million salmon farming industry.
The report, to be published today in the journal of the Royal Society, in Britain, shows how one salmon farm on the B.C. coast caused an explosion of sea lice that spread to juvenile salmon migrating past. The lice then multiplied on the wild fish, leading to a secondary outbreak that spread to other salmon up to 30 kilometres from the farm.
"This is the smoking gun," said one of the scientists, John Volpe, of the School of Environmental Studies at the University of Victoria. "There is no ambiguity in the data whatsoever. It's very, very definitive . . . it's clean and it's conclusive."
Sea lice feed on the flesh and the blood of the salmon and in large numbers will weaken and eventually kill the fish. The parasite is not known to harm people.
Before they encountered the salmon farm the juvenile fish were mostly lice-free, with 4 to 25 per cent infected. The fish that were infected usually had just one louse. After passing the farm, 100 per cent of the wild salmon were infected and the lice load had jumped to 10 to 25 per fish. On the young salmon, which are about the size of a triple-A battery, two lice or more can be lethal.
British Columbia's salmon farming industry is the fourth largest in the world, exporting $400-million annually and supporting about 4,000 jobs. There are 85 active farms in the province, with more planned.
A link between salmon farms and sea lice infections in wild salmon has long been suspected, but as recently as last week the federal Department of Fisheries and Oceans maintained that solid scientific proof was lacking despite years of study.
Dr. Volpe said the study he conducted with Mark Lewis and Martin Krkosek, both with the Centre for Mathematical Biology at the University of Alberta, should leave no doubts.
"The debate [about sea lice] began almost 25 years ago in Scotland and Norway," Dr. Volpe said. "This analysis is a milestone because, for the first time, we've been able to disentangle the role or contribution of the fish farm above and beyond the ambient levels."
Mary Ellen Walling, executive director of the B.C. Salmon Farmers Association, questioned the significance of the study, however.
She said it involved only one farm and no general conclusions can be drawn.
Ms. Walling said the industry is working with the government and other research scientists to understand the sea-lice problem and much work remains to be done.
"There are still a lot of unanswered questions," she said, noting that some research has shown sea lice populations are linked to salinity levels, which vary from area to area.
"I don't agree that there is a body of evidence that is building against salmon farms. We will continue to do the work we need to do to assure the public this is a responsible industry."
Sea lice occur naturally in the environment and infect both farmed and wild salmon by drifting through the water column until a host is found. Fish farm advocates have long argued that the high lice levels being found on wild salmon could be from natural sources just as easily as from farms.
Environmentalists have argued that the densely packed schools of farmed salmon, being held in ocean net cages, were concentrating the lice problem and causing epidemics. But the government has continued to support expansion of aquaculture on the West Coast, saying there was no scientific proof fish farms were damaging wild stocks.
Jennifer Lash, executive director of the Living Ocean Society, said the new research should end debate over whether there is a definitive link between fish farms and sea lice epidemics.
"This is definitive research that proves fish farms are the source of the high levels of sea lice on wild salmon," she said. "Open-net fish farms cannot continue to exist on this coast."