GRANTS PASS, Ore. – A team of Canadian scientists has found the most direct evidence yet that baby salmon pick up fatal infections of sea lice while swimming past salmon farms in British Columbia’s Broughton Archipelago, and that the more salmon farms the more baby salmon die.
“Before we knew there were potential problems,” said Martin Krkosek, a doctoral student at the University of Alberta who was lead author of the study released Monday by the American journal Proceedings of the National Academy of Sciences. “Now it is very clear we have severe problems here.”
In natural conditions, the adult salmon that carry the sea lice aren’t in the migration channels and rivers at the same time as young pink and chum salmon, so the little fish are not infested, said Mark Lewis, University of Alberta senior Canada research chairman in mathematical biology, who oversaw the research.
But fish farms have changed that, raising hundreds of thousands of adults in floating net pens anchored year round in the channels where the young fish migrate. The young pink and chum salmon are only an inch long, and do not yet have scales to protect them from parasites, he said.
Ransom Myers, a professor of biology at Dalhousie University in Nova Scotia, who was not part of the study, said it was the most comprehensive to date on the issue and hoped it would push the Canadian government to take action to protect wild salmon.
Andrew Thomson, acting head of aquaculture for Fisheries and Oceans Canada’s Pacific region, said the agency had yet to review the study, but was monitoring sea lice infestations of wild salmon, doing its own research, and was committed to protecting wild salmon.
“What we’re seeing is infection rates of sea lice vary year by year, and populations of pink salmon show fluctuations year by year,” he said. “It’s a complex issue. We need to do more research on it.”
Marine Harvest, which owns many of the 30 salmon farms in the archipelago, did not return a telephone call to its Campbell River, B.C., office for comment.
When West Coast salmon catches in the United States crashed in the 1990s, farmed salmon filled the gap in supermarket coolers, and Canada now has about 280 salmon farms that produce about 96,000 tons worth $387 million each year. About 70 percent goes to the United States. British Columbia has about 100 salmon farms, and Broughton Archipelago about 30.
There are nine salmon farms in the United States – six in Maine, two in Washington and one in Tennessee.
Concerned about the impacts of hundreds of thousands of salmon crowded into net pens floating in coastal fiords down which baby salmon migrate, environmental groups have campaigned to convince consumers to boycott farmed fish.
Alexandra Morton, a biologist from Broughton Archipelago who took part in the study and is founder of the Raincoast Research Society, said she started looking into the issue in 2001 when a fisherman brought her a wild salmon covered with sea lice and asked her whether salmon farms were the reason.
“Every time one of us publishes on this issue, the Canadian government finds a little loophole and runs with it,” she said. “First they said maybe it’s not coming from the farms. When we nailed that one down, they said maybe they don’t kill the fish. When we nailed that one down they said maybe they don’t kill to affect the population.
“This nails that final loophole down.”
The study examined 17,000 fish, which were netted at regular intervals along three different migration routes over the course of two years. Mortality rates at various points in the migration season ranged from 9 percent to 95 percent.
The study found fish died after being infected with as few as one louse, that the more louse on the fish the more likely it was to die, and that the more salmon farms along the migration route, the more likely the fish were to die. The highest mortality rate, 95 percent, came in the channel with three salmon farms at the end of the migration season, when sea lice were most prevalent. The other two channels had two farms.
“The basic physics says this result should not be surprising,” said Neil Frazer, a professor of physics at the University of Hawaii who worked on the mathematical modeling that went into the study. “When you put a bunch of farmed fish into a system of wild fish and parasites, you automatically are going to greatly increase the number of parasites, because you now have a much better chance of finding a host.”
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