Sea Lice From Fish Farms Devastate Wild Salmon
An Environmental Article from All-Creatures.org

From

Environment News Service
October 2006

Under natural conditions, the adult salmon are far offshore when the juveniles migrate out to sea. But the farms concentrate large numbers of adult salmon near migration paths, forcing the tiny juveniles to swim through clouds of sea lice.

"It takes only one or two sea lice to kill a juvenile pink or chum salmon," said Martin Krkosek, the study's lead author and a PhD candidate at the University of Alberta's Centre for Mathematical Biology. "The juveniles are so vulnerable because they are so small - only one to two inches long."

EDMONTON, Canada, October 2, 2006 (ENS) - Parasites from fish farms kill as much as 95 percent of young wild salmon that migrate past the facilities, according to a new study released today. The research offers a stark warning about the environmental impact of salmon farms, which the authors say must change their operations if wild fish stocks are to survive.

"We often worry about wildlife making humans sick, but here is a case where humans are making wildlife sick," said study co-author Dr. Mark Lewis, a mathematician and biologist at the University of Alberta.

The researchers found that fish farms are dramatically altering the number of parasitic sea lice the juvenile fish are exposed to as they migrate out to sea.

Sea lice feed on flesh and tissue - they are typically carried by adult salmon, which can survive with the parasites. But juvenile salmon are highly vulnerable to the parasites.

Under natural conditions, the adult salmon are far offshore when the juveniles migrate out to sea. But the farms concentrate large numbers of adult salmon near migration paths, forcing the tiny juveniles to swim through clouds of sea lice.

"It takes only one or two sea lice to kill a juvenile pink or chum salmon," said Martin Krkosek, the study's lead author and a PhD candidate at the University of Alberta's Centre for Mathematical Biology. "The juveniles are so vulnerable because they are so small - only one to two inches long."


Canada is the fourth largest producer of farmed salmon, trailing Norway, Chile and the United Kingdom. (Photo courtesy Greenpeace)

The researchers found shocking impacts on the young wild salmon, with mortality rates rising from 9 percent in early spring when the sea lice population was low to 95 percent in late spring when it was higher.

The results of the research have been published in the "Proceedings of the National Academy of Sciences."

The research team, which included biologists and mathematicians from U.S. and Canadian institutions, counted sea lice on more than 14,000 juvenile wild salmon along a 37-mile migration route that takes the fish past open-net salmon farms off the coast of British Columbia., and conducted mortality experiments on more than 3,000 fish.

"We then used mathematical models to combine this information and estimate the total impact of the farms," said Krkosek, who said the study is the first to combine field surveys, experiments and modeling to estimate the total impact of fish farms.

The study's implications paint a worrying picture for wild salmon, which are already in decline from over fishing and degraded habitat.

"The debate is over," added study co-author Alexandra Morton, a biologist with the Raincoast Research Society. "This paper brings our understanding of farm-origin sea lice and Pacific wild salmon to the point where we know there is a clear severe impact."


The researcherd documented that juvenile salmon have little ability to fend off sea lice. (Photo by Alexandra Morton courtesy UAlberta)

Even the best case scenario of an additional 10 percent mortality from farm-origin sea lice could push a fish stock into the red zone, the researchers said, given that only a small of juvenile salmon typically survive to return as adults under normal conditions.

Furthermore, the study "almost certainly underestimates the total mortality of juvenile salmon," added study co-author Dr. Neil Frazer, a physicist at the University of Hawaii. "We considered only the direct effects of sea lice on fish survival. We did not include the secondary effects of increased predation on infected fish."

The researchers suggest that salmon farms at the very least be moved away from migratory corridors and possibly altered to close them off from the open water.

"This study really raises the question of whether we can have native salmon and large scale aquaculture - as it is currently practiced - in the same place," said Dr. Ransom Myers, a fisheries biologist at Dalhousie University.

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