Fish farms linked to sea lice infestations among wild sockeye
Researchers find young salmon migrating past operations in Discovery Islands, Broughton Archipelago pick up heavier load of parasites
By Stephen Hume, Vancouver Sun February 11, 2011 Scientists have linked sea lice infestations in Fraser River sockeye to salmon farms along their migration route.Photograph by: Les Bazso, PNG Files, Vancouver SunLike the bad smell that won't go away, another piece of research in the scientific jigsaw puzzle links British Columbia's salmon farms to sea lice infestations that affect migrating wild salmon.
This time the link is to the iconic wild sockeye stocks of the Fraser River.
Fraser River sockeye are the most important food and subsistence species for more than 40 aboriginal communities, the much-prized foundation for the province's most valuable commercial fishery and a growing target for sports anglers.
The study by scientists from the University of Victoria, Simon Fraser University and several environmental organizations with an interest in salmon conservation used genetic analysis to determine the origin of sockeye from Canada's two most important salmon rivers, the Fraser and the Skeena.
Skeena River sockeye smolts migrate through waters where there are no net cage salmon farms, so it served as a control.
Migrating Fraser River sockeye smolts, on the other hand, must run a gauntlet of fish farms scattered among the islands that choke the narrows between Vancouver Island and the mainland north of Campbell River.
The scientists found that Fraser River sockeye passing salmon farms in the Discovery Islands and Broughton Archipelago picked up a heavier load of sea lice than Skeena River fish migrating through waters where there were no salmon farms.
How important is this discovery?
"It's quite important," says Mike Price, a graduate student at UVic who is one of the researchers. "It indicates that fish farms are a source of one potentially lethal pathogen for migrating sockeye smolts. Is this an indicator for other pathogens? Like most scientific research, ours generates more questions than answers."
But the research paper, Sea Louse Infection of Juvenile Sockeye Salmon in Relation to Marine Salmon Farms on Canada's West Coast, published Tuesday in PloS One, a peer-reviewed open access scientific journal of the Public Library of Science, is the first to demonstrate clearly the potential role of salmon farms in transmitting sea lice to juvenile sockeye salmon.
Sea lice comprise several species of a naturally occurring parasite that preys upon salmon and other fish. The impact of sea lice is mitigated in the wild by the wide dispersal of fish. However, in the massed schools of salmon kept in net cages throughout their life cycle, sea lice populations can explode.
Fish farmers use potent chemicals to control sea lice infestations in their livestock.
Critics of the industry complain that by creating concentrations of sea lice in fish farm pens and the adjacent waters, migrating wild salmon -particularly immature smolts -that pass close by can pick up lethal loads of the parasite in transit.
This research appears to lend weight to that concern.
"The rapid growth of marine salmon farms over the past two decades has increased host abundance for pathogenic sea lice in coast waters, and wild juvenile salmon swimming past farms are frequently infected with lice," the paper says.
It found that juvenile sockeye from the Skeena and swimming through waters free of fish farms carried far fewer sea lice than those from the Fraser sampled on the south coast and swimming past the 18 fish farms operating in the Discovery Islands just north of Campbell River.
Furthermore, the species of sea lice found on specimens captured by the researchers appeared to match the changes in prevalence and proportion of sea lice common at the fish farms they were passing.
The researchers concluded that position relative to salmon farms best explained the relative abundance of the different species of parasite on various specimens.
"Our genetics results demonstrate a major migration corridor past farms for fish that originated in the Fraser River," the paper says. "Our evidence suggests that salmon farms are elevating parasite levels on Fraser River sockeye during their critical early marine migration."
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