Evidence shows sea lice kill young salmon

March 09, 2006, volume 35, no. 5
By Stuart Colcleugh



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An SFU researcher has co-authored a new study providing "direct evidence" that sea lice, which have been linked to lice-infested fish farms, are killing juvenile migrating wild salmon in B.C.'s Broughton Archipelago.

Until now, researchers had strongly suspected that sea lice were killing young wild pink and chum salmon in the area, but without conclusive evidence some government and fish-farm industry officials questioned whether there was a direct link.

The new study by Rick Routledge, a fish population statistician and member of the university's centre for coastal studies and biologist Alexandra Morton of the Raincoast Research Society was published March 3 in the Alaska fish and game department's Alaska Fishery Research Bulletin.

Entitled Mortality Rates for Juvenile Pink and Chum Salmon Infested with Sea Lice in the Broughton Archipelago, the study "provides direct evidence and a simple explanation for recent, major declines in pink and chum returns in the area," says Routledge. "Namely, that a large fraction of the out-migrating juvenile salmon were killed by the heavy lice infestations reported on them. The evidence further shows that these tiny, scale-less juvenile pink salmon are substantially more vulnerable to lice infestations than are the juvenile Atlantic salmon that European scientists have been studying."

Fears that farmed Atlantic salmon are infecting the archipelago's migrating Pacific salmon intensified last year when researchers from the University of Alberta and the University of Victoria documented the spread of sea lice to wild salmon from a fish farm that had 30,000 times the natural level of the parasite. They found that the infection of wild juvenile salmon was 73 times higher than normal levels near the farm and surpassed normal levels for 30 kilometres along the wild migration path.

A B.C. government special committee on sustainable agriculture struck to address public concern over open-net pen salmon farming is due to report its findings in 2007.

For their most recent study, which was partially funded by the Natural Science and Engineering Research Council (NSERC), Routledge and Morton sampled juvenile pink and chum salmon in the Broughton Archipelago, sorted them into groups of increasing lice abundance, and placed them in flow-through containment facilities. They held them for approximately one month, feeding them, cleaning the containers, and keeping the entire setup under round-the-clock surveillance with Morton camping out with her daughter beside the setup to protect the salmon from a marauding otter. They repeated the procedure three times. In each of these repetitions, the mortality rate increased significantly with increasing lice abundance. In the second of these repetitions, pink salmon showed the most dramatic increase - from near zero per cent for uninfested fish to almost 100 per cent for the most heavily infested category.

In their previous study, published Jan. 5 in The North American Journal of Fisheries Management, Routledge and Morton cast doubt on the federal fisheries department's current method for appraising the health of wild salmon once they've passed salmon farms. The method, called the Fulton Condition Factor, uses the weight of a healthy fish as a baseline for determining whether a fish is suffering from lice, on the theory that it will become progressively more emaciated and listless as it is attacked by more lice.

But Morton and Routledge's research showed that affected fish don't lose weight until shortly before they become listless and that they die soon after they show indications of being sick.

Routledge says that important questions need to be addressed through further research before fully effective management plans can be developed.

In the meantime, he says, "to protect these more vulnerable Pacific species, more stringent regulations are needed than the existing European standards, which are designed to protect larger, less vulnerable Atlantic salmon."

At least one major salmon-farming company along the Broughton Archipelago is not waiting for more research. Marine Harvest Canada announced recently that as part of a deal made with environmentalists and a local Indian band it will move approximately 600,000 fish out of its Glacier Bay farm to another facility 15 to 20 kilometres away from the wild salmon migratory route.

Says Routledge: "I call that very significant progress." His study is available online at www.adfg.state.ak.us/pubs/afrb/afrbabst.php#Vol11_2/.

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