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Concerns raised over use of toxic pesticides to fight sea lice Add to ...

A drug long used by the fish farming industry to control sea lice infestations has become increasingly ineffective on the East Coast and is under scrutiny on the West Coast, according to federal government documents obtained under Access to Information.

Slice, which is administered to farmed salmon in their feed, is the only fully registered sea lice treatment in Canada. But the documents show its declining efficacy has forced the industry to seek alternatives – raising concerns that toxic pesticides are being released into the ocean under emergency authorizations.

“Over the last two years, [New Brunswick]salmon farmers have noted growing levels of sea lice tolerance to the in-feed lice control drug Slice,” Claire Dansereau, deputy minister in Fisheries and Oceans, wrote in a memorandum for the minister in September, 2010. “It appears Slice is no longer effective unless applied in triple doses. Farmers have been seeking access to other treatment products including hydrogen peroxide, Salmosan, AlphaMax and Calicide.”

Ms. Dansereau’s memo, among 800 pages of DFO documents obtained for The Globe and Mail by researcher Ken Rubin, shows there has been conflict within government over the use of at least one of those pesticides. The note states that in May, 2009, Health Canada’s Pest Management Regulatory Agency issued “a one-year emergency authorization” for the use of AlphaMax, but that authorization “was initially opposed by Environment Canada on grounds that it would constitute a ‘deleterious substance’ whose use would violate section 36 of the Fisheries Act.”

Ms. Dansereau says the PMRA “issued an Inspector’s Direction to the Chief Veterinarian of the Government of NB forbidding him or any one else in NB to prescribe, possess or distribute AlphaMax.”

But later, “through discussion with PMRA and DFO, Environment Canada was persuaded that the amount of AlphaMax involved would not constitute a ‘deleterious substance’ and they withdrew their Inspector’s Direction.”

Ms. Dansereau wrote that Environment Canada subsequently had second thoughts, and declared it “would not support a new emergency registration of AlphaMax” in the future.

She indicated DFO could expect continued pressure to authorize use of the chemical. “The industry and the provincial government have concluded that the current mix of Salmosan, hydrogen peroxide and Slice is insufficient to effectively control lice levels and that an expanded application of AlphaMax is required,” she wrote.

A New Brunswick Department of Agriculture and Aquaculture study last year found no adverse effect on lobsters held in traps around a farm using AlphaMax. But an undated DFO background note states the chemical “poses a risk to lobster and that its ongoing use will have to be carefully regulated and, perhaps, confined to only certain sites.”

Another internal DFO document says concerns have been raised “over the potential for pesticide resistance in sea lice in British Columbia.”

Mary Ellen Walling, executive director of the British Columbia Salmon Farmers Association, said there have been no signs Slice is losing effectiveness on the West Coast, where a different lice species is encountered, infestations are less frequent and use of the chemical has been more limited. But she said farmers are aware of problems elsewhere, and talks are under way with government about the need to assess alternative treatments.

Pamela Parker, executive director of the Atlantic Canada Fish Farmers Association, said unlike B.C., where there is a single pulse of sea lice in the fall, her members have to deal with a continual inflow of lice. Over the past decades, that has required farmers to use multiple doses of Splice annually, and the result has been that lice have gradually built resistance.

She said her industry is working hard to find alternatives, and wants to develop “a suite” of responses, which could include both pesticides and naturalistic approaches, such as using mussel beds to filter lice from the water.

Matthew Abbott, co-ordinator of Fundy Baykeeper, a conservation group based in St. Andrews, N.B., said his big concern is that, faced with growing lice epidemics, government is being rushed into approving the use of environmentally damaging pesticides.

“There are existing concerns with Slice … now they are using [pesticide]bath treatments that are even more worrisome,” said Mr. Abbott. “We don’t think any pesticide should be used in the ocean. Period.”


Sea lice is a common name for many different species of small, parasitic copepods which occur naturally in the marine environment.

They originate with wild fish, but are associated with commercial salmon farms because epidemics can occur in closely packed pens.

Lice attach themselves to the skin, gills or fins of fish, where they eat the body tissues and blood of the host. In low numbers they do little damage, but in large numbers can cause deep lesions, or weaken the immune response of fish, making them susceptible to diseases. Lice are not harmful to humans.

In their larval stage, tiny sea lice drift with ocean currents. Even as adults they are small, and it would take several to cover the head of a penny.

Lice have long been effectively controlled on farms with the drug Slice, which is added to fish feed. But a growing immunity to Slice, on the East Coast, has led to other treatments, including pesticide baths. Farmers drape tarps around net pens when adding pesticides to the sea water, or they transfer fish to a well-boat, where they are bathed in a holding tank.

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