Sea lice are a problem for salmon farms worldwide. These parasitic crustaceans (which are related to crabs and shrimp) attach to fish and feed on their mucus and tissue, harming the industry’s product. To minimize economic losses, companies use a variety of pesticides to combat sea lice, each with their own disconcerting set of problems.
Sea lice close up by S. Proboszcz
Emamectin benzoate is a pesticide that is added to fish feed, and thereby transported through the fish’s blood to its tissue where it acts on sea lice attached to the salmon’s body. The drug is commonly known as Slice and was recently approved by Health Canada as safe for use from a human health perspective. I was curious to see the science behind its approval, and so I asked a director at Health Canada about it. Surprisingly, she told me I could not see the scientific studies conducted by the pharmaceutical company which produces the drug because it’s “proprietary information”. So basically, Health Canada says it’s safe for you, but they won’t show you the science that validates their approval—science that is generated by the company that sells the drug. Just another example of the secrecy surrounding this industry.
Last year in New Brunswick, sea lice showed signs of resistance to Slice. As with prolonged use of other pesticides, it becomes less effective over time. Since extensive Slice resistance has already occurred in Norway, it isn’t a surprise to see this happen in eastern Canada. Some scientists think it’s only a matter of time before Slice resistance develops in BC.
To combat the lack of efficacy of Slice, salmon farmers in eastern Canada are now going to extreme measures to reduce louse numbers. They’ve contracted a wellboat company—Solvtrans—to pump fish into wells in their boat where they are treated with hydrogen peroxide. At a recent meeting in Victoria, a representative of this management technique revealed that after the treatments, the wastewater and chemicals are simply discharged into the ocean. There are serious concerns regarding the use of bath-type treatments—especially if chemicals are discharged directly into our ecosystems. What happens when these chemicals interact with other substances? What are the long-term effects on ocean ecology?
New Brunswick has also started testing other chemical treatments such as deltamethrin (marketed as the drug Alphamax) by pumping it into net-cages surrounded by temporary ‘skirts’ (or tarps) which serve to theoretically contain the pesticide. According to a Norwegian scientist at a recent conference in Victoria, Alphamax is approved for use as a bath treatment (i.e. in a closed environment), not with the use of skirts. He went on to reveal that once the chemical is pumped into skirted cages, salmon react and instinctively dive to get away from the toxin, inadvertently crushing other fish against the net-cages. This, along with other factors associated with the treatment can cause up to 30% stock mortality. During tests of Alphamax, the New Brunswick Department of Agriculture reported the chemical escaped from the skirt into the marine environment and was detectable in the surrounding water for nearly 10 minutes. The agency admitted they had difficulty in maintaining an effective dose within the skirted cage and didn’t exactly know where the pesticide was going.
This chemical arms race shows no sign of coming to an end and certainly can’t be good for our health, or for the health of the surrounding ecosystem. Closed containment technology could potentially reduce the need for any sea louse treatments—another good reason for this industry to start transitioning now.
Tags: closed containment, pesticides, sea lice farmed salmon
