Sea Lice Pesticide Pollutes Clayoquot Waters

Hydrogen peroxide treatment weakens salmon, triggering disease outbreaks

Dan Lewis

Pesticide well boat in Clayoquot Sound. Photo credit: Clayoquot Action

It’s almost a year since Norwegian-based Cermaq received a permit to use a new pesticide (hydrogen peroxide-based Paramove 50) to control lice on their Atlantic salmon farms in Clayoquot Sound. The permit allows them to dump enough pesticide to fill an Olympic-sized swimming pool into the pristine waters of the UNESCO Biosphere Region.

Salmon lice outbreaks are known to impact wild salmon. Last year had the worst lice infestation ever seen in Clayoquot, with numbers on baby wild salmon smolts as high as 43 per lice fish (one louse can be a fatal load). Lice are also a vector for transmitting disease from farmed fish to wild fish.

As with all salmon lice treatments, resistance to hydrogen peroxide is a problem. Cermaq’s own website shows lice numbers spiking after each round of treatment – and the survivors are the ones with the highest immunity. Repeated treatments quickly breed for pesticide-resistant lice.

Paramove affects the composition of fishes’ mucous layer, making it easier for lice reattachment. Damage from Paramove treatment may also release chemo-attractants, causing lice to be attracted to treated fish. Paramove is known to harm farmed fish and has caused mass die-offs – indeed, Cermaq lost 15% of the fish on one site treated last year.

Pesticide treatment is stressful to farmed salmon, and weakens their immune system. It can take up to two weeks for the fish to recover, during which period they are susceptible to disease outbreaks. According to the Norwegian Veterinary Institute’s 2018 report on fish health, disease erupts in Piscine orthoreovirus (PRV)-infected farmed salmon usually after high-stress “de-lousing or other handling routines.”


Read more: DFO v Wild Salmon – Will a Second Court Win Make Any Difference?


According to research published in 2018, PRV causes Heart Skeletal Muscle Inflammation (HSMI) in Atlantic salmon, but in Pacific chinook salmon, it causes red blood cells to burst. The toxic levels of hemoglobin then overwhelm the liver and kidneys. Unlike farmed salmon, wild fish cannot feed themselves or evade predators (not to mention swim up rivers) unless they are in top form.

Proponents claim that hydrogen peroxide quickly breaks down into water and air, causing no harm to the marine environment. However the pesticide can have a half-life of 28 days in ocean water, and is spread by wind and currents. It will probably primarily affect surface organisms and those living along the shoreline. Wild salmon, herring, and prawn and crab larvae all rear in shallow inshore waters.

Salmon lice are plaguing this industry worldwide, causing expensive losses to industry and harming wild salmon. This problem cannot, and has not, been solved by pesticides. The only solution is to get salmon farms out of the ocean. It’s time for governments to create a transition plan that protects workers and the environment.


Dan Lewis is Executive Director of Clayoquot Action in Tofino.

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