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Sea lice off BC are becoming more resistant to pesticides: study

Every spring, endangered juvenile wild salmon migrate from British Columbia rivers to the Pacific Ocean, but their numbers are dwindling and some fear sea lice parasites are increasingly to blame.

Sea lice are tiny, oval-shaped crustaceans that can cling to the backs of wild salmon, feeding on their skin, muscle tissue and blood.

Adult fish are usually unharmed when a few lice attach themselves, but juveniles with underdeveloped scales can be injured or killed when heavily infested.

Although the parasite occurs naturally in waters off the coast of British Columbia, there have long been concerns about outbreaks at fish farms where open-net enclosures allow lice to pass from farmed fish to young migrating salmon.

“Salmon farms act as this year-round reservoir for sea lice, potentially supplying wild juvenile salmon with sea lice when they normally wouldn’t have it,” said conservation biologist Sean Godwin. .

Godwin is the lead author of a recent study on the status of sea lice in the Pacific Ocean. Together with his fellow researchers, he discovered that the parasite is becoming increasingly resistant to one of the main tools the industry relies on to combat the problem.

“Our article revealed that this tool, which is a known pesticide [as] SLICE, or emamectin benzoate, is becoming less effective and sea lice are developing resistance to it on farms here,” Godwin said.

To assess parasite resistance, “bioassay, treatment and salmon lice count data from 2010 to 2021” were analyzed. During this time, the researchers saw a noticeable decrease in SLICE’s effectiveness.

“It will be harder for salmon farms to control sea lice outbreaks on their farms,” Godwin said.

In the province’s beautiful Clayoquot Sound, Bonny Glambeck routinely uses a fine-mesh net and sample cup to test the waters near fish farms. Glambeck runs the Tofino conservation society known as Clayoquot Action and each year monitors industry lice numbers and tracks wild salmon infestations.

“Sea lice control on fish farms is something that I don’t believe the industry has ever been able to solve,” she said.

“Parasites like these sea lice proliferate in these farms and can then pass them on to wild salmon. With that, we feel like with each passing year and these farms are allowed to pollute the waters with these infestations, they don’t just wipe out another generation of wild salmon.”

Fisheries and Oceans Canada requires that all fish farms located in Canadian coastal waters have a sea lice management plan. The federal department also imposes a limit of three lice per salmon in the spring, when young salmon are migrating and are most vulnerable.

In addition to this, the industry publicly reports monthly the number of lice on each company’s websites.

“The concern is that these levels of lice could build up and then be released to affect migrating wild salmon. The science doesn’t support this, but the concern is there so the industry is responding to this,” said Brian Kingzett.

Kingzett is the Scientific and Policy Director of the BC Salmon Farmers Association. He says the industry has warned the federal government for years about SLICE’s diminishing effectiveness and has long asked Ottawa to approve new pesticide options.

“There are other pest control agents that have been approved in other parts of the world and we would certainly like to add them to our toolbox.”

Although SLICE is the only pesticide approved in Canada, it is not the only option for a fish farm struggling with a lice infestation. Kingzett says other environmentally friendly methods include using specialized delousing boats.

An easily operated vessel can suck fish from ocean pens into tanks where pressurized water is used to forcibly remove any attached lice. According to the industry, all dislodged insects are collected by filters for disposal so that they are not reintroduced into the marine environment.

“Over the past five years, the industry has spent about $100 million importing new technology,” Kingzett said. “Fish farming is an important industry in British Columbia because we are facing a global seafood shortage and the agricultural sector is looking to provide sustainable, high-quality products.

The industry, however, is controversial and there has been an ongoing battle to have all fish farms removed from the province.

Sea lice off BC are becoming more resistant to pesticides: studyAerial footage submitted by Clayoquot Action shows protesters near a fish farm near Tofino, B.C. (Clayoquot Action)

Earlier this month there was a large protest in Tofino involving Indigenous leaders, conservationists and environmentalists. The group took to the waters near a local fish farm to voice their opposition to the industry and call on Ottawa to evict them.

“This is a watershed moment for the salmon farming industry,” said Alexandra Morton, independent biologist and longtime wild salmon activist. “We must do all we can to save wild salmon populations as they are unfortunately on the verge of extinction.”

In response, those who support fish farms say they pose no direct threat to wild salmon and are a vital industry. According to the BC Salmon Farmers Association, there are nearly 5,000 fish farm-related jobs and at least $1 billion “in economic activity” is generated each year.

Despite this, Ottawa has already announced that it is committed to phasing out open-net salmon farms in British Columbia by 2025. Moreover, it is uncertain whether 79 federal fish licenses expiring in June will be renewed.

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