Drug-resistant sea lice an increasing problem for B.C. fish farms, new study finds

Every spring, endangered young wild salmon migrate from BC’s rivers to the Pacific Ocean, but their numbers are declining and some fear that aphid parasites are getting more and more to blame.

Lice are small, oval crustaceans that can cling to the backs of wild salmon and feed on their skin, muscle tissue and blood.

Adult fish are generally not injured when lice attach, but juveniles with underdeveloped scales can be injured or killed when severely infested.

Although the parasite occurs naturally in the waters off the coast of BC, there have long been concerns about outbreaks on aquaculture farms where lice with open nets allow lice to move from farmed fish to young migratory salmon.

“Salmon farms act as this year-round reservoir for sea lice, potentially giving sea lice to wild young salmon when they would not normally get them,” said conservation biologist Sean Godwin.

Godwin is the lead author of a recent study that looked at the condition of sea lice in the Pacific Ocean. Together with his research colleagues, he found that the parasite is becoming increasingly resistant to one of the most important tools that the industry relies on to combat the problem.

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

To assess parasite resistance, “bioassay, treatment and salmon lice count data from 2010 to 2021” were analyzed. During that time, researchers found a remarkable decrease in the effectiveness of SLICE.

“It will be more difficult for salmon farmers to control lice outbreaks on their farms,” ​​says Godwin.

In the province’s fantastic Clayoquot Sound, Bonny Glambeck routinely uses a fine-mesh net and a test cup to test the water near fish farms. Glambeck leads the Tofino-based conservation community known as Clayoquot Action and each year she monitors the number of lice in the industry and tracks wild salmon infestations.

“The control of sea lice on fish farms is something I do not think the industry has ever been able to crack,” she said.

“Parasites like these lice spread on these farms and then they can transmit them to wild salmon. With that, we feel that every year that passes and these farms are allowed to pollute the water with these infestations, they just wipe out another generation of wild salmon.”

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

In addition, the industry reports public redundancies on individual companies’ websites every month.

“The concern is that these lice levels could accumulate and then be released to affect wild migratory salmon. Science does not support that, but there is concern so the industry is reacting to it,” said Brian Kingzett.

Kingzett is the head of science and policy for BC Laxodlare Association. He says the industry has been warning the federal government for several years about the declining effect of SLICE and has long called on Ottawa to approve new pesticide alternatives.

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

Although SLICE is the only approved pesticide in Canada, it is not the only option for a fish farm that is struggling with lice infestations. Kingzett says other environmentally friendly methods include the use of specialized de-lice boats.

An easy-to-use vessel can suck fish from sea-based mounds into tanks where pressurized water is used to forcibly remove any lice. According to the industry, any loosened 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 on importing new technology,” Kingzett said. “Fish farming is an important industry in BC because we are facing a global shortage of shellfish and the farming sector wants to provide sustainable products of high quality.”

However, the industry is controversial and there has been a struggle to get rid of all fish farms in the province.

Aerial photos submitted by Clayoquot Action show protesters near a fish farm not far from Tofino, BC (Clayoquot Action)

Earlier this month, there was a major protest in Tofino involving indigenous leaders, conservationists and environmentalists. The group went to the water near a local fish farm to express their opposition to the industry and urge Ottawa to evict them.

“It’s a do-or-die moment for the salmon farming industry,” said Alexandra Morton, an independent biologist and longtime wild salmon activist. “We must do everything we can to save wild salmon populations because, unfortunately, they are on the verge of extinction.”

In response, those who support fish farming claim that they are not a direct threat to wild salmon and are an important industry. According to the BC Salmon Farmers Association, there are nearly 5,000 jobs linked to fish farms and at least $ 1 billion “in economic activity” generated annually.

Despite this, Ottawa has previously announced that it has committed to phasing out salmon farms with open nets in BC by 2025. In addition, it is uncertain whether 79 federal fish farming licenses that expire in June will be renewed.

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