BC sea lice become more resistant to pesticides: study

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

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

Adult fish are usually not harmed when a few lice attach themselves, but juveniles with underdeveloped scales can be harmed or killed when heavily infested.

Although the parasite occurs naturally in waters off the coast of BC, there has long been concern about outbreaks on aquaculture farms, where open net pens allow lice to pass from farmed fish to young migratory salmon.

“Salmon farms act as a year-round reservoir for sea lice, potentially providing sea lice to wild juveniles when they would not normally catch them,” said conservation biologist Sean Godwin.

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

“Our paper found 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 resistance to the parasite, “salmon lice bioassay, treatment and count data from 2010 to 2021” were analyzed. During that time, the researchers found a noticeable decrease in SLICE’s effectiveness.

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

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

“The control of sea lice on fish farms is something I don’t think the industry has been able to solve,” she said.

“Parasites like these sea lice proliferate on these farms and can then transmit them to wild salmon. With that, we feel that with each passing year and these farms can pollute the waters with these infestations, they are wiping out another generation of wild salmon. “

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

In addition, the industry publicly reports lice counts on individual company websites every month.

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

Kingzett is the director of science and policy for the BC Salmon Farmers Association. He says the industry has been warning the federal government for years about SLICE’s diminishing effectiveness and has long been urging Ottawa to approve new pesticide options.

“There are other anti-parasitic agents that have been approved in other areas of the world and we would certainly like to add them to our toolbox.”

While SLICE is the only approved pesticide in Canada, it is not the only option for a fish farm fighting a lice infestation. Kingzett says other eco-friendly methods include using specialized boats for delousing.

A readily used vessel can suck fish from ocean fences into tanks where pressurized water is used to forcibly remove any trapped lice. According to the industry, any dislodged insects are collected through filters for disposal so they are not reintroduced into the marine environment.

“Over the past five years, the industry has spent about $100 million on importing new technologies,” Kingzett said. “Fish farming is an important industry in BC 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 is an ongoing battle to remove all fish farms from the province.

Aerial footage sent by Clayoquot Action shows protesters near a fish farm not far from Tofino, BC (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 ask Ottawa to evict them.

“It’s a life-and-death moment for the salmon farming industry,” said Alexandra Morton, an independent biologist and longtime wild salmon activist. “We need to do what we can to save wild salmon populations because they are unfortunately on the brink of extinction.”

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

Despite this, Ottawa previously announced that it is committed to phasing out open-net salmon farms in BC by 2025. Furthermore, it is uncertain whether 79 federal fish farm licenses that expire in June will be renewed.

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