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

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

Sea 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 harmed when a few lice attach themselves, but juvenile fish with underdeveloped scales can be harmed or killed when heavily infested.

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

“Salmon farms act as a year-round reservoir for sea lice and may supply sea lice to wild young salmon if they normally wouldn’t get them,” said wildlife biologist Sean Godwin.

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

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

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

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

In the county’s beautiful Clayoquot Sound, Bonny Glambeck regularly uses a fine mesh net and sample cup to test the water near fish farms. Glambeck heads the Tofino-based conservation organization known as Clayoquot Action and each year monitors the number of lice in the industry and monitors infestations of wild salmon.

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

“Parasites like these sea lice multiply on these farms and can then pass them on to wild salmon. With that, we feel like every year that goes by and these farms are allowed to pollute the water with these pests, they are just wiping out a new 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 hatch and are most vulnerable.

In addition, the industry publicly reports the number of lice on individual company websites on a monthly basis.

“The concern is that those levels of lice can build up and then be released back to affect wild migratory salmon. The science doesn’t back that up, but the concern is there, so the industry is responding to that,” says Brian Kingzett.

Kingzett is the science and policy director at the BC Salmon Farmers Association. He says the industry has been warning the federal government about SLICE’s declining efficacy for years, and has long called on Ottawa to approve new pesticide options.

“There are other anti-parasite agents that have been approved in other parts of the world that we would definitely like to add to our toolbox.”

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

An easy-to-use vessel can suck fish from pens in the ocean into tanks where pressurized water is used to forcibly remove any attached lice. According to the industry, all dislodged insects are captured by filters for disposal, so that they do not re-enter the marine environment.

“Over the past five years, the industry has spent about $100 million importing new technologies,” Kingzett said. “Fish farming is an important industry in BC as we face a global seafood shortage and the agricultural sector is looking for high quality sustainable products.”

However, the industry is controversial and there is an ongoing battle to remove all fish farms in the province.

Aerial footage submitted by Clayoquot Action shows 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 took to the waters near a local fish farm to voice their opposition to the industry and call on Ottawa to evict them.

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

In response, those who support the fish farms claim 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 jobs associated with fish farming and at least $1 billion “in economic activity” is generated annually.

Despite this, Ottawa has previously announced its commitment to phase out open-net salmon farms in BC by 2025. In addition, it is uncertain whether 79 federal fish farm licenses that expire in June will be renewed.

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