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

Every spring, endangered juvenile wild salmon migrate from B.C.'s 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 generally not harmed when a few lice attach themselves, but juveniles with underdeveloped scales can be harmed or killed when heavily infested.

While the parasite occurs naturally in the waters off B.C.'s coast, there's long been concern over outbreaks on aquaculture farms where open-net pens make it possible for lice to move from farmed fish to young migrating salmon.

"Salmon farms act as this year-round reservoir for sea lice, potentially providing sea lice to wild juvenile salmon when they wouldn't normally get them," conservation biologist Sean Godwin said.

Godwin is the lead author in a recent study that looked at the state of sea lice in the Pacific Ocean. Along with his fellow researchers, he found the parasite is increasingly becoming resistant to one of the main tools 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 that sea lice are developing resistance to it on farms here," Godwin said.

To assess parasite resistance, "bioassay, treatment and salmon-louse count data from 2010 to 2021" were analyzed. During that time, the researchers found a notable decrease in the effectiveness of SLICE.

"It is going to be more difficult for salmon farms to control sea lice outbreaks on their farms," said Godwin.

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

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

"Parasites like these sea lice proliferate on these farms and then they can pass them on to wild salmon. With that, we feel that every year that goes by and these farms are allowed to pollute the waters with these infestations, they are just 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 places a limit of three lice per salmon during the spring when young salmon are out-migrating and are most vulnerable.

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

"The worry is that those lice levels might accumulate and then be released back to affect wild migratory salmon. The science doesn't support that, but the concern exists so the industry responds to that," said Brian Kingzett.

Kingzett is the science and policy director with the BC Salmon Farmers Association. He says the industry has warned the federal government for years about the waning efficacy of SLICE, and has long called on Ottawa to approve new pesticide options.

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

While 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 environmentally friendly methods include the use of specialized delousing boats.

One readily used vessel can suck fish from ocean-based pens into tanks where pressurized water is used to forcibly remove any attached lice. According to the industry, any dislodged bugs are collected by filters for disposal so they are not reintroduced to the marine environment.

"During the last five years, the industry has spent about $100 million on importing new technologies," Kingzett said. "Fish farming is an important industry in B.C. because we are facing a global seafood shortage and the farming sector is looking to provide sustainable, high-quality product."

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

Aerial footage submitted by Clayoquot Action shows protestors near a fish farm not far from 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.

"It is a do-or-die moment for the salmon farming industry," said Alexandra Morton, who is an independent biologist and longtime wild salmon activist. "We need to do whatever we can to save wild salmon populations because they are sadly on the verge of extinction."

In response, those in support of fish farms argue they are not a direct threat to wild salmon and are a vital 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" is generated annually.

Despite that, Ottawa has previously announced that it's committed to phasing out open-net salmon farms in B.C. by 2025. In addition, it's uncertain if 79 federal fish farm licenses expiring in June will be renewed.