The results of a recently published scientific study show wild salmon populations in the Discovery Islands in British Columbia, Canada, continue to have high levels of sea lice, despite the closure of all salmon farming in the region.
Canada’s Department of Fisheries and Oceans (DFO) announced its plan to close all salmon farming in the Discovery Islands in December 2020, giving farmers in the region just 18 months to shift production. While court orders ended up delaying that timeline, DFO announced on 17 February 2023 it was done renewing licenses for the region, which represented 24 percent of all salmon production in the province.
That announcement came as companies had already begun to pull out of the area, with a Mowi spokesperson telling SeafoodSource at the time it was no longer actively producing any salmon in the region as of February 2023; data from the DFO indicates all salmon farming biomass was removed from the region by 2022.
The DFO, throughout its announcements, said it was taking the action to “protect wild Pacific salmon,” particularly from the threat of sea lice. In June 2024, it followed through on promises to halt salmon farming across the entire province, saying it would effectively ban all open net-pen salmon aquaculture in the province by 30 June 2029.
“The government is firmly committed to taking concrete steps to protect wild Pacific salmon,” former Canadian Minister of Fisheries, Oceans, and the Canadian Coast Guard Diane Lebouthillier said at the time. “Today, I'm announcing the essence of a responsible, realistic, and achievable transition that ensures the protection of wild species, food security, and the vital economic development of British Columbia's First Nations, coastal communities, and others, as we keep working toward a final transition plan by 2025.”
Despite the continued assertion by the DFO that its push to ban salmon aquaculture is to protect wild salmon, the latest research has once again called into question the connection between salmon farming and sea lice on wild salmon. The B.C. Salmon Farmers Association (BCSFA) has long cited a study by the DFO which found little connection between salmon aquaculture and sea lice on wild salmon, science which was later backed up by research in Norway.
The newest study found that despite farming being completely banned in the Discovery Islands and not being present for two years, sea lice levels were once again high on juvenile chum and pink salmon in 2024.
“Sea lice levels on wild salmon in 2024 were among the highest recorded during the last eight-year period in the Discovery Islands, despite the closure of salmon farms. A similar pattern with a low sea lice infestation in 2023 and higher levels of sea lice infestation in 2024 was also observed in the Broughton Archipelago and other areas with and without salmon farms,” Lance Stewardson, one of the paper’s authors, said of the study. “These findings demonstrate that the evidence does not support the narrative of no salmon farms means no sea lice.”
According to the study, the intensity of sea lice infestations – the number of sea lice per infested fish – was also among the highest of the last eight years, despite there being no farmed salmon biomass for two years.
A release from the BCSFA pointed out that salmon farms began to be removed in 2021, and no active farms have been in place since 2022. Eight years of monitoring sea lice population in the region found sea lice levels have remained relatively low, with fluctuations year to year that appear to have little correlation with the amount of farmed salmon biomass in the water.
“This long-term monitoring shows that significant natural sources of sea lice exist,” Stewardson said. “Our findings disprove the claim that salmon farms are the sole driver of sea lice on wild Pacific salmon in the near-shore environment and underscore the need for continued monitoring.”
The latest study counters an earlier one, which attributed a decrease in sea lice abundance on juvenile chum and pink salmon in the period spanning 2020 to 2022 to a decline in salmon farm production.
“Previously, a 96 percent decline in sea lice abundance on juvenile chum salmon and pink salmon from the Discovery Islands between 2020 and 2022 was attributed to the removal of salmon aquaculture in the region,” the study states.
The more recent study, which examined sea lice concentrations using laboratory analysis of frozen samples from 2017 through 2024, found similar low levels of sea lice on chum salmon and pink salmon between 2020 and 2022, as well as in 2023. However, the higher rates in 2024 – two years after all salmon farming had already stopped – showed declines weren’t entirely related to reductions in aquaculture.
The study also said the northwesterly flow of seawater reduces the likelihood that any still-active facilities in adjacent areas contributed to infestations on the wild salmon.
BCSFA Manager of Communications Michelle Franze said the paper is significant, as it dispels the assumption that removing salmon farms results in a decline in sea lice numbers.
