Study finds no link between salmon farm removal and sea lice levels in BC.
A peer-reviewed study published in Diseases of Aquatic Organisms has found that the removal of salmon farms in British Columbia’s Broughton Archipelago has not reduced sea lice levels on wild Pacific salmon.
The paper analysed monitoring data collected between 2016 and 2024, covering a period when aquaculture production in the Broughton was reduced by more than 95 percent, from 21,645 tonnes in 2019 to 614 tonnes in 2024. Despite this reduction, sea lice prevalence on juvenile chum and pink salmon remained unchanged or increased in some years.
Researchers examined nearly 3,000 juvenile salmon and concluded that natural environmental conditions, rather than the presence of farms, were the main drivers of sea lice dynamics.
“This study provides clear scientific evidence that the removal of salmon farms does not invariably lead to reduced sea lice infestation levels on wild Pacific salmon,” said Dr Crawford Revie, professor of data analytics at the University of Strathclyde. “These findings highlight the importance of understanding the range of natural environmental processes that shape sea lice population dynamics.”
Data showed no correlation between salmon farm biomass and lice prevalence. In 2022, lice levels rose despite falling production, while peak production years such as 2017 and 2019 showed lower prevalence.
The findings add to earlier studies in the Discovery Islands and a review by the Canadian Science Advisory Secretariat, which also found no causational link between farm presence and sea lice on wild salmon.
The results come as British Columbia salmon farmers face a federally mandated ban on current ocean-pen systems by 2029, a policy set by the previous government in June 2024. The industry maintains that it provides more than 4,500 full-time jobs and contributes over CAD 1.17 billion to the provincial economy.
The full paper is available here.
