No salmon farms, no sea lice in the Discovery Islands? New scientific paper debunks assumptions

The key argument of anti-aquaculture activists - no salmon farms, no sea lice - has been challenged by the findings of a new scientific paper, which, after eight years of monitoring in the Discovery Islands, has concluded that BC salmon farms do not determine sea lice levels in wild Pacific salmon.

Published in the Journal of Fish Disease, this latest research analyzed wild juvenile chum and pink salmon from 2017 to 2024 in the Discovery Islands region, as defined by Fisheries and Oceans Canada (DFO). The eight years of monitoring revealed that sea lice levels have generally remained low, with natural fluctuations from year to year, as shown in the graphic below.

According to Lance Stewardson, RPBio., CPESC, Director of Mainstream Biological Consulting Inc., and one of the paper's authors, the findings in this scientific research demonstrate that "the evidence does not support the narrative of no salmon farms, means no sea lice."

Sea lice levels in 2024, among the highest despite the closure of salmon farms

Canada's former Minister of Fisheries, Oceans and Coast Guard, Joyce Murray, announced her final decision not to renew the licenses of fifteen open-net Atlantic salmon aquaculture sites in the Discovery Islands, British Columbia, in February 2023, but the phase-out of salmon farms in the area began in 2021, and there have been no active farms since 2022.

The data now analyzed - collected with the participation of local First Nation stewardship staff - reveal that the 2024 sampling recorded some of the highest levels of sea lice observed in wild juvenile salmon over the past eight years.

"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," explained Lance Stewardson.

Significant natural sources of sea lice exist

"This long-term monitoring shows that significant natural sources of sea lice exist. 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," added paper co-author Stewardson.

In a release on these findings, the BC Salmon Farmers Association (BCSFA) noted that the results of this analysis are consistent with 2024 data collected in the Broughton Archipelago and with an extensive literature review published last year, which also identified overestimates of the effects of sea lice from salmon farms on wild Atlantic salmon.

Moreover, salmon farmers of British Columbia added that the Canadian Science Advisory Secretariat's (CSAS) 2022 Science Response, concluding that no statistical correlation exists between sea lice counts on wild and farm-raised salmon populations, further supports the findings of this latest scientific paper on sea lice in the Discovery Islands.