A University of Toronto study has found the environmental DNA of pathogens harmful to fish are 2.7 times more likely to be detected near active salmon farms versus inactive sites. (Kenny Regan photo)

A University of Toronto study has found the environmental DNA of pathogens harmful to fish are 2.7 times more likely to be detected near active salmon farms versus inactive sites. (Kenny Regan photo)

DNA presence of pathogens harmful to fish almost triples near B.C. salmon farms: study

Industry, DFO caution the research does not correlate to disease transmission

Wild salmon may be almost three times more likely to encounter harmful pathogens near salmon farms, a new study has found.

Scientists from the University of Toronto spent three years testing at 58 sites along the B.C. coastline, finding the environmental DNA (eDNA) of 22 viruses, bacteria and other microscopic organisms had a 2.72 times higher probability of being detected near active salmon farms, versus inactive sites.

The pathogens are naturally occurring in B.C. waters but stocked farms have the potential to act like reservoirs of hosts for pathogens.

Lead researcher, Dylan Shea, a PhD candidate at the university’s ecology and evolutionary-biology department, said the occurrence of DNA varied by times and location, adding the study relates only to the presence of DNA, not the risk of infection to fish.

“There are many unknowns between what we observed and the disease implications for any given fish species … but the findings themselves convey a pretty important message. I can say with confidence that salmon farms do increase the risk of exposure to the suite of microparasites we studied.”

Two of the most commonly detected agents include the Erythrocytic necrosis virus, which attacks red blood cells, affecting a fish’s metabolism, and Candidatus Syngamydia salmonis, causing swelling of the internal organs and skin lesions, which can potentially lead to secondary infections.

The study was published in the scientific journal Proceedings of the Royal Society Oct. 21.

READ MORE: Minimal risk to wild salmon from viruses on farmed B.C. salmon: Fisheries Department

Veterinarians on salmon farms verify young salmon are free from a variety of pathogens, including some identified in the recent study, before they’re transferred to open-net pens. The fish undergo regular screenings thereafter.

Shawn Hall, a spokesperson for the B.C. Salmon Farmers Association, said there are other cautions to note in the latest research.

“The study did not look at viable pathogens, but rather fragments that don’t necessarily cause any concerns related to disease,” Hall said. “Also, the study did not test any control sites – different areas of the ocean. Samples were only taken near operating or fallowed salmon farms. Based on this major exclusion of other test sites, it is clear that study results lacks the comprehensive research support.

“Good science and protecting wild salmon will always be the foundation of responsible ocean-based salmon farming in BC. New studies always needs to be looked at with a critical eye focused on how the research was conducted.”

The David Suzuki Foundation, which supported the study, said in a statement the findings call into question recent DFO risk assessments that found the transfer of nine pathogens from farms to wild fish did not pose a significant threat to wild populations, some of which are at their lowest numbers on record. The assessments were spurred by the 2012 Cohen Commission inquiry that recommended a prohibition on salmon farms in the Discovery Islands by September, 2020, if the threshold for disease transmission exceeded “minimal risk”.

“Uncertainty should inspire precaution,” David Suzuki Foundation marine conservation specialist Kilian Stehfest said. “The study’s findings further highlight the importance of applying a precautionary approach when making management decisions based on incomplete evidence with high levels of uncertainty.”

DFO is currently consulting with area First Nations before deciding later this year on whether to renew aquaculture licences in the Discovery Islands. A DFO spokesperson said the University of Toronto study is among many that will be reviewed and incorporated into the fisheries minister’s decision, but stressed the implications of the latest research are still unclear.

“Exposure to pathogen(s) alone is not sufficient to cause disease — the nature of the host, environmental conditions, and exposure dose and duration are all factors that play a role, and are analyzed when assessing risk.”

READ MORE: B.C. salmon farm opponents demand answers from DFO



quinn.bender@blackpress.ca

Get local stories you won't find anywhere else right to your inbox.
Sign up here

Just Posted

March 8 is International Women’s Day. (Stock photo)
Editorial: International Women’s Day can inspire us to recommit to equality

Let’s call out sexism, amplify feminism and keep working toward equality

Police in Nanaimo are turning to the public for help identifying two men suspected of a break-and-enter attempt at a Nicol Street apartment building. (Photo submitted)
Nanaimo RCMP looking for two men suspected of a break-and-enter attempt

Security camera snapped images in Nicol Street apartment building parking lot

Nanaimo Ladysmith Public Schools. (News Bulletin file photo)
COVID-19 case reported at Nanaimo’s Mountain View school

School district advises of March 2-3 exposure dates

An Island Health nurse prepares a dose of COVID-19 vaccine. (Photo courtesy Island Health)
Island Health opening 19 clinics to immunize Vancouver Island residents

Health authority anticipates more than 40,000 people will be immunized over the next month

(News Bulletin file photo)
Nanaimo school district headed toward 26-per cent overcapacity in next 10 years

Using B.C. Assessment and municipal stats, consultant projects more than 18,300 students in 2030

A sports car crashed into a lamp standard and rolled down the hill behind Country Club Centre mall on Sunday night. (Greg Sakaki/News Bulletin)
Sports car crashes into lamp post, rolls down hill behind Nanaimo mall

Driver uninjured in incident Sunday night on Norwell Drive

This image provided by Harpo Productions shows Meghan, The Duchess of Sussex, left, in conversation with Oprah Winfrey. (Joe Pugliese/Harpo Productions via AP)
Race, title and anguish: Meghan and Harry explain royal rift

Meghan said she struggled with concerns within the royal family about her son’s skin colour

Const. Allan Young. Photo: Abbotsford Police Department
Manslaughter charge laid in Nelson death of Abbotsford police officer

Allan Young died after an incident in downtown Nelson last summer

The Pfizer-BioNTech COVID-19 vaccine is administered to a personal support worker at the Ottawa Hospital on Tuesday, Dec. 15, 2020 in Ottawa. Doctors in Alberta have signed an open letter asking for prioritized vaccination of health-care staff who work directly with patients on dedicated COVID-19 units. THE CANADIAN PRESS/Adrian Wyld
COVID vaccines for seniors in B.C.: Here’s how to sign up

Seniors 90+, Indigenous seniors 65+ and Indigenous Elders can book starting March 8

(The Canadian Press)
‘Worse than Sept. 11, SARS and financial crisis combined’: Tourism industry in crisis

Travel services saw the biggest drop in active businesses with 31 per cent fewer firms operating

Pictures and notes in from friends and classmates make up a memorial in support and memory of Aubrey Berry, 4, and her sister Chloe, 6, during a vigil held at Willows Beach in Oak Bay, B.C., on December 30, 2017. THE CANADIAN PRESS/Chad Hipolito
Mother of slain daughters supports recent changes to Canada’s Divorce Act

Sarah Cotton-Elliott said she believed her children took a back seat to arranging equal parenting

The Port Alice pulp mill has been dormant since 2015. (North Island Gazette file photo)
Parts recycled, life returning to inlet as as old Port Alice mill decommissioned

Bankruptcy company oversees de-risking the site, water treatment and environmental monitoring

(Black Press Media files)
Medicine gardens help Victoria’s Indigenous kids in care stay culturally connected

Traditional plants brought to the homes of Indigenous kids amid the COVID-19 pandemic

Most Read