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DNA traces of virus and bacteria harmful to wild salmon three times higher near fish farms, study finds

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By Milthon Lujan

Vancouver, Canada – New research calls into question Fisheries and Oceans Canada’s recent assertion that Discovery Islands open net-pen fish farms pose no more than minimal risk to Fraser River sockeye salmon.

The research, conducted with support from the David Suzuki Foundation and published in a leading scientific journal Proceedings of the Royal Society B: Biological Sciences, shows areas surrounding active salmon farms in the Broughton Archipelago and the Discovery Islands were 2.72 times more likely to contain DNA from disease-causing microscopic organisms such as viruses and bacteria.

“This study suggests that salmon farms increase the exposure of wild fish to disease, adding to the mounting evidence that they put the salmon Canada hopes to recover at risk,” said David Suzuki Foundation marine conservation specialist Kilian Stehfest. “It makes no sense to continue to use public waters for this activity.”

Pisciricksettia salmonis bacteria were among the most frequently found pathogens in all three years of sampling. These bacteria can cause blood poisoning disease in salmon, leading to lethargy, loss of appetite and erratic behaviour like uncoordinated swimming. Fish can also exhibit lesions and hemorrhages in internal organs, skeletal muscles and brains. The study indicates that these bacteria may be more widespread in the Discovery Islands than previously thought and contradicts Fisheries and Oceans’ conclusion that an outbreak is unlikely, undermining the assertion that these bacteria pose minimal risk to wild salmon.

“With the lowest sockeye salmon returns on record, it is more critical than ever to prevent wild salmon from being exposed to infectious agents from open net-pens,” Stehfest said.

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Five of the nine risk assessments underlying Fisheries and Oceans Canada’s decision to allow Discovery Islands salmon farms to remain contain high levels of scientific uncertainty, but their final conclusion did not reflect that.

“Uncertainty should inspire precaution,” 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. Fisheries and Oceans failed to do this when it decided not to remove the Discovery Islands salmon farms by the deadline set by the Cohen Commission.”

Reference (open access):
Research reference: Shea, D., Bateman, A., Li, S., Tabata, A., Schulze, A., Mordecai, G., Krkošek, M. (2020). Environmental DNA from multiple pathogens is elevated near active Atlantic salmon farms. Proceedings of the Royal Society B: Biological Sciences, 287(1937), 20202010. doi:10.1098/rspb.2020.2010 

Source: David Suzuki Foundation

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