While anglers are celebrating a strong start to the salmon season, a new Simon Fraser University study warns coho salmon are under serious threat.
The research, published in the Canadian Journal of Fisheries and Aquatic Sciences, found that coho salmon populations in the north and central coast of B.C. have plummeted by more than a third in the last decade.
Marine heatwaves and overfishing are among the factors behind their sharp decline, according to researchers.
"Alarm bells should be ringing. Our findings support what First Nations have been saying for years - coho salmon populations are under serious threat," says lead author Kyle Wilson, assistant professor at SFU's School of Resource and Environmental Management.
"Unless urgent steps are taken to address the decline, then we could be facing a damaging collapse in their population."
The study looked at populations of coho salmon in 52 rivers along B.C.'s north and central coast and found that the number of spawners dropped 37 per cent in 2020 compared to averages between 2000-2015.
It also found that productivity - the number of offspring produced by spawners - collapsed for many coho populations during marine heatwaves at the end of the last decade.
A marine heatwave is when abnormally high ocean temperatures persist in a particular region for an extended period of time - weeks, months or even years.
Higher ocean temperatures can harm marine wildlife, reducing the amount of available food in marine ecosystems, increasing the metabolic demands of feeding salmon, and altering patterns of rainfall and river flow for juveniles.
"Salmon are typically considered cold water species," says Wilson.
"Higher ocean temperatures mean coho salmon are dealing with heat stress and so need to eat more. But if they can't find food because their prey are also being hit by the higher temperatures, then they're potentially going to starve."
While B.C. anglers have welcomed positive returns of sockeye and pink salmon so far this year, coho migrate later into the winter, making them less visible and harder to study.
Coho salmon also face increased competition for food from pink salmon, whose numbers are at an all-time high in the North Pacific Ocean, in part due to industrial scale hatcheries.
Researchers assessed how commercial and recreational fisheries spanning Indigenous, Canadian and U.S. jurisdictions impede coho population recovery.
"Reducing the harvest from commercial and recreational fisheries, in both Alaskan and Canadian waters, would provide coho salmon with the time and space that they need to adapt to climatic changes," says Wilson.
Wilson says the study is timely as negotiations between Canada and the U.S. over the Pacific Salmon Treaty, which is meant to prevent overfishing and protect salmon stocks, are due to pick up next year.
"Decision makers need to sit-up and take note of the situation," says Wilson. "But it's going to need Indigenous, Canadian and American fishery managers to work together. We need management processes that can adapt quickly to changing conditions.
"The good news is that coho are resilient. They have been in this position before and their numbers have recovered rapidly when the right levers have been pulled and environmental conditions are favourable."
The study was a collaboration between Central Coast First Nations, SFU, Wild Salmon Center and Fisheries and Oceans Canada.
Available SFU Experts
KYLE WILSON, assistant professor, School of Resource and Environmental Management | [email protected]
