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Pacific Salmon Face Massive Die-Offs as Temperatures Rise

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With massive die-offs predicted for salmon populations across North America’s West Coast, as both home and migratory waters grow too hot for their survival, efforts are intensifying to restore and protect habitats and restrict the annual harvest.

From California’s Sacramento River to British Columbia’s Okanagan, and in some coastal waters as well, heat and drought are dealing a fatal blow to millions of salmon, both young ones, and older migrating ones, with none able to withstand rising water temperatures in once-cool streams, rivers, and oceans, reports CBC News. 

Off-the-charts ambient temperatures, combined with drought, could mean the entire population of juvenile salmon currently in the Sacramento River will die this summer, while sockeye salmon have halted their annual migration up the Okanagan River, with the cold-water fish sensing a death trap in waters currently above 23°C. 

The year’s entire salmon run may well be “doomed by heat,” Jesse Zeman, director of the B.C. Wildlife Federation’s fish and wildlife restoration program, told CBC. 

That news is part of an ongoing pattern, with warm temperatures blamed for low spawning populations on the Fraser River in 2016, and for heat-related die-offs in both Alaska and Newfoundland in 2019.  

“Many populations of both Pacific and Atlantic salmon have been in gradual decline for decades,” CBC adds, “and scientists say warmer temperatures and other aspects of climate change have played a role.”

That’s partly because warmer temperatures mean warmer water, which holds less oxygen, leaving the fish struggling to breathe. And in a vicious feedback loop, “warmer temperatures speed up their metabolism, causing them to require more oxygen and food, and also forcing them to swim to find cooler waters, consuming more energy.”

The rivers in which the salmon live as juveniles, and where they will later spawn, are also growing more shallow as glaciers melt, winter snows become uncertain, and spring comes earlier each year. 

And with drought prompting human populations to divert more water for their own use,  “by the late summer, rivers are running low and becoming lethally hot for salmon,” said Aaron Hill, executive director of the Watershed Watch Salmon Society. 

North America’s oceanic salmon populations are also suffering on both east and west coasts, CBC adds, as marine heat waves cause “the large, fatty northern zooplankton” to be replaced with less nutritious southern species. The change in diet weakens the fish, leaving them more vulnerable to predation. 

Ottawa’s recently-announced C$647.1-million Pacific Salmon Strategy Initiative, as well as ongoing efforts by provincial organizations like Nova Scotia’s Margaree Salmon Association and New Brunswick’s Miramichi Salmon Association, are part of a groundswell response to the plight of the heat-stressed salmon. 

Strategies include planting shade trees to further shelter naturally cooler pools in rivers, as well as enlarging the existing pools. Conservationists also stress the need for better land use planning, licencing and regulation of groundwater use, careful monitoring of fish stocks, and the closure of both commercial and recreational fisheries as necessary.