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Fraser River Too Hot for Spawning Sockeye

Oregon State University/wikimedia commons

Scientists are concerned that a sweltering July has left British Columbia’s vast Fraser River too warm for the Sockeye salmon just now beginning to swim hundreds of miles upriver from the Pacific to spawn.

While the endpoint of a salmon’s marathon journey from ocean to the inland gravel nurseries is always the death of the adult fish following egg-laying, officials with Fisheries and Oceans Canada are worried that the Fraser is now so warm that the salmon may die before reaching the nurseries.

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“Daily temperature monitoring by Fisheries and Oceans Canada (DFO) shows the Fraser hitting 20.7°C near Hope, B.C., for some days this week,” CBC reports. “At 18°C, the sockeye don’t swim as well,” while at 19°C, “they slow and show signs of physiological stress.” Water temperatures at or above 20°C “lead to severe stress, with ‘high pre-spawn mortality’.”

While the Fraser has occasionally seen temperatures spike higher, the ones being measured now “are well above the historical average,” said Mike Lapointe, chief biologist for the Pacific Salmon Commission. And, critically, they’re part of a larger pattern of warming that bodes ill for the salmon.

Whereas “from the 1950s to the 1980s, the Fraser would only average two days a year over 19°C,” since 2010 “it’s crossed that threshold an average of 22 days a year,” said David Patterson, head of DFO’s Environmental Watch program.

And while salmon are fairly adaptable, “it’s an open question for scientists” whether the overheating Fraser will prove too much for the sockeye now traversing its waters, CBC reports.

“They’re adapted to warmer temperatures, but not the kind of temperatures they’re being exposed to now,” Lapointe said, during a moment of furnace-like temperatures along the Fraser last week, including a record-breaking 41.4°C in Lytton.

While temperatures are forecast to be less ferocious over the next 10 days, concerns remain high for salmon runs yet to come, particularly since B.C. temperatures typically peak in August.

And even with the current drop in temperatures, the Fraser is far from “fish-friendly,” CBC notes, “with the waters expected to stay above 19°C over that period.”