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Rural Alaska

Record warm water in lower Kuskokwim River likely caused heart attacks in salmon, biologist says

  • Author: Anna Rose MacArthur, KYUK
  • Updated: July 15
  • Published July 15

As record high temperatures swept Alaska recently, many people said the heat was killing them.

For Kuskokwim River salmon, it was actually true. Never-before-seen temperatures in the Kuskokwim River likely sent salmon into cardiac arrest.

Water temperatures near Bethel broke into the lower 70s last week, marking the highest river temperature ever recorded in early July.

Residents along the lower Kuskokwim River from Tuntutuliak to Akiak reported dead salmon floating downstream. Salmon don’t function well past 70 degrees, and the water had pushed just above that limit.

“Essentially, what could happen is salmon metabolism speeds up to the point that they’re having heart attacks and going belly up and floating downriver,” explained Alaska Department of Fish and Game biologist Ben Gray.

Gray and his crew boated from Bethel to Akiak to check it out. Along the way, they counted about 20 dead salmon.

Warm water is also the suspected cause of the higher than normal amount of parasites infesting salmon harvested along the river. That warm water is coming from the ocean. Kuskokwim Bay has run 10 to 12 degrees above average throughout the summer, and each tide pulls that warm water into the lower river.

“And that water is pushing upriver,” Gray said, “and it’s mixing, and we’re having a profile in the water right now where it’s a solid 68 to 70 degrees all the way through.”

Meanwhile, residents throughout the Norton Sound region to the north have reported large numbers of dead pink salmon that have yet to spawn floating in warm waterways.

This article originally appeared at KYUK.org and is republished here with permission.

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