As record high temperatures swept Alaska, many people said that the heat was killing them. For Kuskokwim salmon, it was actually true. Never-before-seen temperatures in the Kuskokwim River likely sent salmon into cardiac arrest.
Earlier this week, water temperatures near Bethel broke into the lower 70s, marking the highest river temperature that’s ever been recorded in early July. This spell was part of a heat wave that shot thermometers to their highest point ever in towns across Alaska.
During this time, 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 amounts of parasites infesting salmon harvested along the river. That warm water is coming from the ocean. Kuskokwim Bay has clocked about 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 have reported large numbers of dead pink salmon that have yet to spawn, floating in warm waterways.