SOURCE: CNN

DATE: August 17, 2019

SNIP: Alaska has been in the throes of an unprecedented heat wave this summer, and the heat stress is killing salmon in large numbers.

Scientists have observed die-offs of several varieties of Alaskan salmon, including sockeye, chum and pink salmon.

Stephanie Quinn-Davidson, director of the Yukon Inter-Tribal Fish Commission, told CNN she took a group of scientists on an expedition along Alaska’s Koyokuk River at the end of July, after locals alerted her to salmon die-offs on the stream.

She and the other scientists counted 850 dead unspawned salmon on that expedition, although they estimated the total was likely four to 10 times larger.

They looked for signs of lesions, parasites and infections, but came up empty. Nearly all the salmon they found had “beautiful eggs still inside them,” she said. Because the die-off coincided with the heat wave, they concluded that heat stress was the cause of the mass deaths.

Quinn-Davidson said she’d been working as a scientist for eight years and had “never heard of anything to this extent before.”

“I’m not sure people expected how large a die-off we’d see on these rivers,” she said.

The water temperatures have breaking records at the same time as the air temperatures, according to Sue Mauger, the science director for the Cook Inletkeeper.

Scientists have been tracking stream temperatures around the Cook Inlet, located south of Anchorage, since 2002. They’ve never recorded a temperature above 76 degrees Fahrenheit. Until now.

On July 7, a major salmon stream on the west side of the Cook Inlet registered 81.7 degrees.

Mauger said she and her team published a study in 2016, creating models outlining moderate and pessimistic projections for how climate change would drive temperatures in Alaska’s streams.

2019 exceeded the value we expected for the worst-case scenario in 2069,” she said.