By JOHANNA EURICH • FEB 7, 2020 KYUK.org
Credit: USGS
Recent research indicates that extremely warm temperatures can turn Alaska’s salmon streams into unfriendly, even lethal habitats. While Alaskan scientists are just beginning to study the impact of warmer temperatures on salmon streams, it is already a familiar reality for many Canadian fish biologists.
Warming temperatures in British Columbia’s Fraser River have long been known to hurt and even kill sockeye salmon. It’s been studied for decades, and Vanessa Von Biela, a biologist with the federal Alaska Science Center, told those attending the Alaska Marine Science Symposium in January that a small increase in river temperatures on the Fraser can mean a lot less salmon spawning.
“More than half the salmon run can die in the river,” Von Biela said. “That includes en route mortality and pre-spawn mortality, where they die on the spawning ground.”
Until recently, the Canadian experience didn’t seem relevant to Alaska’s colder salmon streams, but that’s changing. Alaska’s ocean and streams are now warming faster than those to the south, and last year’s recordbreaking heat delivered dead, unspawned salmon to our streams.
Von Biela saw it coming. A few years ago, she set up experiments to document the temperature tolerance of Yukon River king salmon. She set up tanks to test some of the returning fish as they entered the drainage, to see what temperatures caused heat stress. She had to look for specific genes and proteins because salmon don’t look like they’re in trouble until it’s too late.
“And those salmon tended to look healthy other than they were dead,” she explained.
Von Biela tested Yukon king salmon for six hours in water that was 14 degrees Celsius, or 57 degrees Fahrenheit, all the way up to 21 degrees Celsius, which is 69.8 degrees Fahrenheit.
“And we certainly felt that the ones in 21 degree C[elsius] treatment were stressed, and in fact that was the only treatment where we had mortality. Half of those fish did die,” she said.
The fish that survived the tanks showed changes in both genetic markers and proteins at the various temperatures. This allowed her to create a way to measure heat stress in Yukon kings.
Read the rest of Part I of Salmon in a Warming World