April 15, 2021 — The size of king salmon returning to Western Alaska rivers to spawn has been decreasing over the past few decades. Researchers at the University of Alaska Fairbanks think that they’re closer to understanding why.
Peter Westley and Andrew Seitz are fisheries scientists at the University of Alaska Fairbanks who helped publish new research on king salmon in February. To answer why these salmon are getting smaller, researchers attached tags to the fish that can record the depth and temperature of the water around them. Seitz said that many of the tags on the salmon were recording temperatures above 70 degrees Fahrenheit.
“And we thought, ‘Well, where is it, you know, in the high 70s in the winter in the Bering Sea, even at depth?’ And the only place that we can infer that is that warm is in the belly of a salmon shark,” Seitz said.
Westley and Seitz’s research indicates that returning king salmon are getting smaller because the bigger ones are getting eaten. They said that predators, like salmon sharks, may target the older, larger kings because they stand out. Seitz said that predators’ preference for larger fish may have always existed, but there could just be more predators now than in the past.