Rising temperatures in an Alaska river are causing invasive northern pike to eat more fish, threatening already declining salmon populations. Researchers from the University of Alaska Fairbanks analyzed pike stomach contents and found significant increases in consumption, especially among younger fish. The findings raise concerns about combined effects of climate change and invasive species.
In the Deshka River in Southcentral Alaska, northern pike have shown a marked increase in fish consumption as water temperatures rise. Scientists led by Benjamin Rich at the University of Alaska Fairbanks examined stomach contents from pike collected by the U.S. Fish and Wildlife Service in the summers of 2021 and 2022. They compared these to samples from about a decade earlier, revealing that pike of all ages ate more fish, with year-old pike consuming 63 percent more than before. The study was published in the journal Biological Invasions this year. Benjamin Rich stated, “We expect there will be significant warming in the future, and the amount of fish that pike consume is going to increase with it.” The Deshka River, which flows into the Susitna River, has seen water temperatures above historical averages, mirroring a regional trend of summer air temperatures rising by about 3 degrees Fahrenheit since 1919. Models project pike could boost food intake by another 6% to 12% by 2100. Northern pike, introduced illegally, now prey on struggling Chinook and coho salmon. Although fewer salmon appeared in recent pike stomachs, researchers attribute this to declining salmon numbers rather than less predation. UAF fisheries professor Peter Westley, a co-author, noted, “We know that invasive species and climate are individually associated with freshwater fish extinctions. Those impacts may be working together into the future.” Erik Schoen from UAF's International Arctic Research Center highlighted indirect effects: “It's also important to understand how these changes are affecting salmon indirectly through their predators, prey and pathogens.” Other contributors included researchers from the U.S. Geological Survey and U.S. Fish and Wildlife Service.