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Pike eat more as water warms, threatening native species

Rising temperatures in a Southcentral �ֻ�ֱ�� river have led to a hungrier population of invasive northern pike, a trend that could imperil native salmon and other fish species.

A �ֻ�ֱ��-led research team analyzed the stomach contents of northern pike caught by the U.S. Fish and Wildlife Service in the Deshka River during the summers of 2021 and 2022. The team compared the contents to samples from pike collected a decade earlier.

Pike of every age class ate more fish as temperatures increased, including a huge 63 percent rise among year-old pike.

The in the journal Biological Invasions.

“We expect there will be significant warming in the future, and the amount of fish that pike consume is going to increase with it,” said Benjamin Rich, who led the study while pursuing his graduate degree at the UAF College of Fisheries and Ocean Sciences.

Mean summer air temperatures in the study area have warmed by about 3 degrees Fahrenheit since 1919, including a rise of 0.8 degrees in the past decade. Water temperatures in the Deshka, a tributary of the Susitna River, have also been well above historical norms in recent years, Rich said.

Predicted warming through the 21st century would continue that trend. Modeling predicts a 6%-12% increase in consumption by northern pike by 2100.

The increased appetite of Deshka River pike mirrors observations from other freshwater systems. Warmer water can boost the metabolism of predators, leading to higher energy needs and more aggressive feeding. Those results are especially concerning in Southcentral �ֻ�ֱ��, where illegally introduced northern pike share habitat with declining populations of Chinook and coho salmon.

Among the prey species found in pike stomachs, Chinook and coho actually decreased in number during the decade. That finding probably can be attributed to declining salmon populations in the Deshka.

Salmon are already being stressed by warming temperatures, said UAF professor of fisheries Peter Westley, so the added pressure of more aggressive predators in that environment is a significant concern.

“We know that invasive species and climate are individually associated with freshwater fish extinctions,” said Westley, a co-author of the study. “Those impacts may be working together into the future.”

Erik Schoen, a researcher at UAF’s International Arctic Research Center, said those complex dynamics are important to track. Highly valued species like salmon are just one element in freshwater ecosystems that are affected by warming temperatures.

“There’s been a lot of work done about how changes in temperature affect salmon directly. That’s really important, but salmon aren’t alone in these rivers,” said Schoen, who also contributed to the paper. “It’s also important to understand how these changes are affecting salmon indirectly through their predators, prey and pathogens.”

Other co-authors of the paper included Adam Sepulveda and Jeffrey Falke with the U.S. Geological Survey and Daniel Rinella with the U.S. Fish and Wildlife Service.

ADDITIONAL CONTACTS: Benjamin Rich, barich2@alaska.edu; Erik Schoen, eschoen@alaska.edu; Peter Westley, pwestley@alaska.edu

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