Rising temperatures in the waters of Southcentral Alaska's Deshka River have boosted the appetites of invasive northern pike, to the peril of Chinook and coho salmon and other fish species.
A study led by the University of Alaska Fairbanks researchers, published in February in the journal Biological Invasions, notes that pike of every age class are eating more fish as water temperatures rise, including a 63 percent rise among year-old pike.
Benjamin Rich, who led the study while pursuing a graduate degree at the University of Alaska Fairbanks (UAF) College of Fisheries and Ocean Sciences, said researchers expect there will be significant warming in the future, and the amount of fish pike consume will increase with it.
The big thing to watch will be the cumulative impacts of climate warming, including hatchery issues and endangered species, said UAF fisheries professor Peter Westley, who worked with Rich and Erik Schoen, of UAF's International Arctic Research Center, on the study.
As the area warms, the consequences of pike preying on the other fish will keep increasing, Westley said.
Other study contributors included Adam Sepulveda and Jeffrey Falke of the U.S. Geological Survey, and Daniel Rinella of the U.S. Fish and Wildlife Service.
Warmer water can boost the metabolism of predators, leading to higher energy needs and more aggressive feeding. This is particularly concerning in Southcentral Alaska, where illegally introduced pike share habitat with declining populations of Chinook and coho salmon.
A native species in Interior and Western Alaska, northern pike were illegally introduced to the Susitna River basin in the 1950s. Since then, the predatory fish has become established in more than 150 lakes and rivers in the region.
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, and water temperatures in the Deshka, a tributary of the Susitna River, have also been above historical norms in recent years, Rich said.
Predicted warming through the 21st century would continue that trend. Modeling predicts a 6 percent to 12 percent increase in the consumption of other fish.
This study found decreased amounts of Chinook and coho salmon in pike stomachs over the past decade, a finding researchers attributed to declining salmon numbers in the Deshka River.
Northern pike are just another pressure on salmon already stressed by warming temperatures, Westley said. “We know that invasive species and climate are individually associated with freshwater fish extinctions. Those impacts may be working together into the future.”
Schoen said it is important to understand how changes in temperature are affecting salmon indirectly through their predators, prey, and pathogens.
