Climate change speeds spread of invasive pike in Alaska salmon streams, study finds

An invasive freshwater fish is threatening Alaska’s wild salmon stocks by devouring juveniles in rivers and lakes, the Alaska Beacon reports.

Northern pike were illegally introduced to the southcentral part of the US state in the mid-20th century, and a recent University of Alaska Fairbanks (UAF) study warns that climate change could worsen the problem. 

That’s because as temperatures rise in waterways, invasive pike eat more, researchers found in the peer-reviewed article in 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,” Benjamin Rich, who led the study while a graduate student at UAF’s College of Fisheries and Ocean Sciences, said in a statement released by the university.

The study site was the Deshka River, which flows into the Cook Inlet where commercial salmon harvests take place. The 44-mile river, a tributary of the Susitna River, is also popular for sport anglers.

But Pacific salmon are a lot less abundant in the Deshka now than in the past thanks to the warmer temperatures, which — along with speeding pike metabolism — are spurring more rapid predation on young salmon.

While salmon become more sluggish in warmer temperatures, northern pike thrive and become speedier swimmers, Erik Schoen, a UAF fisheries biologist and a study co-author, explained to the online news outlet.

“If it keeps getting warmer, they get much better at catching salmon,” he said. “They’re amazing ambush predators.”

Deshka pike are actually eating less salmon than they did in past years, analysis of stomach content shows, the researchers reported. But that’s not because they are turning away from salmon. It’s evidence of salmon declines in the river system, they advised.