Without ice, killer whales are preying on bowheads in Alaska’s northern seas

The population of endangered southern resident killer whales has dwindled to 76 individuals. (Holly Fearnbach/NOAA)

For subsistence hunters in the northern parts of Alaska, the bowhead whale has been a part of their diet for generations. However, scientists have found that as sea ice has dwindled in Arctic waters, a new predator has moved in to feed on the marine mammals: killer whales.

It’s not unheard of for killer whales to feed on bowhead whales in subarctic waters. Amy Willoughby is a researcher with the University of Washington specializing in aerial surveys of Arctic marine mammals.

“Killer whale predation on western Arctic bowhead whales has been documented in the shores of Russia and the Bering Sea,” Willoughby said. “For example, the St. Lawrence Island.”

However, in the colder waters north of Alaska, like the Eastern Chukchi and Western Beaufort Seas, sea ice becomes more plentiful, and it was thought that bowhead whales were better protected from predators.

But Willoughby says that sea ice has gotten thinner as Arctic temperatures have risen in recent decades.

Bowhead whales (Photo courtesy of NOAA Fisheries)

“Bowhead whales are thought to have an avoidance strategy to predation by evading predation and hiding out in thicker sea ice,” Willoughby said. “And without that sea ice there, bowhead whales don’t have anywhere to retreat to.”

Willoughby says scientists documented the first direct evidence of killer whale predation in those traditionally sea-ice-rich waters in 2015.

“The mouth was missing. The tongue was missing. The jaw was broken. And it also had healed rake marks on its flipper,” Willoughby said. “And that was kind of the ‘Aha!’ moment where we realized that killer whales might be predating on bowhead whales.”

Researchers began examining bowhead whale carcasses found from 2009 to 2018. Of the 33 whales observed by scientists, 18 of them had evidence of killer whale predation.

(A) The 2015 bowhead calf carcass that provided the first evidence of killer whale predation on a bowhead whale in the U.S. Pacific Arctic. Note rake marks on the calf’s flipper, mouth and jaw. (B and C) Carcasses of young bowhead whales with lethal injuries to the mouth and jaw from killer whale attacks. (Photo courtesy of NOAA Fisheries)

“We can’t technically say that there’s been an increase because there can be a lapse in data and information from years prior,” Willoughby said. “But when we look at the years from 2009 to 2018, killer whales are the primary cause of death.”

Willoughby says scientists don’t know for sure what the long-term effects of killer whale predation on bowhead whales could be, but she speculates bowhead whales may change their migration patterns in response to predation. Additionally, their feeding opportunities could change as a result of killer whales moving in. That could have repercussions on the 11 Inupiat whaling communities that subsist on bowhead whales.

“The Indigenous people that hunt these whales for subsistence have hundreds of years of traditional ecological knowledge to base their efforts off of,” Willoughby said. “And killer whale presence might negate that knowledge that they hold.”

At the very least, she says it’s now more important than ever for scientists to continue to keep an eye on killer whales as they expand their hunting grounds into the coldest parts of the world.

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