As Arctic Sea Ice Retreats, Orcas Are on the Move, Spurring Changes in the Food Chain

Orcas are found all over the globe—from the warmer, tropical waters near the equator to the frigid North and South poles. Their range in the Arctic has usually been limited because venturing into ice-covered areas comes with the risk of getting trapped beneath the ice. But that could be changing soon, Chen Ly reports for New Scientist.

As sea ice melts because of climate change, orcas—also known as killer whales—are venturing into once-icy waters. Their expansion into the Arctic has cascading effects on the food web, other species' behavior and Indigenous communities, Corinne Purtill reports for the New York Times.

"The September Arctic sea ice minimum is declining at an average rate of 13% per decade, when compared to values from 1981 to 2010," Brynn Kimber, research scientist at the University of Washington and the National Oceanic and Atmospheric Administration, says in a press release. "Killer whales are being observed in the Chukchi Sea (in the Arctic Ocean) in months that were historically ice covered and more consistently throughout the summer."

Kimber recently described her team's findings at a meeting of the Acoustical Society of America.

Four different audio recorders placed in different regions of the northwestern Arctic collected eight years' worth of acoustic data, allowing Kimber and her team to eavesdrop on the sea creatures. By identifying the clicks, calls and whistles of cetaceans like whales and dolphins, the team could identify which species are present in the region, where they reside and how many individuals there are, New Scientist reports.

A few years ago, Kimber was analyzing the audio recordings when she heard the shrill call of orcas, she tells the Times.

"When I started the job my mentor told me, 'You won’t see killer whales this far north,'" she says. "Where I would see absolutely none in previous years, in later years I was seeing more and more."

Analysis revealed that orcas were visiting the Bering Strait regularly in summer. Not only were they becoming regulars in the region, but pods arrived earlier in 2019 than they did in 2012, likely due to warming temperatures and the melting ice, New Scientist reports.

Furthermore, as apex predators, orcas are at the top of the food chain and feast on fish, seals and even other cetaceans like bowhead whales and belugas. As orcas move in, Indigenous communities and scientists have observed that more bowhead whale carcasses have been left tattered in the seas, the Times reports.

"Killer whales are really intelligent," Cory Matthews, a researcher with Fisheries and Oceans Canada, tells the Times. "If a new area opens up, they can get in there maybe within the next year and exploit a prey population that could be perhaps really slow to respond to those changes."

But just the orcas' presence is enough to tip the ecosystem's balance as prey species adjust their behavior to hide amongst the sea ice where they're safer, but with depleting ice, prey species are more exposed. This shift could affect breeding success, since adults could be more stressed and have fewer resources to raise healthy offspring, which could affect population size later on, Alison Bosman reports for Earth.com.

Around 40 Indigenous communities reside in the region, and species like narwhals, seals and belugas are key parts of the diet and culture, which could decline as climate change continues to wreak havoc on the poles. 

"With this ice going away, there’s going to be more and more changes in the area. I think this [case] is just one of many," Kimber tells New Scientist. "The different ecosystem shifts we might see and all the various impacts it could have is important to think about."

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Rasha Aridi is a science journalist based in Richmond, Virginia. She has written for Science magazine and Science News for Students. You can find her portfolio at rashaaridi.com.