Brynn Kimber, a research scientist at the University of Washington who works in the National Oceanic and Atmospheric Administration’s Marine Mammal Laboratory, has spent considerable time analyzing audio data recorded in the frigid waters north of Alaska, Canada and Russia. Usually, Mrs. Kimber hears the chatter of bowhead whales, belugas, narwhals and other cetaceans native to that part of the Arctic.
A few years ago, they began to hear a signature cry that acoustic experts describe as that of a disgruntled domestic cat: the piercing cry of an orca. Mrs. Kimber wondered at first if their ears were deceiving them.
“When I started the job, my mentor told me, ‘You won’t see orcas that far north,’” said Ms. Kimber. But as years of data piled up, along with more orca calls in areas where they had never been recorded, that turned out to be no longer true.
“Where I saw absolutely none in previous years, I saw more and more in later years,” said Ms. Kimber. “That was quite unusual.”
The killer whale calls are further evidence of a rapidly changing Arctic. With sea ice receding, killer whales — which are actually dolphins — are now venturing into parts of the sea that were once inaccessible, spending more time in places where they were once seen only sporadically, according to data released by Ms Kimber Thursday. presented at the annual meeting of the Acoustical Society of America in Seattle.
As a result, some of nature’s most effective predators have vastly expanded the scope of their hunting. The change may have significant impacts on animals in the food chain, including humans.
Arctic sea ice has declined significantly in the four decades since satellite monitoring began. In the past 15 years alone, about 75 percent of the ice volume has disappeared, and the remaining ice is thinner and of poorer quality, said Amy Willoughby, a marine mammal biologist at NOAA’s Alaska Fisheries Science Center.
The loss of ice combined with warming water and atmospheric temperatures has affected every level of the Arctic ecosystem. Large mammals like polar bears are struggling to navigate shrinking habitats, while the marine algae at the base of the Arctic food chain are blooming faster and more abundantly than ever before.
In recent years, scientists have noticed a similar upheaval in the behavior of the region’s marine mammals. Orcas are increasingly feasting on bowhead whales. Scientists and native Arctic communities have noticed a growing number of bowhead whale carcasses in the northeastern seas of Chukchi and western Beaufort with signs of orca attack.
Even if the killer whale doesn’t take a single bite, the presence of predators can have far-reaching consequences. Bowhead whales usually retreat to protective patches of dense ice when threatened by orcas, which lack the bowhead bowhead whales’ ability to break through frozen waters for air. An Inuit word, “aarlirijuk,” describes this Greenland fear response, which was developed specifically to evade orcas.
But as the ice recedes, these defenses may prove a liability. Bowhead whales need to spend more time than ever before hiding in thick ice where food options are scarce. Calves that are not yet strong enough to break through the ice can suffocate.
Any decline in Greenland numbers could also affect the food chain: Baleen whales are an important source of food for subsistence hunters in native Arctic communities, Ms Kimber said.
“Orcas are really intelligent,” said Cory Matthews, an Arctic researcher at Fisheries and Oceans Canada. “They consume very quickly. If a new area opens up, they may be able to move in there within the next year and exploit a prey population that may be very slow to respond to those changes.
It could be years, he added, before scientists fully understand the long-term ramifications of how these extremely deadly and newly encouraged hunters are expanding their range in the Arctic.