AK - Bowhead whales' migration patterns have shifted in the Arctic
With ice declining, bowhead whales of the Pacific Arctic are staying longer in the waters up north. A change in migration patterns could affect the bowheads’ health and safety, as well as hunters’ access to the subsistence resource.
Two Oregon State University marine mammal researchers, Angela Szesciorka and Kate Stafford, analyzed 11 years’ worth of recordings of whale songs and looked at sea ice information for a studysupported by the National Science Foundation Office of Polar Programs and published in the journal Movement Ecology in early February. Researchers saw that fluctuations in the sea ice direct changes in bowhead whales’ seasonal migrations.
“When there is less ice in the Bering Sea in late fall, bowheads are more likely to winter north of Bering Strait,” Szesciorka said. “When there is more ice in the Bering Sea — and the Chukchi Sea — they are more likely to winter south of Bering Strait.”
Now the researchers are wondering whether the ice decline leads to more risks in the bowheads’ habitat, such as ship strikes or fishing gear entanglement, Szesciorka said. Access to whaling in some subsistence communities might also change.
“This change is happening very quickly, and it is unclear what the potential impacts might be as the Arctic continues to warm,” Szesciorka said. “If the entire population no longer enters the Bering Sea — and there’s no evidence of that — then bowheads will no longer be accessible by St. Lawrence Island hunters. But again, they have still been getting whales annually so hopefully, that will continue.”
The Bering-Chukchi-Beaufort bowhead population, the largest in the world, appears to be healthy and is growing, nearing 17,000 animals.
In the fall, the whales traditionally travel south, following the new ice in the Bering Strait, Szesciorka said. New ice is easier to travel and breathe through, compared to thick perennial ice up in the Arctic, she explained. When Bering Strait ice melts in spring, whales usually make their way back north, passing Utqiaġvik, Point Hope and other whaling communities in the Arctic and giving whalers a second chance to harvest subsistence food.
The conditions in the Arctic are rapidly changing: The sea ice has decreased about 13% per decade since 1979, covering Arctic waters later and later in fall and building a thinner layer, according to the study. The Bering Strait stays open in winter months more often, the researchers said.
To see how declining ice affects bowheads’ behavior, Szesciorka and Stafford looked at the bowheads’ songs and calls recorded between 2009 and 2021 in the Chukchi Sea, near the entrance of the Bering Strait, Stafford said.
Each year, passive acoustic monitoring devices — hydrophones — were anchored to the ocean floor, and using a large research vessel, researchers would retrieve them from the ocean and download a year’s worth of data. By looking at spectrograms, or visualizations of sounds over time, researchers documented when they heard bowheads passing north and south, Szesciorka said.
In winter and spring, bowhead whales sing songs that can last for hours — perhaps males calling females to mate, according to the study. During the summer and fall, whales also produce simple, low-frequency sounds, unrelated to songs, that likely help animals communicate during their migrations.
Up to 2013, the recordings showed that all bowheads had passed south through Bering Strait in late fall and did not move back north until March, Szesciorka said. After about 2013, the time period with no bowheads north of Bering Strait in the winter got shorter and shorter.
“In 2018 in particular, we heard bowheads almost 24 hours a day north of Bering Strait throughout the winter,” she said. “This pattern has continued to the present day.”