The belugas dove below the sea ice as deep as 850 meters (2,788 feet) hunting for the Arctic cod and Greenland halibut they eat, in dives that averaged 20 minutes, according to an analysis of tracking information collected by satellite from seven belugas over five years.
The deep, long dives are consistent with the whales' blubber layer, which can be 4 inches (10 cm) thick and allows them to withstand frigid waters while waiting for prey or chasing it down, the study found.
Understanding the belugas' behavior and diet is crucial to understanding the threats facing the whales, which include warming Arctic waters due to climate change and potential interference with shipping traffic through the Northwest Passage.
"The ability for them to dive deeply ... could give them an advantage over some of the other marine mammals that can't dive as deep, particularly if the productivity in the very shallow waters declines with a changing climate," said Heather Lynch, a professor of biology at the University of Alaska Fairbanks.
Lynch was the lead author of the study published on Oct. 24 in the journal Biology Letters.
Satellite tracking of belugas is technically demanding and expensive, explained co-author Kristin Laidre, a senior research scientist at the University of Washington's Polar Science Center.
"For the first time we have detailed measurements of when, where, and how deep these Arctic whales dive over entire annual cycles," Laidre said. "Understanding their diving behavior over annual and migration cycles is a foundational step towards understanding how they're going to respond to rapidly changing environmental conditions."
Climate change is causing Arctic sea ice to melt, opening new areas to shipping traffic but diminishing the habitat for many marine mammals.
"If the shipping traffic starts following right behind where the sea ice edge used to be, and that's right over the whales' heads while they're searching for food, that's going to interfere with their foraging and potentially push them out of these really productive areas," Lynch said.
The Northwest Passage consists of sea routes through the Arctic waters of Canada linking the Atlantic and Pacific oceans.
The Canadian government wants to increase ship traffic through the Northwest Passage, and last November Canada said it was investing CAD$1.26 billion (US$950 million) toward port development and upgrades to improve marine navigation and icebreaking in the Arctic region.
The study was also authored by researchers from Fisheries and Oceans Canada and Scripps Institution of Oceanography.
