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The belugas in the Arctic ice

For years now, the white whales of the Beaufort Sea have been making a journey hundreds of miles north from Prudhoe Bay into the Arctic ice off Prince Patrick Island, the westernmost of Canada’s Queen Elizabeth Island chain.

Once home to a remote outpost manned by the U.S. and Canadian military at Mould Bay, the island was abandoned by humans in 1997 in favor of an automated weather station. The humans might have left, but the beluga whales keep coming back.

Scientists have pondered why almost since they started tracking the 3,000-pound marine mammals with satellites in the late 1990s. Both the Eastern Chukchi Sea and Beaufort populations roam beneath the ice  off Prince Patrick, but it is the tracking data for the latter which jumps out to even a casual observer as a cluster of activity.

Now a group of researchers led by Donna Hauser at the University of Washington are theorizing the whales have developed a strategy for exploiting arctic cod populations living under the ice. The theory is based on the  behavior of whales regularly diving to depths of 600 to almost 1,000 feet — depths at which cod are known to concentrate in Arctic waters.

“Arctic cod were most abundant at 200−300 meters in the western Beaufort Sea, and beluga dives within the survey area also most frequently targeted these depths,” the researchers reported. “These results are consistent with a hypothesis that Arctic cod are a primary prey item for Pacific Arctic belugas and suggest that foraging belugas dive to depths that maximize prey encounters.”

Food has pretty clearly attracted belugas from both the Eastern Chukchi and Beaufort populations into areas that are often 90 percent ice, Hauser said in an interview, and clearly arctic cod are a key food source.

But she readily admits scientists don’t know for certain what specific food sources lure these air-breathing mammals into poking around beneath the Arctic ice cap. Because of all the ice, the fish resources of the area are hard to sample.

“We don’t know about fish distribution,” she said. “We don’t have a very good idea of what they’re eating there. We don’t have very good information on their diet.”

What the scientists do have is some really interesting data on diving behavior, including dives to more than a half mile deep in the Canada Basin at the northernmost reaches of the belugas’ range.

“…These deep dives involved a whale reaching its maximum depth before immediately heading to the surface without searching for prey at depth. (Researchers) hypothesized that whales may have used these dives to locate small breathing holes in the dense pack ice during ascent from depth and noted that V-shaped dives were not detected elsewhere,” Hauser and fellow researchers wrote.

“That’s what I think is really amazing about these belugas,” Hauser said; that they are able to make incredibly deep dives into an environment almost wholly covered in ice and somehow find their way back to a hole in the ice above that will allow them to breath.

How did they learn this behavior? What first lured them into these seemingly dangerous but obviously food rich waters? Why do these whales seem now to return from their Bering Sea wintering grounds to the same areas of the Beaufort and Chukchi seas year after year?

“Those are good questions,” Hauser said. “Perhaps there is some sort of social learning going on.”

It is possible the toothy, white whales have, like humans, developed their own fishing traditions that bring them back to the same fishing hole year after year. Then, too, the 15-foot white whales are known risk takers when on the hunt for fishy prey.

Near Anchorage they regularly probe the ever shifting channels of Turnagain Arm in search of food. Often this has led to strandings. A record 20 belugas died in strandings in Cook Inlet in 2003, according to the National Oceanic and Atmospheric Administration.

No one knows how many of these air breathing mammals die trapped below the Arctic ice unable to find a breathing hole, but some surely do. A few are known to fall victim to polar bears, too. The BBC in 2008 captured video of a polar bear hunting belugas at an Arctic ice hole.

These are the risks the whales take to find food in a harsh environment where Hauser wonders what the future holds for them. The scientist grew up in Anchorage watching the Cook Inlet belugas now classified as an endangered species only to find herself studying another group of whales facing threats from a changing environment.

The paper she penned along with five co-authors ends with a bow to an evolving Arctic where “industrial and other human activities (e.g. shipping and other vessels, mining, fishing, and tourism) are expanding and can potentially affect belugas directly (e.g. hearing impairment or stress response) or indirectly alter behavior.

“Although both populations are considered stable stocks, recent evidence for declining growth, body condition, and blubber thickness suggests that ecosystem changes may be affecting belugas through reduced availability or quality of prey. Thus, understanding the behavioral use in each region offers a benchmark for which changes in beluga behavior can be assessed, as well as information to identify ecologically significant areas that may warrant protection.”

 

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