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Polar Bears May Soon Feast on Whale Carcasses. Global Warming is to Blame.

This scavenging strategy saved sleuths of bears in the past, but it’s not sustainable as temperatures climb at unprecedented rates

Polar bears are shown scavenging on the carcass of a dead bowhead whale that washed ashore on Wrangel Island, Russia. (Chris Collins/Heritage Expeditions)
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Climate change is bringing the heat for polar bears—and things are not looking good. The latest development? A shift in their diet, which may soon include regular gorging on blubbery whale carcasses, scientists say.

And, as Craig Welch reports for National Geographic, humans are to blame. The planet’s rising temperatures are steadily melting northerly sea ice, which Arctic polar bears depend on to access their favorite seal-flavored suppers. During the warmer months, when the ice sheets shatter, some bears simply fast on land, waiting until hunting bridges freeze again.

But with each passing year, the number of toasty days climbs, diminishing the amount of time that polar bears are able to spend trekking on ice cover. Disoriented and stranded ashore, they’re being inadvertently starved. And the effects are becoming alarmingly clear: Some bears are experiencing stunted growth and lifespan, and birthing fewer cubs, Welch reports.

As the planet continues to shift, these changes in behavior probably won’t stop here. Unable to hunt their typical prey—fatty ringed seals—polar bears may turn to scavenging the Arctic equivalent of roadkill: whales.

It’s actually a clever move. In polar bear terms, a single bowhead whale can provide as much food as about 1,300 ringed seals, according to a new study published this week in the journal Frontiers in Ecology and the Environment. Voracious eaters like polar bears can wolf down and store large amounts of fat, making whales—whose bodies contain meat and blubber aplenty—a prime choice, even as a plan B.

Just last year, more than 180 bears were seen feasting on an unlucky bowhead corpse off the coast of Chukotka, Russia. And while such sightings are currently uncommon, they may become a mainstay meal for desperate bears sweating out seal starvation. In fact, this scavenging strategy is one these Arctic-faring beasts have used during naturally-occurring upswings in global temperature in the past, like the Eemian interglacial period, which occurred between 130,000 and 115,000 years ago, reports Maddie Stone for Earther.

But the way things are going, we’re slated to experience some pretty unprecedented upticks in temperature by 2040. The world is warming at a rate it never has before, and what was a provisional solution in polar bear past may not hold water as sea levels rise.

“If the rate of sea ice loss and warming continues unmitigated, what is going to happen to polar bear habitat will exceed anything documented over the last million years,” says lead author Kristin Laidre, a marine biologist at the University of Washington’s Polar Science Center, in a press release.

Depending on the season, a sleuth (group of bears) of 1,000 polar bears would need between eight and 20 bowhead whales to sustain themselves for about four months. Areas where whale beachings are common—like the Arctic's Chukchi Sea—might meet such a quota, but with 19 subpopulations of polar bears dotting the Arctic, not every locale can boast the same wealth of whales.

“Greenland, which is very mountainous, is not a place where we get a lot of stranding,” Laidre tells Stone at Earther. “There’s definitely parts of the Arctic where this is unlikely or does not occur.”

But the tricky thing is, when whales die, most just sink to the sea floor. Before a carcass can even start drifting landward, it needs to float, which happens only 10 percent of the time, when the buildup of gasses inside the rotting corpse buoys it to the water’s surface, Stone reports.

To make matters worse, years of human activity—like whaling and coastal and offshore development—have whittled whale populations way down. So, while polar bears can be flexible in the short term, the bottom line is that we’ve left them with pretty sparse options for the decades to come.

As Todd Atwood, a polar bear biologist in Alaska with the U.S. Geological Survey, who was not part of the study, explains to Welch at National Geographic, whale scavenging is just a “Band-Aid.” To heal the wound that whales can only temporarily patch, “we need sea ice,” Laidre tells Welch.

And that means changing our damaging climate-related habits—fast.

About Katherine J. Wu
Katherine J. Wu

Katherine J. Wu is a PhD student in Microbiology and Immunobiology at Harvard University and Co-Director Emeritus of Science in the News, a graduate student organization that trains young scientists to communicate science to the general public. She is also a 2018 AAAS Mass Media Fellow at Smithsonian magazine. Website: katherinejwu.com

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