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Polar Bears Dive for Longer: Evolution at Work?

Aug 02, 2015 04:49 PM EDT
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Polar bears, it seems, haven't given up the good fight just yet. Researchers recently observed these animal diving for longer and further than ever before - a hint that the species might still be developing new adaptations to support their unusual lifestyle.

That's at least according to a study recently published in the journal Polar Biology, which details how a Ian Stirling, from the University of Alberta in Canada, and Rinie van Meurs, a Dutch naturalist and polar expedition leader, saw something incredible while observing polar bears in the Norwegian archipelago of Svalbard.

"The maximum dive duration for a wild polar bear (Ursus maritimus) of any age is unknown, and opportunities to document long dives by undisturbed bears are rare," the researchers explained.

That's why they were there in the first place - to study the animals as they struggle to cope with shrinking hunting grounds and a changing ecosystem. Past studies have even found that polar bear diets might be changing, with some bears adding dolphin to the menu. (Scroll to read on...)

Traditionally, polar bears dive from seasonal sea ice for their food, hunting seals and even scavenging the occasional whale carcass (narwhal, beluga, etc). The animals even dive for Arctic kelp to munch on, staying submerged for up to 30 seconds at a time. The longest known polar bear dive - until now - lasted about as long as your average large mammal (human included) can hold its breath: 1 minute and 12 seconds.

And yet, earlier last year, Stirling and van Meurs witnessed a polar bear dive without resurfacing for three times that duration - an incredible feat that only highly aquatic mammals and some well-trained humans can pull off.

According to the study, the bear in question was stalking a trio of bearded seals that had been lounging on an ice flow. The researchers, who observed and recorded the hunt from the deck of a ship, say that the bear had been swimming towards the seals at a calm pace, but at about 50 meters (164 ft) away, it slipped under the water to avoid detection by its skittish prey. The bear swam for 190 seconds without surfacing.

Unfortunately, when the bear finally "exploded" out of the water and onto the ice, the seals slipped away. However, the hungry animal did show scientists just how much they've been underestimating these unique bears. It is possible, Stirling and van Meurs suggest, that evolution could even still be in play. (Scroll to read on...)

"Polar bears diverged from brown bears (Ursus arctos) about 4-500,000 years ago, which is recent in evolutionary terms," the researchers wrote. "Thus, it is possible that the ability to hold its breath for so long may indicate the initial development of a significant adaptation for living and hunting in its marine environment."

"However," they added, "increased diving ability cannot evolve rapidly enough to compensate for the increasing difficulty of hunting seals."

It's no secret that polar bears populations are not in good shape. Even the subject of this latest study, while an incredible diver, was notably emaciated. Thanks to gradually warming seas, the duration of the Arctic sea ice season is growing shorter and shorter, even as the ice continues to thin at worrying rates. Some have even estimated that the flux of the sheet will stop entirely within our lifetime, leaving polar bears with nowhere to hunt.

In light of this, experts have already estimated that unless polar bears pull off one heck of a hat trick, they will be gone before 2100.

For more great nature science stories and general news, please visit our sister site, Headlines and Global News (HNGN).

- follow Brian on Twitter @BS_ButNoBS

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