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Narwhal More at Risk From Warming Than Polar Bear?

John Roach
for National Geographic News
April 29, 2008
 
A porpoise with a long, spiraled tusk that inspired the myth of the unicorn ranks higher than the polar bear on a new list of marine mammals most at risk due to Arctic warming.

That's because the narwhal, also known as the corpse whale, may be slightly more sensitive to habitat changes.

All Arctic marine mammals are at risk from warming, which is melting sea ice and shifting the distribution and abundance of prey, the report authors say.

Polar bears rely on sea ice to hunt, and at least one study has suggested that two-thirds of the bears could disappear by 2050 if climate change continues.

But the bears live all over the circumpolar Arctic, and their habitat is unlikely to melt all at once, giving them time to potentially shift their range.

The narwhal, by contrast, mostly sticks to waters between Canada and Greenland (see map), said study leader Kristin Laidre, an oceanographer at the University of Washington in Seattle.

The species' restricted geographic distribution, combined with specific migration routes and a specialist diet, make it just barely more at risk based on the criteria set out for the new analysis, Laidre said.

Her team's report, which ranked the vulnerability of 11 Arctic and subarctic marine mammals, was published last week in the journal Ecological Applications.

Faithful Narwhals

Narwhals spend a few months each summer in ice-free, shallow bays in the high Arctic. In the fall they migrate to deep, mostly ice-covered habitats where they feed.

"They have very specific migration routes and what we call site fidelity," Laidre said.

The animals never vary from their routes and return to the same summer and wintering grounds year after year.

No other porpoises or whales spend much time in the heavily ice-covered regions in the winter, meaning the narwhals face little competition for the Greenland halibut and squid that make up most of their diet.

But as the Arctic warms, different predator species could move in while prey species may move out.

Scientists are concerned that narwhals will be unable to adapt to rapid changes in their ecosystem.

"A contrast is the beluga whale, which is similar to the narwhal but able to exploit many different kinds of habitat in the Arctic and feed on many different kinds of prey species," Laidre said.

Whether or when the changing habitat might drive the narwhal to extinction, she added, is unknown.

Even if most of the population dies out, a few pockets of suitable habitat could remain indefinitely.

Conservation Status

The World Conservation Union lists the narwhal as "data deficient" because too little is currently known about its population status. The animal is also not listed as a threatened or endangered species under the U.S. Endangered Species Act.

Laidre noted that the species' conservation status is outside the scope of her team's assessment.

Should a petition be filed, however, the process may prove less contentious than the current proposal to designate the polar bear as an endangered species, said Kassie Siegel, climate program director with the Center for Biological Diversity in Joshua Tree, California.

Yesterday Siegel's organization won a lawsuit against the U.S. government that requires the Bush Administration to decide by May 15 whether to list the bears.

In its suit, the center alleged that oil and gas development in polar bear habitat has been taking precedence over actions to protect the species.

But the narwhal is found primarily outside U.S. territory, so listing it in the U.S. would offer the animals fewer protections from actions such as offshore drilling.

"We don't have that kind of control over the habitat of the narwhal," Siegel said. "So it wouldn't be as big a deal."
 

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