Polar bears (Ursus maritimus) got a long-awaited boost on November 23 when the U.S. Fish and Wildlife Service (FWS) finally designated more than 485,000 square kilometers of "critical habitat" for the species, which is listed as "threatened" under the Endangered Species Act (ESA). The critical habitat was first proposed in October 2009, and a ruling was due this past June 30, but the FWS obviously did not make that date. The habitat was also reduced by about 33,500 square kilometers from what was originally planned (pdf) to "accurately reflect the U.S. boundary" as well as exempt five U.S. Air Force bases and several native communities.

The critical habitat—95 percent of which is sea ice—includes barrier islands and onshore areas where mothers den their young, along with offshore sea ice. It doesn't do a huge amount to protect polar bears, but it does require federal agencies operating in the area to "ensure their actions...do not harm polar bear populations." The FWS announcement acknowledges that the polar bear's greatest threat is "the melting of its sea-ice habitat caused by human-induced climate change," but this plan doesn't specifically take any action to mitigate climate change. (The plan also protects existing oil-drilling operations in the region.)

In related news the National Oceanic and Atmospheric Administration (NOAA) on Friday proposed listing ringed seals (Pusa hispida), a main prey source for polar bears, as a threatened species in the Arctic Basin due to the loss of sea ice that the seals depend on to survive. The seals are already protected under the Marine Mammal Protection Act of 1972. One of the five ringed seal subspecies, the Saimaa ringed seal (Pusa hispida saimensis), which is found only Finland, is currently protected by the Endangered Species Act to prevent its import. NOAA's new plan would add the four additional ringed seal subspecies, plus unrelated bearded seals, to the ESA. The public can comment on the plan until the end of January, and NOAA has a full year to make its final decision on protecting the seals.

Speaking of seal blubber, the fatty substance may be more vital to polar bear survival than previously known. It is not just a primary source of calories; it may be the best food polar bears can physically eat. According to new research by evolutionary biologists from the University of California, Los Angeles, polar bear skulls are not strong enough to eat the same food as their neighbors from the south, grizzly bears, which often consume barks, grasses and other tough foods. Herbivores and omnivores typically require much stronger skulls than carnivores because the muscles that attach their jaws to their skulls need to be much more powerful. Seal blubber, on the other hand, is soft and does not require much chewing. Climate change has been driving polar bears farther south, whereas grizzlies have been driven north in search of food, so the two species could soon find themselves competing for food, a competition the polar bears may not be physically capable of winning.

Another new study speaks to the importance of preserving the polar bear's prey. The study, by researchers from Durham University in England and the Zoological Society of London, suggests that large predators—like polar bears, tigers and lions—are particularly vulnerable to climate change and other changes in their habitats because they have to work so hard to get enough prey to eat. The study concludes that both predators' habitats and their prey need to be preserved for the large meat-eaters to survive in the wild.

Understanding polar bear habits and behaviors remains key to their survival. Russia's Ministry of Natural Resources recently sought to better understand its own polar bears by tagging three females with radio collars to follow their migration habits. (Only female polar bears can carry radio collars because the males' necks are wider than their heads and the transmitters slip off too easily.)

Getting back to the topic of melting sea ice, recent radio collar evidence collected by the World Wildlife Fund International (WWF)-Canon Polar Bear Tracking Program found that over the last three to four years polar bears have been swimming much greater distances—500 to 650 kilometers at a time—as their icy habitats melt. Some have been spotted swimming with their young on their backs. The WWF says is not new behavior but it has not been observed by scientists before. Geoff York, WWF's polar bear conservation coordinator, says cubs will be more at risk when having to swim long distances in cold waters because they "lack the capacity of adults to thermoregulate in cold water."*

All of this news builds up to a potential change in the polar bears' status under the ESA. In response to a lawsuit from several conservation organizations, U.S. District Court Judge Emmett Sullivan has given the FWS until December 23 to explain why the polar bear should only be listed as "threatened" instead of "endangered" under the ESA. The higher category would offer the bears more protection and require greater effort to preserve them.

At issue is how much weight is placed on the "imminence" of a species' possible extinction when considering placing it on the ESA. According to the Natural Resources Defense Council, "the government's own models show that polar bears face over an 80 percent chance of becoming extinct by mid-century throughout much of their range." That seems imminent enough, although the lawsuit actually seeks to remove the use of "imminence" as the primary decision-making factor for the ESA, something that exists only in practice, not in the actual law.

So...expect more polar bear news right before Christmas. Hopefully it won't involve a piece of coal (or a gallon of oil) in their stockings.

Photo via Wikipedia

*Editor's Note (12/14/10): This paragraph was revised after posting to more accurately and thoroughly depict research on swimming polar bears and their cubs. The original also incorrectly stated polar bears swimming with their young on their backs is new behavior that had not been observed before. Such behavior is not new, but it had not been observed previously by scientists.