The problem with gathering an accurate census on polar bears is that the apex predators wander far and wide in their hunt for food. Some of the globe-trekking carnivores have been known to travel thousands of miles and back again, crossing international boundaries and vast bodies of water along the way.
Unlike the remote cabin in the woods, where census workers for the U.S. government have been known to sweep in on snowmachine to turn the cabin’s human occupants into usable statistics for government population estimates, performing a head count of polar bears across the Arctic isn’t nearly as easy or as methodical.
The current best estimates among international scientists places the world’s polar bear population at 20,000 to 25,000. While researchers from the five polar bear nations — the United States, Canada, Russia, Greenland and Norway — say the numbers are reasonable, they acknowledge some uncertainty with those figures.
“It’s the best we have,” explained Eric Regehr, a polar bear scientist with the U.S. Fish and Wildlife Service in Alaska. The numbers represent “a mix of good, medium and poor estimates,” he added.
Regehr, who has studied polar bears in the U.S. and Canada for a decade, is among the U.S. members of the Polar Bear Specialist Group (PBSG), a smaller working group of scientists throughout the far north collaborating under the auspices of the International Union for Conservation of Nature’s Species Survival Commission.
Current projections predict that by 2050, sea ice in the Arctic will be gone, and in another several decades polar bears in Alaska may follow. This was among the reasons why the U.S. government listed the polar bear as a threatened species in 2008, and why other countries experiencing similar trends have moved similarly to assign to the bears various levels of decline or impending peril.
But if the population estimates are off, how much does it really matter in an era when climate change is rapidly depleting the amount and quality of sea ice that make up the bears’ natural habitat. Ice that formed last winter, which creates the jumbled conveyer belt bears live on and ride in search of seals, melted faster and more substantially this fall than in any other year on record.
“Would it make a big difference if we were a little off? It probably doesn’t,” Regehr said.
In the short term, bears might be able to adapt in small groups to more extensive stays on land. But in the long term, given the bears’ fundamental relationship to sea ice and the nutrient-rich food produced by the ocean, it will matter. “Polar bears won’t have enough time to eat seals, get fat and have cubs,” he said.
Polar bears across the globe
Among the circumpolar regions, 19 separate groups of polar bears are recognized. They are not genetically distinct enough to be considered separate populations, but are different enough in range and home turf to be sub-divided. And several of the subpopulations have dual citizenship, drifting during migration between countries.
In 2009, the PBSG came up with what at the time was a comprehensive status assessment of the bears based on available science. Eight of the subpopulations were categorized as in decline, two were listed as stable, and only one was considered to be increasing. Of the 19 groups of bears, seven lacked data with which scientists could make a determination.
The data, which in some cases is more than a decade old, is scheduled to be updated by the PBSG in 2013.
In Canada, Inuit hunter Gabriel Nirlungayuk thinks the science and the doomsday interpretations environmentalists have derived from it don’t accurately portray reality. He works as director of wildlife and environment for Nunavut Tunngavik Inc., an Inuit organization that evolved after a land claims settlement and advocates for the rights of hunters to harvest bears and other animals for survival.
Nirlungayuk points to changes at Western Hudson Bay as evidence that polar bears can adapt. In 2004, the Western Hudson Bay population of polar bear was thought to stand at about 935 animals. If predictions of risk due to warming and lack of sea ice were correct, the population of bears in this part of Canada could have dropped to around 600. The predictions hit home for the Inuit, who experienced reduced hunting opportunities as a result of management decisions aimed at conservation. Harvest limits once as high as 48 bears in prior years were slashed to eight.
According to 2009 data from the PBSG, more than 800 polar bears were allowed for harvest across the various regions. Since then, as managers have tweaked numbers in response to current population trends, numbers have shifted.
Traditional hunters in Nunavut had said they were seeing more bears in recent years than the scientific models predicted. Then, in 2011, the government of Nunavut conducted its own survey, discovering more than 1,000 bears present along the areas shores of the full Western Hudson Bay boundary.
“It wasn’t a surprise to Nunavut,” Nirlungayuk said. “Inuit are quite clear that this population is not in decline. It is not in dire straits as the scientific community is suggesting.”
So who’s right?
Different ways of knowing
The science community has tended to rely on aerial surveys, radio collars and a method called capture-recapture. Native communities have relied on first-hand observations and generations of accumulated knowledge.
“Those things tell us different things, and we should pay attention to both of them,” said Terry DeBruyn, a polar bear researcher with the U.S. Fish and Wildlife Service and Regehr’s colleague.
In capture-recapture studies, researchers concentrate on getting good genetic and health information from a fraction of the overall population. As these studies are done year after year, the continuum of data allows scientists to gauge the overall population’s size and health based on things like how fat or thin the bears are, how many young they produce, and whether the young survive.
But the study areas don’t get an overall bird’s-eye view of an entire region at a particular point in time, as can occur with an aerial survey — information Nirlungayuk believes is also instructive, in addition to what hunters are seeing in their daily lives.
“Inuit are out there 365 days a year. Helicopters have limitations and cannot go out to the open sea. Inuit travel out to the sea ice, to the floe’s edge. What we are seeing has to be accounted for,” Nirlunguyak said.
Yet, aerial surveys have their own drawbacks: They can’t assess the health of the individual bears observed, nor do they reflect trends in whether more or fewer bears are being seen, and if so, why. Taken alone, aerial surveys are merely a snapshot it time.
Coordinating surveys across five nations in vast and often harsh terrain can be both difficult and expensive. The more consistent the research method over time, the more reliable the conclusions that can be drawn from it. More information is better than less, even if it’s the combination of an aerial survey and a capture-recapture survey. But using the data together to draw meaningful conclusions is tricky.
Stable or in peril?
“There is currently a lot of variability in how the subpopulations (of polar bear) are doing,” Regehr said. “The media perception that they are all doing terrible is not accurate.”
In Alaska the southern Beaufort Sea population, which shares its range with Canada, was thought in 2006 to total about 1,526 animals, but still in decline and at moderate risk of future declines due to loss of sea ice. This is the same group of polar bear that showed up in force this fall in the village of Kaktovik, with at least 80 animals coming to shore to feast on whale carcasses from that community’s seasonal whale hunt.
More bears on land during a low-ice summer reinforces the assessment. Yet west of the Beaufort Sea region, the assessment numbers may be about to shift and may be better than initially thought.
In 2009, when the PBSG issued its population status reports, it listed the Chukchi Sea population, which Alaska shares with Russia, as being of unknown size, but one thought to be in decline because of anecdotal reports about possible over-harvesting in Russia. But now, newer research yet to be published has scientists reconsidering the status designations of the Chukchi population, Regehr said. It appears the bears in this area are reproducing well and maintaining good body condition.
If polar bear populations are stable, or only modestly declining, have fears over their long-term fate been overblown?
The science community, including Regehr, Dubruyn, and George Durner of the U.S. Geologic Survey, says no.
Polar bears are ice-dependent animals. Although they are flexible, adaptable, smart and survivors, Regehr doesn’t believe the long-term outlook in the face of sea ice loss bodes well for the bears.
In the short term, say the next 5-10 years, bears may continue to do very well. But in the long term, amid severe sea ice retreat, small groups of bears may adapt to life on land or longer stays on land, but likely won’t thrive. There is no replacing the nutritional value of fat ice seals, the bears’ favorite meal. Life on land would mean they would have to adapt to eating berries, plants or ground squirrels, and maybe salmon from streams. And they would be competing with brown bears for access to food and territory. Even if polar bears win the fight, chances are land-based meals alone won’t provide enough nutrients to support their massive size, Regehr said.
“There are limits to adaption,” Durner said, echoing Regehr’s comments. “Polar bears couldn’t be polar bears living on land.”
For example, he pointed out, the Gulf of Alaska — hundreds of miles south of the Arctic Ocean — has plenty of seals, yet no polar bears have ventured there. Polar bears have always made their living on the ice — it’s where they hunt, rest, travel and sometimes den.
“If sea ice is substantially reduced from their environment, they won’t survive,” he said.
Contact Jill Burke at jill(at)alaskadispatch.com
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