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The Truth About

Polar Bear Numbers 

April 2012      


Nearing Bear

You may have seen recent headlines stating that the Western Hudson Bay polar bear population--widely considered the most endangered--is, in fact, "healthy and abundant."

 

Sadly, that's not the case. So what's going on?

 

The media flurry stems from a press release on a preliminary study of the Western Hudson Bay population that relied on a different methodology (aerial vs. capture-recapture) and larger geographic survey area than previous studies.

 

Dr. Steven C. Amstrup, PBI's chief scientist, says that media reports have made the serious mistake of comparing the aerial survey--with a point estimate of 1,013 polar bears--to a capture-recapture study from 2004 showing 934 bears.

 

"It's not a meaningful comparison," he says. "It's reasonable to expect there would be more polar bears in a larger geographic area than a smaller one. But even if the new aerial survey focused on exactly the same geographic area, it wouldn't be surprising to derive a slightly different population estimate when using a different survey method."

 

He adds that from the standpoint of population welfare, it's the trend in numbers that is critical, not a single survey from one point in time--so the aerial count will

Survey

become meaningful only after several years of data are available.

 

"A single point estimate of population size says nothing about whether the trend is up, down, or stable. Trend can only be addressed by multiple point estimates collected over time."

 

Dr. Amstrup says the new aerial survey does, however, include a piece of information relevant to trend: Of the 701 polar bears actually counted during the survey, only 22 (or about 3%) were yearlings--a very low percentage. By comparison, in Alaska during the good ice years of the 1980s, about 15% of the animals observed were yearlings.

 

"If that 3% figure is even close to the number of surviving yearlings out there now, it's not at all clear to me how the Hudson Bay population could be sustaining itself," he says. "This observation is very much in line with the previously

Mom and cub on back published indications that survival--especially of young--is declining."

 

The release in question was issued by a Nunavut group interested in increasing polar bear hunting quotas.

 

Scientists who study polar bears emphasize that their concern about polar bears is focused on the future. Because polar bears rely on the sea ice to reach their prey, sea ice losses from a warming Arctic threaten their survival.

 

"The available data from Hudson Bay indicate declining condition and survival," says Amstrup. "But in the bigger picture, whether any one population is currently declining, stable, or increasing is beside the point. Ultimately, all polar bears will disappear from their current ranges if we do not mitigate the rise in greenhouse gases."

 

 

Find out how you can play a role in ensuring a brighter future for polar bears by visiting the Take Action! page of our website.

Photo Credits:

Bear Photos by Daniel J. Cox/NaturalExposures.com;

Survey Photo by BJ Kirschhoffer

 

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