Plants and Animals

Polar bears (Ursus maritimus) have become a symbol of global warming, and their predicted decline a sign of worst to come, but until very recently population estimates were really just educated guesses. Current polar bear numbers are estimated to total between 20,000 and 25,000.

On May 14 2008, when announcing the decision to list polar bears as threatened under the U.S. Endangered Species Act, Secretary for the U.S. Department of Interior, Dirk Kempthorne stated,

“Although the population of bears has grown from a low of about 12,000 in the late 1960’s to approximately 25,000 today, our scientists advise me that computer modeling projects a significant population decline by the year 2050.”

But there are no published papers or reports to support the claim that there were about 12,000 polar bears forty years ago.

At the 1968 meeting of International Union for the Conservation of Nature (IUCN) Polar Bear Specialist Group in Alaska, the Canadian Wildlife Service representatives suggested that numbers were as low as 5,000 in the 1950s and 1960s.

Current Chairman of the IUCN Polar Bear Specialist Group, Andrew Derocher, has stressed,

“The early estimates of polar bear abundance are a guess. There is no data at all for the 1950-60s. Nothing but guesses. We are sure the populations were being negatively affected by excess harvest (e.g., aircraft hunting, ship hunting, self-killing guns, traps, and no harvest limits). The harvest levels were huge and growing. The resulting low numbers of bears were due only to excess harvest but, again, it was simply a guess as to the number of bears.”

But how can Dr Derocher be sure that polar bear populations were being negatively affected by harvesting if there is no hard data on population numbers for the same period?

In 1972, at the 3rd Working Meeting of the IUCN Polar Bear Specialist group the Norwegian representative, Thor Larson, suggested there were as many as 20,000 in the late 1960s. Larson said,

“Merely by summarising the various national counts, which still must be considered inaccurate, one reaches the conclusion that the worlds total polar bear population is probably closer to 20,000 animals, than to the lower figures often suggested.”

Just maybe there have always been about 20,000 polar bears in the Arctic?

Nichole Hoskin is a research assistant at the Institute of Public Affairs and is adding to the Environmental Wiki associated with this blog.

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Other blog posts by Nichole Hoskin on polar bears include:
Polar Bears Can Survive where there is no Summer Sea Ice: A Note from Nichole Hoskin, August 20, 2008. https://jennifermarohasy.com.dev.internet-thinking.com.au/blog/archives/003342.html

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There has been a dramatic reduction in the extent of summer sea ice in the Arctic since 1870, Chart 1.

Drawn by Nichole Hoskin using data from Arctic Climate Research at the University of Illinois

Australian television’s Four Corners showed a program on August 4, 2008, entitled ‘Tipping Point’ claiming that the disappearance of summer sea ice in the Arctic could have drastic consequence for polar bears.

Interestingly there is no summer sea ice in western Hudson Bay in the Canadian Arctic and there are polar bears.

According to polar bear experts, Douglas Clark and Ian Stirling (1998), “The polar bear population that inhabits western Hudson Bay spends the period from late July through early November on shore because the annual ice melts completely.”

Scientists previously thought that these polar bears sustained themselves on stored fat during this ice-free period, however, Derocher et al (1993), found that juvenile males and female polar bears would eat vegetation, such as alpine blueberries, crowberries, grasses and sedge, when marine mammals were unavailable because of the absence of summer sea-ice. This conclusion was based on examination of droppings and observations of signs of feeding on berries, such as berry stained teeth and fur, on polar bears captured in inland areas of western Hudson Bay between 1986 and 1992.

While there is evidence that females and offspring eat berries during the ice-free period, it is unclear whether eating berries significantly contributes to the total energy budget of polar bears. However, Derocher et al argue that eating vegetation “could significantly influence the condition of bears and in turn influence survival, particularly of cubs” and that “the patterns found in western Hudson Bay illustrate the physiological and behavioural plasticity of polar bears.”

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Douglas C. Clark and Ian Stirling, ‘Habitat Preferences of Polar Bears in the Hudson Bay Lowlands during Late Summer and Fall’, (1998) Ursus 10, pp 243-250 at 243 and 248.

Andrew E. Derocher, Dennis Andriashek and Ian Stirling, ‘Terrestrial Foraging by Polar Bears during the Ice-Free Period in Western Hudson Bay’, Arctic (1993) 46(3), pp 251-254 at 251 and 253.

ABC 4 Corner’s ‘The Tipping Point, broadcast August 4, 2008. Reporter: Marian Wilkinson
http://www.abc.net.au/4corners/content/2008/s2323805.htm