Modern methods of tracking polar bear populations have been implemented
only since the mid-1980s, and are expensive to perform consistently over a
large area.[26] The most accurate counts require flying a helicopter in the
Arctic climate to find polar bears, shooting a tranquilizer dart at the bear
to sedate it, and then tagging the bear.[26] In Nunavut, some Inuit have
reported increases in bear sightings around human settlements in recent
years, leading to a belief that populations are increasing. Scientists have
responded by noting that hungry bears may be congregating around human
settlements, leading to the illusion that populations are higher than they
actually are.[26] The Polar Bear Specialist Group of the IUCN takes the position
that "estimates of subpopulation size or sustainable harvest levels should
not be made solely on the basis of traditional ecological knowledge
without supporting scientific studies."[27]
Of the 19 recognized polar bear subpopulations, 8 are declining, 3 are
stable, 1 is increasing, and 7 have insufficient data.[6][23]
Global warming
The IUCN, Arctic Climate Impact Assessment, United States Geological
Survey and many leading polar bear biologists have expressed grave concerns
about the impact of global warming, including the belief that the current
warming trend imperils the survival of the species.[22][112][113][114][115][116]
The key danger posed by global warming is malnutrition or starvation due to
habitat loss. Polar bears hunt seals from a platform of sea ice. Rising
temperatures cause the sea ice to melt earlier in the year, driving the
bears to shore before they have built sufficient fat reserves to survive the
period of scarce food in the late summer and early fall.[76] Reduction in
sea-ice cover also forces bears to swim longer distances, which further
depletes their energy stores and occasionally leads to drowning.[117] Thinner sea
ice tends to deform more easily, which appears to make it more difficult
for polar bears to access seals.[51] Insufficient nourishment leads to lower
reproductive rates in adult females and lower survival rates in cubs and
juvenile bears, in addition to poorer body condition in bears of all
ages.[22]
In addition to creating nutritional stress, a warming climate is expected
to affect various other aspects of polar bear life: Changes in sea ice
affect the ability of pregnant females to build suitable maternity dens. As the
distance increases between the pack ice and the coast, females must swim
longer distances to reach favored denning areas on land.[22] Thawing of
permafrost would affect the bears who traditionally den underground, and warm
winters could result in den roofs collapsing or having reduced insulative
value.[22] For the polar bears that currently den on multi-year ice,
increased ice mobility may result in longer distances for mothers and young cubs to
walk when they return to seal-hunting areas in the spring.[22]
Disease-causing bacteria and parasites would flourish more readily in a warmer
climate.[51]
Problematic interactions between polar bears and humans, such as foraging
by bears in garbage dumps, have historically been more prevalent in years
when ice-floe breakup occurred early and local polar bears were relatively
thin.[112] Increased human-bear interactions, including fatal attacks on
humans, are likely to increase as the sea ice shrinks and hungry bears try to
find food on land.[112][118]
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_http://en.wikipedia.org/wiki/Polar_bear_
(http://en.wikipedia.org/wiki/Polar_bear)