Polar bears; on their way to extinction
By: Ragnhild Hårvik, Vet. Med. 1st. year
The Polar
bear, Ursus maritimus, is the largest bear and predator in the world. It
is a part of the very vulnerable ecosystem of the arctic drift-ice. Because of
the changing habitat, the polar bear annually migrates for long distances to
find its primary food resource, the Ring seals, Phoca hispida, and the Bearded
seals, Erignathus barbatus. And is highly dependent of
the drift-ice for its living.
In a study
done by the Norwegian polar institute, a group of scientists monitored the
movements of 74
female Polar bears in a period of 13 years.
The migration of the bears tells how
much space one bear needs for its survival, and therefore also how much space
the whole population needs.
They found that the movements of the Polar bears differs according to
month, and is primarily done by the polar bear it self (active displacement).
The individual movements of the bears, indicated that migration often is due to search of
better food resources.
The
seasonally changing habitat is also an important process underlying the annual
migrations.
The sea ice differ in extent during the season. It has its maximum
in April, where it extends 800km south of what it is in September, at its minimum.
According to this, the Polar bear migrates northwards during summer ice
decrease, and wanders southwards as the winter ice enlarges the territory.
Following
the drift-ice of the
250 000km2.
Due to its
annual migration, the Polar bears of the
They are
therefore depending on access to large amount of prey. They therefore navigate
through the moving sea ice to find territories of preferred habitat.
The Polar
bears tend to prefer closed annual ice in early summer, due to the Ring seals
pupping season. The pups have large amount of fat, which the polar bear needs.
The rest of
the season, they stay close to the open areas near the ice edge, where the
ecosystem is more productive and therefore attracts the seals.
The female
Polar bear often chose terrestrial ice when building her den, where she will
stay for months during her pregnancy. When she retreats with her cubs, she has
not eaten for up to 7 months and depend on good spring
ice conditions to get to a habitat with large amount of seals.
As the
Norwegian research team has shown, the Polar bears are highly adapted to the
harsh environment of the drift-ice, of which it also is highly dependent on.
With the
knowledge of the polar bears dependency of its environment; how does the
melting of the arctic drift ice affect the Polar bears?
Since the
1960’s the thickness of the drift-ice has been reduced by over 40%. This is due
to longer and warmer summers. The prospects for the future is
even more disturbing, as analyses show reduction of the summer ice for up to
50%. And some analyses even prospect that there will be no summer ice.
A Shorter
summer-hunting season will affect the Polar bears capability of surviving the
harsh winter, Because the summer season is when the
bear eat the most.
The melting
ice is probably most critical for the female bears, which emerge from
the dens with cubs and are in desperate need for good spring- and summer-ice
conditions in order to find enough food to survive. Longer summers,
means longer periods of fasting, and the mother will not be able to
give her cubs the proper nutrition they need.
A warmer
climate can also separate the dens from the summer-ice feeding spots, which
forces the female and cubs to swim for longer distances, something the cubs are
not likely to survive.
Another problem
with the loss of its habitat, is that the Polar
bear eventually will be isolated into smaller groups. This will give
less genetic variation, and therefore weaker individuals with less chance
of surviving.
What will
happen with the Polar bear population in the future is highly uncertain, but
the environmental changes has already started to show
its fatal consequences.
Dead Polar
bears, stranded on drifting ice flakes has become a common sight for fishers
living in the
- only time will show if the Polar bear is capable of
surviving the environmental changes.
Sources:
Mette Mauritzen, Andrew E.
Derocher, Olga Pavlova, Øystein Wiig.(2002) . Female polar bears, Ursus
maritimus, on the
http://www.forskning.no/Artikler/2003/oktober/1067514315.64
http://acia.cicero.uio.no/factsheets/2_polar_bears_on_ice.pdf
http://www.int.iol.co.za/index.php?set_id=1&click_id=143&art_id=vn20051009102733324C727118
http://icb.oxfordjournals.org/cgi/content/abstract/44/2/163
http://news.bbc.co.uk/1/hi/sci/tech/1894740.stm