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From The Sunday Times UK
December 18, 2005
Polar bears drown as ice shelf melts
Will Iredale
SCIENTISTS have for the first time found evidence that polar bears
are drowning because climate change is melting the Arctic ice shelf.
The researchers were startled to find bears having to swim up to 60
miles across open sea to find food. They are being forced into the
long voyages because the ice floes from which they feed are melting,
becoming smaller and drifting farther apart.
Although polar bears are strong swimmers, they are adapted for
swimming close to the shore. Their sea journeys leave them them
vulnerable to exhaustion, hypothermia or being swamped by waves.
According to the new research, four bear carcases were found floating
in one month in a single patch of sea off the north coast of Alaska,
where average summer temperatures have increased by 2-3C degrees
since 1950s. The scientists believe such drownings are becoming
widespread across the Arctic, an inevitable consequence of the
doubling in the past 20 years of the proportion of polar bears having
to swim in open seas.
"Mortalities due to offshore swimming may be a relatively
important and unaccounted source of natural mortality given the
energetic demands placed on individual bears engaged in long-distance
swimming," says the research led by Dr Charles Monnett, marine
ecologist at the American government's Minerals Management Service.
"Drowning-related deaths of polar bears may increase in the
future if the observed trend of regression of pack ice
continues." The research, presented to a conference on marine
mammals in San Diego, California, last week, comes amid evidence of a
decline in numbers of the 22,000 polar bears that live in about 20
sites across the Arctic circle.
In Hudson Bay, Canada, the site of the most southerly polar bears, a
study by the US Geological Survey (USGS) and the Canadian Wildlife
Service to be published next year will show the population fell 22%
from 1,194 in 1987 to 935 last year. New evidence from field
researchers working for the World Wildlife Fund in Yakutia, on the
northeast coast of Russia, has also shown the region's first evidence
of cannibalism among bears competing for food supplies. Polar bears
live on ice all year round and use it as a platform from which to
hunt food and rear their young. They hunt near the edge, where the
ice is thinnest, catching seals when they make holes in the ice to
breath. They typically eat one seal every four or five days and a
single bear can consume 100lb of blubber at one sitting.
As the ice pack retreats north in the summer between June and
October, the bears must travel between ice floes to continue hunting
in areas such as the shallow water of the continental shelf off the
Alaskan coast - one of the most food-rich areas in the Arctic.
However, last summer the ice cap receded about 200 miles further
north than the average of two decades ago, forcing the bears to
undertake far longer voyages between floes. "We know short swims
up to 15 miles are no problem, and we know that one or two may have
swum up to 100 miles. But that is the extent of their ability, and if
they are trying to make such a long swim and they encounter rough
seas they could get into trouble," said Steven Amstrup, a
research wildlife biologist with the USGS.
The new study, carried out in part of the Beaufort Sea, shows that
between 1986 and 2005 just 4% of the bears spotted off the north
coast of Alaska were swimming in open waters. Not a single drowning
had been documented in the area. However, last September, when the
ice cap had retreated a record 160 miles north of Alaska, 51 bears
were spotted, of which 20% were seen in the open sea, swimming as far
as 60 miles off shore. The researchers returned to the vicinity a few
days later after a fierce storm and found four dead bears floating in
the water. "We estimate that of the order of 40 bears may have
been swimming and that many of those probably drowned as a result of
rough seas caused by high winds," said the report. In their
search for food, polar bears are also having to roam further south,
rummaging in the dustbins of Canadian homes. Sir Ranulph Fiennes, the
explorer who has been to the North Pole seven times, said he had
noticed a deterioration in the bears' ice habitat since his first
expedition in 1975.
"Each year there was more water than the time before," he
said. "We used amphibious sledges for the first time in
1986." His last expedition was in 2002, when he fell through the
ice and lost some of his fingers to frostbite.
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