Less Polar Bear Cubs Surviving in Alaska
Pastor Dale Morgan
Nov 16, 7:31 PM EST
*Less Polar Bear Cubs Surviving in Alaska*
By DAN JOLING
Associated Press Writer
ANCHORAGE, Alaska (AP) -- Far fewer polar bears cubs are surviving off
Alaska's northern coast, a federal government report released Wednesday
has concluded.
The study of polar bears in the south Beaufort Sea, which spans the
northern coasts of Alaska and western Canada, also found that adult
males weigh less and have smaller skulls than those captured and
measured two decades ago.
The study does not directly blame the changes on a decline in sea ice.
However, fewer cubs and smaller males are consistent with other
observations that suggest changes in sea ice may be adversely affecting
polar bears, the study said.
The study warns that the decline in cub survival and the smaller adult
males are the same conditions that preceded a decline in the polar bears
of western Hudson Bay, Canada, where the population dropped 22 percent
in 17 years.
Advocates seeking protections for U.S. polar bears say the report proves
their point.
"It's just another example of seeing all of the impacts that scientists
have previously predicted coming to pass," said Kassie Siegel of the
Center for Biological Diversity in Joshua Tree, Calif. Siegal is the
lead author of the petition seeking to list polar bears as threatened
under the Endangered Species Act.
"The Grim Reaper of global warming is now clearly killing polar bear
cubs," said Deborah Williams, president of Alaska Conservation
Solutions, an Anchorage-based group aimed at halting climate change.
"This study should be interpreted as a cry from the North to reduce
greenhouse gases."
The report stopped short of saying the Beaufort Sea polar bear
population, one of two in Alaska, had declined.
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However, "Significant changes in cub survival and physical stature must
ultimately have population level effects," the report concluded.
The report estimates the Beaufort Sea polar bear population at 1,526,
down from a previous estimate of 1,800 bears. That would be a 15 percent
decline, but researchers said the current study used different methods
of counting.
The Beaufort Sea bears is one of two Alaska stocks. The other is the
Bering-Chukchi stock off Alaska's northwest coast, a population shared
with Russia.
Polar bears are classified as marine mammals because they spend much of
their lives on sea ice. The listing petition claims that polar bears are
threatened because of drastic declines in ocean ice due to global
warming. A decision by the U.S. Fish and Wildlife Service on listing
America's polar bears as threatened is due next month.
Polar bears depend entirely on sea ice for survival, according to the
USGS report. Warming has caused major changes and scientists foresee
more melting.
"Because more profound declines in sea ice area and extent are predicted
for these northern regions, continued monitoring and conservative
management of the SBS (Southern Beaufort Sea) polar bear population is
warranted," the report concluded.
Siegel said the effects of shrinking sea ice are occurring exactly as
summarized by the scientists quoted in her group's listing petition.
"Only it's happening sooner than they thought," she said.
The USGS report compared data on cubs collected from 1990 through last
spring to studies from 1967-89.
Females give birth in January and emerge from dens with new cubs in
March or early April. Cubs typically accompany their mother for 2.3 years.
For polar bears measured during autumn months, the number of surviving
cubs born that spring declined from a mean of .61 cubs per female to a
mean of .25 cubs per female.
"This decline can only be explained by lower survival of cubs after den
emergence," the report said.
Changes in the physical stature of polar bears, both body weight and
skull size, appeared to parallel the decline in cub survival, the study
said. The decline occurred even though bears measured in the latter
study were older. The study called the decline significant.
"Such changes in physical stature may suggest different impacts of
reduced summer sea ice on adult male and female polar bears," the study
said.
In spring, adult males often forgo foraging opportunities and focus on
finding females for mating, the study said. Entering the summer in
relatively poorer nutritional shape, they may be more vulnerable to
summer sea ice retreat, which can separate polar bears from the most
productive foraging habit, the study said.
Reduced foraging opportunity for adult females usually is first
reflected in poorer survival of their young, the study said.
Several recent observed deaths were directly related to sea ice retreat
or changes in food availability associated with sea ice retreat.
In autumn 2004, four polar bears drowned trying to swim from short and
distant pack ice. During winter and spring 2004, researchers recorded
evidence of three polar bears hunting, killing and eating other polar bears.
Last spring, three adult females and one yearling were found dead. Three
of the bears had depleted their lipid stores, an indication they had
starved. The fourth, one of the adult females, was largely scavenged,
and cause of death could not be determined. However, her death was
unusual, the study said, because prime-age females in the past have had
high survival rates.
"These anecdotal observations, in combination with both the changes in
survival of young and in physical stature reported here, suggest
mechanisms by which a changing sea ice environment can affect polar bear
demographics and the status of populations," the report said.
The authors of the report are Eric V. Regehr and Steven C. Amstrup of
the U.S. Geological Survey and Ian Stirling of the Canadian Wildlife
Service.
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On the Net:
USGS report, Polar Bear Population Status in the Southern Beaufort Sea:
http://pubs.water.usgs.gov/ofr20061337
Center for Biological Diversity:
http://www.biologicaldiversity.org/swcbd/species/polarbear/index.html