Nature
21 May 2008
453, – (2008) | doi:10.1038/453432a
News
Polar bear numbers set to fall
Climate-change icon gains ‘threatened’ status from United States.
Rachel Courtland
In a long-anticipated decision hailed as a
victory by environmental groups, the United
States last week declared the polar bear (Ursus
maritimus) a ‘threatened’ species. But this
heightened protection status may have little
bearing on the animals’ ultimate fate.
The listing, announced by secretary of the
interior Dirk Kempthorne on 14 May, connects the
continuing retreat in Artic sea ice due to global
warming with large potential reductions in the
polar-bear population. Last autumn, the US
Geological Survey concluded that the animals are
likely to lose 42% of their summer sea ice
habitat by mid-century, cutting the world’s
polar-bear population – estimated at 25,000 – by
two-thirds.
Despite this dramatic projection, researchers
note that polar bears range across a variety of
nations, each with its own conservation
approaches, and a variety of habitats, each of
which will be affected differently by climate
change. Their fates may vary from place to place,
too.”I don’t believe the polar bear will go
extinct, but in some areas they will be heavily
reduced and may disappear,” says veterinary
biologist Christian Sonne of the National
Environmental Research Institute in Roskilde,
Denmark. Factors other than global warming
compound stress on the bears, including the
accumulation in fat of polychlorinated biphenyls
and other pollutants that lower reproductive
capacity and weaken the immune system.
Projecting the fate of a creature that ranges
over more than 25° of latitude is difficult. The
polar-bear specialist group of the International
Union for Conservation of Nature (IUCN) has
identified 19 distinct populations that live in
markedly different habitats (see map). “Some
populations are clearly in far more trouble than
others,” says biologist Ian Stirling of the
Canadian Wildlife Service in Edmonton, Alberta.
For instance, bears that spend the majority of
their time on ice may have to migrate long
distances to maintain their lifestyle, an
additional stress if food is scarce. But polar
bear populations in the Canadian archipelago may
be fairly stable in the next few decades, as
projections suggest that summer sea ice there
will be more persistent.
Still others, such as the southernmost
populations around Canada’s Hudson Bay, may
already be experiencing the effects of climate
change. Recent studies have shown that such bears
are losing valuable hunting time in the spring,
when the animals take in most of the year’s
energy by fattening up on nesting ringed seals.
West of Hudson Bay, young bears are less likely
to survive after earlier sea-ice break-ups, a
process which now occurs roughly three weeks
earlier than it did 30 years ago1. South of the
bay, the mass-to-body-length ratio of bears in
Ontario has more than halved2 since the early
1980s.
Need to adapt
Some bear populations may be able to adapt by
spending more time on land, but much depends on
how quickly the Arctic ice changes. “I think it
depends on how fast this happens,” says biologist
Erik Born of the Greenland Institute of Natural
Resources in Nuuk. “Polar bears in some sense are
behaviourally flexible, but they are also really
specialized to hunt on sea ice.”
In the face of sea-ice declines, the best way to
manage the bear may be to minimize other threats,
Stirling says – to protect denning areas,
minimize offshore activities and human traffic,
reduce hunting or ensure hunts “move over to
bears that are going to die anyway”.
That may depend heavily on what circumpolar
states do next. The US listing, which was forced
by an environmental lawsuit in 2005, places polar
bears under the auspices of the powerful
Endangered Species Act. But officials wrote the
rule in such a way that the 1972 Marine Mammal
Protection Act can take precedence. This means
that the listing may add no additional
limitations to offshore oil and gas drilling.
Kempthorne also argued that the new listing could
not be used to regulate greenhouse-gas emissions.
No circumpolar state regulates greenhouse-gas
emissions specifically to protect the polar bear.
Norway, which has had the strongest protections,
upgraded the bear’s status to ‘vulnerable’ on its
Red List of imperilled species after the IUCN did
the same in 2006. But “that doesn’t change
anything,” says Dag Vongraven of the Norwegian
Polar Institute in Tromsø. Norway’s outright ban
on hunting is the only regulatory structure to
protect polar bears in that country, he says.
The United States, Greenland (under home rule
from Denmark) and Canada permit limited hunting.
Russia has outlawed polar bear hunts, but illegal
kills are thought to be common, says Vongraven.
Canada is also considering whether to upgrade the
polar bear’s status. Last month, a government
advisory committee announced that it would not
recommend raising the bear’s status to
‘threatened’ from ‘species of concern’, a move
that could impact hunting activities. A decision
will be made after August, when the group’s final
recommendations are sent to environment minister
John Baird.
Legal battles
In the United States, the new listing is likely
to be challenged. “There will clearly be a series
of lawsuits over this that will take a long time
to resolve,” says Holly Doremus, an environmental
lawyer at the University of California, Davis. In
particular, she says, exempting federal agencies
from consulting with the Fish and Wildlife
Service on projects involving greenhouse-gas
emissions is unlikely to withstand judicial
review. “I think the Bush administration is just
trying to kick this to the next administration
because they don’t know how to deal with it,” she
says.
In the meantime, prompted by other environmental
lawsuits, the Fish and Wildlife Service is
considering adding other species – including the
emperor penguin – to the endangered or threatened
species lists, partly because of threats from
climate change.
And polar bears are likely to remain at the top
of the international agenda for the foreseeable
future. “Certainly the polar bear has become that
iconic figure that will hopefully become the
rallying point for that kind of discussion to
take place,” says Lyle Laverty, assistant
secretary for Fish, Wildlife and Parks.
Next year, officials in the bear’s range states
plan to meet in Tromsø, Norway, to discuss
management options. It will be the first such
meeting in 28 years.
References:
1. [author]Regehr, E. V.[/author],
[author]Lunn, N. J.[/author], [author]Amstrup, S.
C.[/author] & [author]Stirling, I.[/author]
[journal]J. Wildl. Mgmt[/journal]
[volume]71[/volume], [pages]2673-2683[/pages]
([copyright]2007[/copyright]).
2. [author]Obbard, M. E.[/author] _et
al_. Temporal Trends in the Body Condition of
Southern Hudson Bay Polar Bears Climate Change
Research Information Note Number 3, Ontario
Ministry of Natural Resources
([copyright]2006[/copyright]).
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