The Polar Bears in ANWR
- Arctic Refuge's coastal tundra provides America’s only land denning habitat for polar bears, serving primarily the Beaufort Sea population. (2)
Dangers
- hunted throughout most of their range.
- polar bears of the Beaufort Sea region are exposed to mineral and petroleum
extraction and related human activities such as shipping, road-building, and
seismic testing (Stirling 1990).
Movement
-Polar bears were observed to move more than 4 km/hr for extended periods, but
mean hourly rates of movement varied from 0.30-0.96 km/hr.
-Movement rates varied significantly among months: they generally were lowest
in spring and late summer and highest in early winter (Amstrup 1995, Amstrup
et al. 2000). Geographic displacements from the beginning to the end of each
month were smaller for females with cubs of the year than for single females,
and larger in November than in April.
-Total annual movements ranged from 1,454-6,203 km. Bears that spent part of
the year in dens moved less than others, but non-denning classes of bears did
not differ in total annual movement (Amstrup 1995, Amstrup et al. 2000).
-Beaufort Sea polar bears kept their movements within boundaries outside of
which they seldom ventured. Annual activity areas ranged from 12,730 km2 to
596,800 km2. Monthly activity areas ranged from a mean of 344 km2 for females
with cubs in April to 11,926 km2 for females with yearlings in December
(Amstrup 1995, Amstrup et al. 2000).
Breeding
-Amstrup et al. (2001) and McDonald and Amstrup (2001) suggested that the
number of polar bears in the Southern Beaufort Sea population grew at more
than 3% per year between 1967 and 1998, reaching an estimated population that
could be as high as 2,500 animals.
-Survival of adults, as calculated from life tables, was higher and survival
of young lower when the population was large. Survival rates of adult Beaufort
Sea polar bears, however, were as high or higher than those measured anywhere
else.
-Although numbers of young produced per female when the population was small
(<0.40) and when it was large (<0.38) were similar, litters of more than one
yearling were more frequent when the population was small.
Death
-In this study hunting explained 85% of the documented deaths of adult female
polar bears (Amstrup and Durner 1995). Natural mortalities were not commonly
observed among prime age animals (Amstrup and Nielsen 1989), and we still know
little about the proximate causes of natural deaths among polar bears.
Effects of Petroleum on Polar Bears
-Although contact with hydrocarbons can have serious ramifications for polar
bears (Amstrup et al. 1989), the polar bearÂ’s apparent rapid population growth
has spanned the entire history of petroleum development in arctic Alaska
(Amstrup 2000, Amstrup et al. 2001, McDonald and Amstrup 2001). This suggests
that managed resource development can be compatible with healthy polar bear
populations. Also encouraging is the new ability to estimate potential impacts
that oil spills may have on polar bears. That ability has major ramifications
for assessing risks of a variety of potential developments (Durner et al.
2001b).
-Effects of the increasing human intrusions into the polar bear environment
have not been observed at a population level, suggesting that proactive
management can assure coexistence of polar bears and human developments.
Endangered?
-Estimated numbers of bears at the close of the study were relatively large.
Early estimates suggested the additional loss of as few as 30 bears each year
might push the total take from the population to the maximum sustained yield
(Amstrup et al 1986, Amstrup and DeMaster 1988). Excess take did precipitate a
decline in the 1960s and 1970s. Hence, although populations may now be near
historic highs, managers must be alert to possible changes in human
activities, including hunting and habitat alterations that could precipitate
future declines.
- because polar bears have a low rate of reproduction and a greater success of cubbing in land-based dens, onshore denning habitat is crucial to the survival of the species. (2)
Refrences
(1) http://www.absc.usgs.gov/1002/section8.htm
(2) http://www.savealaska.com/sa_anwr.html
costiner"at"mit.edu
Last updated: Nov. 12,
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