In 1981 the IUCN Polar Bear Specialist Group agreed that the world population was between 20,000 and 40,000. As of 1988 the most accepted estimate for the Alaska populations was 3,000-5,000. Wind, upwellings and currents along some shores or downwind from islands bring nutrients to the surface here, and keep the sea ice from coalescing. The coastal shear zone between shore- fast ice and the moving pack is also rich for similar reasons. These areas are vital to marine mammals and migrating birds, and to polar bears, which often hunt in such places.
Ringed seals are the bears' principal prey.
They also hunt bearded seals and occasionally the more dangerous walrus. Normally solitary hunters, they have an impressive range of strategies, learn quickly, and show immense patience, power and speed. It has been calculated that their caloric needs require one ringed seal every six and a half days. Arctic foxes live on the sea ice in winter by scavenging polar bear kills. Since their prey is available year-round, polar bears do not hibernate like brown bears, except pregnant females, who spend about five months in dens to give birth to their cubs.