Wildlife: Polar Bears

Polar bear photos
Polar bears depend on sea ice as a hunting platform. —Credit: Daniel J. Cox / National Science Foundation

Polar bears are found only in the Arctic, where they are the largest land carnivores. Polar bears prefer multiyear ice for protective cover and for a platform to hunt their favorite food, ringed seals. During the summer, they eat very little while they wait for the ocean to freeze. In areas such as eastern Baffin Island and Hudson Bay, where most or all of the pack ice melts by mid- to late summer, the entire bear population must come ashore for two to four months in summer and early fall to wait for the ice to freeze again, the World Wildlife Federation reports.

Although polar bears are considered capable swimmers, they have not often been observed swimming far from land. A 2006 study in Polar Biology concluded that poor sea ice cover in the Arctic may contribute to increased polar bear mortality by forcing the animals to swim excessive distances between land and the pack ice edge.

Since the start of the continuous satellite record in 1979, Arctic sea ice has declined in all seasons, particularly in summer. However, sea ice hasn't declined the same way in all places, and polar bear populations have experienced different fates in different parts of the Arctic. The Arctic Report Card: Update for 2014 provided an overview of polar bear health, assessed by the International Union for Conservation of Nature/Species Survival Commission-Polar Bear Specialist Group (IUCN/SSC-PBSG). The study examined 19 polar bear sub-populations across the Arctic. Although the researchers couldn't determine population health everywhere, they found declines in four sub-populations, stability in five sub-populations, and an increase in one sub-population.

Polar-bear subpopulation map from ARC
Polar bear fortunes varied across the Arctic, according to a 2013 study by the IUCN/SSC-PBSG. The study found population growth in one sub-population (blue), stability in five sub-populations (yellow), and declines in four sub-populations (orange). Sub-populations with unknown trends appear white/transparent. —Credit: Arctic Report Card: Update for 2014 / NOAA Climate.gov

Although the study found a relationship between sea ice conditions and polar bear health, that relationship was not necessarily straightforward. In Hudson Bay, for example, female bear survival correlated strongly with sea ice conditions, but male survival correlated primarily with subsistence-hunting pressure from humans. Other factors could complicate the ice-bear relationship, such as the width of the continental shelf, preferred habitat of seals (polar bears' main food source). In places where the continental shelf is narrow, such as the Beaufort Sea, poor sea ice conditions could exacerbate polar bears' difficulties in catching prey. Still, the study found greater population declines in areas with a greater number of reduced-ice days, such as the Beaufort Sea.

Last updated: 3 April 2020