Polar Bears In Depth
Movements
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Whereas movements of polar bears in the Beaufort Sea are impressive in their magnitude, movements of bears in areas of more dynamic ice may be even greater. The mean activity area size for six bears followed by satellite telemetry in the Chukchi Sea was 244,463 km2 (Garner et al. 1990). The mean annual distance moved by those bears was 5542 km. The potential mobility of polar bears in regions of volatile ice was illustrated by a mean rate of northerly spring movement of 14.1 km/day at a time when ice was moving as much as 15.5 km/day in the opposite direction (Garner et al. 1990).
In contrast, Schweinsburg and Lee (1982) reported maximum activity areas of <23,000 km2 in the Canadian Arctic Archipelago. Ferguson et al. (1999) also reported very large-scale movements for polar bears in the volatile sea-ice conditions of Davis Strait and Baffin Bay, and much smaller movements for bears in the interior of the Canadian Arctic Archipelago. The sea-ice of the Chukchi and Beaufort Seas and Baffin Bay is more dynamic and unpredictable than the ice in much of the Canadian Arctic Archipelago. The mobility of polar bears appears to be directly related to that variability (Garner et al. 1990, 1994; Gloersen et al. 1992; Messier et al. 1992; Ferguson et al. 2001).
Seasonal movement patterns of polar bears serve to emphasize the role of sea-ice in their life cycle. In the Beaufort Sea, the largest monthly activity areas were in JuneJuly and NovemberDecember. These also were the months of highest movement rate. This matches the patterns of ice ablation and formation observed in the area (Gloersen et al. 1992). Polar bears catch seals mainly by still-hunting (Stirling and LaTour 1978). The volatile summer and autumn ice must minimize predictability of seal hunting opportunity. That unpredictability could require longer movements and larger activity areas during seasons of freeze-up and break-up. From May through August, measured net monthly movements of polar bears in the Beaufort Sea were significantly to the north for all bears. In October bears moved back to the south (Stirling 1990; Amstrup et al. 2000). Those movements appeared to be correlated with general patterns of ice formation and ablation. Between May and August, the ice of the southern Beaufort Sea is degrading (Gloersen et al. 1992). October is usually the month of freeze-up in the southern Beaufort Sea and may be the first time in months when ice is available over the shallow water near-shore. Polar bears summering on the persistent pack ice quickly move into shallow-water areas as soon as new annual ice forms in autumn, and they disperse easterly and westerly as ice solidifies through winter.
In contrast, Schweinsburg and Lee (1982) reported maximum activity areas of <23,000 km2 in the Canadian Arctic Archipelago. Ferguson et al. (1999) also reported very large-scale movements for polar bears in the volatile sea-ice conditions of Davis Strait and Baffin Bay, and much smaller movements for bears in the interior of the Canadian Arctic Archipelago. The sea-ice of the Chukchi and Beaufort Seas and Baffin Bay is more dynamic and unpredictable than the ice in much of the Canadian Arctic Archipelago. The mobility of polar bears appears to be directly related to that variability (Garner et al. 1990, 1994; Gloersen et al. 1992; Messier et al. 1992; Ferguson et al. 2001).
Seasonal movement patterns of polar bears serve to emphasize the role of sea-ice in their life cycle. In the Beaufort Sea, the largest monthly activity areas were in JuneJuly and NovemberDecember. These also were the months of highest movement rate. This matches the patterns of ice ablation and formation observed in the area (Gloersen et al. 1992). Polar bears catch seals mainly by still-hunting (Stirling and LaTour 1978). The volatile summer and autumn ice must minimize predictability of seal hunting opportunity. That unpredictability could require longer movements and larger activity areas during seasons of freeze-up and break-up. From May through August, measured net monthly movements of polar bears in the Beaufort Sea were significantly to the north for all bears. In October bears moved back to the south (Stirling 1990; Amstrup et al. 2000). Those movements appeared to be correlated with general patterns of ice formation and ablation. Between May and August, the ice of the southern Beaufort Sea is degrading (Gloersen et al. 1992). October is usually the month of freeze-up in the southern Beaufort Sea and may be the first time in months when ice is available over the shallow water near-shore. Polar bears summering on the persistent pack ice quickly move into shallow-water areas as soon as new annual ice forms in autumn, and they disperse easterly and westerly as ice solidifies through winter.