Polar Bears In Depth
Distribution
FIGURE 27.1. Approximate worldwide winter distribution of polar bears (light gray). Polar bears are distributed throughout most ice-covered seas of the Northern Hemisphere. Hatched areas indicate known coastal regions preferred for maternal denning. Only in the Beaufort Sea adjacent to Alaska is denning in the pack-ice thought to be common. Click image to enlarge.
Polar bears occur only in the Northern Hemisphere. Their range is limited to areas in which the sea is ice covered for much of the year. Over most of their range, polar bears remain on the sea-ice year-round or visit land only for short periods. Polar bears are common in the Chukchi and Beaufort Seas north of Alaska. They occur throughout the East Siberian, Laptev, and Kara Seas of Russia and the Barent's Sea of northern Europe. They are found in the northern part of the Greenland Sea, and are common in Baffin Bay, which separates Canada and Greenland, as well as through most of the Canadian Arctic Archipelago (Fig. 27.1). Because their principal habitat is the sea-ice surface rather than adjacent land masses, they are classified as marine mammals. In most areas, pregnant females come ashore to create a den in which to give birth to young. Even then, however, they are quick to return to the sea ice as soon as cubs are able. In some areas, notably the Beaufort and Chukchi Seas of the polar basin, many females den and give birth to their young on drifting pack ice (Amstrup and Gardner 1994).
Polar bears are most abundant in shallow-water areas near shore and in other areas where currents and upwellings increase productivity and keep the ice cover from becoming too solidified in winter (Stirling and Smith 1975; Stirling et al. 1981; Amstrup and DeMaster 1988; Stirling 1990; Stirling and Øritsland 1995; Stirling and Lunn 1997; Amstrup et al. 2000). Despite apparent preferences for the more productive waters near shorelines and polynyas (areas of persistent open water), polar bears occur throughout the polar basin including latitudes >88°N (Stefansson 1921; Papanin 1939; Durner and Amstrup 1995).
Because they derive their sustenance from the sea, the distribution of polar bears in most areas changes with the seasonal extent of sea-ice cover. In winter, for example, sea-ice extends as much as 400 km south of the Bering Strait, which separates Asia from North America, and polar bears extend their range to the southernmost extreme of the ice (Ray 1971). Sea-ice disappears from most of the Bering and Chukchi Seas in summer, and polar bears occupying these areas may migrate as much as 1000 km to stay with the southern edge of the pack ice (Garner et al. 1990, 1994). Throughout the polar basin, polar bears spend their summers concentrated along the edge of the persistent pack ice. Significant northerly and southerly movements appear to be dependent on seasonal melting and refreezing of ice near shore (Amstrup et al. 2000). In other areas, for example, Hudson Bay, James Bay, and portions of the Canadian High Arctic, when the sea-ice melts, polar bears are forced onto land for up to several months while they wait for winter and new ice (Jonkel et al. 1976; Schweinsburg 1979; Prevett and Kolenosky 1982; Schweinsburg and Lee 1982; Ferguson et al. 1997; Lunn et al. 1997).
Until the 1960s, the prevalent belief was that polar bears wandered throughout the Arctic. Some naturalists felt that individual polar bears were carried passively with the predominant currents of the polar basin (Pedersen 1945). Researchers have known for some time that is not the case (Stirling et al. 1980, 1984). However the advent of radiotelemetry (Amstrup et al. 1986), including the use of satellites (Fancy et al. 1988; Harris et al. 1990; Messier et al. 1992; Amstrup et al. 2000), detailed knowledge of polar bear movements was not available.
Polar bears are most abundant in shallow-water areas near shore and in other areas where currents and upwellings increase productivity and keep the ice cover from becoming too solidified in winter (Stirling and Smith 1975; Stirling et al. 1981; Amstrup and DeMaster 1988; Stirling 1990; Stirling and Øritsland 1995; Stirling and Lunn 1997; Amstrup et al. 2000). Despite apparent preferences for the more productive waters near shorelines and polynyas (areas of persistent open water), polar bears occur throughout the polar basin including latitudes >88°N (Stefansson 1921; Papanin 1939; Durner and Amstrup 1995).
Because they derive their sustenance from the sea, the distribution of polar bears in most areas changes with the seasonal extent of sea-ice cover. In winter, for example, sea-ice extends as much as 400 km south of the Bering Strait, which separates Asia from North America, and polar bears extend their range to the southernmost extreme of the ice (Ray 1971). Sea-ice disappears from most of the Bering and Chukchi Seas in summer, and polar bears occupying these areas may migrate as much as 1000 km to stay with the southern edge of the pack ice (Garner et al. 1990, 1994). Throughout the polar basin, polar bears spend their summers concentrated along the edge of the persistent pack ice. Significant northerly and southerly movements appear to be dependent on seasonal melting and refreezing of ice near shore (Amstrup et al. 2000). In other areas, for example, Hudson Bay, James Bay, and portions of the Canadian High Arctic, when the sea-ice melts, polar bears are forced onto land for up to several months while they wait for winter and new ice (Jonkel et al. 1976; Schweinsburg 1979; Prevett and Kolenosky 1982; Schweinsburg and Lee 1982; Ferguson et al. 1997; Lunn et al. 1997).
Until the 1960s, the prevalent belief was that polar bears wandered throughout the Arctic. Some naturalists felt that individual polar bears were carried passively with the predominant currents of the polar basin (Pedersen 1945). Researchers have known for some time that is not the case (Stirling et al. 1980, 1984). However the advent of radiotelemetry (Amstrup et al. 1986), including the use of satellites (Fancy et al. 1988; Harris et al. 1990; Messier et al. 1992; Amstrup et al. 2000), detailed knowledge of polar bear movements was not available.
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