Polar Bears In Depth
Movements
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FIGURE 27.8. The circumpolar range of polar bears is subdivided, according to observed movement patterns, into 20 hypothesized populations or stocks. 1, Western Hudson Bay; 2, southern Hudson Bay; 3, Foxe Basin; 4, Lancaster Sound; 5, Baffin Bay; 6, Norwegian Bay; 7, Kane Basin; 8, Queen Elizabeth Islands; 9, Davis Strait; 10, Gulf of Boothia; 11, M'Clintock Channel; 12, Viscount Melville Sound; 13, northern Beaufort Sea; 14, southern Beaufort Sea; 15, Chukchi Sea; 16, Laptev Sea; 17, Novaya Zemlya; 18, Svalbard; 19, East Greenland; 20, Arctic basin. Boundaries are constantly being adjusted as new data and ecological insights are obtained. SOURCE: Adapted from Lunn et al. (2003:23). Click image to enlarge.
Just as the labile nature of the sea-ice results in annual variability in the distribution of suitable habitat for polar bears, it also eliminates any benefit to polar bears of defending territories. The location of resources is less predictable than resources on which terrestrial predators depend. Seals tend to be distributed over very large areas at low densities (Bunnell and Hamilton 1983). Furthermore, their distribution, density, and productivity are extremely variable among years (DeMaster et al. 1980; Stirling et al. 1982; Stirling and Øritsland 1995). As radiotelemetry studies have shown, female polar bears show only general fidelity to seasonal feeding areas (Ferguson et al. 1997; Amstrup et al. 2000). Absence of strict fidelity, especially during breeding and denning seasons (Garner et al. 1994; Amstrup and Gardner 1994), essentially prohibits defendable territories. Males similarly must be free of the need to defend territories if they are to maximize their potential for finding mates each year (Ramsay and Stirling 1986b).
Although there may be limited spatial segregation among individual polar bears, telemetry studies have demonstrated spatial segregation among groups or stocks of polar bears in different regions (Schweinsburg and Lee 1982; Amstrup et al. 1986, 2000; Garner et al. 1990, 1994; Messier et al. 1992; Amstrup and Gardner 1994; Bethke et al. 1996; Ferguson et al. 1999). Patterns in spatial segregation suggested by telemetry data, survey and reconnaissance, marking and tagging studies, and traditional knowledge resulted in recognition of 19 partially discrete polar bear groups (Lunn et al. 2002:2135). There is considerable overlap in areas occupied by members of these groups, and boundaries separating the groups have been adjusted as new data were collected. Nonetheless, these boundaries are thought to be ecologically meaningful, and the units they describe are managed as populations.
A 20th polar bear population may occur in the central polar basin (Table 27.1). It is unclear whether bears that occur in this region are simply visitors from populations nearer to islands and continental shorelines or whether there are animals that spend all of their time in these high-latitude regions far from any land. The frequency of recent observations deep in the polar basin, however, mandates recognition that a separate stock could occur there (Fig. 27.8).
Although there may be limited spatial segregation among individual polar bears, telemetry studies have demonstrated spatial segregation among groups or stocks of polar bears in different regions (Schweinsburg and Lee 1982; Amstrup et al. 1986, 2000; Garner et al. 1990, 1994; Messier et al. 1992; Amstrup and Gardner 1994; Bethke et al. 1996; Ferguson et al. 1999). Patterns in spatial segregation suggested by telemetry data, survey and reconnaissance, marking and tagging studies, and traditional knowledge resulted in recognition of 19 partially discrete polar bear groups (Lunn et al. 2002:2135). There is considerable overlap in areas occupied by members of these groups, and boundaries separating the groups have been adjusted as new data were collected. Nonetheless, these boundaries are thought to be ecologically meaningful, and the units they describe are managed as populations.
A 20th polar bear population may occur in the central polar basin (Table 27.1). It is unclear whether bears that occur in this region are simply visitors from populations nearer to islands and continental shorelines or whether there are animals that spend all of their time in these high-latitude regions far from any land. The frequency of recent observations deep in the polar basin, however, mandates recognition that a separate stock could occur there (Fig. 27.8).
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