Subpopulation size 907 (95% CI: 548-1270), current trend Declining, trend relative to historic level Reduced.
Status table outtake
Status and delineation
Research on polar bears in the southern Beaufort Sea (SB) subpopulation has been ongoing since 1967 (Amstrup et al. 1986, Stirling 2002). Radio-telemetry and mark-recapture studies through the 1980s indicated that polar bears in the region comprised a single subpopulation, with an eastern boundary between Paulatuk and Baillie Island, Northwest Territories, Canada, and a western boundary near Icy Cape, Alaska, USA (Amstrup et al. 1986, Amstrup and DeMaster 1988, Stirling et al. 1988). Analyses of relocations of polar bears carrying satellite radio collars using probabilistic models suggested that, rather than exhibiting distinct boundaries, there were areas of overlap between the SB and adjacent subpopulations (Amstrup et al. 2004; Amstrup et al. 2005). The results of that study suggested that at Barrow, Alaska, in the west, 50% of polar bears were from the SB subpopulation and 50% were from the Chukchi Sea (CS) subpopulation, and that at Tuktoyaktuk, Northwest Territories, Canada, to the east, there was a 50% probability of polar bears being either from the SB or the northern Beaufort Sea (NB) subpopulation. Based on this analysis, most polar bears in the vicinity of the current eastern boundary near Pearce Point, Northwest Territories, are probably members of the NB subpopulation. To address this issue, resource managers have shifted the eastern boundary westward to 133° W longitude (due north of Tuktoyaktuk, Northwest Territories, Canada). A similar boundary shift, or a change in the way harvest is allocated among subpopulations, may be required on the western side of the SB subpopulation where it borders the CS subpopulation (Amstrup et al. 2005). Given the large-scale changes taking place in the seasonal patterns of freeze-up and breakup (Stroeve et al. 2014), and the larger database now available, re-analyses of SB subpopulation borders and harvest management at 10-15 year intervals may be useful. Sound management requires that current scientific information be used to define biologically relevant polar bear subpopulations. This presents an increasing challenge, as sea ice loss and increased variability in sea ice extent have the potential to affect polar bear movements and distribution, including the breakdown of historic subpopulation boundaries (Derocher et al. 2004).
The size of the SB subpopulation was first estimated to be approximately 1,800 animals in 1986 (Amstrup et al. 1986). Survival rates of adult females and dependent young were estimated from radio-telemetry data collected from the early 1980s to the mid-1990s (Amstrup and Durner 1995). Through the 1980s and early 1990s, observations suggested that abundance was increasing. Amstrup et al. (2001) found that abundance may have reached as many as 2,500 polar bears in the late 1990s. However, that estimate was not considered reliable due to small sample sizes and very wide confidence intervals on estimates for the latter years of that study. Therefore, management decisions continued to be based on an estimate of 1,800 individuals. Results from an intensive mark-recapture study conducted from 2001-2006 in both the USA and Canada indicated that the SB subpopulation included 1,526 (95% CI = 1,211 – 1,841) polar bears in 2006 (Regehr et al. 2006). This study and others found that the survival and breeding of polar bears were negatively affected by changing sea ice conditions, and that population growth rate was strongly negative in years with long ice-free seasons, such as 2005 when Arctic sea ice extent reached a record low (Hunter et al. 2007, Regehr et al. 2010). Most recently, a follow-up mark-recapture study using data collected from 2001-2010 estimated abundance in 2010 to be 907 (95% CI = 548 – 1,270) polar bears. This suggests that the size of the subpopulation declined between the late 1990s and 2010. However, it is important to note that there is the potential for un-modeled spatial heterogeneity in mark-recapture sampling that could bias both survival and abundance estimates.
Declines in polar bear body condition, stature, and reproduction have been linked to multi-year trends of declining sea ice (Rode et al. 2010), and an assessment of temporal patterns of feeding ecology found that the number of bears in a physiological fasting increased from the mid-1980s to the mid-2000s (Cherry et al. 2009). Sea ice habitat is declining due to a negative trend in sea ice extent and a lengthening melt season (Stroeve et al. 2014), resulting from the continuing effects of climate warming.
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