Southern Beaufort Sea (SB)

Subpopulation size 1526 (95% CI: 1211-1841), current trend Declining, trend relative to historic level Reduced.

Status table outtake

Size Trend Human-caused removals 2009–2013
Estimate /
95% CI
Year Method Relative to historic level
(approx. 25-yr past)
Current (approx. 12-yr
period centered on present)
5-yr mean 3-yr mean Last year
Potential Actual Potential Actual Potential Actual
1526
1211-1841
2006Physical capture-recaptureReducedDeclining4635.67342.37041
See also the complete table (all subpopulations)

Habitat quality

Decreased annual availability of pack ice over the continental shelf

Comments, vulnerabilities and concerns

Current and projected habitat decline, declining body condition, declining survival rates.

Status and delineation

Southern Beaufort Sea subpopulation mapThe Southern Beaufort Sea area. See also the complete map (all subpopulations).

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 more recent satellite relocations using probabilistic models indicate that, rather than exhibiting distinct boundaries, there are areas of overlap between the SB and adjacent subpopulations (Amstrup et al. 2004; Amstrup et al. 2005). At Barrow, Alaska, in the west, it is estimated that 50% of polar bears are from the SB subpopulation and 50% are from the Chukchi Sea (CS) subpopulation. At Tuktoyaktuk, Northwest Territories, Canada, in the east, there is 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, user groups, scientists and resource managers are discussing a western shift of the SB-NB boundary. One proposal has been to move it west to 133° W longitude (due north of Tuktoyaktuk, Northwest Territories, Canada) but a line further east is also under consideration. 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). 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. 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 suggests that the size of the subpopulation declined between the late 1990s and 2006, although low precision in the previous estimate of 1,800 precluded a statistical determination. Subsequent analyses of the 2001-2006 data using multistate and demographic models indicated that the survival and breeding of polar bears during this period were affected by 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). However, it is important to note that there is the potential for un-modeled spatial heterogeneity in mark-recapture sampling that could bias survival and abundance estimates. A thorough re-assessment of survival and abundance is underway and a final result is anticipated in late 2014. The SB subpopulation is currently considered to be declining due to a negative trend in sea ice conditions, particularly over the continental shelf, resulting from the continuing effects of climate warming. If the region continues to lose high quality polar bear hunting habitat as forecasted by global climate models (Durner et al. 2009), it is likely that the SB subpopulation could face extirpation by mid-century (Amstrup et al. 2010).
 

References

Amstrup, S. C., Stirling, I. and Lentfer, J. W. 1986. Past and present status of polar bears in Alaska. Wildl. Soc. Bull. 14:241-254.

Amstrup, S. C. and DeMaster, D. P. 1988. Polar bear Ursus maritimus. Pp. 39-56 In Lentfer, J. W. (ed.). Selected Marine Mammals of Alaska: Species Accounts with Research and Management Recommendations. Marine Mammal Commission, Washington, DC, USA.

 

Amstrup, S.C. and Durner, G.M. 1995. Survival rates of radio-collared female polar bears and their dependent young. Can. J. Zoology 73:1312-1322.

Amstrup, S. C., McDonald, T. L. and Stirling, I. 2001. Polar bears in the Beaufort Sea: A 30-year mark-recapture case history. J. Agr. Biol. Environ. Stat. 6:221-234.

Amstrup, S. C., York, G., McDonald, T. L., Nielson, R. and Simac, K. 2004. Detecting denning polar bears with forward-looking infrared (FLIR) imagery. Bioscience 54:337-344.

Amstrup, S. C., Durner, G. M., Stirling, I. and McDonald, T. L.2005. Allocating harvests among polar bear stocks in the Beaufort Sea. Arctic 58:247-259.

Amstrup, S.C., DeWeaver, E.T., Douglas, D.C., Marcot, B.G., Durner, G.M., Bitz, C.M. and Bailey, D.A. 2010. Greenhouse gas mitigation can reduce sea-ice loss and increase polar bear persistence. Nature 468: 955-960.

  Stirling, I. 2002. Polar bears and seals in the eastern Beaufort Sea and Amundsen Gulf: A synthesis of population trends and ecological relationships over three decades. Arctic 55:59-76.

Derocher, A. E., Lunn, N. J. and Stirling, I. 2004. Polar bears in a warming climate. Integr Comp Biol 44:163-176. 

 

Durner, G. M., Douglas, D. C., Nielson, R. M., Amstrup, S. C., McDonald, T. L., Stirling, I., Mauritzen, M., Born, E. W., Wiig, O., DeWeaver, E., Serreze, M. C., Belikov, S. E., Holland, M. M., Maslanik, J., Aars, J., Bailey, D. A. and Derocher, A. E. 2009. Predicting 21stcentury polar bear habitat distribution from global climate models. Ecol. Monogr. 79:25-58.

Hunter, C. M., Caswell, H., Runge, M. C., Regehr, E. V., Amstrup, S. C. and Stirling, I. 2007. Polar bears in the Southern Beaufort Sea II: Demography and population growth in relation to sea ice conditions. U.S.Geological Survey Administrative Report, U.S. Department of the Interior. Reston, Virginia, USA. 51 pp.

Regehr, E. V., S. C. Amstrup, and I. Stirling. 2006. Polar bear population status in the southern Beaufort Sea. U.S. Geological Survey Administrative Report, U.S. Department of the Interior. Reston, Virginia, USA. 20 pp.

Regehr, E.V., Hunter, C.M., Caswell, H., Amstrup, S.C. and Stirling, I. 2010. Survival and breeding of polar bears in the southern Beaufort Sea in relation to sea ice. J. Anim. Ecol.79:117-127.
Stirling, I., Andriashek, D., Spencer, C. and Derocher, A.E. 1988. Assessment of the polar bear population in the eastern Beaufort Sea. Final Report to the Northern Oil and Gas Assessment Program. Canadian Wildlife Service, Edmonton, Alberta, Canada. 81 pp.