Southern Beaufort Sea (SB)

Subpopulation size 907 (95% CI: 548-1270) from 2010 and a declining trend.

Status table outtake

Size Sea ice metrics Human-caused removals 2010–2014
Estimate /
95% CI
Year Method Change in spring ice retreat / Change in fall ice advance (days per decade) Change in summer sea ice area (percent change per decade) 5-yr mean Last year
Potential Actual Potential Actual
907
548-1270
2010Physical capture-recapture-8.7/8.7-20.5142.2 (SB+NB)83 (SB+NB)133 (SB+NB)57 (SB+NB)
See also the complete table (all subpopulations)

Comments, vulnerabilities and concerns

Potential and actual removals merged for NB and SB due to unresolved boundary. Concerns include declining body condition, periods of low survival, and growing reliance on land during summer.

Status and delineation

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

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 (NWT), 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. 2004b; 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, NWT, to the east, there was a 50% probability of polar bears being either from the SB or the northern Beaufort Sea (NB) subpopulation. To address the issue of overlapping boundaries, resource managers in Canada shifted the eastern boundary westward to 133° W longitude (due north of Tuktoyaktuk) in 2014. 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).

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) and observations suggested that abundance was increasing. Results from a 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). That 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 former record low (Hunter et al. 2010, Regehr et al. 2010). The most recent analysis (covering the  years 2001-2010) showed that survival estimates remained low through 2007 and increased through 2009, resulting in an abundance estimate of 907 (95% CI = 548 – 1,270) polar bears present in 2010 (Bromaghin et al. 2015). However, it is important to note that here is the potential for un-modeled spatial heterogeneity in mark-recapture sampling, resulting from field crews being unable to sample the entire geographic reach of the population boundaries, which could bias both survival and abundance estimates. A recent Traditional Knowledge study from Canada concluded that the numbers of polar bears in regularly used hunting areas have remained relatively stable within living memory (Joint Secretariat 2015).

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 state increased from the mid-1980s to the mid-2000s (Cherry et al. 2009). These data support the hypothesis that energy balance of polar bears has changed in the southern Beaufort Sea, which may explain observed declines in survival. Sea ice habitat for polar bears is declining due to declines in sea ice extent (Stroeve et al. 2014), resulting from the continuing effects of climate warming. Atwood et al. (2016) and Pongracz and Derocher (2016) found that polar bears in the SB are spending significantly more time on land, which is correlated with the extent of ice retreat. Further, while on land, many polar bears feed on the subsistence-harvested bowhead whale remains aggregated at Cross Island near the Prudhoe Bay industrial infrastructure and Barter Island near the community of Kaktovik (Herreman andPeacock 2013, Rogers et al., 2015). Increased polar bear activity near human settlements may increase the risk of human-bear interactions.

For the purposes of this assessment, we (IUCN/SSC/PBSG) will adopt interim use of the revised boundary between SB and NB used by management authorities in the Northwest Territories and Yukon Territory.

References

Amstrup, S. C., Stirling, I. and Lentfer, J. W. 1986. Past and present status of polar bears in Alaska. Wildlife Society Bulletin 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. Canadian Journal of Zoology 73:1312-1322.

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.

Atwood, T.C., Peacock, E., McKinney, M., Douglas, D.C., Lillie, K., Wilson, R., Terletzky, P., and Miller, S.. 2016. Rapid environmental change drives increased land use by an Arctic marine predator. PLOS One 11(6):e0155932. doi:10.1371/journal.pone.0155932.

Bromaghin J, Amstrup S, McDonald T, Stirling I, Derocher A, Richardson E, Regehr E, Douglas D, Durner G, and Atwood TC. 2015. Polar bears in the Beaufort Sea: population decline and stabilization in the 2000’s. Ecological Applications 25:634-651.

Cherry, S.G., A.E. Derocher, I. Stirling, and E.S. Richardson. 2009. Fasting physiology of polar bears in relation to environmental change and breeding behavior in the Beaufort Sea. Polar Biology 32:383-391.

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. Ecological Monographs 79:25-58.

Herreman, J. and Peacock, E. 2013. Polar bear use of a persistent food subsidy: Insights from non-invasive genetic sampling in Alaska. Ursus 24:148-163.

Pongracz, J.D., and Derocher, A.E. 2016. Summer refugia habitat of polar bears (Ursus maritimus) in the southern Beaufort Sea. Polar Biology DOI 10.1007/s00300-016-1997-8.

Hunter, C.M., H. Caswell, M.C. Runge, E.V. Regehr, S.C. Amstrup, and I. Stirling. 2010. Climate change threatens polar bear populations: a stochastic demographic analysis. Ecology 9:2883-2897.

Joint Secretariat. 2015. Inuvialuit and Nanuq: A Polar Bear Traditional Knowledge Study. Joint Secretariat, Inuvialuit Settlement Region. 304 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. Journal of Animal Ecology79:117-127.

Rode, K.D., Amstrup, S.C., and Regehr, E.V. 2010. Reduced body size and cub recruitment in polar bears associated with sea ice decline. Ecological Applications 20:768−782.

Rogers, M.C., Peacock, E., Simac, K.S., O'Dell, M.B., and Welker, J.M. 2015. Diet of female polar bears in the southern Beaufort Sea of Alaska: evidence for an emerging alternative foraging strategy in response to environmental change. Polar Biology doi:10.1007/s00300-015-1665-4.

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.

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.

Stroeve, J.C., Markus, T., Boisvert, L., Miller, J., and Barrett, A. 2014. Changes in Arctic melt season and implications for sea ice loss. Geophysical Research Letters 41:1216−1225.