Southern Beaufort Sea (SB)

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

Status table outtake

Subpopulation size Subpopulation trend Sea ice metrics 1979-2018 Human-caused removals 2013/2014–2017/2018
Estimate and uncertainity Method and type of evidence Year and citation Long term (approx 3 generations) Short term (approx 1 generation) Change in date of spring ice retreat / fall ice advance (days per decade) Change in summer sea ice area (percent change per decade) 5-year mean
Quota (bears per year) Actual (% of total population)
907
548-1270
Physical C-R2010Likely decreased (1998 to 2010)Likely decreased (2001 to 2010)-9.7/8.6-25.3134.4 (SB+NB)62.4 (3.3%)
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, growing reliance on land during summer, and increased potential for human-polar bear conflict arising from increased industrial development of Alaska's coastal plain.

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 suggested that at Utqia─čvik (formerly 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, and changed the allocation of harvest between the SB and NB. A similar boundary shift and change in the way harvest is allocated 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 had increased (Amstrup et al. 2001). 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 in 2010 (Bromaghin et al. 2015). However, it is important to note that there 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). Multiple assessments of temporal patterns of feeding ecology found that the number of bears that are in a physiological fasting state in April/May increased from the mid-1980s to the mid-2010s (Cherry et al. 2009, Rode et al. 2018). These data support the hypothesis that energy balance of polar bears has changed in the southern Beaufort Sea, which may explain declines in survival observed in the mid-2000s. The availability of sea ice habitat for polar bears (Durner et al. 2009) is reduced with declining sea ice extent (Stroeve et al. 2014), resulting from the continuing effects of climate warming. Atwood et al. (2016) and Pongracz and Derocher (2017) 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 and Peacock 2013, Rogers et al., 2015). Increased polar bear activity near human settlements may increase exposure to terrestrial-based pathogens (Atwood et al. 2017) and the risk of human-bear interactions.

For the purposes of the 2019 Subpopulation Status Assessment, the PBSG adopted interim use of the revised boundary between SB and NB used by management authorities in the Northwest Territories and Yukon Territory.

References

Reference list