Northern Beaufort Sea (NB)

The population has likely decreased since 2006, when it was estimated to approximately 980 (95% CI: 825-1135) animals based on mark-recapture.

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)
980
825-1135
Physical C-R2006Likely decreased (2006 to 2018)Likely decreased (2013 to 2018)-7.2/2.6-6.5142.2 (SB+NB)83 (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 make population trends difficult to  assess. Concerns include declining body condition, periods of low survival, and growing reliance of part of population on land during summer. Breakup becoming earlier and freeze-up later, resulting in longer period of open water and unavailability of prime fast ice feeding habitat in spring. Fact that recorded harvest level is less than half the total allowed quota is likely at least partly the result of population decline.

Status and delineation

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

Studies of movements and abundance estimates of polar bears in the eastern Beaufort Sea have been conducted using telemetry and mark-recapture at intervals since the early 1970’s (Stirling et al. 1975, Demaster et al. 1980, Stirling et al. 1988, Lunn et al. 1995). As a result, it was recognized that there were separate populations in the North and South Beaufort Sea areas (NB and SB) and not a single population as was suspected initially (Stirling et al. 1988, Amstrup et al. 1995, Taylor and Lee 1995, Bethke et al. 1996). The density of polar bears using the multi-year ice of the northernmost area was lower than it was further south. The subpopulation estimate of 1,200 (Stirling et al. 1988) for NB was believed to be relatively unbiased at the time but the most northerly areas of the northwestern coast of Banks Island and M’Clure Strait were not permitted to be completely surveyed because of concern about disruption to guided polar bear sport hunters at the same time. The most northerly region of the NB subpopulation were later surveyed in 1990–92; the densities encountered were low, few subadult bears were seen, and the ratio of marked to unmarked polar bears was similar to that in the southern portion of the subpopulation. A mark-recapture survey, completed in 2006 suggested that the size of the NB subpopulation to be 980 ± 155, and that it has remained stable over the previous three decades, probably because ice conditions have remained stable and the harvest has been maintained within sustainable limits (Stirling et al. 2011). The amount of ice remaining over the continental shelf in NB in late summer fluctuates. Analyses using data from satellite tracking of female polar bears and spatial modeling techniques suggest that the boundary between NB and SB may need to be moved somewhat to the west of its current eastern limit at Pearce Point, in response to changing patterns of breakup and freeze-up resulting from climate warming (Amstrup et al. 2004, Amstrup et al. 2005). In 2014, the boundary (for management purposes within the Inuvialuit Settlement Area) between NB and SB was moved to the vicinity of Tuktoyaktuk on the basis of TEK (citation) and older satellite telemetry data (Amstrup et al. 2004). 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

Reference list