Baffin Bay (BB)

New population estimate of 2826 (2012-13) improves subpopulation status

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)
2826
2059-3593
Genetic C-R2012-2013Data deficientData deficient-6.1/3.9-18.9137.8135.8 (4.8%)
See also the complete table (all subpopulations)

Comments, vulnerabilities and concerns

Due to evidence that sampling design and environmental conditions likely resulted in an underestimate of abundance in the 1990s, the estimates of abundance for the 1990s and 2010s are not directly comparable and trend cannot be determined.  Satellite telemetry analyses comparing movements of adult females in 1990s to 2000s indicate reduced seasonal ranges, increased isolation, 30+ days more on land on Baffin Island in summer, reduced body condition, reduced cub recruitment with early sea ice breakup, and increased swimming.

Status and delineation

Baffin Bay subpopulation mapThe Baffin Bay area. See also the complete map (all subpopulations).

Based on movements of adult females with satellite radio-collars and recaptures of tagged animals, the Baffin Bay subpopulation is bounded by the North Water Polynya to the north, Greenland to the east and Baffin Island, Canada, to the west (Taylor and Lee 1995; Taylor et al. 2001; Laidre et al. 2012). A distinct southern boundary at Cape Dyer on Baffin Island in Nunavut, Canada is evident from the movements of tagged bears (Stirling et al. 1980; Peacock et al. 2012) and from polar bears monitored by satellite telemetry (Taylor et al. 2001). This boundary overlaps with the northern boundary of the Davis Strait subpopulation. Studies of microsatellite genetic variation have not revealed significant differences between polar bears in BB and neighboring Kane Basin, although there was significant genetic variation between polar bears in BB and those in Davis Strait (Paetkau et al. 1999; Peacock et al. 2015; Malenfant et al. 2016; SWG 2016). However, polar bears in BB cluster with bears in northern Davis Strait (Peacock et al. 2015).

An initial subpopulation estimate of 300 – 600 bears in BB was based on mark-recapture data collected in spring (1984 – 1989) in which the capture effort was restricted to shore-fast ice and the floe edge off northeast Baffin Island. However, work in the early 1990s showed that an unknown proportion of the subpopulation was typically offshore during the spring and, therefore, unavailable for capture. A second study (1993 – 1997) was carried out during September and October, when all polar bears were thought to be ashore in summer retreat areas on Bylot and Baffin islands (Taylor et al. 2005). Taylor et al. (2005) estimated the number of polar bears in BB at 2,074 ± 226 (SE). A 3-year genetic mark-recapture survey (via biopsy darting) was completed in 2014 resulting in a new population estimate, survival rates, and habitat use analyses (SWG 2016). The mean estimate of total abundance of the BB subpopulation in 2012-2013 was 2,826 (95% CI = 2,059-3,593) polar bears. Due to evidence that the sampling design and environmental conditions resulted in an underestimate of abundance in the 1990s, these two estimates are not directly comparable and trend in abundance cannot be determined.

Satellite telemetry data and habitat selection studies in the 2000s indicate a number of ecological changes related to sea ice loss in Baffin Bay. There has been a significant reduction in the range of the subpopulation in all months and seasons when compared to the 1990s. The most marked reduction is a 60% decline in subpopulation range size in summer. Emigration from Baffin Bay has declined since the 1990s, especially with a reduction of bears moving from BB into Davis Strait and Lancaster Sound. The total number of bears marked during studies in 2011-2012 in BB was equivalent to ~34% of the estimated population size.  Despite this, instances of emigration were ≤ 1% of the recaptures and recoveries of marks for the BB subpopulation.

Compared to the 1990s, adult female BB bears now use significantly lower sea-ice concentrations in winter and spring and spend 20-30 more days on land on Baffin Island in the summer ice-free season.  Changes in maternity denning have been observed; entry dates into maternity dens are >1 month later in the 2000s than the 1990s. Furthermore, the first date of arrival on land by pregnant females is significantly earlier in the 2000s. Maternity dens in the 2000s occurred at higher elevations and steeper slopes than the 1990s, likely due to reduced snow cover.

References

Reference list