Southern Hudson Bay (SH)

A recent estimate produced by means of distance sampling is 780 bears (2016). Body condition of bears has declined since the 1980s.

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)
780
590-1029
Mark-recapture distance sampling2016Very likely decreased (1986 to 2016)Likely decreased (2012 to 2016)-1.9/3.1-8.551.636.4 (4.7%)
See also the complete table (all subpopulations)

Comments, vulnerabilities and concerns

Increased time ashore due to changes in breakup and freeze-up; declining body condition; declining survival rates, especially of cubs-of-the-year. 2016 abundance estimate was 17% lower than 2011/2012 estimate.  Similar rate of change in abundance in neighbouring Western Hudson Bay subpopulation.

Status and delineation

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

Boundaries of the Southern Hudson Bay polar bear subpopulation are based on observed movements of marked and collared bears (Jonkel et al. 1976; Kolenosky and Prevett 1983; Kolenosky et al. 1992; Obbard and Middel 2012; Middel 2014). The range of the SH subpopulation includes much of eastern and southern Hudson Bay and James Bay and large expanses of the coastline of Ontario and Québec as well as areas up to 120 km inland (Kolenosky and Prevett 1983; Obbard and Walton 2004; Obbard and Middel 2012).

An initial estimate of population size of 763 ± 323 animals was derived through a 3-year (1984–1986) capture-recapture study conducted in mainland Ontario (Kolenosky et al. 1992). This estimate was subsequently adjusted to 1000 for management purposes by the Canadian Polar Bear Technical Committee because areas away from the coast may have been under-sampled due to the difficulty of locating polar bears in the boreal forest and some areas in James Bay were not sampled (Lunn et al. 1998). A re-analysis of the 1984-1986 capture data produced an estimate for the study area of 641 (95% CI = 401–881 for those years (Obbard 2008; Obbard et al. 2007). A subsequent 3-year capture-recapture study conducted over the same geographical area and with similar capture effort (2003-05) produced an estimate of 673 (95% CI 396-950; Obbard 2008). An analysis of bears captured on Akimiski Island in James Bay during 1997 and 1998 resulted in the addition of 70–110 bears to the total subpopulation estimate (Obbard 2008). While the results of the two capture-recapture studies suggest that abundance was unchanged between 1984-86 and 2003-05, body condition declined and survival rates in all age and sex categories tended to decline between the two capture periods, although point estimates were not significantly different because of the overlap in confidence intervals (Obbard et al. 2006; Obbard 2008).

Intensive aerial surveys were conducted during the fall ice-free season over mainland Ontario (same geographic area as for the capture–recapture studies) and Akimiski Island in 2011, and over the remaining islands in James Bay, the coastal areas of Québec from Long Island to the SH–FB border, and the off-shore islands in eastern Hudson Bay in 2012. Results of this mark-recapture-distance-sampling (MRDS) analysis provided an estimate of 860 bears (95% CI: 580–1,274) in the mainland Ontario, neighboring islands, and Akimiski Island portions of the SH management unit during the 2011 ice-free season. The estimate for the 2012 survey was 83 bears (SE 4.5) in the 2012 study area. Thus, combining the aerial survey results from 2011 and 2012 yielded an overall estimate of 943 (SE: 174, 95% CI: 658–1350) for SH (Obbard et al. 2015). Overall, despite the difference in methodologies, assumptions, and biases between capture–recapture studies and aerial surveys, the evidence suggests it is likely that abundance of the subpopulation was unchanged between 1986 and 2012.

The ice-free season within the SH boundaries increased by about 30 days from 1980 to 2012 (Obbard et al. 2016; Stern and Laidre 2016). Concurrently, body condition declined in all age and sex classes, though the decline was less for cubs than for other social classes (Obbard et al. 2016).

The intensive aerial survey was repeated in September 2016 to assess recent trend in abundance.  All areas in Ontario, Nunavut and Québec were sampled within a 3-week period to ensure complete coverage within the same year. Results suggest that abundance declined 17% from 943 bears (95% CI: 658–1350) in 2011/2012 to 780 (95% CI: 590–1029) in 2016. The proportion of yearlings declined from 12% of the population in 2011 to 5% in 2016, whereas the proportion of cubs remained similar (16% in 2011 vs. 19% in 2016) suggesting low survival of the 2015 cohort (Obbard et al. 2018).
 

References

Reference list