A just-released report on the most recent (2016) survey shows Western Hudson Bay polar bear numbers were still stable despite predictions that this subpopulation would be wiped out completely (reduced to zero) due to low Arctic sea ice.
The authors of the report on the August 2016 aerial survey of the Western Hudson Bay polar bear subpopulation (Dyck et al. 2017) state clearly that the only trends they could find were that the number of adult males increased somewhat over 2011 estimates and the number of females either declined or remained stable. The overall population estimate was a bit lower (11% less) compared to the 2011 survey but the difference is not statistically significant. Therefore, the population status must be stable.
2011 estimate: 949 bears (using comparable data, range 618-1280), litter size 1.43
2016 estimate: 842 bears (using comparable data, range 562-1121), litter size 1.63
[cf. Foxe Basin [stable], from 2009-2010 survey (Stapleton et al. 2016) litter size was 1.54]
An 11% decline in WH numbers since 2011 is most definitely NOT the decline to ZERO (extirpation) we were told to expect with Arctic sea ice as low as it has been since 2007 (Crockford 2017, see list of annual minimum extents 2007-2017 here).
Note: The percentage decline from 2011 to 2016 for Western Hudson Bay polar bears is 11%, NOT 18% as claimed recently by Andrew Derocher on twitter: it is not appropriate to compare the official 2011 estimate of 1030 (Stapleton 2014) to the 2016 estimate of 842 because the methods used to generate the estimates were different (Dyck et al. 2017). The authors of the report state that the estimate for 2011 that’s comparable to 2016 is 949.
An 11% decline from 1030 would be 917 bears, a statistically insignificant decline that is also biologically insignificant and therefore, so slight as to indicate a stable population.
Predicted sea ice at 2050 and 2080 shown below (see Crockford 2017 for details):
Quotes, map, and table from the Dyck et al. 2017 report (pdf here) are copied below.
Money Quote (Dyck et al. 2017:38):
“Results from both the distance sampling and coastal survey analyses suggest a stable to declining adult female segment of the population and an increasing adult male segment. While trends are apparent in both data sets, neither are statistically significant.” [my bold]
Population size estimate 2016: 842 bears (range 562-1121), assessed August 2016; the estimate for 2011 using comparable data was 949 bears (range 618-1280).
Compared to the last aerial survey estimate in 2011 (Stapleton et al. 2014):
“…the difference between the 2 estimates was not significant.”
Litter size for cubs-of-the-year (COY) improved since the 2011 survey (see Table 10 below from the report) and now exceeds Southern Hudson Bay and Foxe Basin subpopulation litter size estimates for the 2010-2011 (when both were considered stable).
Crockford, S.J. 2017 V3. Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus). PeerJ Preprints 2 March 2017. Doi: 10.7287/peerj.preprints.2737v3 Open access. https://doi.org/10.7287/peerj.preprints.2737v3 pdf here.
Dyck, M., Campbell, M., Lee, D., Boulanger, J. and Hedman, D. 2017. Aerial survey of the Western Hudson Bay polar bear sub-population 2016, final report (26 June 2017). Status report 2017-xx, Nunavut Department of Environment, Wildlife Research Section. Igloolik, Nunavut. pdf here.
Stapleton S., Atkinson, S., Hedman, D. and Garshelis, D. 2014. Revisiting Western Hudson Bay: using aerial surveys to update polar bear abundance in a sentinel population. Biological Conservation 170:38-47.
Stapleton, S., Peacock, E. and Garshelis, D. 2016. Aerial surveys suggest long-term stability in the seasonally ice-free Foxe Basin (Nunavut) polar bear population. Marine Mammal Science 32:181-201.
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