Spring in the Arctic is April-June (Pilfold et al. 2015). As late April is the peak of this critical spring feeding period for most polar bear populations, this is when sea ice conditions are also critical. This year, as has been true since 1979, that sea ice coverage is abundant across the Arctic for seals that are giving birth and mating at this time as well as for polar bears busy feeding on young seals and mating.
Below is a chart of sea ice at 25 April 2018, showing sea ice in all PBSG polar bear subpopulation regions:
Some Arctic subregions below, in detail.
Canada (from CIS)
Weekly stage of development, by area (from the west): brown is very thick, multiyear ice (2-5m thick) and dark green is thick first year ice (>1.2m). Note the area of shallow water (i.e. the continental shelf, <300m) is very narrow along the north coast of Alaska) and how close multiyear ice is to shore this year (seals and bears do best in first year ice):
Barents Sea (from NIS)
Compare the ice coverage above to what it was in the spring of 2015, just before the most recent survey that showed numbers around Svalbard (and likely beyond) had risen by 42% (Aars et al. 2017; Crockford 2017, 2018).
Aars, J., Marques,T.A, Lone, K., Anderson, M., Wiig, Ø., Fløystad, I.M.B., Hagen, S.B. and Buckland, S.T. 2017. The number and distribution of polar bears in the western Barents Sea. Polar Research 36:1, 1374125. https://www.tandfonline.com/doi/full/10.1080/17518369.2017.1374125
Crockford, S.J. 2017. 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
Crockford, S.J. 2018. State of the Polar Bear Report 2017. Global Warming Policy Foundation Report #29. London. pdf here.
Pilfold, N. W., Derocher, A. E., Stirling, I. and Richardson, E. 2015. Multi-temporal factors influence predation for polar bears in a changing climate. Oikos 124: 1098-1107. http://onlinelibrary.wiley.com/doi/10.1111/oik.02000/abstract
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