Polynyas are critical for polar bear spring feeding

Areas of open water or thin ice in spring are essential for the survival of Arctic species, as I emphasized in my recent peer-reviewed paper on polar bear ecology. Sea ice is still abundant in spring (April-June), which is the critical feeding period for polar bears: they must consume about 2/3 of the total calories they need for the entire year. Most of those calories come from newborn seals (ringed, bearded, and harp).

In southern areas, such as Hudson Bay and Davis Strait, virtually all of this feeding is completed by the end of May, making June a time of opportunistic hunting for most bears: if they find a seal, they will kill and eat it but if not, they can do without. That’s not just my opinion but the reason given by polar bear specialists themselves to explain why Southern Hudson Bay polar bear numbers had not declined in the 2000s despite a sudden increase in the ice-free season:

…even though break-up has advanced by up to 3-4 weeks in portions of Hudson Bay it still occurs no earlier than late June or early July so does not yet interfere with opportunities to feed on neonate ringed seal pups that are born in March-April in eastern Hudson Bay. Therefore, losing days or weeks of hunting opportunities during June and July deprives polar bears of the opportunity to feed on adult seals, but does not deprive them of the critical spring period when they are truly hyperphagic. [Obbard et al. 2016:29]

Polynyas worldwide

From my paper, without the labels (Crockford 2022, open access). Some polynyas, like the huge area off Siberia, are not often actually open water but areas of thin ice that seals and bears can break through easily. Because of that, they are often difficult to spot on sea ice charts.

Sea ice at mid-May

Canada (15 May 2022)

Arctic as a whole (15 May 2022)

Closeups by region (13 May 2022)

Bering/Chukchi/Beaufort (13 May 2022)

Barents/Kara Seas (13 May 2022)

Canadian East Coast/Western Greenland (13 May 2022)

References

Crockford, S. J. 2022. Polar bear fossil and archaeological records from the Pleistocene and Holocene in relation to sea ice extent and open water polynyas. Open Quaternary 8(7): 1-26. https://doi.org.10.5334/oq.107

Obbard, M.E., Cattet, M.R.I., Howe, E.J., Middel, K.R., Newton, E.J., Kolenosky, G.B., Abraham, K.F. and Greenwood, C.J. 2016. Trends in body condition in polar bears (Ursus maritimus) from the Southern Hudson Bay subpopulation in relation to changes in sea ice. Arctic Science 2(1):15-32. https://doi.org/10.1139/as-2015-0027

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