Posted onSeptember 30, 2021|Comments Off on Sea ice growth after the summer minimum begins in the Canadian Arctic Archipelago
The Arctic sea ice minimum was declared to have been reached on 16 September this year (4.72 mkm2), breaking no records.
Ice extent can only go up from this point forward but at this time of year, it happens slowly and isn’t noticeable in the Arctic Basin as much as it is in the Canadian Arctic Archipelago. As I wrote about last year, new ice development in the fall next to shore creates upwelling conditions that attract fish and seals, and therefore provides feeding opportunities for polar bears.
The same process likely happens when new ice forms next to old ice. These few weeks of developing sea ice, wherever they occur, are the last chance polar bears have to replace weight lost over the summer before the cold and darkness of winter reduces hunting opportunities to virtually nil.
Posted onNovember 11, 2020|Comments Off on Shorefast ice formation and the fall feeding season for polar bears
What may seem like a silly question is actually fundamental to polar bear survival: in the fall, why do Western Hudson Bay bears correctly expect to find seals in the new ice that forms offshore? Why are seals attracted to that new ice – called ‘shorefast ice’ or ‘fast ice’ – when they would clearly be safer out in the open water where there is no ice and no bears?
As the picture below attests, polar bears can and do kill ringed seals in the new ice that forms off the coast of Western Hudson Bay even when it is but a narrow strip of thin ice – and so close to shore their successes can be caught on camera.
Three adult male polar bears share a seal kill on the newly-formed ice off Wapusk National Park, Western Hudson Bay. 5 November 2020. Buggy cam, Explore.org
A different bear was also filmed killing another seal on 31 October. And these are only the kills we know about along a very short stretch of coast – the killing is almost certainly going on up and down the entire coast, into James Bay (see below), where there is just as much ice but no cameras.
As far as I am aware, this seal killing by polar bears goes on in newly-formed shorefast ice everywhere across the Arctic in early fall, not just in Hudson Bay. Although the timing varies, virtually everywhere in the peripheral seas of the Arctic Ocean (Barents, Kara, Laptev, Chukchi, Beaufort, as well as Baffin Bay and Davis Strait), shorefast ice forms before the mobile ice pack expands to meet the ice developing from shore.
This shorefast ice formation in fall provides a predictable but short-lived source of prey for polar bears as they strive to regain some of the weight lost over the summer.