Five years of polar bear habitat at June 20 around the Arctic

Five years worth of sea ice maps for the same date is hard to come by in this country, since the Canadian Ice Service does not archive their daily sea ice maps. However, due to some forethought, I have at hand ice maps going back to 2012 for the longest day of the year for Canada and archives for other regions provide similar perspective at the solstice.

Polar_Bear_male on sea ice_Regehr photo_March 21 2010_lg

Few photos of polar bears in June likely exist – too early for most bears to come ashore and the ice too unstable for humans to be offshore [photo above is dated March].

Compare the five maps for Canada and eastern Alaska below. Notice the differences for Hudson Bay: it may seem ironic, but 2012 (which had the lowest September minimum since 1979 due to an August storm) had the most typical Hudson Bay breakup/melt pattern compared to previous years. [Keep in mind this recent post about how much ice can remain even when almost none is visible on the ice maps]

In many regions, polar bear hunting efforts are seldom successful after early June because young-of-the-year seal pups have taken to the water to feed, which means the only prey still on the ice are predator-savvy adults and subadults that have an easy time escaping in the rapidly breaking up ice fields. Bears that come ashore in June likely are not missing much – a little less ice than usual at this time of year is not going to make much difference.

Overall, despite doom and gloom predictions we heard in March 2016 (“wintertime extent hits another record low”), sea ice extent (courtesy NSIDC) at 20 June 2016 was the same at this date as it was in 2010 and 2012 at this time of year – which essentially marks the end of the primary feeding period for polar bears (except for those that live in the Canadian Arctic Archipelago, where seals give birth a bit later in the spring).

Sea ice at 20 June_2016 vs 2012 and 2010_NSIDC interactive

And did polar bears die in droves due to conditions in 2010 or 2012, in any subpopulation around the Arctic affected by low sea ice levels? No, they did not. In fact, the subpopulation that had the most recent survey done (Svalbard portion of the Barents Sea – 2015) was not only found to be thriving but numbers had increased markedly (42%) over 2004 levels. Now that’s resilience!


Canada and Alaska at 20 June, 2012-2016

Sea ice extent Canada 2012 June 20

Sea ice extent Canada 2013 June 20_CIS

Sea ice extent Canada 2014 June 20

Sea ice extent Canada 2015 June 20 CIS

Sea ice extent Canada 2016 June 20 CIS

 

Critical feeding period for polar bears is now over

 

Relative importance of seasons polar bear graphic_PolarBearScience_June2016

 

Global sea ice coverage at 20 June 2016

masie_all_zoom_4km 2016 June 20

Map above from NSIDC Masie; below from the US Naval Research Lab.

Ice thickness Navy forecast June 20 2016

 

Sea ice extent Barents Sea at 20 June

Svalbard sea ice extent 2016 June 20_NIS

Given ice levels right now (above, from the Norwegian Ice Service), I expect few bears will be spending the summer onshore in Svalbard but will hang out instead around Franz Josef Land in Russia. Too bad for Norwegian polar bear biologists (what do you do when your study animal moves to another country?) but not any kind of catastrophe for the bears.

Barents Sea ice is even lower this year than it was in 2012 at the same date (below), yet by 2015 (a good ice year), Svalbard polar bear numbers were up 42% over the 2004 count.

Barents Sea ice 2012 June 20

That’s as much evidence as anyone would need to demonstrate that ice levels around Svalbard are not critical to Barents Sea polar bears as a whole – when ice levels are low in the west, they simply shift east (where ice levels are less volatile).

The real question is: why would any sensible biologist think they would not?

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