Hudson Bay update – lots of sea ice well positioned for polar bears to get ashore

There is slightly less ice this year in Hudson Bay than last year but it is hugging tight against the western shore, which means polar bears in Western and Southern Hudson Bay will be able to stay out on the ice (if they want to) until August.

Sea ice extent Canada 2016 July 15_CIS

The latest weekly ice graph from the Canadian Ice Service (for 9 July) below shows average ice coverage this year (and more than there was in 1976 and 1977):

Hudson Bay same week 9 July 1971-2016

[By the way, the IUCN Polar Bear Specialist Group website is still “under construction” allowing them to avoid mentioning the less-than-dire conclusions contained in the 2015 IUCN Red List assessment]

More ice maps below, comparing previous years.

And But as a new paper by one of Andrew Derocher’s students published a few days ago shows (discussed here – along with a discussion of tight satellite collars), some polar bears actually make full use of sea ice even if the concentration is very low – even when it is undetected by satellite images. In fact, a recent tweet of Derocher’s demonstrates that point beautifully – at least 4 bears he and his colleagues are tracking appear to be in open water (see below).

Derocher uses ice data for his WHB polar bear tracking maps that show only the most concentrated ice, even though he is well aware that some bears use any scrap of ice they can find at this time of year  – since he recently co-authored two papers on that very topic (Cherry, Derocher and Lunn 2016; Pongracz and Derocher 2016). The Canadian Ice Service (CIS) and NSIDC Masie charts use data from several sources to generate daily maps that show a more accurate picture (but they still probably miss some of it).

As was true at the end of June, according to NSIDC Masie ice charts, the amount and pattern of ice on 12 July 2016 was slightly less than it was in 2009 but the coverage was very similar – 2009 was the year when polar bears left the ice as late as they did in 1992 (the latest breakup year since 1979, discussed most recently here).

12 July 2016, to compare to previous years:

masie_all_r10_v01_2016194_4km

12 July 2009, latest breakup year since 1979:

masie_all_r10_v01_2009193_4km

CIS map for 14 July 2016 below:

Sea ice extent Canada 2016 July 14_CIS

Last year (2015, below), more of the remnant sea ice was in central and eastern Hudson Bay rather than along the west coast (where polar bears depart the ice to spend the summer) but still, there were no reports of starving bears in Churchill:

Hudson Bay breakup July 14 2015_CIS

In 2014, little remnant ice remained at this date but it was well positioned for polar bears to get ashore:

Sea ice extent Canada 2014 July 14 CIS

In 2013, there was less ice remaining at this date than this year (and it was less concentrated) but it was positioned similarly, making it easy for Western Hudson Bay and Southern Hudson Bay bears to reach the shore:

Sea ice extent Canada_2013 July 16_CIS

References
Cherry, S.G., Derocher, A.E., and Lunn, N.J. 2016. Habitat-mediated timing of migration in polar bears: an individual perspective. Ecology and Evolution. DOI 10.1002/ece3.2233 Open access. http://onlinelibrary.wiley.com/doi/10.1002/ece3.2233/full

Pongracz, J.D. and Derocher, A.E. 2016. Summer refugia of polar bears (Ursus maritimus) in the southern Beaufort Sea. Polar Biology. 08 July 2016
DOI 10.1007/s00300-016-1997-8 http://link.springer.com/article/10.1007/s00300-016-1997-8

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