Again this year – contrary to predictions – there has been no early breakup of the sea ice on Hudson Bay and even though it’s the height of summer, there is plenty of ice throughout the Arctic to act as a feeding platform for polar bears. This makes it unlikely there will be a longer-than-average summer fast for polar bears again this year.
Figure 1. NSIDC MASIE map for June 21, 2014.
Sea ice maps around the Arctic for June 21 (and June 24, for Hudson Bay) reviewed and discussed below in relation to polar bear habitat — have a look.
Spring through early summer is the critical feeding time for polar bears, regardless of where they live (see previous discussion, with references, here). During these months (February through June), the bears gorge on young fat seal pups to see them through leaner times later in the year – whether late summer ice-free period or mid-winter darkness.
Figure 2. Female and cubs feeding on the ice. USGS photo.
It’s a messy business, being a carnivore – especially for an all-white bear (Fig. 1). Polar bears would not be nearly so photogenic if they weren’t so fastidious about cleanliness, washing themselves off both during and after each meal.
Take a look at the various ice maps below. The only area where the ice is lower than usual for this time of year (to an extent that might affect polar bears) is around Svalbard in the Barents Sea region, conceded by sea ice specialists to be largely a natural phenomenon.
[Recall the claim that polar bear females around Svalbard in the Barents Sea population had ‘suffered’ a dramatic drop in cub production this year? It turns out, the bears being tracked may just have gone elsewhere, a possibility that Norwegian biologist Jon Aars conceded in an interview published at Polar Bears International (May 30, 2014), but did not come out in mainstream media report:
“Aars emphasized that the survey did not conclude whether the drop in birth rate was because bears denned elsewhere, or if the population’s reproductive rate suffered after several low ice years.” [my bold]
In other words, many of the females Aars was tracking may simply have made their dens elsewhere and produced cubs as usual. The careful wording of these statements is a red-flag – Aars never did say (in any interview I read) how many of his 29 females failed to return to their traditional den site, he just said how many cubs were counted. The possibility of females denning elsewhere is not surprising – see the post I wrote in April about a WWF report suggesting bears in the Svalbard region were adapting to changing fall ice conditions by moving from their traditional denning areas.]
Figure 3. NSIDC sea ice extent at June 21, 2014 (a “MASIE” product), close-up of the Barents Sea region (Svalbard is the large island group in the center of this image, with the Franz Josef Land island group above). Click to enlarge.
Figure 4. NSIDC sea ice extent at June 21, 2014 (a “MASIE” product), close-up of the Bering, Chukchi and Beaufort Seas, labels added. Note there is still ice around Wrangel Island (an important polar bear denning area) and lots of ice off the coast of Alaska. Bears in this area of the Arctic generally stay on the ice as it retreats – only a small percentage of bears spend the ice-free period on land. Click to enlarge.
Figure 5. NSIDC sea ice extent at June 21, 2014 (a “MASIE” product), close-up of Hudson Bay. See additional maps below for more detail. Click to enlarge.
Hudson Bay ice coverage is relatively high again this year, for this date – see the Canadian Ice Service maps below for 2014 compared to 2013 and 2012. Click to enlarge them.
Figure 6. Hudson Bay ice coverage at June 21, 2014. Canadian Ice Service.
Figure 7. Hudson Bay ice coverage at June 20, 2013. Canadian Ice Service.
Figure 8. Hudson Bay ice coverage at June 20, 2012. Canadian Ice Service.
Also, below is today’s Hudson Bay map. Note that a peculiarity of ice melt in the bay is that the last of the ice to disappear is along the southwest shore.
Figure 9. Hudson Bay ice coverage at June 24, 2014. Canadian Ice Service.
Click to enlarge.
As the earliest date that Western Hudson Bay was reduced to 30% ice coverage between 1991 and 2009 was June 17 (in 1999, see detailed discussion here and Table 1 below), we are well past the point of an early breakup, since well over 50% ice remains today (to my eye, anyway).
As polar bears in Western Hudson Bay have been shown to leave the ice about one month (average 28.3 days) after the ice declines to 30%, it suggests their summer fast this year will not start until late July or after.
See the Western Hudson Bay breakup date table copied below, from that March 21, 2013 post.
Table 1. Breakup dates for Western Hudson Bay 1991 to 2009, as defined by Cherry et al. 2013. Details in previous post here.
In other words, unless the ice melts very rapidly within the next couple of days, there will be no earlier-than-average breakup for Western Hudson Bay again this year and unless freeze-up this fall is very late (which it hasn’t been for years), polar bears of Western Hudson Bay will not endure a longer-than-average summer fast. And given the conditions elsewhere, it seems likely the same will be true for polar bears throughout the Arctic.
References
Cherry, S.G., Derocher, A.E., Thiemann, G.W., Lunn, N.J. 2013. Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics. Journal of Animal Ecology 82(4):912-921.
http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12050/abstract
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