Due to the atypical pattern of sea ice melt on Hudson Bay this year, 2015 will definitely be a later than average breakup year – perhaps not as late as 1992 but maybe almost as late as 2009. Easing into the first days of Arctic summer, there is still a lot of polar bear habitat left on Hudson Bay, especially in the east.
Although official breakup in 2009 was only a little later than usual (9 July), bears came ashore about the same time (after mid-August) as they did in 1992, when breakup was very late (30 July). With the pattern this year being so unusual (and the melt so slow over the last few weeks), who knows how late it could be before the last bears leave the ice in 2015?
There is definitely more sea ice this year on the bay than there was last year, when breakup was about average for the last 24 years.
UPDATE 2 July 2015: CIS weekly ice coverage graphs added to the end of this post. Hudson Bay ice highest since 2009 and Davis Strait highest since 1994! Have a look.
I didn’t talk much about Hudson Bay breakup last year because I was traveling overseas. However, official breakup occurred around 1 July (using the new, 30% method), with most bears onshore about 2-3 weeks after (Cherry et al. 2013).
On 6 July 2014, Polar Bears International provided a tracking map for 30 June 2014 (copied in Fig. 1 above), and asked Andrew Derocher’s University of Alberta graduate student Alysa McCall (McCall et al. 2015) to comment on breakup conditions for 2014:
“So far, the ice is melting about on track,” says McCall, “with most of the open water around the west coast of Hudson Bay.”
None of the collared bears have come ashore yet, the scientist says. Her advice on bears to follow: “Bears R and G are still pretty far out on the ice and will be especially interesting to watch.” [my bold]
Note that two bears on the 30 June 2014 map (Fig. 1) were out in the middle of the bay – some bears actually move around quite a bit, although others are more restrained in their movements (Parks et al. 2006; see also previous post).
At least three of McCall’s subjects last year appeared to be in open water – an example of the famous “20% of collared bears on ice that doesn’t exist” phenomenon (see previous post here).
A couple of days later (8 July 2014), PBI posted a tracking/sea ice map at 8 July and commented:
“The map below from scientist Alysa McCall at the University of Alberta shows that one polar bear from each population is now on land (Bear I for the Western Hudson Bay population, Bear F for Southern Hudson Bay). Bear I is on the coast just north of Churchill.
McCall says that the ice is breaking up rapidly now, so by next week more polar bears will probably be onshore.
The only collared bear still far out on the bay is Bear R. “She has quite a distance to travel to reach land if that’s where she actually is,” says McCall. “We might be looking at a dropped collar.” [my bold]
This year it’s a whole new ball game.
Compare ice coverage this year and last (in Fig. 1), to 30 June 2013 (Fig. 2, below). There was much more open water in the east in 2013 but less in the west. Breakup in 2013 was later than average.
Sea ice coverage on Hudson Bay, according to NSIDC (Fig. 3), is the highest it’s been at this date for the last 5 years at least (they only show five years).
Melt proceeded rapidly after 30 June last year (Fig. 4) – but notice how many bears appear to be on the remnant ice at 8 July, even though it doesn’t look like there’s much present.
And as is usual for this date – the official last day of Arctic spring – there is still sea ice present in every one of the 19 subpopulation regions (Fig. 7), with at least 30-40% concentration – even on Hudson Bay (Fig. 5).
Virtually all of this ice is estimated to be greater than 30 cm thick (Fig. 6), which is plenty thick enough to support a full grown male polar bear. Work on polar bears in the Canadian Arctic around Baffin Bay (Ferugson et al. 2000) has shown that the bears routinely hunt on ‘young ice’ (0.1-0.3m), and there’s no reason to assume they would not use melting ice of similar thickness as well.
UPDATE 2 July 2015:
Hudson Bay ice is still above 50% coverage this week (Fig. 8), the highest it’s been at this date since 2009 and about what it was in 1971 (except there has seldom, if ever, been so much ice in the east as there is this year):
Foxe Basin, which includes bears in the northern half of Hudson Bay, has average coverage this week (Fig. 9), which is still much higher than 1968 levels:
And finally, ice in the northern half of Davis Strait (Fig. 10) is well above average this week and the highest it’s been since 1994 (and higher than 1971)!
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.
Ferguson, S. H., Taylor, M. K., and F. Messier 2000. Influence of sea ice dynamics on habitat selection by polar bears. Ecology 81:761-772. http://www.esajournals.org/doi/abs/10.1890/0012-9658%282000%29081%5B0761%3AIOSIDO%5D2.0.CO%3B2
McCall, A.G., Derocher, A.E., and Lunn, N.J. 2015 in press. Home range distribution of polar bears in western Hudson Bay. Polar Biology. DOI 10.1007/s00300-014-1590-y
Parks, E.K., Derocher, A.E., Lunn, N.J. 2006. Seasonal and annual movement patterns of polar bears on the sea ice of Hudson Bay. Canadian Journal of Zoology 84:1281–1294.
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