Since 1971, there has been no year when there was as much ice left on Hudson Bay as there is this year at August 13th, except 1992 – the year when Mt. Pinatubo seemingly affected Hudson Bay ice levels but not any other region in Eastern Canada or the Beaufort Sea. Odd, that – see the graphs below.
Doesn’t mean that much to polar bears, since they will mostly be fasting whether they are onshore for the summer or riding the ice – they primarily live off their fat this time of year. Still, the relative ice levels are interesting because it could impact freeze-up dates later this fall, which will influence the bears’ ability to hunt before the winter fast sets in.
Hudson Bay “departure from normal” for 10 August 2015 (CIS, click to enlarge):
Ice concentration at 13 August 2015 (CIS):
As I pointed out before:
Not a single one of the research reports on WHB bears, for periods that included 1990, mention that breakup in 1990 was especially early, even though virtually all commented at length about the especially late breakup in 1992 (Derocher and Stirling 1995; Stirling and Lunn 1997; Lunn et al. 1997; Stirling et al. 1999; Stirling et al. 2004; Stirling and Parkinson 2006; Regehr et al. 2007; Stirling and Derocher 2012).
All of the reports cited above blame the late breakup of Hudson Bay ice in 1992 primarily on the Mt. Pinatubo eruption. Interestingly, ice coverage for 1992 doesn’t stand out for any other neighbouring North American region, at least at this point in the season, the way Hudson Bay does in the graph above. See other Canadian Ice Service graphs below, note the start dates may vary (click to enlarge).
Derocher, A.E. and Stirling, I. 1995. Temporal variation in reproduction and body mass of polar bears in western Hudson Bay. Canadian Journal of Zoology 73:1657-1665. http://www.nrcresearchpress.com/doi/abs/10.1139/z95-197#.VYD6pEZmzGs
Lunn, N.J., Stirling, I., Andriashek, D. and Kolenosky, G.B. 1997. Re-estimating the size of the polar bear population in Western Hudson Bay. Arctic 50(3):234-240. Open access. http://arctic.journalhosting.ucalgary.ca/arctic/index.php/arctic/article/view/1105
Regehr, E.V., Lunn, N.J., Amstrup, S.C., and Stirling, I. 2007. Effects of earlier sea ice breakup on survival and population size of polar bears in Western Hudson Bay. Journal of Wildlife Management71: 2673-2683. http://onlinelibrary.wiley.com/doi/10.2193/2006-180/abstract
Stirling, I. and Derocher, A.E. 2012. Effects of climate warming on polar bears: a review of the evidence. Global Change Biology 18:2694-2706 doi:10.1111/j.1365-2486.2012.02753.x
Stirling, I. and Lunn, N.J. 1997. Environmental fluctuations in arctic marine ecosystems as reflected by variability in reproduction of polar bears and ringed seals. In Ecology of Arctic Environments, Woodin, S.J. and Marquiss, M. (eds), pg. 167-181. Blackwell Science, UK.
Stirling, I., Lunn, N.J. and Iacozza, J. 1999. Long-term trends in the population ecology of polar bears in Western Hudson Bay in relation to climate change. Arctic 52:294-306. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/935/960
Stirling, I., Lunn, N.J., Iacozza, J., Elliott, C., and Obbard, M. 2004. Polar bear distribution and abundance on the southwestern Hudson Bay coast during open water season, in relation to population trends and annual ice patterns. Arctic 57:15-26. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/479/509</a
Stirling, I. and Parkinson, C.L. 2006. Possible effects of climate warming on selected populations of polar bears (Ursus maritimus) in the Canadian Arctic. Arctic 59:261-275. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/issue/view/16.