Polar bear habitat in the eastern Bering Sea has expanded since the official spring “maximum extent” was called for late February, and Davis Strait sea ice is tied for 2nd highest since 1971 for this week. Both regions have healthy polar bear populations and spring conditions suggest this will continue into this year.
Although the melt season is underway, as of yesterday (22 April, Julian day 112) overall Arctic sea ice extent (Fig. 1) was higher than it was on the same date in 2014, 2007, and 2004 (see also Fig. 2). Despite the record low extent in February (Fig. 3), that pessimists at Polar Bears International suggested was relevant to polar bear heath and survival, I showed that was misleading.
Sea ice maps and charts tell the story of current polar bear habitat throughout the Arctic.
Following up from last week’s sea ice update, it’s worth noting that Bering Sea ice (which is naturally quite variable) often does not reach its maximum extent until late April, a month or so after the Arctic as a whole is at its maximum extent in late March. That means plenty of ice for the next month or so in the Bering Sea, from which Chukchi Sea polar bears can hunt baby seals. After that, in June and perhaps part of July, the sea ice feeding platform will be over the Chukchi Sea proper. Fattening up time for Chukchi Sea polar bears.
Fat polar bears will be well-equipped for a few months of fasting over the coming summer, whether they are on land or on the ice. The last report on Chukchi Sea polar bears captured in early spring (mid-March to mid-May), where polar bears are known to “occasionally occupy ice as low as 15% concentration” (Rode et al. 2014:79), showed they were some of the fattest bears in the Arctic and reproducing well (Rode et al. 2013, 2014; Rode and Regehr 2010). These characteristics are accepted indicators of a healthy population — Chukchi bears were doing better in 2011 than they were doing in the 1980s.
The researchers got this result despite the marked decline in extent of summer sea ice in the Chukchi Sea in 2011 compared to 1986 (which included the 2nd lowest (2007) extent since 1979), and in marked contrast to the expectation that the bears would be found to have “reduced body condition” and “decreased reproduction and/or cub survival” as a result (Rode et al. 2013).
As I commented two years ago:
“It’s certainly going to be hard to make a case that polar bears are starving and dying because of global warming if the bears aren’t starving or dying, but getting fatter instead.”
From the 2010 interim report by the study’s investigators (Rode and Regehr 2010:4):
“…three adult males weighed over 1200 lbs and the heaviest bear was 1353 lbs, which is a record for spring research in Alaska.”
So much for summer ice extent being the critical indicator of polar bear health in the Chukchi Sea!
Over in Davis Strait, 2015 is tied for 2nd highest extent for this week (along with 1983 and 1993) – last year (2014) was the highest. The long-term trend since 1971 calculated by the Canadian Ice Service for ice coverage this week in Davis Strait is increasing (Fig. 4, below).
For the Canadian East Coast as a region, ice is well above average for this date (note the quasi-decadal undulating pattern since 1969, from above average to below and back, although this has not been quite so pronounced since the early 2000s):
Sea ice is still below average in the Barents Sea (below) due to the state of the cyclical Atlantic Multidecal Oscillation (AMO), but there is still quite a bit of ice for polar bears to use as a platform for hunting seals.
Rode, K.D., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2013. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Oral presentation by Karyn Rode, 28th Lowell Wakefield Fisheries Symposium, March 26-29. Anchorage, AK. Abstract below, pdf here.
Rode, K.D., Regehr, E.V., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2014 [in print]. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20(1):76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract
Rode, K. and Regehr, E.V. 2010. Polar bear research in the Chukchi and Bering Seas: A synopsis of 2010 field work. Unpublished report to the US Fish and Wildlife Service, Department of the Interior, Anchorage. pdf here.
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