Polar bear specialist Andrew Derocher reported that two of his 23 tagged polar bears were still on the sea ice, a phenomenon that’s been happening since at least 2015 at breakup. Instead of heading to shore when the sea ice concentration dwindles below 50% coverage, some bears are choosing to lounge around on decaying bits of ice, sometimes into late July or well into August, until they must finally swim ashore. There is no evidence that the bears continue to successfully hunt seals under these conditions but no evidence either that their choice to stay on the ice rather than move to land at this time of year has had any negative impact on their health or survival.
Posted onAugust 9, 2020|Comments Off on Many W Hudson Bay polar bears still offshore at 7 August despite apparent low ice levels
Contrary to all expert expectations, five female polar bears (45%) out of eleven that had tracking collars attached last year were still out on the sea ice that’s lingering along the western shore of Hudson Bay as of 7 August. And if five collared bears are out there, then there are almost certainly many more without collars doing the same thing. This pattern of bears staying out on the ice long after the so-called ‘critical threshold’ of 50% concentration has passed has been going on since at least 2015 and many bears on tracking maps in July and August appear to be on ice that doesn’t exist.
There are two explanations for this pattern and both are likely true: 1) much more ice actually exists on Hudson Bay than satellites can detect and 2) polar bear experts are wrong that Western Hudson Bay polar bears head to land soon after sea ice concentration drops below 50%. Models that predict a catastrophic future for Western Hudson Bay polar bears (Castro de la Guardia et al. 2013; Molnar et al. 2020) assume that ice coverage of less than 50% in summer greatly reduces polar bear survival. However, if polar bears do not always head to land when sea ice drops below 50% then the models cannot possibly describe their future accurately. In other words, depending on the discredited ‘worst case’ RCP8.5 climate scenario for the most recent polar bear survival model that extrapolates from Western Hudson Bay bear data to many other subpopulations, as I discussed previously, may not be its only fault.