A tundra grizzly was again caught on the live cam set up for polar bears last week (15 August) but was too late for interspecies hankypanky, even as some polar bears lingered on invisible offshore sea ice.
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.
Video below taken by Explore.org webcam set up on the shore of Wapusk National Park south of Churchill on 15 August 2022, which may be the same bear spotted in late May. Any polar bears are well past breeding by this time, so there are no hybridization possibilities, even though polar bears had been spotted in this area just days before. Note that grizzlies spotted along the shore of Hudson Bay since 2008 have moved south from Nunavut.
The chart of tagged and collared polar bears at 17 August, showing two bears on ice that does not appear to exist (note that if these tagged bears are still on this ice, there are almost certainly other bears there as well):
A better sea ice chart for the week of 15 August 2022, showing remnant thick ice:
Canada Ice Services tells us this is much more ice than average for this date:
As I said in 2020 when similar conditions occurred in August:
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.
For at least the last five years now Western Hudson Bay polar bears have stayed out on melting summer ice when it was well below 50% concentration; the same phenomenon of bears tracking to what looks like open water has also shown up for Southern Beaufort bears.
“4 W Hudson Bay polar bears ashore. Amazing how long they’re staying offshore as ice this low would usually have them all on land. So many still on the ice suggests a behaviour shift (i.e., behavioural plasticity). The @ualbertaScience polar bear crew is studying this.”
Only recently, however, are Derocher and his colleagues giving any thought to the possibility that polar bears might not have rigid responses to changing sea ice conditions. Before this, polar bear experts looked at the sea ice conditions in the 1980s and figured that was what polar bears absolutely required (Amstrup et al. 2007; Castro de la Guardia et al. 2013, 2017; Durner et al. 2007; Stirling et al. 1999): they apparently never considered the possibility that the bears could do perfectly well with less.
Amstrup, S.C., Marcot, B.G. & Douglas, D.C. 2007. Forecasting the rangewide status of polar bears at selected times in the 21st century. US Geological Survey. Reston, VA. Pdf here
Castro de la Guardia, L., Derocher, A.E., Myers, P.G., Terwisscha van Scheltinga, A.D. and Lunn, N.J. 2013. Future sea ice conditions in Western Hudson Bay and consequences for polar bears in the 21st century. Global Change Biology 19:2675–2687. doi: 10.1111/gcb.12272
Castro de la Guardia, L., Myers, P.G., Derocher, A.E., Lunn, N.J., Terwisscha van Scheltinga, A.D. 2017. Sea ice cycle in western Hudson Bay, Canada, from a polar bear perspective. Marine Ecology Progress Series 564: 225–233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Durner, G.M., Douglas, D.C., Nielson, R.M., Amstrup, S.C. and McDonald, T.L. 2007. Predicting 21st-century polar bear habitat distribution from global climate models. US Geological Survey. Reston, Virginia. Pdf here.
Molnár, P.K., Bitz, C.M., Holland, M.M., Kay, J.E., Penk, S.R. and Amstrup, S.C. 2020. Fasting season length sets temporal limits for global polar bear persistence. Nature Climate Change. https://doi.org/10.1038/s41558-020-0818-9
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 [open access]
August 21, 2022 at 07:22PM