Western Hudson Bay polar bears: still some out on the sea ice, some causing trouble

As of Monday (19 July), more polar bears had come ashore near Churchill and on the shores of Wakusp National Park but some are still out on the bay. The pattern of ice breakup this year means most bears will come ashore well south of Churchill and make their way north over the summer and fall. There have been two Churchill ‘problem’ bear reports so far but not one for this week, so I’ll go ahead and post without it.

Note that the earliest average date ashore for all bears (not the date the first bear hit the beach) for WH bears was 9 June (Julian day 160), which happened in 1999. Hasn’t been that early since, although a few years afterward had most bears ashore at mid-June (2003, 2011) [Day 180 is 29 June]. However, this means that the first bear on the beach at 28 June this year is nowhere close to ‘early.’ From Castro de al. Guardia et al. 2017, which only goes up to 2015, showing that up to that point, the average date bears were ashore was late June-early July (but it’s been later than that since, especially for the last few years):

Three of Andrew Derocher’s six remaining females with collars were ashore on Monday, which leaves three still offshore along with all the other bears that are doing the same thing. The first one came ashore two weeks ago, so there has hardly been a stampede. Notice the two bears that appear to be in open water but is almost certainly ice that the satellites cannot ‘see’ or is <50% concentration:

According to his map, only a bit of ice is left on Hudson Bay. However, even polar bear researchers know that satellites are notoriously bad at getting the amount of ice correct at this time of year and can underestimate ice amounts by up to 50% in Hudson Bay. They are usually forced to acknowledge this in their papers but don’t bother on social media or when talking to reporters. For example, the evidence that Andrew Derocher is fully aware that this is the case comes from one of his student’s papers, on which he is a co-author (Castro de la Guardia et al. 2017:227) [my bold]:

In general, passive microwave derived sea ice data are associated with an underestimation error of up to 30% during breakup and freeze-up throughout the marginal ice zone and seasonal ice regions in the Northern Hemisphere (e.g. Cavalieri et al. 1991, Comiso et al. 1997, Markus & Dokken 2002). In Hudson Bay, passive microwave sea ice concentration can underestimate sea ice concentration by up to 50% compared with CISDA (Agnew & Howell 2003). Underestimation biases of passive microwave data are associated with the presence of wet snow and melt ponds during breakup, and with areas covered by frazil ice and young ice during freeze-up (Agnew & Howell 2003).

In other words, contrary to predictions made by polar bear specialists, some bears are happy to deal with melt ponds and wet snow rather than come ashore, especially on Hudson Bay. This rather plays havoc with the most recent predictive model uses old Hudson Bay data – collected before this propensity to stay late on diminishing ice was fully apparent – to predict a future of extinction for polar bears worldwide (Castro de la Guardia et al. 2013; Molnar et al. 2020). And it means there was likely much more ice on Hudson Bay for the week of 19 July than even the Canadian Ice Service chart below suggests:

It’s looking to me like the average date ashore for WH polar bears in 2021 will come out to be around the first week in July but it might be 10 years or more before we see that data appear in a publication. Funnily enough, some of these researchers seem to have lost their drive to publish data as soon as possible now that it no longer fits their narrative.

Churchill Problem Bear Reports

I notice that this year there are no comments about the condition of the bears causing problems around Churchill (same was true last year). Odd, compared to 2019 and 2017. Perhaps I’m wrong but I expect whoever composes these reports has been advised that informing the public that bears are in excellent condition is ‘unhelpful’.

References

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/

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

via polarbearscience

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July 22, 2021 at 11:30AM

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