Amid crying over low Arctic ice, W Hudson Bay polar bears leave ice as late as 2009

Reposted from Dr. Susan Crockford’s Polar Bear Science

Posted on August 27, 2020 |

Amid crying over low Arctic ice, W Hudson Bay polar bears leave ice as late as 2009

This year, the last collared Western Hudson Bay polar bear to leave the ice left as late, or later, than the last collared bear did in 2009 (which was an unusually late breakup year) and so far, all bears spotted have been in good physical condition despite inhabiting one of the most southern regions of the Arctic. All the while, sea ice experts have been hand-wringing about low Arctic sea ice –– in general and as polar bear habitat.Polar bear Cape East 0 Wakusp NP _24 Aug 2020 earlierPolar bear Cape East 0 Wakusp NP _24 Aug 2020 earlier

A female with two yearling cubs on the shore of Wakusp National Park, Western Hudson Bay on 24 August 2020. Taken via livecam from almost a mile away.

By the third week of August this year, there was only a small patch of ice evident off Churchill in Western Hudson Bay, see below:

Hudson Bay weekly stage of development 2020 Aug 17Hudson Bay weekly stage of development 2020 Aug 17

However, at least one bear with a satellite tracking collar stayed on that bit of ice until about 21 August, see tracking map below provided by Andrew Derocher, University of Alberta:

Derocher 2020 WHB tracking map 21 Aug_last bear ashore north of ChurchillDerocher 2020 WHB tracking map 21 Aug_last bear ashore north of Churchill

Said Derocher (22 August 2020) about the late date breakup and delays coming ashore: “One good year doesn’t help the population much but it’s better than a bad year.” Except he said something similar last year after admitting conditions had been good and like the 1980s, which he now seems to have forgotten. As of this summer, WH polar bears have now had six good years by any unbiased measure of the concept: ‘one good year’, year after year.

2020 vs. 2009

The last time that polar bears in Western Hudson Bay came off the ice so late in the summer was in 2009. Breakup of sea ice on Western Hudson Bay was unusually late and bears accordingly came ashore much later than the previous two decades – but even still, as far as I can tell from the published data (Cherry et al. 2013; Castro de la Guardia et al. 2017), the last collared bear came off the ice in 2009 on about August 19 or 20 (Day 231 or 232). Derocher announced his last bear came ashore on or about 21 August in 2020.

Hudson Bay weekly stage of development 2009_Aug 17Hudson Bay weekly stage of development 2009_Aug 17

Condition of bears

Below is a video taken from a distance by one of the livecams on the shore of Wakusp National Park southeast of Churchill in Western Hudson Bay on 24 August 2020. This female with two cubs in good condition (the same group as in the still shot above) got spooked by something – probably a male bear approaching – and took off at a run across the tundra. But watch which of the three bears was first to notice something was up.

On 26 August, along the same stretch of shoreline, a solitary fat bear wandered by:

Polar bear fat Cape East Wakusp NP _26 Aug 2020Polar bear fat Cape East Wakusp NP _26 Aug 2020

Polar Bear Alert Program Weekly Reports

Oddly, there has still been no first report of the season from the polar bear alert program. On Tuesday (25 August), I phoned Manitoba Conservation and the person I talked to said conservation officers had only just been sent out to Churchill this week. He didn’t say if this was a Covid-19 delay or whether there had been no need until now. However, it does suggest we won’t see a report until next week with some kind of assessment of how the bears are doing.

Arctic sea ice

Just to balance the above, it is certainly true that sea ice cover over the Arctic is near its yearly low. However, there is still quite a lot of ice left at 27 August 2020:

masie_all_zoom_4km 2020 August 25masie_all_zoom_4km 2020 August 25

Keep in mind when you hear all the ‘sky is falling’ rhetoric that sea ice returns in the fall, as it did even after the lowest and second-lowest summer ice extents since 1979 (in 2012 and 2007/2016, respectively), see ice cover below at 15 November 2016, two months after a low at 15 September.

masie_all_zoom_4km 2016 Nov 15masie_all_zoom_4km 2016 Nov 15

During this time of ice retreat, most bears endure a 4-5 month fast whether they are onshore or spend the summer on the remaining ice. But that’s OK, because all polar bears can survive and even thrive with a summer fast of 4-5 months as long as they get enough to eat during the spring (Crockford 2017, 2019).

References

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/

Cherry, S.G., Derocher, A.E., Thiemann, G.W., Lunn, N.J. 2013. Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics. Journal of Animal Ecology 82:912-921. http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12050/abstract

Crockford, S.J. 2017. Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus). PeerJ Preprints 19 January 2017. Doi: 10.7287/peerj.preprints.2737v1 Open access. https://peerj.com/preprints/2737/

Crockford, S.J. 2019. The Polar Bear Catastrophe That Never Happened. Global Warming Policy Foundation, London. Available in paperback and ebook formats.

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August 28, 2020 at 12:50PM

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