Reposted by Polar Bear Science
Published on November 3, 2020
This will be one of the shortest ice-free seasons for polar bears in western and southern Hudson Bay in at least 20 years.
Hudson Bay Sea Ice on November 2, 2020. NSIDC Masie card.
Last week, sea ice began to form on the shores of Hudson Bay, from the north end to south into James Bay. So far, the near-coast ice that has formed is only a narrow strip along the coast, but it is thickening and widening from day to day. So unless things change dramatically, by the end of the week the bears should all be on the ice, an exodus from the coast that hasn't happened so early in WH since 1993 (1979 at the earliest).
The last polar bear marked with WH did not leave the ice until August 21st this year. So if he's on the ice by the end of this week, he's only spent 11 weeks on land – less than 3 months. Even the first bears to come ashore in mid-July only spent around 16 weeks on land – at least a month less than a decade ago (Stirling and Derocher 2012). Four months on land was the historical average for Western Hudson Bay bears in the 1970s and 1980s (Stirling et al. 1977, 1999). This year, most polar bears will only have spent about 13 to 14 weeks on land since they didn't come ashore until early August.
Freezing dates since 1979
I use a definition of "freezing" that describes the behavior of polar bears towards newly formed ice, not the date when ice cover in the bay reaches 50% in autumn (e.g. Lunn et al. 2016). According to a recalculation of the WH data, which go back to 2015 and 1979 (Castro de la Guardia 2017, see graphic below), the bears left for the ice in the 1980s around November 16 when freezing (10% sea ice cover) ± 5 days. The bears left the ice on November 6th (Julian Day 310) at the earliest, in 1991 and 1993.
The first week of November is very early for bears entering the ice.
Figure 3 from Castro de la Guardia (2017) shows the freeze and dissolution dates as well as ice-free days 1979-2015 for Western Hudson Bay and shows that the earliest freeze dates since 1979 (top panel) were on November 6th, day 310 ( 1991 and 1993).
Therefore, the November 10-12 (days 314-316) freeze dates for 2017, 2018, and 2019 are among the earliest recorded freeze dates since 1979 (the earliest is November 6th, day 310, 1991 and 1993), even earlier than the 1980s average. And 2020 is even earlier.
Almost all bears in western Hudson Bay leave the shore within about 2 days after sea ice concentrations reach 10% (Castro de la Guardia 2017), although bears in southern Hudson Bay leave the coast when they reach around 5% . In other words, the bears are going as fast as they possibly can. As I discussed in 2016 relating to newly published studies (Obbard et al. 2015, 2016) on the status of bears in Southern Hudson Bay (SH):
“… SH polar bears left the ice (or returned to it) when the average ice cover near the coast was about 5%. This finding is further evidence that the meteorological definition of “break-up” (date of 50% ice cover) used by many researchers (see discussion here) is unsuitable for describing the seasonal movements of polar bears on and off the coast. "
The earliest freeze date for Southern Hudson Bay appears to be November 11th (Julian Day 315), based on dates in a 2016 article by Obbard and colleagues. Hence, the freeze is early for these bears as well.
While this is the best of six very good years for the polar bears in western Hudson Bay, activist polar bear scientists continue to sell the public their false message of doom based on data from years ago. As mentioned earlier, polar bear data from western Hudson Bay was used those good years ago (i.e. only through 2009) for the latest model (Molnar et al. 2020) to predict future conditions for polar bears in other parts of the Arctic. Those good years for sea ice and bears were simply ignored in long-term projections.
Hide the good news
The polar bear biologist Derocher recently said that the timing of sea ice formation this year was "normal":
Yesterday's satellite image shows little ice near Rankin Inlet. It's -11 ° C, so ice should be forming soon. The timing is about normal. The first ice forms in NW Hudson Bay. The ice moves southward along the coast east of Churchill in wind and south, where many polar bears wait. https://t.co/EQH390707H pic.twitter.com/vbWnbT0p0c – Andrew Derocher (@AEDerocher) October 28, 2020
However, Canadian Ice Service maps indicate otherwise.
In the Deviation From Normal table for the week of November 2, 2020, sea ice formation along the entire west coast of Hudson Bay is below “greater than normal” and “much greater than normal” (blue and dark blue). Only the northern parts are a bit smaller than normal (pink):
The day passes for Hudson Bay North and South for November 3rd are listed below: Dark purple areas ("gray ice") were light purple ("new" ice) the day before:
WH polar bears and sea ice photos
The same triplet litter was likely seen again on October 31st that was spotted in September while making his way to the ice. How many of these triplet litters are there? They are rarely seen today, although they used to be common. The last one before was photographed north of Churchill in 2017. Although these large litters are rarer today than they used to be, they have not disappeared. In other regions, triplet bedding is an indicator of a healthy population.
Mom with triplet boys, Oct 31, 2020. Dave Allcorn photo.
All the bears hanging around waiting for the sea ice were fat and healthy (e.g. below).
Three Fat Bears, October 31, 2020. Wakusp National Park.
On Saturday, a mother polar bear went on the ice with two cubs and caught a seal (below).
Polar bears kill seals, October 31, 2020. Wakusp National Park.
Mother with two boys, sea ice in the background. Wakusp National Park, November 3, 2020.
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's perspective. Marine Ecology Progress Series 564: 225-233. http://www.int-res.com/abstracts/meps/v564/p225-233/
Lunn, N.J., Servanty, S., Regehr, E.V., Converse, S.J., Richardson, E. and Stirling, I. 2016. Demographics of an Apex Predator at the Edge of Its Range – Effects of Changing Sea Ice on Polar Bears in Hudson Bay. Ecological Applications 26 (5): 1302-1302. 1320. DOI: 10.1890 / 15-1256
Molnár, P.K., Bitz, C.M., Holland, M.M., Kay, J.E., Penk, S.R. and Amstrup, S.C. 2020. The length of Lent sets time limits for the global persistence of polar bears. Nature climate change. https://doi.org/10.1038/s41558-020-0818-9
Obbard, M. E., Stapleton, S., Middel, K. R., Thibault, I., Brodeur, V. and Jutras, C. 2015. Estimation of the frequency of polar bear subpopulation in southern Hudson Bay based on aerial photographs. Polar Biology 38: 1713- 1725.
Obbard, M.E., Catt, M.R.I., Howe, E.J., Middel, K.R., Newton, E.J., Kolenosky, G.B., Abraham, K.F. and Greenwood, C. J. 2016. Body condition trends in polar bears (Ursus maritimus) from the Southern Hudson Bay subpopulation in relation to changes in sea ice. Arctic Science 2: 15-32. DOI: 10.1139 / AS-2015-0027
Stirling, I. and Derocher, A. E. 2012. Global Warming Effects on Polar Bears: A Review of the Evidence. Global Change Biology 18:2694-2706. doi: 10.1111 / j.1365-2486.2012.02753.x
Stirling I, Jonkel C., Smith P., Robertson R., Cross D. 1977. The ecology of the polar bear (Ursus maritimus) along the west coast of Hudson Bay. Canadian Wildlife Service Occasional Paper No. 33. pdf here.
Stirling, I., Lunn, N. J. and Iacozza, J. 1999. Long-term trends in polar bear population ecology in Western Hudson Bay related to climate change. Arctic 52:294-306. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/935/960