Western Hudson Bay polar bears have been leaving shore for the rapidly thickening sea ice since at least 8 November (bear above was heading out 10 Nov.). However, Polar Bears International chose not to mention the unusually early freeze-up until the week-long (5-11 November) doomsday bombardment they call “Polar Bear Week” was almost over.
It’s worse than that: two days earlier, PBI’s activist spokesperson Steven Amstrup apparently told the Sierra Club (“People Show Up for Polar Bear Week, But the Ice Hasn’t Yet”; 8 November 2017) that “the bears are still waiting on shore for that ice to freeze” even though ice development had been well on its way for days at that point. As if freeze-up on 10 November came as a big surprise to him, with no warning whatsoever.
Apparently, they didn’t want their naive and gullible supporters to know at the beginning of Polar Bear Week that the sea ice loss of which PBI spokespeople rant about constantly (Save Our Sea Ice) was a total non-issue this year: breakup was not earlier than usual and new ice began developing off Churchill at about the same time it did in the 1980s (last week of October).
As I discussed last year regarding a newly-published studies (Obbard et al. 2015, 2016) on the status of Southern Hudson Bay (SHB) bears:
“…SHB polar bears left the ice (or returned to it) when the average ice cover near the coast was about 5%. This finding is yet more evidence that the meteorological definition of “breakup” (date of 50% ice cover) used by many researchers (see discussion here) is not appropriate for describing the seasonal movements of polar bears on and off shore.”
That post (with its list of references) is worth another look for its discussion of the following points: the definition of freeze-up; the relationship of official freeze-up and breakup dates to the dates that bears depart; the overall health and survival of Western and Southern Hudson Bay polar bears.
Below I dissect the misinformation that PBI calls “science communication” in their attempt to minimize the damage caused by this early freeze-up to their message of looming catastrophe for polar bears.
Bottom line: Not only was freeze-up early this year, 2017 will go down as one of the earliest WHB freeze-up years since 1979 and for Southern Hudson Bay bears as well, since as of 13 November there is concentrated ice all the way into James Bay.
“Polar Bears Returning to the Ice” (10 November 2017), the day before the end of Polar Bear Week:
“We’re cautiously optimistic that the bay will freeze earlier than last year’s very delayed freeze-up, giving the bears the first good start they’ve had in quite a few years.”
But they go on to add (my bold):
“But does this mean we no longer need to worry about the Western Hudson Bay polar bears? York said that it’s important to look at this year’s freeze-up within the context of natural variation and long-term trends.
Last year at the same time, for example, the bears looked out to an ice-free bay and the tundra was only lightly dusted with snow. Freeze-up didn’t occur until late December, prolonging the fasting period for the population.
While this year’s closer to average freeze-up is good news for the Western Hudson Bay bears, it’s part of natural, year-to-year variation, as the chart below shows.”
The chart they show? A graph of Arctic sea ice extent for October, as if freeze-up of Hudson Bay was a proven proxy of that metric (which it clearly is not): ice levels in 2012 were the lowest since 1979 yet 2012 was not an especially late freeze-up year (Castro de la Guardia 2017, Fig. 3 copied below).
In the PBI missive, York also deliberately conflates freeze-up date with the date that bears left the ice to resume hunting in 2016. This leaves readers who don’t know the difference to assume that bears did not leave shore until late December, which couldn’t be further from the truth. Bears left the end of the first week in December in 2016, no later than in other late freeze-up years (such as 1998 and 2010: see graph below from Cherry et al. 2013, where Day 340 is December 6).
Below, Hudson Bay sea ice coverage for the week of 26 November, 1971-2016 (CIS) shows that 1971 and 1981 were also years of late freeze-up along the coast of western Hudson Bay (although some years known to have had late freeze-up (e.g. 1983, Ramsay and Stirling 1988) show higher values than expected, likely reflecting ice coverage in the northern portion of the bay rather than along the west coast near Churchill):
It’s interesting to note that while freeze-up was late in 2016 (a warm El Niño year similar to 1998), 1999 was also a relatively late freeze-up year (as late as 1983, see Lunn et al. 2016, not shown, and Castro de la Guardia 2017, see below), but 2017 was not.
Remember, however, that the relative change in the dates that bears left the shore between the 1980s and recent years is only about 1 week, on average (with lots of variation).
Western Hudson Bay bears leave the shore within about 2 days of sea ice concentration reaching 10% (Castro de la Guardia 2017; Cherry et al. 2013), although as noted above, Southern Hudson Bay bears leave when it reaches about 5%: in other words, the bears go as soon as they possibly can.
This year, there was enough ice by 8 November for many bears to leave shore and by 10 November (see ice chart below), most bears were on their way (first photo in this post). Remember that females with cubs are almost alway the last to leave.
According to a recalculation of data that goes up to 2015 and back to 1979 (Castro de la Guardia 2017), in the 1980s bears left the ice at freeze-up (10% sea ice coverage in WHB) about 16 November ± 5 days while in recent years (2004-2008) they left about 24 November ± 8 days, a difference of 8 days.
This also means that a freeze-up date of 10-12 November (Day 314-316) this year is not “closer to average” — as the PBI story states — it’s one of the earliest freeze-up dates since 1979 (the earliest being 6 November, Day 310), see Fig 3 from Castro de la Guardia 2017 below.
Polar bear guide Kelsey Eliasson, on the ground near Churchill, noted yesterday (12 November) that virtually all bears had already left for the ice (see first comment).
A final note: if PBI spokesperson Amstrup had been right about his predictions of Arctic sea ice and polar bear survival back in 2007 when he was the head of the US Geological Survey’s polar bear research team, there would be no polar bears at all in Hudson Bay right now (Crockford 2017), not a thriving population of fat, healthy bears.
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://ift.tt/2lruEp5
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://ift.tt/ZcUKVG
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. http://ift.tt/2jB2S8i
Lunn, N.J., Servanty, S., Regehr, E.V., Converse, S.J., Richardson, E. and Stirling, I. 2016. Demography of an apex predator at the edge of its range – impacts of changing sea ice on polar bears in Hudson Bay. Ecological Applications, in press. DOI: 10.1890/15-1256
Obbard, M.E., Stapleton, S., Middel, K.R., Thibault, I., Brodeur, V. and Jutras, C. 2015. Estimating the abundance of the Southern Hudson Bay polar bear subpopulation with aerial surveys. Polar Biology 38:1713-1725.
Obbard, M.E., Cattet, M.R.I., Howe, E.J., Middel, K.R., Newton, E.J., Kolenosky, G.B., Abraham, K.F. and Greenwood, C.J. 2016. Trends in body condition in polar bears (Ursus maritimus) from the Southern Hudson Bay subpopulation in relation to changes in sea ice. Arctic Science, in press. 10.1139/AS-2015-0027
Ramsay, M.A. and Stirling, I. 1988. Reproductive biology and ecology of female polar bears (Ursus maritimus). Journal of Zoology London 214:601-624.
November 13, 2017 at 03:11PM