Tag Archives: Arctic

Sea ice is critical habitat for polar bears from late fall through late spring only

Sea ice is said to be “an essential habitat for polar bears” but that’s an overly simplistic advocacy meme as ridiculous as the “no sea ice, no polar bears” message with which the public is constantly bombarded. Polar bears require sea ice from late fall to late spring only: from early summer to mid-fall, sea ice is optional. Historical evidence of polar bears that spent 5 months on land during the summer of 1874 proves an extended stay ashore is a natural response of polar bears to natural summer ice retreat, not a consequence of recent human-caused global warming. Sea ice is a seasonal requirement for polar bears: it’s not necessary year round.


[This PBI newsletter from 2011 repeats this meme and Andrew Derocher’s recent tweet conveys a similar message (“Sea ice loss = habitat loss for polar bears”)]

As long as sea ice is available from late fall through late spring (December to early June) and accompanied by abundant seal prey (sometimes it isn’t, see Derocher and Stirling 1995; Stirling 2002; Stirling et al. 1981, 1982, 1984), polar bears can survive a complete or nearly complete fast from June to late November (and pregnant females from June to early April the following year). That’s the beauty of their Arctic adaptation: fat deposited in early spring allows polar bears to survive an extraordinary fast whether they spend the time on land or sea ice.

Young and very old bears, as well as sick and injured ones, are the exception: these bears often come ashore in poor condition and end up dying of starvation — as a much-publicized bear on Baffin Island who likely had a form of cancer did last summer (Crockford 2018). Competition with bigger, stronger bears means these bears can’t keep what they are able to kill and they are most often the bears who cause problems. Starvation is the leading natural cause of death for polar bears because if they cannot put on the fat they need in spring, they will not survive the low food months of summer and winter, whether they are on land or out on the sea ice (Amstrup 2003). Continue reading

Spring feeding for polar bears is over – sea ice levels are now largely irrelevant

Polar bears in virtually all regions will now have finished their intensive spring feeding, which means sea ice levels are no longer an issue. A few additional seals won’t make much difference to a bear’s condition at this point, except perhaps for young bears that haven’t had a chance to feed as heavily as necessary over the spring due to inexperience or competition.

Polar bear feeding by season simple_Nov 29 2015

The only seals available on the ice for polar bears to hunt in early July through October are predator-savvy adults and subadults. But since the condition of the sea ice makes escape so much easier for the seals to escape, most bears that continue to hunt are unsuccessful – and that’s been true since the 1970s. So much for the public hand-wringing over the loss of summer sea ice on behalf of polar bear survival!

Polar bears in most areas of the Arctic are at their fattest by late June. They are well prepared to go without food for a few months if necessary – a summer fast is normal for polar bears, even for those that spend their time on the sea ice.

Putting on hundreds of pounds of fat in the spring to last through periods of food scarcity later in the year (at the height of summer and over the winter) is the evolutionary adaptation that has allowed polar bears to live successfully in the Arctic.
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At the winter maximum, still about the same polar bear habitat this year as 2006

There is no evidence that slightly less winter sea ice than the average since 1979 has had any negative impact on polar bear health or survival: the difference is simply not biologically meaningful to Arctic animals.

PB_male on ice_Regehr USFWS_March 2010_labeled

Polar bear on winter sea ice around the yearly maximum in the Beaufort Sea, 2010 (March 21).

NASA’s 23 March 2018 announcement regarding the Arctic sea ice maximum this year:

“Sea ice in the Arctic grew to its annual maximum extent last week, and joined 2015, 2016 and 2017 as the four lowest maximum extents on record, according to scientists at the NASA-supported National Snow and Ice Data Center (NSIDC) and NASA.”

Except, what they don’t tell you is that 2006 had almost the same extent as 2018 and 2006 wasn’t far behind according to the official, averaged data presented at NSIDC’s Arctic Sea Ice News & Analysis:

Arctic sea ice Maximum 10 lowest extents_NSIDC 23 March 2018

Current conditions at the winter maximum (at 17 March 2018, from NSIDC Masie, extent measured at 14.7 mkm2, using software able to discern more ice than used for the figures in Table 1), shown below: Continue reading

W Hudson Bay freeze-up one of earliest since 1979, not “closer to average”

Tundra Buggy Cam_10 Nov 2017_bear headed offshore pmWestern 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 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.

Hudson Bay North daily ice stage of development 2017_Nov 10

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.

Sea ice Canada 2017 Nov 13

UPDATE 14 November 2017: CBC Radio broadcasted an interview yesterday with a recent visitor to Churchill who was remarkably candid about what he saw regarding polar bears, sea ice, and what he heard from locals about freeze-up (“the earliest since 1991”). It corroborates what I’ve reported here. Worth a listen (about 8 minutes):

“Brian Keating: Polar bears in Churchill, Manitoba” (The Homestretch, November 13, 2017, Season 2017, Episode 300312418)

The closest Doug Dirks has come to seeing a live polar bear was at the Calgary Zoo many moons ago. But naturalist Brian Keating has just returned from another trip to Churchill, Manitoba. He joined Doug Dirks with the details of that frosty adventure.


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Fat healthy polar bear update: hundreds of not-starving bears attracted to dead whale

Are the hundreds of polar bears spending the summer on Wrangel Island in the Chukchi Sea starving and desperate for any scrap of food? Hardly! Photos taken by Russian tourists on a cruise ship (19 September 2017) show a huge number of already-fat, healthy bears converging on a dead bowhead whale washed up on a beach. Most of these bears would have been without food since at least early August, when the last sea ice disappeared around the island, and will return to the ice by November.

Wrangel Island bears on whale_29 Sept 2017 SUN

This is what The Sun reported (29 September), based on a Siberian Times story (my bold):

The extraordinary sight was witnessed by tourists on an Arctic cruise aboard the Finnish-built MV Akademik Shokalskiy.

A source at Wrangel Island Nature Reserve said: “There were at least 230 polar bears, including single males, single females, mothers with cubs and even two mothers with four cubs each.”

Experts called the sight of so many polar bears together “unique”.

The huge number could in fact amount to as much one per cent of the entire world’s population of the creatures.

Tourists initially thought the bears were a flock of sheep after viewing them from a distance, The Siberian Times reports.

But as the boat drew closer, the lucky holidaymakers realised what they were witnessing.

Fat cubs of the year are seen in the photo below, from the Siberian Times story:

Wrangel Island bears on whale_29 Sept 2017 Siberian TimesA self-proclaimed science-based news site (LiveScience, 29 September) that picked up the story of this unique event had the temerity to suggest the bears might have been “hungrier than usual” due to global warming.

It deliberately conflates predictions of future starving bears due to low sea ice levels with this observation of many obviously not-starving bears checking out an attractive food source (my bold):

“It’s unclear, however, whether climate change had made these particular bears hungrier than usual. The frequency of starving polar bears is expected to increase as the climate warms and sea ice declines — not just because of climate change directly, but because ice loss is taking away seals, their main food source, Steven Amstrup, chief scientist at Polar Bears International, a nonprofit research organization dedicated to studying polar bears, told Live Science in 2015.”

Except that there is no evidence that ice loss is “taking seals away” — certainly not in the Chukchi Sea. Chukchi Sea seals have been found to be doing better with less ice than they were when there was more ice in the 1980s.

More below, including the location of Wrangel Island and sea ice maps.

UPDATE 2 October 2017: Sea ice in the Chukchi Sea has been lower this summer than over the last few years but the polar bears spending the ice-free season on Wrangel Island are still in good to excellent condition:

r02_Chukchi_Sea_ts_4km at 2017 Oct 1

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Late winter polar bear habitat 2017 vs. 2006 and 2011 shows no trend

Here is a bit of historical perspective for rational readers trying to make sense of the doom-mongering of others that current sea ice conditions spell trouble for polar bears, given that the winter maximum extent for 2017 reached a new seasonal low (keeping in mind that NSIDC does not publish error bars for these measurements, which helps elevate such pronouncements to “news”).

Ice extent (courtesy NSIDC’s MASIE) at 25 March (Day 84) is below for 2017, 2011 and 2006, almost 3 weeks after the winter maximum was declared at 7 March for 2017, 9 March for  2011, and 12 March for 2006. Extent at the maximum for 2006 was estimated at 14.68 mkm2, 14.42 mkm2 for 2017, and 14.67 mkm2 in 2011 (what tiny differences make headlines these days).

Remember: there are no polar bears in the Sea of Okhotsk or in the Baltic Sea (marked with an * below) yet ice in those regions is included in the Arctic totals used to determine maximum seasonal extent. Much (and sometimes, all) of the “Arctic” variation in extent at this time of year is accounted for by variation in Sea of Okhotsk and Baltic Sea coverage.

Sea ice day 84 March 25 2017_2011_2006 labeled

Bottom line: total winter ice extent for the Arctic ≠ winter polar bear habitat and neither have changed much in a decade.

See close up of the above graphic below.

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New paper updates lack of trend in W Hudson Bay breakup/freeze-up dates to 2015

A newly-published paper shows that there has been no trend in the time Western Hudson Bay polar bears spent onshore between 2001-2015 due to sea ice conditions at breakup or freeze-up (previously available to 2010 only), despite the marked decline of global sea ice since 2007.


Figure 3 from Castro de la Guardia and colleagues (2017) showing freeze-up and breakup dates and ice-free days 1979-2015 for Western Hudson Bay. Figure with caption, copied below, explains symbols.

Previously, a 2007 paper by Eric Regehr and colleagues for WHB bears up to 2004, which was used to support the US bid to list polar bears as ‘threatened’ with extinction, concluded that between 1984 and 2003, bears were spending 3 weeks longer onshore than they did in the 1980s.

The big news from Castro de la Guardia et al. (2017) is that polar bears spent longer onshore from 1979-2015 by … 3 weeks. That is, no change from the situation in 2004. Wow!

Note the population size of the entire WHB subpopulation has also not declined since 2004 and is currently estimated at about 1030, based on a 2011 aerial survey (Stapleton et al. 2014).

Thanks to Andrew Derocher for the heads-up tweet.

From the abstract (my bold):

We found that the ice-free period in this region lengthened by 3 ± 0.8 wk over the period 1979−2015. Polar bears migrated onshore 2 wk earlier and offshore 1 wk later in the period 2005−2015 than in 1980−1989.

Here is the region in question, illustrated by Fig. 1 from the paper:

castro-de-la-guardia-et-al-derocher-2017-fig-1a-locationThe significant information contained in this paper is breakup and freeze-up dates and length of the ice-free period data for 2010-2015, which has been unavailable until now. More excerpts and comments below, including Figure 3 with its caption. Continue reading