Tag Archives: facts

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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Polar bear habitat update mid-May: little change since 1989 despite CO2 increase

Sea ice habitat for polar bears has not become progressively worse each year during their season of critical feeding and mating, as some scaremongers often imply. It’s true that absolute extent of Arctic ice is lower this spring than it was in 1979. However, according to NSIDC Masie figures, polar bear habitat at mid-May registers about 12 million km2, just as it did in 2006 (although it is distributed a little differently); other data show spring extent has changed little since a major decline occurred in 1989, despite ever-rising CO2 levels.

Polar bear feeding_Shutterstock_sm

In other words, there has been virtually no change in sea ice cover over the last 12 years, despite the fact that atmospheric CO2 has now surpassed 410 parts per million, a considerable and steady increase over levels in 2006 which were about 380 ppm (see below, from the Scripps Oceanographic Laboratory, included in the Washington Post story 3 May 2018):

Scripps CO2 curve at 29 April 2018

Not only that, but if rising CO2 levels were responsible for the decline of sea ice and implied effects on polar bears since 1979 (when CO2 levels were around 340 ppm), why has spring ice extent been so variable since 1989 (when the first big decline occurred) but so little changed overall since then? See the NSIDC graph below for April:

Sea ice 2018 April average_NSIDC graph

This year on day 134 (14 May), global ice cover registered 12.3 mkm2:

masie_all_zoom_4km 2018 May 14

In 2016 on the same day, the overall extent was much the same but there was more ice in the Chukchi and Bering Seas and less in the eastern Beaufort:

masie_all_zoom_4km 2016 May 14

More close-up charts of different regions below for 2018 vs. 2016, showing more detail.

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Polar bear numbers, margins of error, & consequences for conservation status

Large margins of error in polar bear population estimates means the conservation status threshold of a 30% decline (real or predicted) used by the US Endangered Species Act and the IUCN Red List is probably not valid for this species.

Polar_Bear_Biologist_USFWS_working_with_a_Bear_Oct 24 2001 Amstrup photo

Several recent subpopulation estimates have shown an increase between one estimate and another of greater than 30% yet deemed not to be statistically significant due to large margins of error. How can such estimates be used to assess whether population numbers have declined enough to warrant IUCN Red List or ESA protection?

What do polar bear population numbers mean for conservation status, if anything?

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Low Bering Sea ice mostly due to south winds, no data on an impact for polar bears

Sea ice in the Bering Sea this winter was said to be the lowest since the 1850s, largely driven by persistent winds from the south rather than the usual north winds although warm Pacific water was a factor early in the season (AIRC 2018). But what, if any, impact is this surprisingly low winter and spring ice cover likely to have on Chukchi Sea polar bear health and survival?

Rode and Regehr 2010_Chukchi_report2010_Fig1_triplets_labelled

In fact, research on Chukchi Sea polar bears has included so few examples of individuals utilizing the Bering Sea in winter (Jan-March) and early spring (April-May) that any conclusions regarding an impact from this year’s sea ice conditions are likely to be invalid. In short, we don’t know what will happen since it has not happened before within living memory; the opinions of polar bear specialists must be taken with a grain of salt because so many of their previous assumptions have turned out to be wrong (Crockford 2017a,b, 2018), see here, here, and here. Seals, walrus and polar bears are much more flexible and resilent to changes in habitat conditions than most modern biologists give them credit for and consequently, it will be fascinating to see how the ice will change over the coming months and how the animals will respond.

Sea ice extent 2018 March average NSIDC

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Polar bear habitat update early spring 2018

Spring in the Arctic is April-June (Pilfold et al. 2015). As late April is the peak of this critical spring feeding period for most polar bear populations, this is when sea ice conditions are also critical. This year, as has been true since 1979, that sea ice coverage is abundant across the Arctic for seals that are giving birth and mating at this time as well as for polar bears busy feeding on young seals and mating.

Polar_Bear_male on sea ice_Alaska Katovik Regehr photo_April 29, 2005_sm labeled

Below is a chart of sea ice at 25 April 2018, showing sea ice in all PBSG polar bear subpopulation regions:

masie_all_zoom_4km 2018 April 25

Some Arctic subregions below, in detail. Continue reading

Amstrup & colleages can’t refute my critique of their 2007 polar bear survival model, Part 1

It’s been more than a year since I first published my scientific manuscript at PeerJ Preprints (a legitimate scientific forum) on the failure of Amstrup’s 2007 USGS polar bear survival model (Crockford 2017), a year waiting in vain for the polar bear community to comment. They either couldn’t be bothered or knew they couldn’t refute it – I haven’t known for sure which. But I do now.

Beaufort Sea male polar bear USGS_2005 Amstrup photo

Polar bear specialists didn’t comment because they couldn’t refute it in the scholarly manner required by PeerJ: all they could do is tear it down with derision, misdirection and strawman arguments.

I know this because the damage control team for the polar-bears-are-all-going-to-die-unless-we-stop-using-fossil-fuels message wasn’t activated over my fully-referenced State of the Polar Bear Report for 2017 (Crockford 2018) released on International Polar Bear Day last month, but for a widely-read opinion piece I’d written for the Financial Post published the same day (based on the Report) that generated three follow-up radio interviews.

By choosing to respond to my op-ed rather than the Report or my 2017 paper, biologists Andrew Derocher and Steven Amstrup, on behalf of their polar bear specialist colleagues1, display a perverse desire to control the public narrative rather than ensure sound science prevails. Their scientifically weak “analysis” of my op-ed (2 March 2018), published by Climate Feedback (self-proclaimed “fact checkers”), attempts damage control for their message and makes attacks on my integrity. However, a scientific refutation of the premise of my 2017 paper, or The State of the Polar Bear Report 2017, it is not (Crockford 2017, 2018).

Derocher further embarrasses himself by repeating the ridiculous claim that global polar bear population estimates were never meant for scientific use, then reiterates the message with added emphasis on twitter:

Derocher tweet 2018 Feb 28 quote

Just as the badly written Harvey et al. (2017) Bioscience paper said more about the naked desperation of the authors than it did about me or my fellow bloggers, this attempt by the polar bear community’s loudest bulldogs to discredit me and my work reveals their frustration at being unable to refute my scientifically supported conclusion that Amstrup’s 2007 polar bear survival model has failed miserably (Crockford 2017).

Part 1 of my detailed, fully referenced responses to their “analysis” of my op-ed are below.  Part 2 to follow [here]. Continue reading