Tag Archives: Pilfold

Most Beaufort polar bears swim from ice floe to floe during breakup, study shows

swimming3_USGS

You may have seen the headlines in Canadian news outlets over the last 2 days.
“Polar bears swimming farther as sea ice recedes, study shows”

“Melting sea ice forces polar bears to swim longer, farther: study”  [“Bear biologist Andrew Derocher says the forced swims are particularly hard on mothers with young cubs”]

“Polar bears swimming longer, farther because of melting sea ice, study finds”

Oddly, none of the above news reports said where the paper was published or mentioned the name of the lead author – only University of Alberta co-author Andrew Derocher was interviewed (see the only press release I could find here, issued by the San Diego Zoo where the lead author is now employed).[update: CBC ran another story a day later that corrected these omissions]

But what did the study actually say?

Significantly, no bears died while swimming during the two lowest sea ice extent summers since 1979 and no evidence was presented that swims were “particularly hard on mothers with young cubs.” The quotes from the paper below sum it up for Beaufort Sea (BS) bears (the inclusion of Hudson Bay (HB) bears in this study seems gratuitous and potentially misleading, since only a few swam anyway – only 15 out of 59):

“….91% (91/100) of the swims in the BS occurred before the annual September minimum sea ice extent had been reached.  In the BS, 81% (29/36) of swims started and ended in pack ice…

So, despite what may be implied during media moments, Beaufort Sea polar bears were  not frantically trying to reach the sea ice from land so that they could attempt to keep feeding over the summer – most of their swimming was done during breakup in July and August from one bit of pack ice to another and they showed no evidence of harm from doing so. Map from the study and more quotes below.
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Polar bear biologists try – again – to blame S. Beaufort thick spring ice on global warming

The trouble is, sea ice researchers and atmospheric scientists have not drawn that conclusion, despite what a new paper by Pilfold and colleagues imply. It shows just what lengths desperate IUCN Polar Bear Specialist Group  (PBSG) biologists will go to in order to link the recent decline of Southern Beaufort bear numbers to global warming while ignoring similar past declines.

Beaufort Sea pressure ridges_Spring 1949 wikipedia sm

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Polar bears out on the sea ice eat few seals in summer and early fall

We hear endlessly about the polar bears ‘forced’ to go without food for months because of receding summer sea ice — what about all the bears that stay out on the ice over the summer? Presumably, those bears keep hunting for seals – but how many do they actually catch?

Polar Bear Breaks Ice

[Update 9 February 2015: Just to be clear, this post is based on the facts available in the peer reviewed literature — if you think I have missed something, let me know via the “Contact us” page above]
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Record sea ice loss in 2007 had no effect on polar bears, Chukchi study confirms

One aspect of the recently published study on Chukchi Sea polar bears (Rode et al.2014 [now in print] 2013; see here and here) has not been stressed enough: their finding that the differences in overall condition between bears in the Chukchi and Southern Beaufort Seas came down to disparities in spring feeding opportunities and therefore, the condition of spring sea ice.

The fact that spring — not summer — is the most critical period for polar bears is something I’ve pointed out before (see here and here, for example) but it’s worth repeating at this time of year, when all eyes are on the annual ice minimum. It is often treated as a given that the decline in extent of summer sea ice in the Arctic since 1979 has been detrimental to polar bears. However, this is an assumption that we can now say is not supported by scientific evidence (see summary of that evidence here).

The results published by Rode et al. (2014 2013) not only add further support to the conclusion that declines in summer sea ice have not harmed polar bears, but should put the matter to rest – unless new evidence to the contrary is produced.

Chukchi bears, the report tells us, had more food available in the spring than Southern Beaufort bears (see map below) and this was the primary reason that bears were doing very well in the Chukchi and not quite as well in the Southern Beaufort. And because the polar bears for this study were captured and measured in mid-March to early May, from 2008 to 2011, they reflect spring-time conditions for 2008-2011 as well as year-round conditions from 2007 through 2010.

This means that the annual low ice extent for 2007 (record-breaking at the time), in the fall before this study began, had no discernible negative effect on either Chukchi or Southern Beaufort polar bears – and neither did similarly low annual minimums in two of the three remaining years of the study (Fig 1).

Figure 1. Sea ice extent at August 27, 2007 – the lowest extent that year (downloaded September 15, 2013 from IARC-JAXA, Arctic Sea-ice Monitor). At the time, it was the lowest extent recorded since 1979 (2012 broke that record). This (2007) was the fall before the Rode & Regehr study on Chukchi/Southern Beaufort polar bears began (2008-2011). The ice was almost as low in September 2008 and 2010, while 2009 was more like 2013.

Figure 1. Sea ice extent at August 27, 2007 – the lowest extent that year (downloaded September 15, 2013 from IARC-JAXA, Arctic Sea-ice Monitor). At the time, it was the lowest extent recorded since 1979 (2012 broke that record). This (2007) was the fall before the Rode & Regehr study on Chukchi/Southern Beaufort polar bears began (2008-2011). The ice was almost as low in 2008 and 2010, while 2009 was more like 2013.

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