Category Archives: Population

Abrupt summer sea ice decline has not affected polar bear numbers as predicted

Yes, Arctic sea ice has declined since satellite records began in 1979 but polar bears have adjusted well to this change, especially to the abrupt decline to low summer sea ice levels that have been the norm since 2007.

Global pb population size sea ice 2017 July PolarBearScience

Some polar bear subpopulations have indeed spent more time on land in summer than in previous decades but this had little negative impact on health or survival and while polar bear attacks on humans appear to have increased in recent years (Wilder et al. 2017), the reasons for this are not clear: reduced summer sea ice is almost certainly not the causal factor (see previous post here).

Ultimately, there is little reason to accept as plausible the computer models (e.g. Atwood et al. 2016; Regehr et al. 2016) that suggest polar bear numbers will decline by 30% or more within a few decades: even the IUCN Red List assessment (Wiig et al. 2015) determined the probability of that happening was only 70%.

Arctic sea ice has never been a stable living platform (Crockford 2015): it shifts from season to season, year to year, and millennia to millennia. Without the ability to adapt to changing conditions, Arctic species like polar bears and their prey species (seals, walrus, beluga, narwhal) would not have survived the unimaginably extreme changes in ice extent and thickness that have occurred over the last 30,000 years, let alone the extremes of sea ice they endured in the last 200,000 years or so.

Some biologists continue to hawk doomsday scenarios for polar bears due to summer sea ice loss but the truth is that their previous predictions based on sea ice declines failed so miserably (e.g. Amstrup et al. 2007) that it’s impossible to take the new ones seriously — especially since the basic assumptions that caused the first predictions to fail have not been corrected, as I’ve stated in print (Crockford 2017:27):

In summary, recent research has shown that most bears are capable of surviving a summer fast of five months or so as long as they have fed sufficiently from late winter through spring, which appears to have taken place since 2007 despite marked declines in summer sea ice extent.

The assumption that summer sea ice is critical feeding habitat for polar bears is not supported.

Recent research shows that changes in summer ice extent generally matter much less than assumed in predictive polar bear survival models of the early 2000s as well as in recent models devised to replace them (Amstrup et al. 2010; Atwood et al. 2016a; Regehr et al. 2015; Regeher et al. 2016; Wiig et al. 2015), while variations in spring ice conditions matter more.

As a consequence, the evidence to date suggests that even if an ‘ice-free’ summer occurs sometime in the future ­ defined as sea ice extent of 1 million km2 or less (Jahn et al. 2016) ­ it is unlikely to have a devastating impact on polar bears or their prey. [my bold]

The abrupt drop in summer sea ice that occurred in 2007 was not predicted by experts to occur until mid-century yet the predicted decimation of polar bears worldwide expected under those conditions (a loss of 2/3 of the global total, to only about 6660-8325 bears) not only did not happen, it did not come even close to happening (Crockford 2017; see also my recent books, Polar Bear Facts & Myths, and Polar Bears: Outstanding Survivors of Climate Change, sidebar).

Instead, the global population grew from about 22,550 bears in 2005 to about 28,500 bears in 2015. And while this might not be a statistically significant increase (due to the very wide margins of error for polar bear estimates), it is absolutely not a decline.

The present reality is that low summer sea ice cover since 2007 has not caused polar bear numbers to decline and therefore, polar bears are not a species in trouble. This suggests that even if the Arctic should become briefly ice-free in summer in the future, polar bears are likely to be only minimally affected and not become threatened with extinction. Polar bears are outstanding survivors of climate change: recent research and their evolutionary history confirm this to be true.

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Polar bear counts for W Hudson Bay: ‘core’ area numbers are not comparable

Polar bear population estimates for Western Hudson Bay have recently become contentious because one specialist has been making statements that confuse the issue. As we all wait for the release of the report on the WHB aerial survey of 2016, it’s worth going over the recent history of these counts and what they have revealed.

Churchill_Polar_Bear_2004-11-15 Wikipedia

The official count for bears in WHB (used by the IUCN Polar Bear Specialist Group, the IUCN Red List, and Environment Canada) is 1030, based on an aerial survey of the entire region conducted in 2011 (Stapleton et al. 2014).

Since last year, Andrew Derocher (University of Alberta) has been telling any media pundit who will listen that WHB polar bears have declined from about 1200 bears in the 1980s to only 800 or so bears today (one example here) — a statement that is clearly not true.  In recent months, however, whether due to complaints from the public or from his colleagues, he’s qualified that statement by saying it’s the number of bears in the “core” area of WHB that has declined.

But is Derocher’s revised statement a clear scientific interpretation of the facts? Have a look at the details below and see if you come to the same decision I have: that it’s not possible to compare WHB ‘core’ area polar bear population estimates over time.

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Southern Beaufort sea ice melt in May: good news for polar bears or catastrophe?

Last week biologist Andrew Derocher recently implied via twitter that less sea ice in the eastern portion of the Southern Beaufort (SB) this year at mid-May is harmful to polar bears (calling it “a hole in the ice where polar bears used to live“), but both long-term and short-term data don’t support such a glass-half-empty interpretation.

Not only does spring breakup of sea ice in the SB normally begin with such open patches of water (see the video above from last year) — driven by the powerful currents of the Beaufort Gyre, not ice melt (explained in detail here) — it may actually be necessary for the survival of local seals, polar bears and whales in spring and early summer (Citta et al. 2015; Crawford et al. 2015; Harwood et al. 2015; Stirling et al. 1981).

As I’ve pointed out before, the biggest threat to SB bears is thick sea ice in spring and its associated late breakup, a 2-3 year-long phenomenon unique to this region known to have occurred about every 10 years since the early 1960s (well documented in the scientific literature) but which has not (as far as I know) happened since 2004-2006.

In other words, a considerable patch of open water and less concentrated ice in the eastern SB around Cape Bathurst is almost certainly a good thing for this particular subpopulation (see previous post here for an in-depth discussion) because historically, when a polynya of some extent has not formed by April or May it has been devastating for local marine mammals.

The fact that an extensive patch of open water existed at mid-May in this region last year and the year before (2015 and 2016) — with no public hue-and-cry about a great dying of SB bears from Derocher or anyone else — suggests that open water in the eastern SB this year is likely to be beneficial for SB polar bears, or at least benign. Continue reading

IUCN PBSG insists the 2015 Barents Sea polar bear count was not an increase

Similar to the spin on the 2013 Baffin Bay/Kane Basin polar bear population survey, the IUCN Polar Bear Specialist Group now insists the latest count of the Barents Sea subpopulation is not evidence of an increase in numbers since 2004, as the leader of the study announced in 2015.

Svalbard polar bear_Aars August 2015-NP058930_press release

This is Part 2 of the big surprises in the latest version of the polar bear status table published by the IUCN Polar Bear Specialist Group (PBSG) on 30 March 2017. See last post here regarding the PBSG population size estimates that no longer concur with the 2015 Red List assessment, including the global total — even though PBSG members wrote the report (Wiig et al. 2015, and its Supplement).

Here I want to focus on the results of subpopulation surveys that were made public after the 2015 Red List assessment was published, particularly the Barents Sea estimate.

While the 2013 Baffin Bay and Kane Basin estimates (SWG 2016) have been added to the new PBSG table, any suggestion that these might indicate population increases are strong discounted. Similarly, contrary to initial reports by the principal investigators of the survey, the PBSG insist that the Barents Sea population has not actually increased since 2004, which you may or many not find convincing.

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IUCN Specialist Group now rejects polar bear numbers it used for 2015 IUCN Red List review

Is there a mutiny in the works between the IUCN Red List and the IUCN Polar Bear Specialist Group (PBSG) over polar bear population estimates or has there simply been a breach of ethics? What else explains the fact that some of the subpopulation estimates used by the PBSG to support the status of ‘vulnerable’ for the IUCN Red List in 2015 are unacceptable to them in 2017? And why are the PBSG refusing to embrace the Red List global estimate of 22,000-31,000?

2015 IUCN Red List estimates vs IUCN PBSG 2017

The latest version of the IUCN PBSG status table was posted online 30 March 2017 without fanfare or even a note on their home page. It seems the result came from much discussion at their official meeting last summer (June 2016) that they say continued into early March 2017.

2017 population status update early March headline

PBGS members voted to reject four subpopulation estimates used in the 2015 Red List polar bear status review  — even though the inclusion of those numbers was required in order for the Red List status of ‘vulnerable’ to be upheld. The group has also chosen not to update their global population page with the Red List estimate of 22,000-31,000.

And surprise, surprise — now that only one subpopulation out of nineteen worldwide has shown a recent decline, the PBSG have removed the “trend” columns from their summary table for subpopulations.

Welcome to conservation ‘science’ practiced by IUCN polar bear specialists.
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Experts’ vision of an ice-free summer is already wrong & benefitting polar bears

Polar bear populations in most of the Canadian Arctic Archipelago (CAA) must be booming, as they are elsewhere. That’s because the ‘experts’ were even more wrong in their predictions of future sea ice conditions than most people realize: they expected the CAA would remain choked with ice during a ‘nearly ice-free’ summer driven by human-caused global warming.

polar-bear-feeding_shutterstock_sm

Wang and Overland 2012 fig 3b marked

Map presented by Wang and Overland (2012: Fig 3) shows what these experts thought a ‘nearly ice-free’ summer would look like, which they expected to occur by 2030 or so.

Look at the map from Wang and Overland (2012) above, which is what they thought a ‘nearly ice-free’ summer would look like in the year 2030 or so.

Wang and Overland used the same models used by USGS biologists to predict the future survival of polar bears based on habitat loss (Amstrup et al. 2007; Atwood et al. 2016; Durner et al. 2007, 2009). Note the thick ice in the CAA — what USGS experts call the ‘Archipelago’ sea ice ecoregion (denoted by white in the map), indicating ice about 1 metre thick (2-3 feet) — expected to remain at the height of summer in 2030.

[Earlier renditions of sea ice projections (e.g. ACIA 2005) show something similar. The second update of the ACIA released just yesterday (AMAP 2017, described here by the CBC) has prudently included no such firm predictions in their Summary for Policy Makers, just dire warnings of future catastrophe. But see the 2012 update.]

 

The problem is that ice in this region has been largely absent most summers since 2006, even though overall ice extent has been much more extensive than expected for a ‘nearly ice-free’ summer, as I show below.

This is not another “worse than we thought” moment (Amstrup et al. 2007) — this is sea ice models so wrong as to be useless: failed models used to inform future polar bear survival models that got the bears declared ‘threatened’ with extinction in the US in 2008 (Crockford 2017).

It also means polar bears are almost certainly doing much better than recent population counts indicate, since only one subpopulation out of the six in the CAA has recently been assessed. But since polar bear specialists have consistently underestimated the adaptability of this species and the resilience of the Arctic ecosystem to respond to changing conditions, it’s hard to take any of their hyperbole about the future of polar bears seriously. Continue reading

Global polar bear population size is about 28,500 when updates are included

Polar bear numbers have risen since 2005, no matter how you look at it:

Svalbard polar bear Jon Aars_Norsk Polarinstitutt

USGS estimated 24,500 (average) polar bears in 2005.

IUCN estimated 26,500 (average of 22,000-31,000) in 2015
(assessment completed in July, released in November).

Subpopulation surveys completed or reported after July 2015 (Baffin Bay, Kane Basin, Barents Sea) added ~2,000 bears.

This brings the adjusted average total at 2015 to ~28,500.

This may not be a statistically significant increase but it is also not the catastrophic decline that was predicted to occur in association with the abrupt drop of summer sea ice in 2007 to a new average of about 3-5 mkm2 [updated 1 June 2017].

Crockford 2017_Slide 12 screencap

Explained in full in this published paper, pgs 20-21:

Crockford, S.J. 2017 V3. 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 2 March 2017. Doi: 10.7287/peerj.preprints.2737v3 Open access. https://doi.org/10.7287/peerj.preprints.2737v3