Tag Archives: breakup dates

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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Polar bears have not been harmed by sea ice declines in summer – the evidence

PB  logo colouredThe polar bear biologists and professional activists of the IUCN Polar Bear Specialist Group (PBSG) continue to insist that since 1979 increasingly smaller amounts of Arctic sea ice left at the end of summer (the September ice minimum) have already caused harm to polar bears. They contend that global warming due to CO2 from fossil fuels (“climate warming” in their lexicon) is the cause of this decline in summer ice.

In a recent (2012) paper published in the journal Global Change Biology (“Effects of climate warming on polar bears: a review of the evidence”), long-time Canadian PBSG  members Ian Stirling and Andrew Derocher (both of University of Alberta) summarized their position this way:

“Climate warming is causing unidirectional changes to annual patterns of sea ice distribution, structure, and freeze-up. We summarize evidence that documents how loss of sea ice, the primary habitat of polar bears (Ursus maritimus), negatively affects their long-term survival”

I’ve spent the last year examining their evidence of on-going harm, but in addition, I’ve looked at the evidence (much of it not mentioned in the Stirling and Derocher paper1) that polar bears have either not been harmed by less sea ice in summer or have thrived in spite of it.

This is a summary of my findings. I’ve provided links to my original essays on individual topics, which are fully referenced and illustrated. You are encouraged to consult them for complete details. This synopsis (pdf with links preserved, updated; pdf with links as footnotes, updated) complements and updates a previous summary, “Ten good reasons not to worry about polar bears” (pdf with links preserved; pdf with a foreword by Dr. Matt Ridley, with links as footnotes).

Update 8 September 2013: to include links to my post on the recently published Chukchi population report; updated pdfs have been added above.

Update 22 January 2014: added figure comparing March vs. September sea ice extent using the same scale, from NOAA’s “2014 Arctic Report Card,” discussed here.
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Baffin Bay polar bear status – waiting for the count

Here’s a quick summary of the status of Baffin Bay polar bears, a subpopulation I’ve not previously discussed in detail. Nothing especially earth-shattering here, except perhaps to wonder about the involvement of the World Wildlife Fund (WWF) in a new helicopter survey of the region.

Baffin Bay (Fig. 1) is north of Davis Strait. It lies between western Greenland and Baffin Island in the eastern Arctic.

Unlike the other north/south neighbour-pair of Western/Southern Hudson Bay   (which I discussed previously), the sea ice history for Baffin Bay/Davis Strait is not as similar: Davis Strait bears have a much longer on-shore fast than Baffin Bay bears (see last post here). However, all four of these subpopulations have ‘seasonal sea ice’ – that is, the ice melts completely in late mid-to-late summer, forcing bears onshore for varying lengths of time until fall freeze-up.

Figure 1. The Baffin Bay subpopulation region lies north of Davis Strait (map on the left from Vongraven and Peacock 2011: Fig. 3) and management is shared between Canada (Nunavut) and Greenland. In total area, it covers 1.08 million km2 and its “suitable ice habitat in spring” (according to Taylor and Lee 1995) is 413,500 km,2 somewhat less than Davis Strait. The map on the right shows the sea ice extent at the end of March 2010 (NSIDC), the winter maximum.

Figure 1. The Baffin Bay subpopulation region lies north of Davis Strait (map on the left from Vongraven and Peacock 2011: Fig. 3) and management is shared between Canada (Nunavut) and Greenland. In total area, it covers 1.08 million km2 and its “suitable ice habitat in spring” (according to Taylor and Lee 1995) is 413,500 km2, somewhat less than Davis Strait. The map on the right shows the sea ice extent at the end of March 2010 (NSIDC), the winter maximum.

A peer-reviewed paper published last year (Rode et al. 2012) compared body condition vs. sea ice changes in Davis Strait and Baffin Bay (discussed here). But while that research contributed to an updated population estimate for Davis Strait (Peacock et al. 2013, discussed here), it did not do the same for Baffin Bay. This is likely because the body condition work in Baffin Bay was split between spring and fall, and it has already been determined that many Baffin Bay bears are offshore in the spring and not available for counting using shore-based methods.

That’s a shame, because the last population estimate was completed back in 1997 (Taylor et al. 2005) and it is now seriously out of date.

However, it appears the Government of Nunavut is currently in the process of surveying this region by helicopter, so a new population estimate should be available soon.

But this aspect of the survey might surprise you — a press release issued February 11, 2013 by WWF contained the following statement:

Results from the above-noted surveys will be completed and shared beginning in April 2013.

WWF made contributions of $82,000 to the Government of the Northwest Territories and $111,000 to the Government of Nunavut via Environment Canada, towards the total costs of these surveys. These funds were raised through the Arctic Home campaign from engaged Canadians and matched by The Coca-Cola Company.”  [my bold]

So, of the hundreds of millions the WWF pulls in from donations, they passed along less than $100,000 [$96,500 plus an equal contribution by Coca-Cola) to offset “the total costs of the survey.

We are not told what those total costs are, but I expect they run well over a million dollars for a multiyear/multi-region project like this, perhaps over two million. Which makes $96,500 rather a drop in the bucket. That might have paid for some of the jet fuel for the helicopters used for the survey, but probably not all of it.

Status details below.
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Baffin Bay-Davis Strait ice concentration comparison – why use the “summer mean”?

I’ve been in the process of looking at the status of polar bears in the Baffin Bay region, which lies to the north of Davis Strait (Fig. 1), but a related issue caught my attention that I think deserves discussion.

Figure 1. Polar bear subpopulations defined by the Polar Bear Specialist Group (PBSG). Note that Baffin Bay, Davis Strait, Western Hudson Bay and Southern Hudson Bay are all similar in that they become ice-free by early fall (the September minimum) or before.

Figure 1. Polar bear subpopulations defined by the Polar Bear Specialist Group (PBSG). Note that Baffin Bay, Davis Strait, Western Hudson Bay and Southern Hudson Bay are all similar in that they become ice-free by early fall (the September minimum) or even before.

Recall that in a recent post on the Beaufort Sea ice extent comparison offered by the National Snow and Ice Data Center (NSIDC) here, I commented:

What puzzled me was why they featured only the last 7 years when satellite data go back to at least 1979. Is there something in that data they don’t want us to see?”

Something similar struck me about the analysis of sea ice in Baffin Bay and Davis Strait conducted by polar bear researchers Karyn Rode and colleagues (Rode et al. 2012). In their comparison of body condition (relative fatness) of bears in Davis Strait and Baffin Bay (see previous post here), they introduced an entirely new sea ice metric – “mean daily summer sea ice concentration,” defined as the mean of values between May 15 and October 15 each year based on ice charts provided by the Canadian Ice Service.

Why invent a metric that has never been used (as far as I know) for analysis of polar bear health, survival or success?

Why not use breakup dates, as has been done for decades for subpopulations in Hudson Bay (e.g. Cherry et al. 2013), where the ice also disappears in late summer?

Is there something in the ice data for Baffin Bay and Davis Strait that Rode and colleagues don’t want us to see?

Since I had already made a composite of Cryosphere Today ice maps at July 12 for my discussion of the Chukchi/Beaufort NSIDC analysis mentioned above, it was relatively easy to look at what was going on in Baffin Bay and Davis Strait on that date in mid-summer. Keep in mind that ice extent and concentration at July 12 records the state of polar bear habitat prior to the late summer decline in sea ice that occurs every year.

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