Tag Archives: population size

Polar Bear Specialist Group population status update – officially postponed

I kept a close watch on the website of the IUCN Polar Bear Specialist Group (PBSG) over the weekend to see if an actual population status update might eventually appear (see my last post).

Nothing all weekend, but today (Monday, February 3), the “Population status – Status table” tab (where the 2010 status table was inserted on Friday), returned an error message — the out-of-date status table put up on the day an updated one was promised was simply gone.

However, I noticed that the last sentence of the original December 16, 2013 “Population status reviews announcement had been changed, without any indication that it had been amended.

From December 16, 2013 until February 2, 2014 that last sentence said:

“The new status table and assessments will be published as they are available in web format no later than February 1, 2014.

Now it reads:

“The new status table and assessments will be published as they are available in web format in February, 2014.” [my bold]

The date stamp on this page is February 3, 2014, see screen cap below.

What do you call this — “Bayesian transparency”? I think it means a polar bear population status update may be forthcoming…sometime.

PBSG Population status reviews_Feb 3 2014 notice

Barents Sea polar bear status and sea ice declines

So far, I’ve not discussed the Barents Sea subpopulation in very much detail, except in comparison to other groups. For example, the Barents is considered to be the same type of sea ice “ecoregion” as the Chukchi Sea and the Southern Beaufort (discussed here). Previous studies on the Barents Sea polar bear population (Derocher 2005) indicate it may have recovered from extreme levels of overhunting (discussed here) and had stabilized, or was increasing very slowly, as early as 2002 (discussed here) — similar to what has happened in Davis Strait (discussed here).

Figure 1. Polar bear subpopulations, with the Barents Sea region highlighted; map courtesy the IUCN Polar Bear Specialist Group (PBSG), extra labels added.

Figure 1. Polar bear subpopulations, with the Barents Sea region highlighted; map courtesy the IUCN Polar Bear Specialist Group (PBSG), extra labels added.

The most recent Barents Sea population estimate was done in 2004 (2,650; range ~1900-3600), based on an aerial survey (Aars et al. 2009). Aerial surveys are the only practical method of establishing population counts in regions like this where many bears never set foot on land. The previous estimate for the Barents (1982) was “2,000-5,000” but its accuracy was considered “poor” (discussed here).

The IUCN Polar Bear Specialist Group (PBSG), in their most recent report, lists the Barents Sea population as “data deficient” for status, current trend and estimated risk of decline within 10 years (Obbard et al. 2010:62, Table 1) and the “notes” for this entry say:

Population estimate is based on a new aerial survey. There was likely an increase in the subpopulation size after 1973 until recently. Current growth trend is unknown.

This 2004 estimate is now almost a decade old and potentially no longer an accurate representation of what’s happening in the Barents Sea. The most up-to-date information has not yet been published but it is available online. It’s eye-opening to say the least, if only that it appears to be yet another example of a polar bear population that is so far not showing signs of being harmed by sea ice declines, as I’ve discussed before (here).

[Update October 15, 2013: I’ve simplified the text discussion and figure regarding the Aars and Andersen denning study from the original posted]

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Southern Hudson Bay subpopulation status, farthest south of all polar bears

“The Arctic” is a bit hard to define. While the Arctic Circle works as a good boundary for some purposes and the 100C isotherm for July for others, neither work for polar bears because several subpopulations live well south of these limits (Fig. 1).

In the east, Western Hudson Bay, Southern Hudson Bay and Davis Strait are all located well south of the Arctic Circle and the first two (and half of Davis Strait) are beyond the 100C July isotherm as well. In the western Arctic, the Chukchi Sea subpopulation is within the 100C July isotherm but at least half of its bears reside south of the Arctic Circle (Fig. 1) in the Bering Sea (see previous post here).

Unique amongst all of these is Southern Hudson Bay – all of its polar bears make maternity dens and/or spend the summer south of 600N.

Southern Hudson Bay (SH) bears live in the Canadian provinces of Ontario, while Western Hudson Bay (WH) bears reside in Manitoba and Nunavut. The two groups mix over the winter but appear to spend the summer/fall in their respective regions (Stirling et al. 2004). [See previous posts on Western Hudson Bay bears here, here, and here]

“Further south” in the Arctic usually means warmer, with open water present more weeks every summer, sea ice for fewer weeks over the winter. So, shouldn’t the bears of Southern Hudson Bay be already suffering more harm from global warming than virtually all other subpopulations, including those in Western Hudson Bay?

After all, Western Hudson Bay bears appear to have experienced a statistically significant decline in numbers, among other effects (Regehr et al. 2007; Stirling and Derocher 2012) — surely Southern Hudson Bay bears are doing worse?

You’d think so, but they aren’t.

Figure 1. Boundary limits for “the Arctic” (top map) such as the Arctic Circle (dashed line) or the 100C isotherm for July (solid red line) would not include several polar bear subpopulations that live south of these.

Figure 1. Boundary limits for “the Arctic” (top map) such as the Arctic Circle (dashed line) or the 100C isotherm for July (solid red line) would not include several polar bear subpopulations that live south of these.

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Global population of polar bears has increased by 2,650-5,700 since 2001

The official population estimates generated by the IUCN Polar Bear Specialist Group (PBSG) give the impression that the global total of polar bears has not changed appreciably since 2001:

2001 PBSG report                  21,500-25,000

2005 PBSG report                  20,000-25,000

2009 PBSG report                  20,000-25,000

2013 PBSG website                20,000-25,000

However, some accounting changes were done between 2001 and 2009 (the latest report available) that mean a net increase in numbers had to have taken place (see summary map below and previous post here. Note this is a different issue than the misleading PBSG website graphic discussed here).

And while it is true that population “estimates” are just that — rather broad estimates rather than precise counts — it is also true that nowhere do the PBSG explain how these dropped figures and other adjustments were accounted for in the estimated totals. 

The simple details of these changes are laid out below, in as few words as I could manage, to help you understand how this was done and the magnitude of the effect. It’s a short read — see what you think.

UPDATE February 14, 2014a new status table has been released, see new post here 

UPDATE February 18, 2014 — see graphs of the 1981-2013 estimates here.

Polar bear subpopulations as defined by the PBSG: Top, in the 2001 report; Bottom, 2009 report. Map courtesy PBSG, with a few labels added and the subpopulations identified where “accounting” changes or adjustments to estimates took place.SB, Southern Beaufort; NB, Northern Beaufort; VM, Viscount Melville; MC, M’Clintock Channel; LS, Lancaster Sound; GB, Gulf of Boothia; NW, Norwegian Bay; KB, Kane Basin; WH, Western Hudson Bay. Click to enlarge.

Polar bear subpopulations as defined by the PBSG: Top, in the 2001 report; Bottom, 2009 report. Map courtesy PBSG, with a few labels added and the subpopulations identified where “accounting” changes or adjustments to estimates took place.
SB, Southern Beaufort; NB, Northern Beaufort; VM, Viscount Melville; MC, M’Clintock Channel; LS, Lancaster Sound; GB, Gulf of Boothia; NW, Norwegian Bay; KB, Kane Basin; WH, Western Hudson Bay. Click to enlarge.

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Guest post: How ‘science’ counts bears

This essay by Dr. Jim Steele, professor emeritus, San Francisco State University, is reblogged from a July 3 2013 post at WUWT post, with Dr. Steele’s permission. I am not a field biologist and have never done a mark-recapture study but Dr. Steele has. His perspective on the way polar bear biologists count bears and estimate survival in the Southern Beaufort is a perfect companion to yesterday’s post, a related post that I’ll put up later this week, and this one from December, among others. I’ve added links to the references cited in this essay where they are available, as is my custom. See the original post for Jim’s responses to comments and questions.

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Guest post by Jim Steele   “How ‘science’ counts bears”

The Inuit claim “it is the time of the most polar bears.” By synthesizing their community’s observations they have demonstrated a greater accuracy counting Bowhead whales and polar bears than the models of credentialed scientists. To estimate correctly, it takes a village. In contrast the “mark and recapture” study, which claimed the polar bears along South Beaufort Sea were victims of catastrophic global warming and threatened with extinction, relied on the subjective decisions of a handful of modelers.

In mark and recapture studies, the estimate of population abundance is skewed by the estimate of survival. For example, acknowledging the great uncertainty in his calculations of survival, in his earlier studies polar beat expert Steven Amstrup reported three different population estimates for bears along the South Beaufort Sea. If he assumed the adult bears had an 82% chance of surviving into the next year, the models calculated there were 1301 bears. If survivorship was 88%, the abundance climbed to 1776 bears. If he estimated survivorship at a more robust 94%, then polar bear abundance climbed to 2490.1 Thus depending on estimated survival rates, a mark-and-recapture study may conclude that the population has doubled, or that it has suddenly crashed.

Here are the simplified basics of estimating survival.

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Gulf of Boothia, unheralded Arctic utopia, has the highest density of polar bears worldwide

The issue of polar bear population density (# of bears per 1000 km2) came up a few posts ago, during my discussion of the new Davis Strait population study by Lily Peacock and colleagues (here). Since the various polar bear subpopulations across the Arctic are so different in size, calculating the density of bears in the various regions generates an interesting metric of how well the regional populations are doing relative to each other.

Almost 20 years ago, Taylor and Lee (1995) did just that: they determined the density of polar bears in the various Canadian subpopulations, as of the 1990s. Surprisingly, the ‘leader’ among those, by a wide margin, was one of the smallest in geographic area: the Gulf of Boothia. Located in the central Canadian Arctic (see Figs. 1 and 2 below), in the 1990s, tiny Gulf of Boothia supported a density of 10.4 polar bears per 1000 km2, the highest density of all regions examined.

 Figure 1. The Gulf of Boothia (circled) is right in the middle of the Canadian Arctic. In terms of geographic area, it is one of the smallest of all 19 subpopulations worldwide: at only 170,000 km2, only the Norwegian Bay and Kane Basin subpopulation regions, also in Canada (just to the north of Gulf of Boothia), are smaller at 150,000 and 155,000 km2 respectively (Vongraven and Peacock 2011). The Gulf of Boothia supports the highest density of polar bears known.Modified from map of polar bear protected areas provided by Environment Canada.


Figure 1. The Gulf of Boothia (circled) is right in the middle of the Canadian Arctic. In terms of geographic area, it is one of the smallest of all 19 subpopulations worldwide: at only 170,000 km2, only the Norwegian Bay and Kane Basin subpopulation regions, also in Canada (just to the north of Gulf of Boothia), are smaller at 150,000 and 155,000 km2 respectively (Vongraven and Peacock 2011). The Gulf of Boothia supports the highest density of polar bears known. Modified from the map of polar bear protected areas provided by Environment Canada.

But this density value for Gulf of Boothia was based on the 1986 population estimate of 900 bears – what is the most current figure?

For that, we need an updated population assessment. That was done in 2000 and it generated an estimate of 1,592 ± 361 bears (Taylor et al. 2009).

Taylor et al. (2009:791) said this about their assessment:

Our results suggest population size had increased steadily under a harvest regimen of approximately 40 bears/yrand added, “Barber and Iacozza (2004) found no trends in Gulf of Boothia sea ice conditions or ringed seal habitat suitability indices in the interval 1980-2000.

In other words, despite there being no trend in either sea ice conditions or habitat for seals – and a yearly harvest of 40 bears – polar bear numbers in the Gulf of Boothia increased significantly (by almost 700 bears) during the twenty years between 1980 and 2000. Even if the 1986 estimate of approximately 900 bears was somewhat less accurate than the more recent one, the fact that tiny Gulf of Boothia can support 1,592 bears is surely a remarkable feat.

Using this new population estimate and the same area of ‘available habitat’ used by Taylor and Lee in 1995, I calculated the most recent density at a spectacular 18.3 bears per 1000 km2! [note this is exactly what Peacock et al (2013) did to get their density value of 5.1 bears/1000 km2, discussed here.] But I didn’t update just Gulf of Boothia, I did them all.

The updated density values for Gulf of Boothia and several other Canadian subpopulations are listed in Table 1 below. Note that aside from Davis Strait, as far as I know these density figures have not been published elsewhere: you’re seeing them here for the first time.

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Signs that Davis Strait polar bears are at carrying capacity

Exciting news about polar bears in eastern Canada: the peer-reviewed paper on the Davis Strait subpopulation study has finally been published (Peacock et al. 2013). It concludes that despite sea ice having declined since the 1970s, polar bear numbers in Davis Strait have not only increased to a greater density (bears per 1,000 km2) than other seasonal-ice subpopulations (like Western Hudson Bay), but it may now have reached its ‘carrying capacity.’

This is great news. But where is the shouting from the roof-tops? This peer-reviewed paper (with its juicy details of method and analysis results), considered by some to be the only legitimate format for communicating science, was published February 19, 2013. No press release was issued that I could find and consequently, there was no news coverage. Funny, that.

There was a bit of shouting back in 2007 when the study ended and the preliminary population count was released – polar bear biologist Mitch Taylor is quoted in the Telegraph (March 9 2007) as saying:

“There aren’t just a few more bears. There are a hell of a lot more bears.”

There was also a CBC news item in January 2007 and a Nunatsiaq|Online report in October 2009 when the official government report was completed. But these were all based on preliminary information and focused on the population increase only.

This new paper (Peacock et al. 2013) reveals that the story in Davis Strait is about more than simple population growth. Small wonder no one is drawing attention to it. Continue reading

Misleading “State of the Polar Bear” graphic still not fixed

UPDATE FEBRUARY 19, 2014The misleading “State of the Polar Bear” graphic is now GONE (as of January 31, 2014). A new 2013 status table is offered by the PBSG here. It has detailed text explanations and harvest information, with references, hyperlinked to each subpopulation entry (“Press the subpopulation hyperlink and more information will appear“) and may have replaced the “State of the Polar Bear” graphic that the PBSG commissioned for upwards of US$50,000, although the PBSG website says it is being “updated [A pdf copy of the 2013 colour table is here, and my commentary on it is here.] I have left the original post as is, below.

This is an update regarding the IUCN Polar Bear Specialist Group (PBSG)’s fancy, multilevel State of the Polar Bear web graphic that I discussed previously here, here, and here.

To refresh your memory, two points about this graphic stand out, both regarding polar bear population estimates:

1) The population estimates listed on the Nations map (copied below) add up to 22,600-32,000 - far higher than the official estimate of 20,000-25,000 polar bears worldwide.

2) The population estimates listed on the upper layer of the Subpopulation map add up to just 13,036 – not even close to the official estimate of 20,000-25,000 polar bears worldwide.
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Matt Ridley’s foreword to my “10 good reasons not to worry” list – “We should be listening to Susan Crockford”

Benny Peiser over at the Global Warming Policy Foundation has just posted an essay by well-known author Matt Ridley (including “The Rational Optimist”), entitled “We should be listening to Susan Crockford” which is included as a foreword to a pdf of my earlier post, “Ten good reasons not to worry about polar bears.”

This stand-alone pdf is especially suitable for sharing with friends and policy makers.

I encourage you to have a look.

Why is the US pushing to ban polar bear trade? Polar bears have been saved

One of the items on the agenda at the upcoming 16th meeting of the signatories to the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) in Bangkok Thailand (3-14 March, 2013) is a proposal to upgrade the polar bear from Appendix II to Appendix I status - prepared by the US Fish & Wildlife Service. The suggested change is based on what is claimed to be “a marked decline in the population size in the wild, which has been inferred or projected on the basis of a decrease in area of habitat and a decrease in quality of habitat.” If this proposition is adopted by CITES, it would be illegal to trade legally harvested polar bear parts of any kind.

The US tried this maneuver at the last CITES meeting in 2010 and it failed rather miserably. I see little reason to believe it will pass this year, even though the US is actively campaigning and has motivated activists worldwide to pressure other countries to vote in their favour (see “Activists push for international ban on legal trade in polar bear items” which discusses the absurdity of the World Wildlife Fund (WWF) not supporting the CITES proposal because they want to keep the focus on model-predicted future “threats” of global warming, see Clark et al. 2012, abstract below).

But here’s the question I have for all the folks involved in this CITES petition and other similar proposals to upgrade the conservation status of the polar bear to a “threatened” or “endangered” level: why is all this time, money and effort going toward ever-more restrictive regulations for a species that has clearly been saved but about which we still know so little?

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