Fact checkers fail to refute polar bear number increases despite extensive ‘expert’ rhetoric

There’s seems to be something about polar bears that really sets off the climate change fact-checkers. Mention that the situation for the bears is not quite as dire as we were told they would be 15 years ago and they can’t wait to sink their teeth in.

In early September this year, an Australian a woman I’ve never heard of gave a lecture to students at her former girl’s school and in the process made some critical remarks about Al Gore’s ‘An Inconvenient Truth’. Gina Rinehart said, among other things:

“I’d heard that senior school students in a previous headmistress’s time, were having to watch … An Inconvenient Truth. Catchy title, but sadly short on delivery as far as truth is concerned, e.g. the sad loss of polar bears, when actually their numbers have increased…”

The folks who ‘fact-check’ at the Australian Broadcasting Corporation (ABC) seemed to feel that Ms. Rinehart needed to be taken down a peg for the temerity of that remark, perhaps as it afforded an opportunity to take me down along with her: it seems some things I’ve said or published over the last few years were identified by her office as the source of her remark that polar bear numbers had increased.

In a long-winded essay of more than 2,500 words published yesterday (26 October 2021) the fact checkers provide one of the best examples yet of how convoluted is the official answer to the question: have overall polar bear numbers declined or increased over time? They interviewed a number of experts from the Polar Bear Specialist Group (PBSG) who had a lot to say but claimed it is impossible to address the global population issue.

Sadly, the question of how many polar bears exist today compared to decades ago is unnecessarily complicated and messy, as I discovered years ago. I dealt with this topic in my latest book, The Polar Bear Catastrophe That Never Happened, so for now I’ll just quote a bit from one of the chapters and let you decide for yourselves if the experts quoted by the ABC fact-checkers have a strong enough case to say without question that Rinehart was wrong. For example, you might ask why the PBSG experts used the estimate generated for the Kara Sea subpopulation of about 3,000 bears compiled by Russian researchers (Matishov et al. 2014) for their official IUCN 2015 assessment (Wiig et al. 2015; Regehr et al. 2016) but didn’t include that number in this ‘fact-check document – or why they similarly used an estimate of 2,000 for East Greenland for the 2015 assessment but provide no number for this ‘fact-check’. I’ll probably have more to say later.

Excerpt from Chapter 10 of The Polar Bear Catastrophe That Never Happened (pg. 106-109) [with some new emphasis added]

As part of past status reports, the PBSG has traditionally estimated a range for the total number of polar bears in the circumpolar Arctic. Since 2005, this range has been 20–25,000. It is important to realize that this range never has been an estimate of total abundance in a scientific sense, but simply a qualified guess given to satisfy public demand.

[Proposed footnote to the PBSG Circumpolar Action Plan, 30 May 2014, Dag Vongraven in an email to me; emphasis in original]

The fact that the global population size for the 1960s was never agreed upon by polar bear specialists isn’t the only problem: recent population size estimates have also been low-balled. This makes it look like little has changed since international protection was given to polar bears across the Arctic in the early 1970s.

But the notion that there has been no recovery of population sizes since then is simply not plausible. As I mentioned in Chapter 2, it was clear as early as the late 1980s that numbers had rebounded substantially due to conservation efforts. Most studied populations had doubled in size (Amstrup et al. 1986; Andersen and Aars 2016; Larsen 1986; Stirling et al. 1977b).

In his 1988 book about polar bears, Ian Stirling suggested that by the late 1980s (Taylor and Lee 1995:151):

… the total population might be as large as 40,000 animals because of incomplete or inaccurate survey data.

What he meant by this comment is that global estimates presented by polar bear specialists assume the number of bears in several large regions of the Arctic is zero, or that they have otherwise inadequate data. As a consequence, Stirling felt the upper end of the range of an estimate that included those regions would have been close to 40,000 in 1986.

For example, in 2009 the global population size estimate offered by the PBSG was 20,000–25,000, a range which was unchanged since 2005 (Aars et al. 2006; Obbard et al. 2010). That 2009 estimate was the sum of all subpopulations that had any kind of an estimate, rounded up or down{Footnote: The actual totals were 19,608–25,162, with a mid-point of about 22,500}.

However, this estimate of 20,000–25,000 didn’t include all regions of the polar bear’s range: it left out three large regions that were home to substantial numbers of bears: the Chukchi Sea, East Greenland, and the Kara Sea. In addition, the estimate used for the Laptev Sea was long out-of-date and almost certainly far too low.

Altogether, excluding any kind of reasonable estimate for these four subpopulations probably underestimated the average total given by the PBSG in 2009 by at least 10,000, and the total range by more than 20,000. Moreover, using plausible methods to revise all out-of-date subpopulation estimates, as explained in the next section, would put the current global average higher than Stirling’s highest estimate for the late 1980s.

The global estimate for polar bear numbers should simply be the sum of all the subpopulation estimates, however they are defined. Officially, in 2015, the IUCN and PBSG put the global total at about 26,000 (22,000–31,000), figures that included all of the subpopulation estimates. But many of these were decades out of date, with little hope of being revised, while others have been updated since then (Table 3a, b).

I’ve taken the liberty of proposing a new estimate that resolves these issues and brings those figures up to date. I suggest that the sea ice ecoregion concept is useful for revising these estimates, as long as the Southern Beaufort Sea subpopulation is left out (because of its unique sea ice conditions).

By that I mean it is possible to suggest that the out-of-date Laptev Sea subpopulation estimate of 1000 is unaccountably far below others in the Divergent ecoregion (Table 4). Covering roughly 2.5 million square kilometres in area (both land and sea), the Laptev Sea is considerably larger than both the Chukchi and Kara Seas (which cover only about 1.7 mkm2 each), yet is similarly dominated by the continental shelf habitat that’s considered ideal for polar bears (Hamilton and Derocher 2018).

There is no evidence to suggest that the Laptev Sea, which has both mainland and offshore island habitats suitable for denning (including the eastern half of the Severnaya Zemlya archipelago and all of the New Siberian Islands), should not contain many more bears than have been estimated for the Chukchi or Kara Seas – in other words, more than 3,000. Therefore, a more plausible current estimate for the Laptev Sea is about 4,000 bears, with a range of 2,022–6,444 (using a similar ratio for the range as given for the 2016 estimate for the Chukchi Sea, discussed in detail below).

As I’ve mention previously (Chapter 4), a similar extrapolation to the one I calculated for the Barents Sea (Table 3) based on survey results for the Svalbard half of the region, was used by USGS researcher Eric Regehr and colleagues (AC SWG 2018; Regehr et al. 2018) for the Chukchi Sea: they used data from a small area within US territory to extrapolate to the entire Chukchi Region. In addition, based on their 2016 estimate for the Chukchi Sea, Regehr and colleagues further extrapolated their estimate to include the entire Chukchi/Southern Beaufort region shared by the US and Russia. This method generated an estimate of 4,437 (2,283–9,527): in other words, with `significant uncertainty.’ Subtracting the estimate for the Chukchi alone would put the 2016 estimate for the US/Russian portion of the Southern Beaufort at about 1,500 (761–3,583), also with `significant uncertainty.’{Footnote: For the purposes of this exercise, I conservatively use the estimate of 1500 to apply to the entire S. Beaufort, including the Canadian portion}.

That’s rather more than the estimate of 907 (548–1,270) calculated in 2010 for the entire Southern Beaufort (including the Russian/US portion and the Canadian portion). This is the first hint from specialists that the Southern Beaufort population has recovered from the 2004–2006 decline due to thick spring ice, as it did from a similar 1974–1976 decline (Bromaghin et al. 2015).

Details of my approach to estimating populations in some of the other subpopulations can be found in Appendix B.

The final projected mid-point estimate is 39,226 (range 26,142 to 57,727), shown in Table 5. I contend this overall increase of about 56% over the estimate of about 25,000 (range 21,500-28,500) calculated by the PBSG in 1993 (Wiig et al. 1995: 24) is not only scientifically plausible but it’s about the kind of increase we’d expect more than three decades after Ian Stirling suggested that an upper limit of about  40,000 polar bears may have existed in 1986.

Keep in mind that using my benchmark figure of 10,000 for the late 1960s, the 1993 estimate of 25,000 was a 150% increase or more than double. The lower end of my projected range is about the same as the 2015 IUCN PBSG mid-point estimate of 26,000 and the upper end is what Inuit and other Arctic residents are afraid might be true.

The 56% increase projected for 2018 might be just barely statistically significant but most importantly paints a more realistic picture of polar bear abundance at the present time than does the IUCN assessment.

Appendix B Additional notes on  population estimates (pg. 151-152)

The Arctic Basin is a bit of a black hole population-wise, since it’s unclear if any bears actually live there year round or if those spotted in the area simply use it as a spring feeding area and/or summer refuge, so I’m happy to leave that as zero. But recent surveys put the Chukchi number at about 2,937 (1,522–5,944) and the Kara Sea at 3,200 (2,700–3,500) (AC SWG 2018; Matishov et al. 2014; Regehr et al. 2018; Wiig et al. 2015).

In addition, the estimate of 2,000 for East Greenland used for the IUCN Red List assessment in 2015 (Wiig et al. 2015; Regehr et al. 2016) was the low end of an estimate of 2,000–4,000 proposed in 1993 (Wiig et al. 1995:22, 24). That estimate was reduced officially to `unknown’ by 1997 even though it was noted that a minimum population size of about 2,000 (and perhaps as large as 2,500) would be required to support the intensity of harvest that occurred in the 1990s (Derocher et al. 1998:25, 29).

I suggest a quite plausible estimate for East Greenland in 2018 is 3,000 bears (range 1,522–5,955, the same as the Chukchi estimate range). For all areas, I used broad error ranges for my projections that are similar to those used for aerial surveys of similar regions.

Similarly, the Northern Beaufort Sea subpopulation is currently likely to be the higher of two estimates calculated by biologists in 2006 (Stirling et al. 2011): while the lower estimate has been used since then (980; 825–1,135), I suggest the higher one (1,300; 750–1,800) is more appropriate now, given recent documented increases in most other subpopulation regions like Svalbard, Baffin Bay and Kane Basin, which grew by 42%, 36% and 118%, respectively, over previous estimates.

References from book

Aars, J., Lunn, N. J. and Derocher, A.E. 2006. Polar Bears: Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group, Seattle, Washington, 20-24 June 2005. Occasional Paper of the IUCN Species Survival Commission 32. IUCN, Gland, Switzerland.

AC SWG 2018. Chukchi-Alaska polar bear population demographic parameter estimation. Eric Regehr, Scientific Working Group (SWG. Report of the Proceedings of the 10th meeting of the Russian-American Commission on Polar Bears, 27-28 July 2018), pg. 5. Published 30 July. US Fish and Wildlife Service. https://www.fws.gov/alaska/fisheries/mmm/polarbear/bilateral.htm

Amstrup, S. C., Stirling, I. and Lentfer, J. W. 1986. Past and present status of polar bears in Alaska. Wildlife Society Bulletin 14: 241-254.

Andersen, M. and Aars, J. 2016. Barents Sea polar bears (Ursus maritimus): population biology and anthropegenic threats. Polar Research 35: 26029.

Bromaghin, J.F., McDonald, T.L., Stirling, I., Derocher, A.E., Richardson, E.S., Rehehr, E.V., et al. 2015. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications 25: 634–651.

Derocher, A., Garner, G.W., Lunn, N.J., and Wiig, Ø. (eds.) 1998. Polar Bears: Proceedings of the 12th meeting of the Polar Bear Specialists Group IUCN/SSC, 3-7 February, 1997, Oslo, Norway. Gland, Switzerland and Cambridge UK, IUCN.

Hamilton, S. and Derocher, A.E. 2019. Assessment of global polar bear abundance and vulnerability. Animal Conservation 22(1):83-95. doi:10.1111/acv.12439

Larsen, T. 1986. Population biology of the polar bear (Ursus maritimus) in the Svalbard area. Skriter NR. 184. Monograph of the Norwegian Polar Institute, Oslo.

Matishov, G.G., Chelintsev, N.G., Goryaev, Y. I., Makarevich, P.R. and Ishkulov, D.G. 2014. Assessment of the amount of polar bears (Ursus maritimus) on the basis of perennial vessel counts. Doklady Earth Sciences 458: 1312-1316.

Obbard, M.E., Theimann, G.W., Peacock, E. and DeBryn, T.D. (eds.) 2010.Polar Bears: Proceedings of the 15th meeting of the Polar Bear Specialists Group IUCN/SSC, 29 June-3 July, 2009, Copenhagen, Denmark. Gland, Switzerland and Cambridge UK, IUCN.

Regehr, E.V., Laidre, K.L, Akçakaya, H.R., Amstrup, S.C., Atwood, T.C., Lunn, N.J., Obbard, M., Stern, H., Thiemann, G.W., and Wiig, Ø. 2016. Conservation status of polar bears (Ursus maritimus) in relation to projected sea-ice declines. Biology Letters 12: 20160556.

Regehr, E.V., Hostetter, N.J., Wilson, R.R., Rode, K.D., St. Martin, M., Converse, S.J. 2018. Integrated population modeling provides the first empirical estimates of vital rates and abundance for polar bears in the Chukchi Sea. Scientific Reports 8 (1) DOI: 10.1038/s41598-018-34824-7  https://www.nature.com/articles/s41598-018-34824-7

Stirling I, Jonkel C, Smith P, Robertson R, Cross D. 1977b. The ecology of the polar bear (Ursus maritimus) along the western coast of Hudson Bay. Canadian Wildlife Service Occasional Paper No. 33.

Stirling, I., McDonald, T.L., Richardson, E.S., Regehr, E.V., and Amstrup, S.C. 2011. Polar bear population status in the northern Beaufort Sea, Canada, 1971-2006. Ecological Applications21: 859-876.

Taylor, M., and Lee, J. 1995. Distribution and abundance of Canadian polar bear populations: a management perspective. Arctic 48: 147-154.

Wiig, Ø., Amstrup, S., Atwood, T., Laidre, K., Lunn, N., Obbard, M., et al. 2015. Ursus maritimus. The IUCN Red List of Threatened Species 2015: e.T22823A14871490. Available from http://www.iucnredlist.org/details/22823/0

Wiig, Ø., Born, E.W., and Garner, G.W. 1995. Polar Bears: Proceedings of the 11th Working Meeting of the IUCN/SSC Polar Bear Specialists Group, Copenhagen, Denmark, 25-27 January 1993. Occasional Paper of the IUCN Species Survival Commission, No. 43. IUCN, Gland, Switzerland.

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