Global polar bear estimates may not be what experts claimed they were
Last week (May 22), I received an unsolicited email from Dr. Dag Vongraven, the current chairman of the IUCN Polar Bear Specialist Group (PBSG).
The email from Vongraven began this way:
Below you’ll find a footnote that will accompany a total polar bear population size range in the circumpolar polar bear action plan that we are currently drafting together with the Parties to the 1973 Agreement. This might keep you blogging for a day or two.” [my bold]
It appears the PBSG have come to the realization that public outrage (or just confusion) is brewing over their global population estimates and some damage control is perhaps called for. Their solution — bury a statement of clarification within their next official missive (which I have commented upon here).
Instead of issuing a press release to clarify matters to the public immediately, Vongraven decided he would let me take care of informing the public that this global estimate may not be what it seems.
OK, I’ll oblige (I am traveling in Russia on business and finding it very hard to do even short posts – more on that later). The footnote Vongraven sent is below, with some comments from me. You can decide for yourself if the PBSG have been straight-forward about the nature of their global population estimates and transparent about the purpose for issuing it.
Here is the statement that the PBSG proposes to insert as a footnote in their forthcoming Circumpolar Polar Bear Action Plan draft:
“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. It is also important to note that even though we have scientifically valid estimates for a majority of the subpopulations, some are dated. Furthermore, there are no abundance estimates for the Arctic Basin, East Greenland, and the Russian subpopulations. Consequently, there is either no, or only rudimentary, knowledge to support guesses about the possible abundance of polar bears in approximately half the areas they occupy. Thus, the range given for total global population should be viewed with great caution as it cannot be used to assess population trend over the long term.” [my bold]
So, the global estimates were “…simply a qualified guess given to satisfy public demand” and according to this statement, were never meant to be considered scientific estimates, despite what they were called, the scientific group that issued them, and how they were used (see footnote below).
All this glosses over what I think is a critical point: none of these ‘global population estimates’ (from 2001 onward) came anywhere close to being estimates of the actual world population size of polar bears (regardless of how scientifically inaccurate they might have been) — rather, they were estimates of only the subpopulations that Arctic biologists have tried to count.
For example, the PBSG’s most recent global estimate (range 13,071-24,238) ignores five very large subpopulation regions which between them potentially contain 1/3 as many additional bears as the official estimate includes (see map below). The PBSG effectively gives them each an estimate of zero.
Figure 1. Based on previous PBSG estimates and other research, there may be ~6,000-9,000 (perhaps less but maybe more) bears living in the regions marked in black that are not included in the most recent PBSG “global population estimate” – their population estimates are “zero.” CS, Chukchi Sea; LS, Laptev Sea; KS, Kara Sea; EG, East Greenland; AB, Arctic Basin.
Based on previous PBSG estimates and other research reports, it appears there are probably at least another 6,000 or so bears living in these regions and perhaps as many as 9,000 (or more) that are not included in any PBSG “global population estimate”: Chukchi Sea ~2,000-3,000; East Greenland, ~ 2,000-3,000; the two Russian regions together (Laptev Sea and Kara Sea), another ~2,000-3,000 or so, plus 200 or so in the central Arctic Basin. These are guesses, to be sure, but they at least give a potential size
In other words, rather than assigning a “simple, qualified guess” for these subpopulations that have not been formally counted as well as those that have been counted (generating a total figure that is indeed a “global population estimate,” however inaccurate), the PBSG have been passing off their estimate of counted populations as a true global population estimate, with caveats seldom included.
Healthy Polar Bears, Less Than Healthy Science – A lecture by Dr. Susan J. Crockford – House of Lords, 11 June 2014