Global population of polar bears has increased by 2 650 5 700 since 2001 Posted on July 15 2013 Comments Off
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.
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.
Changes in the early 2000s Between 2001 and 2005 the Queen Elizabeth Islands region in northern most Canada (see map above) was dropped altogether as a distinct subpopulation (along with its estimated 200 bears) and the tentative total of 2 000 bears estimated for East Greenland was also dropped (from both minimum and maximum portions of the 21 500 25 000 range).
In addition about 1 000 was added to the minimum and about 1 000 subtracted from the maximum totals because a new more accurate estimate for the Barents Sea became available in 2004 replacing the guess of 2 000 5 000 used in the 2001 report.1
That means between 2001 and 2005 due to accounting and upgrade changes only a total of 1 200 bears was removed from the minimum portion of the global estimate and 3 200 removed from the maximum portion of the global estimate changes that had nothing to do with documented declines in subpopulations. These changes were all the result of differences in the way the data was presented (or not).
As a consequence if the total population of polar bears had otherwise been unchanged or declined in the early 2000s the total in 2005 should have been 20 300 21 800 or less. However the official total for 2005 was given as 20 000 25 000 reflecting a reduction of 1 500 in the minimum portion of the estimate only (i.e. down from 21 500 25 000 in 2001).
This means there must have been a net increase of 300 3 200 bears (average 1 750) among the remaining subpopulations during the early 2000s. A comparison of the tables suggests these increases occurred in the Lancaster Sound Gulf of Boothia and Davis Strait subpopulations.
Changes in the late 2000s In 2009 the tentative total of 2 000 bears estimated for the Chukchi Sea subpopulation was dropped from both the minimum and maximum total estimates because it was deemed not accurate enough 2 000 became zero even though bears are well known there (see previous posts here and here).
In addition in the 2009 report the Barents Sea subpopulation estimate was changed given as 2 997 (2 299 4 116) in 2005 based on studies completed in 2004 it was adjusted down to 2 650 (1 900 3 600) in 2009 based on the same 2004 data. This adjustment dropped another 350 bears from the minimum total2 and a whopping 500 bears from the maximum total (numbers rounded to keep things simple 2) that again had nothing to do with a documented change in the number of bears in the Barents Sea but rather a change in accounting.
But did the total estimate of polar bears worldwide in 2009 drop from 20 000 25 000 to 17 650 22 500 to reflect the removal of the Chukchi estimate and the adjustment in the Barents Sea figure No it did not.
Now the Barents Sea estimate is not the only subpopulation estimate that was 'adjusted' from one number to another based on the same survey data but since we are tracking the Barents Sea figures from a guess in the 2001 report to a scientific estimate in 2009 it's important to include this final adjustment
As a consequence because the global estimate did not change between 2005 and 2009 there must have been another net increase of 2 350 2 500 polar bears among the remaining subpopulations in the late 2000s.
In summary in order for the worldwide estimate of polar bears to have remained virtually unchanged since 2001 the global population must have increased by 2 650 5 700 bears (average 4 175) between 2001 and 2013. These increases did not off set the slight declines in other subpopulations as the unchanging totals imply but were in addition to them.
In other words it appears that the global population of polar bears could not have remained stable since 2001 it had to have increased by an average of almost 4 200 bears
Footnotes 1. The Barents Sea subpopulation was roughly estimated to have been 2 000 5000 in 2001. This means that of the 20 000 25 000 total estimate 2 000 of the 20 000 minimum came from the Barents Sea and 5 000 of the 25 000 maximum came from the Barents Sea. However the contribution of Barents Sea bears to the total changed in 2005 because a new more accurate estimate became available (stated as 2 997 average range of 2 299 4 116 ). No other subpopulation estimate except the Barents Sea changed from a tentative educated guess to a science based estimate between 2001 and 2012 so I contend it is valid to include this as an accounting change.
2. In 2005 as far as I can tell 2 997 of the 20 000 total minimum estimate came from the Barents Sea and 4 116 of the 25 000 maximum estimate came from the Barents Sea (that s because in contrast to previous years in 2005 the total estimate range (i.e. 20 000 25 000 ) appears to be the total of the average estimate for each subpopulation (rather than the minimum) and the total of the maximum estimate for each subpopulation see previous post here.
References2001 PBSG report Lunn N.J. Schliebe S. and Born E.W. (eds.). 2002. Polar Bears Proceedings of the 13th working meeting of the IUCN/SSC Polar Bear Specialists Group 23 28 June 2001 Nuuk Greenland. Gland Switzerland and Cambridge UK IUCN.
2005 PBSG report Aars J. Lunn N. J. and Derocher A.E. (eds.) 2006. Polar Bears Proceedings of the 14th Working Meeting of the IUCN/SSC Polar Bear Specialist Group 20 24 June 2005 Seattle Washington USA. Occasional Paper of the IUCN Species Survival Commission 32. IUCN Gland Switzerland and Cambridge UK.
2009 PBSG report 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.
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