Large margins of error in polar bear population estimates means the conservation status threshold of a 30% decline (real or predicted) used by the US Endangered Species Act and the IUCN Red List is probably not valid for this species.
Several recent subpopulation estimates have shown an increase between one estimate and another of greater than 30% yet deemed not to be statistacally significant due to large margins of error. How can such estimates be used to assess whether population numbers have declined enough to warrant IUCN Red List or ESA protection?
What do polar bear population numbers mean for conservation status, if anything?
Posted in Conservation Status, Population
Tagged baffin bay, declining, Derocher, errors, ESA, estimate, facts, IUCN Red List, numbers, polar bear, population, science, significance, statistics, Svalbard, western hudson bay
A just-released report on the most recent (2016) survey shows Western Hudson Bay polar bear numbers were still stable despite predictions that this subpopulation would be wiped out completely (reduced to zero) due to low Arctic sea ice.
The authors of the report on the August 2016 aerial survey of the Western Hudson Bay polar bear subpopulation (Dyck et al. 2017) state clearly that the only trends they could find were that the number of adult males increased somewhat over 2011 estimates and the number of females either declined or remained stable. The overall population estimate was a bit lower (11% less) compared to the 2011 survey but the difference is not statistically significant. Therefore, the population status must be stable.
2011 estimate: 949 bears (using comparable data, range 618-1280), litter size 1.43
2016 estimate: 842 bears (using comparable data, range 562-1121), litter size 1.63
[cf. Foxe Basin [stable], from 2009-2010 survey (Stapleton et al. 2016) litter size was 1.54]
An 11% decline in WH numbers since 2011 is most definitely NOT the decline to ZERO (extirpation) we were told to expect with Arctic sea ice as low as it has been since 2007 (Crockford 2017, see list of annual minimum extents 2007-2017 here).
Note: The percentage decline from 2011 to 2016 for Western Hudson Bay polar bears is 11%, NOT 18% as claimed recently by Andrew Derocher on twitter: it is not appropriate to compare the official 2011 estimate of 1030 (Stapleton 2014) to the 2016 estimate of 842 because the methods used to generate the estimates were different (Dyck et al. 2017). The authors of the report state that the estimate for 2011 that’s comparable to 2016 is 949.
An 11% decline from 1030 would be 917 bears, a statistically insignificant decline that is also biologically insignificant and therefore, so slight as to indicate a stable population.
Predicted sea ice at 2050 and 2080 shown below (see Crockford 2017 for details):
Quotes, map, and table from the Dyck et al. 2017 report (pdf here) are copied below.
Posted in Conservation Status, Population, Sea ice habitat
Tagged decline, Derocher, estimate, extirpated, facts, increasing, polar bear, population, significant, size, slight, stable, statistics, status, survey, western hudson bay
CBS News published a predictably one-sided “Cover Story” this morning (14 February 2016) about Churchill, Manitoba – the self-proclaimed Polar Bear Capital of the World.
This is the online version of a Sunday morning TV special that’s not available where I live. It’s yet another example of how the media feeds the politics of polar bears and prevents the advancement of science. Here’s my take on this CBS effort.
Posted in Advocacy, Conservation Status, Population
Tagged Amstrup, assessment, capital, CBS, Churchill, estimate, facts, IUCN Polar Bear Specialist Group, IUCN Red List, polar bear, Polar Bears International, population, predictions, save our sea ice, science, western hudson bay
Results of this fall’s Barents Sea population survey have been released by the Norwegian Polar Institute and they are phenomenal: despite several years with poor ice conditions, there are more bears now (~975) than there were in 2004 (~685) around Svalbard (a 42
30% increase) and the bears were in good condition.
Oddly, in a September report right after the count, biologist Jon Aars reported them in “excellent” condition, with some of them “as fat as pigs.” I guess “good” is the same as “excellent.”
Bears in the Russian portion of the Barents Sea were not counted this year because the Russians would not allow it; the previous total count, from 2004, was 2,650 (range ~1900-3600) for the entire region.
In the map above (courtesy the IUCN Polar Bear Specialist Group), the Svalbard archipelago is on the left (Norwegian territory) and the archipelagos of Franz Josef Land and Novaya Zemlya on the right (Russian territory).
Oddly, the comments made by lead researcher Jon Aars to a Norwegian newspaper (in English), which picked this up yesterday (“Polar bears make a comeback” ), were far more positive than those in the press release (which is likely all that western media will see).
UPDATE 24 December 2015: The new population survey number for Svalbard is actually a 42% increase over the 2004 number. Thanks to Arvid Oen, a WUWT reader, for alerting Anthony Watts to the error, and to Anthony for passing it along. Title and text fixed accordingly, apologies to any others who have picked this up. Cheers and Merry Christmas.
Posted in Conservation Status, Population, Sea ice habitat, Uncategorized
Tagged Aars, Arctic Fallacy, Barents Sea, estimate, expert opinion, facts, increase, information, IUCN, Norwegian Polar Institute, PBSG, polar bear, population size, sea ice, Svalbard
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.
Posted in Population
Tagged Aars, Derocher, estimate, global numbers, IUCN Polar Bear Specialist Group, Obbard, PBSG, polar bear, population size, Stirling, Vongraven