Why did the Southern Beaufort polar bear population survey stop in 2010? It’s clear that the recently-published and widely-hyped new study stopped before the population rebound from a known decline was complete.
The researchers of the recently-published paper knew before starting their mark-recapture study in 2007 that the population decline had taken place. They also knew why the numbers dropped and that previous declines, caused by similar conditions, had been followed by a full recovery.
Did they really think a full recovery in population numbers was possible in only three years, when cubs born in 2007 would not yet have been old enough to reproduce?
In fact, a US Fish and Wildlife Service (USFWS) fall survey of Southern Beaufort polar bears in 2012 found numbers were higher than they had been in a decade.
To recap, the new paper (Bromaghin et al. 2014, in press) took numbers from previous studies that revealed a statistically insignificant decline from 2004-2006 and formulated a new kind of model that suggested the decline had actually been more severe, between 25-50%. The only new data reported was collected between 2007 and 2010 (details here).
Survival of polar bears started to improve markedly by 2007 (a year of very low summer sea ice) and the population had recovered by 2010 to ~900 (range 606-1,212). The authors looked, but found no correlation of the decline with summer sea ice conditions as predicted by the IUCN Polar Bear Specialist Group (PBSG) earlier this year.
However, the USFWS reported in their 2013/2014 Polar Bear Newsletter [pdf here, pg. 17, lower right] that their fall aerial survey results showed that in 2012 the population was “high” compared to previous years and that bears were in “average” condition.
“The number of polar bears observed in 2012 was high relative to similar surveys conducted over the past decade. Body condition appeared relatively normal for this time of year with most bears reported to be in average body condition.”
Why would the authors of the 2014 paper cherry-pick their end dates, when they had to have known when they submitted their paper for publication that the population size had continued to recover beyond 2010?