[MARMAM] New paper asks: Has recent summer sea ice loss caused polar bear populations to crash?

sjcrock at shaw.ca sjcrock at shaw.ca
Sun Jan 22 17:43:50 PST 2017

I am pleased to announce the publication of the following paper: 

Crockford, S.J. 2017. Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus). PeerJ Preprints 19 January 2017. Doi: 10.7287/peerj.preprints.2737v1 Open access. https://peerj.com/preprints/2737/

Has recent summer sea ice loss caused polar bear populations to crash?

A paper published 19 January finds that predictions of polar bear population crashes due to summer sea ice loss are based on a scientifically unfounded assumption. Specifically, the paper addresses the basic premise upon which predicted population declines linked to modeled habitat loss were made by polar bear specialists back in 2006 and 2008 (by the International Union for the Conservation of Nature, IUCN, and the US Fish and Wildlife Service, USFWS), and concludes that when assessed as a testable hypothesis against data collected since then, it must be rejected. 

Those mid-2000s survival assessments predicted significant population declines of polar bears would result by mid-century as a consequence of summer sea ice extent reaching approximately 3-5 mkm2 on a regular basis: in 2006, the IUCN predicted a >30% decline in total population would occur, while in 2008, the USFWS predicted the global population would decline by an astonishing 67%. Most shocking, perhaps, was the USFWS prediction that ten subpopulations within two vulnerable sea ice ecoregions would very likely disappear entirely when summer sea ice routinely reached levels of 3-5 mkm2.

But summer sea ice declined much faster than anyone expected. In fact, those low ice levels of 3-5 mkm2 that were not expected until mid-century have occurred regularly since 2007. By 2015, polar bears had been living through the grim reality of their predicted future for almost 10 years, as the sea ice graphic below shows. This early realization of predicted sea ice levels meant the ‘sea ice decline = population decline’ assumption for polar bears could be tested against actual survival data (i.e., observations). 

As it turns, data collected between 2007 and 2015 by field biologists reveal that polar bear numbers have not declined as predicted and no subpopulation has been extirpated. Several subpopulations expected to be at high risk of decline have remained stable and at least one showed a marked increase in population size over the entire period, despite marked sea ice loss. Another at-risk subpopulation was not counted but showed marked improvement in reproductive parameters and body condition with less summer ice - the hallmarks of a stable or increasing population. 

The hypothesis that repeated summer sea ice levels of below 5 mkm2 will cause significant population declines in polar bears must be rejected. This result indicates the USFWS and IUCN judgments to list polar bears as threatened or vulnerable based on future risks of habitat loss back in 2006 and 2008 were scientifically unfounded and suggests that similar dire predictions for Arctic seals and walrus may be likewise flawed. Ultimately, the lack of a demonstrable ‘sea ice decline = population decline’ relationship for polar bears almost certainly invalidates recent survival models that predict catastrophic population declines should the Arctic become ice-free in summer.


The forum for this paper is PeerJ Preprints, a non-peer-reviewed publication service which Canadian ringed seal biologist Dr. Steven Ferguson has also recently used: 

Ferguson et al. 2016. Demographic, ecological and physiological responses of ringed seals to an abrupt decline in sea ice availability. DOI:10.7287/peerj.preprints.2309v1  https://peerj.com/preprints/2309/

Susan J. Crockford, Ph.D. (Zoology/Evolutionary Biology/Archaeozoology)
Adjunct Professor (Anthropology/Graduate Studies) email: scrock at uvic.ca
University of Victoria, British Columbia, Canada
Pacific Identifications Inc. (www.pacificid.com)
6011 Oldfield Rd., RR 3
Victoria BC V9E 2J4
phone (250) 721-7296 fax (250) 721-6215
email: sjcrock at shaw.ca
**see my author website www.susancrockford.com **
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