Last week (24 February 2021), The Guardian was promoting a study that claims polar bears now use four times more energy than expected to survive because of ‘major ice loss’ in the Arctic, as a way of suggesting that the animals are already on their way to extinction.
But like many papers of this type, this study by Anthony Pagano and Terri Williams (Pagano and Williams 2021) is yet another model describing what biologists think may be happening based on experimental data collected from individual bears, not a conclusion based on evidence collected from subpopulations with the worst amounts of ice loss.
This is actually a review paper: a summary of what is known about measured energy use by polar bears in lab or zoo contexts (i.e. experimental evidence) – not what happens to bears under a variety of circumstances in the real world on a regular basis. What real-life evidence they use comes from studies on individual bears in the Southern Beaufort (Pagano et al. 2018; Whiteman 2018) in a year that thick spring ice made ringed seal pups scarce (and thus left some bears in less than ideal condition) or from studies of swimming SB bears (Pagano et al. 2012; Pilfold et al. 2016). Such models depend entirely on assumptions which may not be appropriate to apply across the board.
To support their claim, the authors cite a paper published last year by Laidre and colleagues (Laidre et al. 2020) about an apparent decline in body condition and cub survival among Baffin Bay polar bears that seemed to be correlated with declining summer sea ice, despite the fact that the study looked at no other possible factors except ice loss and that the population has been stable.
In addition, Laidre and colleagues included a rather important caveat for their study not mentioned in the Pagano and Williams paper:
“We note, however, that the functional and temporal relationships between declines in body condition and recruitment, and declines in subpopulation size, are poorly understood and that the trend of the BB subpopulation is currently unknown.”
More importantly, however, they ignore strongly contradictory evidence from the Chukchi and Barents Seas, hoping no one will check. However, if their premise was true – that bears in general are using four times as much energy to survive because of sea ice loss – then polar bears in the Barents Sea should be almost gone due to starvation. Barents Sea bears have been dealing with almost four times as much sea ice loss as those in Baffin Bay (Regehr et al. 2016, see graphs below) and according to Pagano and Williams, should not have been in better condition in 2015 than they were before 2005: yet the evidence shows they were (Lippold et al. 2019).
Numerous studies have documented that Chukchi Sea bears are also thriving despite having had only slightly less summer ice loss as those in Baffin Bay (AC SWG 2018; Crockford 2017, 2019; Regehr et al. 2018; Rode et al. 2014, 2015, 2018).
Polar bear specialists fail to mention such contradictions because they hope journalists and policy makers won’t notice: they hype the examples that fit their narrative and ignore or downplay the rest. I’m here to call them out on that kind of subterfuge.
AC SWG 2018. Chukchi-Alaska polar bear population demographic parameter estimation. Eric Regehr, Scientific Working Group (SWG. Report of the Proceedings of the 10th meeting of the Russian-American Commission on Polar Bears, 27-28 July 2018), pg. 5. Published 30 July 2018. US Fish and Wildlife Service. https://www.fws.gov/alaska/fisheries/mmm/polarbear/bilateral.htm pdf here.
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/
Laidre, K.L, Atkinson, S., Regehr, E.V., Stern, H.L, Born, E.W., Wiig, Ø., Lunn, N.J. and Dyck, M. 2020. Interrelated ecological impacts of climate change on an apex predator. Ecological Applications 30(4): e02071. https://doi.org/10.1002/eap.2071
Lippold, A., Bourgeon, S., Aars, J., Andersen, M., Polder, A., Lyche, J.L., Bytingsvik, J., Jenssen, B.M., Derocher, A.E., Welker, J.M. and Routti, H. 2019. Temporal trends of persistent organic pollutants in Barents Sea polar bears (Ursus maritimus) in relation to changes in feeding habits and body condition. Environmental Science and Technology 53(2):984-995.
Pagano, A.M., Durner, G.M., Amstrup, S.C., Simac, K.S. and York, G.S. 2012. Long-distance swimming by polar bears (Ursus maritimus) of the southern Beaufort Sea during years of extensive open water. Canadian Journal of Zoology 90: 663-676.
Pagano, A.M., Durner, G.M., Rode, K.D., Atwood, T.C., Atkinson, S.N., Peacock, E., Costa, D.P., Owen, M.A. and Williams, T.M. 2018. High-energy, high-fat lifestyle challenges an Arctic apex predator, the polar bear. Science 359 (6375): 568 DOI: 10.1126/science.aan8677
Pagano, A.M. and Williams, T.M. 2021. Physiological consequences of Arctic sea ice loss on large marine carnivores: unique responses by polar bears and narwhals. Journal of Experimental Biology 224:jeb228049. doi:10.1242/jeb.228049 https://jeb.biologists.org/content/224/Suppl_1/jeb228049
Pilfold, N.W., McCall, A., Derocher, A.E., Lunn, N.J., and Richardson, E. 2016. Migratory response of polar bears to sea ice loss: to swim or not to swim. Ecography in press. http://onlinelibrary.wiley.com/doi/10.1111/ecog.02109/abstract
Regehr, E.V., Hostetter, N.J., Wilson, R.R., Rode, K.D., St. Martin, M., Converse, S.J. 2018. Integrated population modeling provides the first empirical estimates of vital rates and abundance for polar bears in the Chukchi Sea. Scientific Reports 8 (1) DOI: 10.1038/s41598-018-34824-7 https://www.nature.com/articles/s41598-018-34824-7
Regehr, E.V., Laidre, K.L, Akçakaya, H.R., Amstrup, S.C., Atwood, T.C., Lunn, N.J., Obbard, M., Stern, H., Thiemann, G.W., & Wiig, Ø. 2016. Conservation status of polar bears (Ursus maritimus) in relation to projected sea-ice declines. Biology Letters 12: 20160556. http://rsbl.royalsocietypublishing.org/content/12/12/20160556
Rode, K. and Regehr, E.V. 2010. Polar bear research in the Chukchi and Bering Seas: A synopsis of 2010 field work. Unpublished report to the US Fish and Wildlife Service, Department of the Interior, Anchorage. pdf here.
Rode, K.D., Regehr, E.V., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2014. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20(1):76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract
Rode, K. D., R. R. Wilson, D. C. Douglas, V. Muhlenbruch, T.C. Atwood, E. V. Regehr, E.S. Richardson, N.W. Pilfold, A.E. Derocher, G.M Durner, I. Stirling, S.C. Amstrup, M. S. Martin, A.M. Pagano, and K. Simac. 2018. Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity. Global Change Biology http://onlinelibrary.wiley.com/doi/10.1111/gcb.13933/full
Rode, K.D., Wilson, R.R., Regehr, E.V., St. Martin, M., Douglas, D.C. & Olson, J. 2015. Increased land use by Chukchi Sea polar bears in relation to changing sea ice conditions. PLoS One 10 e0142213.
Whiteman, J.P. 2018. Out of balance in the Arctic. Science 359 (6375):514-515.