Some inconvenient polar bear facts supported by scientific literature

The evidence that polar bears have not been harmed by recent declines in sea ice is contained in the scientific literature, no matter what some researchers say when they talk to the media.

Here’s a few of those facts (not all, by any means), with the references to back them up:

• Southern Beaufort bear numbers did not fall in the mid-2000s due to global warming or summer sea ice loss but because of thick spring sea ice conditions that were as bad as a similar event that occurred in 1974-1976 – a fact that’s well documented in the scientific literature (Amstrup et al. 1986; Bromaghin et al. 2015; Burns et al. 1975; Lentfer 1976; Harwood et al. 2000, 2012; Pilfold et al. 2015; Smith 1987; Stirling 2002; Stirling and Lunn 1997; Stirling et al. 1980, 1982). See this post: Biggest threat to polar bears reconsidered [especially the appendix]
• Recent loss of sea ice in the Beaufort Sea (April/May 2016) has been due to the actions of the massively strong current called the Beaufort Gyre.  See this post (with NASA video) Beaufort Sea fractured ice due to strong Beaufort Gyre action – not early melt
• The polar bear who swam the longest may have lost 22% of her body weight but that is a meaningless figure – other research shows that 22% was less than she would have lost if she’d stayed on land (Derocher and Stirling 1995; Durner et al. 2011; Pagano et al. 2012; Pilfold et al. 2016 in press). See this post: Longest-swimming polar bear lost less weight than if she had stayed onshore
• Although it’s true that polar bears that spend the summer on the sea ice of the Arctic Basin don’t catch very many seals, biologists assume most bears eat very little over the summer regardless of where they spend it – on land or on sea ice (Derocher et al. 2002; Pilfold et al. 2015; Hammill and Smith 1991; Stirling 1974; Stirling and Øritsland 1995). See these posts: Polar bears out on the sea ice eat few seals in summer and early fall and Summer habitat for most polar bears is either shoreline or sea ice in the Arctic Basin
• Starvation is the leading cause of death for young bears, sick or injured bears, and very old bears – it’s just a fact of life for this apex predator with no natural enemies (Amstrup 2003:602). Here’s what Amstrup said about natural mortality:
  

  “Starvation of independent young as well as very old animals must account for much of the natural mortality among polar bears… Also, age structure data show that subadults aged 2-5 years survive at lower rates than adults (Amstrup 1995), probably because they are still learning hunting and survival skills. … I once observed a 3-year-old subadult that weighed only 70 kg in November. This was near the end of the autumn period in which Beaufort Sea bears reach their peak weights (Durner and Amstrup 1996), and his cohorts at that time weighed in excess of 200 kg. This young animal apparently had not learned the skills needed to survive and was starving to death.”

References
Amstrup, S.C. 2003. Polar bear (Ursus maritimus). In Wild Mammals of North America, G.A. Feldhamer, B.C. Thompson and J.A. Chapman (eds), pg. 587-610. Johns Hopkins University Press, Baltimore.

Amstrup, S.C., Stirling, I. and Lentfer, J.W. 1986. Past and present status of polar bears in Alaska. Wildlife Society Bulletin 14: 241–254.

Bromaghin, J.F., McDonald, T.L., Stirling, I., Derocher, A.E., Richardson, E.S., Rehehr, E.V., Douglas, D.C., Durner, G.M., Atwood, T. and Amstrup, S.C. 2015. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications 25(3):634-651. http://onlinelibrary.wiley.com/doi/10.1890/14-1129.1/abstract

Burns, J. J., Fay, F. H., and Shapiro, L.H. 1975. The relationships of marine mammal distributions, densities, and activities to sea ice conditions (Quarterly report for quarter ending September 30, 1975, projects #248 and 249), pp. 77-78 in Environmental Assessment of the Alaskan Continental Shelf, Principal Investiagors’ Reports. July-September 1975, Volume 1. NOAA, Environmental Research Laboratories, Boulder Colorado. [available online] pdf here.

Derocher, A.E. and Stirling, I. 1995. Temporal variation in reproduction and body mass of polar bears in western Hudson Bay. Canadian Journal of Zoology 73: 1657-1665.

Derocher, A.E., Wiig, Ø., and Andersen, M. 2002. Diet composition of polar bears in Svalbard and the western Barents Sea. Polar Biology 25 (6): 448-452. http://link.springer.com/article/10.1007/s00300-002-0364-0

Durner, G.M. and Amstrup, S.C. 1996. Mass and body-dimension relationships of polar bears in northern Alaska. Wildlife Society Bulletin 24(3):480-484.

Durner, G.M., Whiteman, J.P., Harlow, H.J., Amstrup, S.C., Regehr, E.V. and Ben-David, M. 2011. Consequences of long-distance swimming and travel over deep-water pack ice for a female polar bear during a year of extreme sea ice retreat. Polar Biology 34: 975-984.

Lentfer 1976. Polar bear management and research in Alaska 1974-76. Pg. 187-197 in [Anonymous]. Polar Bears: Proceedings of the 6th meeting of the Polar Bear Specialists Group IUCN/SSC, 7 December, 1976, Morges, Switzerland. Gland, Switzerland and Cambridge UK, IUCN. http://pbsg.npolar.no/en/meetings/

Harwood, L.A., Smith, T.G. and Melling, H. 2000. Variation in reproduction and body condition of the ringed seal (Phoca hispida ) in western Prince Albert Sound, NT, Canada, as assessed through a harvest-based sampling program. Arctic 53(4): 422 – 431.

Harwood, L.A., Smith, T.G., Melling, H., Alikamik, J. and Kingsley, M.C.S. 2012. Ringed seals and sea ice in Canada’s western Arctic: harvest-based monitoring 1992–2011. Arctic 65: 377–390.

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.

Pilfold, N. W., Derocher, A. E., Stirling, I. and Richardson, E. 2015 in press. Multi-temporal factors influence predation for polar bears in a changing climate. Oikos. http://onlinelibrary.wiley.com/doi/10.1111/oik.02000/abstract

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

Rode, K.D., Peacock, E., Taylor, M., Stirling, I., Born, E.W., Laidre, K.L. and Wiig, Ø. 2012. A tale of two polar bear populations: ice habitat, harvest and body condition. Population Ecology 54: 3–18.

Rode, K.D., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W. and Budge, S. 2013. Comparison in polar bear response to sea ice loss in the Chukchi and southern Beaufort Seas. Oral presentation at the 28th Lowell Wakefield Fisheries Symposium, March 26–29. Anchorage, AK.

Rode, K. D., Pagano, A.M., Bromaghin, J.F., Atwood, T.C., Durner, G.M. and Simac K.S. 2014a. Effects of capturing and collaring on polar bears: Findings from long-termresearch on the southern Beaufort population. Wildlife Research 41(4): 311–322.

Rode, K.D., Regehr, E.V.,Douglas,D.,Durner, G.,Derocher, A.E., Thiemann, G.W. and Budge, S. 2014b. 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.

Smith, T.G. 1987. The Ringed Seal, Phoca hispida, of the Canadian Western Arctic. Canadian Bulletin of Fisheries and Aquatic Sciences 216. Department of Fisheries and Oceans, Ottawa.

Stirling, I. 1974. Midsummer observations on the behavior of wild polar bears (Ursus maritimus). Canadian Journal of Zoology 52: 1191-1198. http://www.nrcresearchpress.com/doi/abs/10.1139/z74-157#.VR2zaOFmwS4

Stirling, I. 2002. Polar bears and seals in the eastern Beaufort Sea and Amundsen Gulf: a synthesis of population trends and ecological relationships over three decades. Arctic 55 (Suppl. 1): 59–76.

Stirling, I. and Lunn, N.J. 1997. Environmental fluctuations in arctic marine ecosystems as reflected by variability in reproduction of polar bears and ringed seals. In: Ecology of Arctic Environments,Woodin, S.J. and Marquiss, M. (eds). Blackwell Science.

Stirling, I. and Øritsland, N. A. 1995. Relationships between estimates of ringed seal (Phoca hispida) and polar bear (Ursus maritimus) populations in the Canadian Arctic. Canadian Journal of Fisheries and Aquatic Sciences 52: 2594 – 2612. http://www.nrcresearchpress.com/doi/abs/10.1139/f95-849#.VNep0y5v_gU

Stirling, I., Schweinsburg, R.E., Kolenasky, G.B., Juniper, I., Robertson, R.J. and Luttich, S. 1980. Proceedings of the 7th meeting of the Polar Bear Specialists Group IUCN/SSC, 30 January-1 February, 1979, Copenhagen, Denmark. Gland, Switzerland and Cambridge UK, IUCN, pp. 45–53.

Stirling, I, Kingsley, M. and Calvert, W. 1982. The distribution and abundance of seals in the eastern Beaufort Sea, 1974–79. Canadian Wildlife Service Occasional Paper 47. Edmonton.

Whiteman, J.P., Harlow, H.J., Durner, G.M., Anderson-Sprecher, Albeke, S.E., Regehr, E.V., Amstrup, S.C., and Ben-David, M. 2015. Summer declines in activity and body temperature offer polar bears limited energy savings. Science 349 (6245):295-298.