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Some inconvenient polar bear facts supported by scientific literature

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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.

USGS w_polarbearscience_caption 2016

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 thickspring 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 theBeaufort GyreSee 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

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