New Scientist has an article coming out next week takes a fairly reasoned approach to the polar bear conservation issue. It acknowledges that polar bear numbers have not declined in recent years even though summer sea ice dropped dramatically but goes on to perpetuate a number of myths that might not have happened if the author had done his homework or quizzed his other experts as thoroughly as he did me.
The survivors: is climate change really killing polar bears? Rapid global warming is said to be ringing the death knell for polar bears, by melthing their icy hunting grounds. But the reality is more complex. Fred Pearce, New Scientist 10 February 2018. Online now.
In the aftermath of the Harvey et al. BioScience fiasco, journalist Fred Pearce asked for an interview about my recent paper (Crockford 2017). Here is what he had to say in print about my role in polar bear conservation controversies (my bold):
“Some critics of this approach dismiss the whole idea that polar bears are in trouble. “They are doing just fine,” says Susan Crockford at the University of Victoria in Canada. She says the extinction forecasts are already demonstrably false because the rapid retreat of sea ice hasn’t caused a crash in bear numbers. Crockford has been widely criticised for her links to organised climate sceptic groups, and her blogs have become an irritant for mainstream researchers. Nonetheless, the question remains: how are the bears doing so well on vanishing ice?”
I would have been nice if he’d mentioned that a 40% decline in summer sea ice was not expected to occur until 2050, a point he admitted in our correspondence was spelled out out in the literature but what he settled for is not too bad for a compromise, considering who he was writing for:
“The question now is whether the treaty’s success is about to be undone by the disappearance of sea ice. Polar bears can swim for days, so there is little risk of mass drownings. But they face complex decisions about where to find enough seals to eat.
Here, two conflicting trends are at work. One is the diminishing extent of sea ice. During most Arctic summers, it is 40 per cent smaller than half a century ago. In some areas, like the Hudson Bay, ice is absent for three or four months running. This forces bears to spend ever longer on land, where they fast or graze on berries and birds’ eggs – a natural strategy, but one that has its limitations.
While total loss of ice is bad for bears, a second trend could be a boon. Until recently, a large proportion of Arctic sea ice was typically many metres thick, the result of many years’ winter growth. Now, what regrows in winter is predominantly thin annual ice. In March 2016, the average thickness was just 1.2 metres, compared with 3.6 metres in 1975. Polar bears do best in areas with annual ice, because thinner ice makes for a richer ecosystem, says Ian Stirling at the University of Alberta. More light reaches the water underneath, boosting plankton growth, and this ripples all the way up the food chain to seals.
The two contradictory trends are problematic for forecasts combining an assumption that bear numbers will closely track sea ice extent with forecasts of how fast the ice will melt. Using those assumptions, in 2007, the US Geological Survey predicted a two-thirds decline by mid-century. In 2015, the IUCN settled on a bear population drop of between 30 and 50 per cent.”
The last sentence seems to suggest that the 2015 prediction (which actually said there was only a 70% chance that a decline of 30% or more would happen at all, see Wiig et al. 2015 supplement; Regehr et al. 2016) should let polar bear specialists off the hook for being spectacularly wrong in the “science” they used to get polar bears listed in 2008. You might agree, but I don’t.
There are a number of other issues in the article but I don’t have time to pick the whole thing apart. One last gaff deserves mention, however, and that’s the discussion of hybrids (my bold):
“Another intriguing aspect is the extent to which the two species of bear have continued to interbreed, thanks to the large amount of DNA they share, says Ceiridwen Edwards of the University of Huddersfield, UK. It isn’t clear if this interbreeding helped them survive or whether it simply happened when the two species crossed paths. More recently, researchers have also found polar bears mating with grizzlies. There are reports of “grolar” or “pizzly” hybrids around Hudson Bay.
It isn’t too fanciful to imagine that hybrids could thrive as “pure” polar bears fade away. In the end, the polar bears’ route to salvation may be to morph back into the brown bears from which they came.”
Pearce clearly misssed the news that the claimed hybrid shot in Western Hudson Bay was proven to be a blonde grizzly by DNA analsysis after some high-profile speculation weeks earlier. Polar bear specialist Ian Stirling was quoted as saying, “I think it’s 99 per cent sure that it’s going to turn out to be a hybrid” but it turned out he was 100% wrong.
As for the last two sentences, sorry Fred: it is too fanciful. A comprehensive DNA study of hybrids reported from the western Canadian Arctic since 2006 showed they were the eight offspring of a single polar bear female that mated with two grizzly bear males (Pongracz et al. 2017), disproving the claim of recent widespread hybridization due to global warming (e.g. Kelly et al. 2010; Post et al. 2013). Another study examined a large sample of polar bear DNA and found no evidence of recent hybridization (Peacock et al. 2015). Hybridization happens rarely and is not increased by reduced sea ice but by increased numbers of grizzly males wandering north (or southeast) from Nunavut in spring.
Read the rest here, subscription needed. Overall, not great but a step in the right direction.
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 2 March 2017. Doi: 10.7287/peerj.preprints.2737v3 Open access. https://doi.org/10.7287/peerj.preprints.2737v3
Kelly, B., Whiteley, A., and Tallmon, D. 2010. Comment: The Arctic melting pot. Nature 468:891.
Pearce, F. 2018. The survivors: Is climate change really killing polar bears? New Scientist 3164 (10 February).
Pongracz, J.D., Paetkau, D., Branigan, M. and Richardson, E. 2017. Recent hybridization between a polar bear and grizzly bears in the Canadian Arctic. Arctic 70:151-160.
Post, E., Bhatt, U.S., Bitz, C.M., Brodie, J.F., Fulton, T.L., Hebblewhite, M., Kerby, J., Kutz, S.J., Stirling, I., Walker, D.A. 2013. Ecological consequences of sea-ice decline. Science 341:519-524. DOI: 10.1126/science.1235225
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.
Wiig, Ø., Amstrup, S., Atwood, T., Laidre, K., Lunn, N., Obbard, M., Regehr, E. & Thiemann, G. 2015. Ursus maritimus. The IUCN Red List of Threatened Species 2015: e.T22823A14871490. Published online here; PDF copy of report here;
PDF of supplement here.
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