Previously, I summarized preliminary results of polar bear research in the Chukchi Sea undertaken between 2008 and 2011 by US Fish & Wildlife biologist Eric Regehr and US Geological Survey researcher Karyn Rode. At the time, a peer-reviewed paper on this study was promised shortly.
It now appears this paper is indeed on the way. I’m sure of that because a few weeks ago, I came across a conference presentation given by Karyn Rode that is a summary of the upcoming Chukchi research paper. The title of both presentation and ‘in review’ paper is:
“Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations.”
Rode’s slide presentation (given at the annual Lowell Wakefield Fisheries Symposium at the end of March, in Anchorage, Alaska) was posted online by the symposium organizers. It provides some very interesting details on the status of Chukchi Sea bears compared to bears in the Southern Beaufort, and contains some mighty “inconvenient” conclusions that should raise some eyebrows.
I’ve summarized these details and conclusions below in point form, below the maps.
Figure 1. Chukchi and Beaufort Seas (from Wikipedia), upper. ‘Chukchi Sea’ polar bears are shared between the USA and Russia; ‘Southern Beaufort’ bears are shared between the US and Canada, lower (from PBSG, with labels added). Pink dots are the subpopulations featured in the Rode et al. presentation and upcoming paper.
Presentation summary (direct quotes are from the presentation text):
- The amount of sea ice decline (September minimum) in the Chukchi Sea was twice the decline documented in the Southern Beaufort.
- Anthropogenic global warming (“climate change” in their lexicon) is anticipated to have the following effects on polar bears: “ loss of access to prey; reduced body condition; decreased reproduction and/or cub survival.” [‘body condition’ means relative fatness]
- However, what they found was that “body condition and reproduction of polar bears in the Chukchi Sea either improved or remained stable between 1986 and 2011.” [In fact, their data showed that for body weight, only adult females were similar in both periods (1986-1994 vs. 2008-2011) – all of the other age classes (yearlings and subadults of both sexes) were in better condition (heavier) in the later study period.]
- “Reproductive indices (yearlings per female and yearling litter size) were also similar between time periods.” In other words, there was no decline over time associated with marked declines in sea ice.
- Both male and female polar bears in the Chukchi Sea were larger (heavier) than those in the Southern Beaufort: Chukchi males were described as “much heavier.” In other words, not only was there no decline in body condition associated with marked declines in sea ice, body condition improved – the opposite of expected.
- In the Chukchi supopulation, there were more females with yearlings (indicating their cubs had survived the first year) than in the Southern Beaufort and these yearlings were also heavier (in better condition). In other words, there was no decline in cub survival associated with marked declines in sea ice, contrary to expected. [see Fig. 2 below]
- Bears in the Chukchi “appear to have more access to prey” than bears in the Southern Beaufort, despite the fact that the sea ice decline was greater in the Chukchi. In other words, there appeared to be a greater access to prey associated with marked declines in sea ice, the opposite of expected.
- Only 5% of Chukchi bears were found to be fasting in the spring, compared to about 20% of bears in the Southern Beaufort. [This appears to support the conclusion that bears in the Southern Beaufort occasionally have trouble finding food because of thick shorefast ice in the spring, discussed in this recent post, rather than because there is less ice at the end of the summer]
- In the Southern Beaufort, there was a decline in body condition and reproduction between 1986 and 2006, despite the fact that the decline in sea ice extent in September was much less than in the Chukchi: “size, condition and apparent cub survival declined” in the Southern Beaufort. In other words, S. Beaufort bears appeared to be much more strongly affected by a much smaller decline in summer ice extent – this is almost certainly because it is not the summer extent that’s causing the problem but extra-thick ice in spring.
Some of the conclusions are especially revealing; my comments in square brackets:
- “The relationship between polar bears and their habitat appears to be more complex than more ice = more bears.”
[In other words, it may also be true that less ice
≠ fewer bears;
for example, see posts here and here, on Davis Strait polar bears]
- “Bears in more southern regions may experience more sea ice loss but be buffered to some degree by more productive ecosystems.”
[In other words, bears in more southern regions are not more vulnerable than bears further north, as Stirling and Derocher (2012) have stated: “If the climate continues to warm and eliminate sea ice as predicted, polar bears will largely disappear from the southern portions of their range by mid-century.”]
- “**Messaging this complexity to the public” [“**” in original]
[In other words, this is a big problem – how do polar bear biologists maintain the “message” they wish to present to the public that global warming is harming polar bears by diminishing their habitat when the evidence not only refutes it, but proves the opposite – that some bears do better with less ice]
Ah, yes – the ‘messaging’ problem. I expect that the “messaging the complexity” portion of their published paper, when it finally appears, is going to be an extremely entertaining read. It’s certainly going to be hard to make a case that polar bears are starving and dying because of global warming if the bears aren’t starving or dying, but getting fatter instead.
Figure 2. Female Chukchi Sea polar bear with one and a half year old (“yearling”) triplet cubs, not mentioned in the 2013 presentation by Rode and colleagues but included in the Rode and Regehr (2010) report to US Fish & Wildlife. Also not mentioned in the presentation: that in 2010, “three adult males weighed over 1200 lbs and the heaviest bear was 1353 lbs, which is a record for spring research in Alaska.” (Rode and Regehr 2010:4). See previous post here.
References
Rode, K.D., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2013. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Oral presentation by Karyn Rode, 28th Lowell Wakefield Fisheries Symposium, March 26-29. Anchorage, AK. Abstract below, pdf here.
Rode, K.D., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. in review [journal not indicated]. “Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations.”
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.
Stirling, I. and Derocher, A.E. 2012. Effects of climate warming on polar bears: a review of the evidence. Global Change Biology 18 (9): 2694-2706 doi:10.1111/j.1365-2486.2012.02753.x http://onlinelibrary.wiley.com/doi/10.1111/j.1365-2486.2012.02753.x/abstract
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