In my last post, Western Hudson Bay polar bears are not like the others – Part 1 I stopped at the point where the following question arose: “The documented decline in cub survival and condition of females documented above occurred between 1985 and 1992 – what about now?”
I promised to address that question in a separate post because it revealed some interesting issues that deserve star billing.
What I found might surprise you: apparently, virtually all of the data supporting a decline in the western Hudson Bay polar bear population since 1985 has been collected but has not been published. This revelation came from none other than the 2012 summary by Ian Stirling and Andrew Derocher that I’ve mentioned before here.
[updated Sept. 28, 2012 – reference added, see below]
Stirling and Derocher (2012:2699) state that “the mean mass of adult females [in western Hudson Bay] declined (by about 20%) between 1980 and 2007 (Fig. 5).” It is this parameter (mean body mass of females), what they call “a proxy for body condition”, that has apparently had detrimental effects on reproduction (including production of triplets (litter size) and age at weaning) and cub survival that is “statistically linked to the progressively earlier breakup of sea ice.”
However, it turns out that the data used to construct Figure 5 (as well as Figure 4, “relationship between date of breakup and the physical condition of adult females and adult males…”) is not only out of date (it goes to 2007 only) but it uses unpublished data.
Not even “paper submitted” or “in review” but information collected from studies that have not been peer-reviewed and data that cannot be verified. [two similar figures appear in Stirling 2011, pgs. 290 (“fig. 20”) & 285 (“fig. 19”), see my review of his book here].
I’ve copied Figure 5 from the Stirling and Derocher paper below. The “Stirling and Parkinson 2006” paper cited in the original caption presents data from 1980 to 2004 only, which means the additional data (2005-2007) are held by in the private archives of Nick Lunn and Ian Stirling.
So what about the evidence that cub survival and other reproductive parameters (like litter size and age at weaning) in the WHB population have changed as a result of declines in the body condition of females since 1985?
Regarding recent proportion of independent yearlings (weaned 1.5 year olds), Stirling and Derocher (2012:2698) state:
“the proportion of independent yearlings fell from over 81% before 1980 to a mean of 34% in 1980-1992 (Derocher & Stirling, 1995). By the late 1990s, the proportion of independent yearlings dropped to <10% (Stirling et al., 1999) and by the early 2000s was almost nonexistent (I. Stirling, unpublished data).”
Regarding incidence of triplets, Stirling and Derocher (2012:2698) state:
“Triplet litters, which comprised 12% of 265 litters between 1980 and 1992 (Derocher & Stirling, 1995), are now rarely seen (I. Stirling, unpublished data).“
[update Sept. 28, 2012: Robinson et al. (2012:139) also cite unpublished data from Ian Stirling (“I. Stirling, Canadian Wildlife Service, personal communication“) for the statement that triplets are “less commonly observed today.” ]
Again, not “paper submitted” or “in review” but “take Ian Stirling’s word for it, you don’t need to see the numbers.” Conclusions based on information collected from studies whose methods have not been peer-reviewed, using data that cannot be verified by anyone.
So in fact, all three of the biological parameters that Derocher and Stirling (2012) claim changed in a significant way since the early 2000s in WHB – that are “statistically linked to progressively earlier breakup of sea ice” – are based on unpublished data. They have drawn conclusions based on data that we are not allowed to see.
If Stirling has up-to-date information that conclusively demonstrates how dire this situation is, why on earth has he – or whoever collected it – not published that data?
While Stirling and Derocher (2012) claim to “summarize the evidence” that documents the effects of “climate warming” on polar bears, it turns out there has been no published data available for size of WHB litters or proportion of independent yearlings since 1998 (Stirling et al. 1999) – 14 years ago – and no more recent data on cub survival in WHB since 1992 – 20 years ago (Derocher and Stirling 1995).
There has been no more recent data published on body mass of lone females since 2004, or of adult males and females with cubs in WHB since 1998 – 14 years ago – (Stirling et al. 1999:296; Stirling and Parkinson 2006:265), even though this is the data that suggests “climate warming” has been negatively impacting WHB polar bears since 1985!
And those dates of spring breakup of Hudson Bay sea ice that are apparently correlated to changes in polar bear life history traits? Those data are unpublished as well. See Stirling and Derocher’s (2012) figure 3 below, where the published data available stops at 1998 (taken from Stirling et al. 1999), even though the graph goes to 2007. And since it is now 2012, that graph is woefully out of date.
Why on earth did Stirling and Derocher not update that graph? Could it be that the data from 2009 (a very late breakup year) would make their line flatten out? See my discussion of a virtually identical figure that appears in Stirling 2011, reviewed here.
**In summary, much of the data that apparently nails the lid on the coffin for the conclusion that recent declines of WHB polar bears are correlated to sea ice change has apparently been collected but no one has bothered to publish it.**
[In my next post, “Western Hudson Bay polar bears are not like the others – Part 2”, I will explore the possibility that rather than responding to the effects of global warming, western Hudson Bay polar bear numbers may simple be returning to ‘normal’ after a period of natural population growth in response to the intense over-harvests that occurred between 1890 and 1930 and again from 1950 to 1968. This explanation has been suggested as a distinct possibility in the past (e.g. Derocher and Stirling 1995) but seems to have been abandoned recently in favor of blaming reduced sea ice due to “climate warming” exclusively. More on that soon.]
Derocher, A.E. 2005. Population ecology of polar bears at Svalbard, Norway. Population Ecology 47:267-275.
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. http://www.nrcresearchpress.com/doi/abs/10.1139/z95-197
Robinson, R., Smith, T.S., Kirschloffer, B.J., and Rosa, C. 2012. Polar bear (Ursus maritimus) cub mortality at a den site in northern Alaska. Polar Biology 35:139-142. http://rd.springer.com/article/10.1007/s00300-011-1013-2
Stirling, I. and Derocher, A.E. 2012. Effects of climate warming on polar bears: a review of the evidence. Global Change Biology 18:2694-2706. doi:10.1111/j.1365-2486.2012.02753.x
Stirling, I., Lunn, N.J. and Iacozza, J. 1999. Long-term trends in the population ecology of polar bears in Western Hudson Bay in relation to climate change. Arctic 52:294-306.
Stirling, I. and Parkinson, C.L. 2006. Possible effects of climate warming on selected populations of polar bears (Ursus maritimus) in the Canadian Arctic. Arctic 59:261-275. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/issue/view/16.
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