Even though polar bear experts admit there has been no trend in sea ice breakup or freeze-up dates since 2001 – and both Canadian and International experts say this subpopulation is stable – the public is still being misled about the status and condition of polar bears in Western Hudson Bay.
The latest example of misinformation about Western Hudson Bay polar bears appears in a feature story carried by the campus newspaper of York University (Ontario, Canada), meant to highlight the work of biology graduate student Luana Sciullo.1
The May 18, 2015 “Top Story” from York University’s campus newspaper, produced primarily for the benefit of academic faculty and university staff members, was written by unknown “special contributor” Tom Nightingale: “Canada’s polar bears are becoming more vulnerable due to effects of climate change.”
The second paragraph of this piece contains the first bit of misleading information:
“Of the 19 global subpopulations of polar bears, three are currently thought to be in decline – with Western Hudson Bay, a region encompassing southern Nunavut and northern Manitoba, showing a population decline at historic levels.” [my bold]
The “historical” reduction refers to in the IUCN Polar Bear Specialist Group report excerpt (copied again below, click to enlarge) was a drop from about 1,200 bears in 1987 to about 1,030 bears in 2011.
What that statement doesn’t tell you is that virtually all of that decline occurred in the late 1980s/early 1990s – the population hasn’t changed appreciably in size since then (Lunn et al. 2013). The IUCN PBPSG currently lists this subpopulation as “stable,” as does Environment Canada.
The second bit of misinformation comes from Sciullo herself:
“Since we have nearly 20 years of biopsies on this subpopulation, we can determine if diet and body condition have changed over time and attempt to identify potential habitat shifts that may have occurred during the same timescale,” Sciullo explains. “Our preliminary work shows body condition of females in the fall has declined over a 10-year period.” [my bold]
[Read the entire story here]
While Sciullo’s statement could be honest and true if the average body condition changed from “very fat” (Fig. 1) to simply “fat” (or even from “fat” to “normal”), that would not necessarily mean that the bears are currently in danger of starving or failing to reproduce.2 We’d have to see the actual data to know if the bears were in trouble – something no one has bothered to provide.
Figure 1. Another photo of the very fat female discussed by Ramsay and Stirling (1988:614). Captured in July 1984, she weighed 410 kg (910 lbs) (this picture was taken before a tag was glued on her head). However, she had been captured 8 months before (November), after the disastrous winter of 1983, when she weighed only 99 kg (218 lbs). See the recent discussion at PBI. Picture taken by Ian Stirling 1984, Canadian Wildlife Service. Click to enlarge.
As I’ve pointed out before, there is still no published account of this supposed decline in body condition of Western Hudson Bay polar bears:
“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!”
Conclusion: Western Hudson Bay polar bear numbers are NOT currently declining and there has been NO TREND in sea ice breakup and freeze-up dates since 2001. If there has been a change in body condition of females in the fall in the last 10 years, it cannot be due to sea ice changes since 2001.
[Note: Body condition of Southern Hudson Bay polar bears, another stable subpopulation (Obbard et al. 2013), also declined from 1980s levels but was found NOT to be correlated with sea ice conditions (Obbard et al. 2006, 2007)]
Below is a summary of the state of Western Hudson Bay status (repeated here):
An internal government report has finally been released on recent (2005-2011) WHB mark-recapture work (PDF HERE; discussed here) but it contains a population estimate only. It has no figures on changes (if any) on number of cubs, size of litters, or condition of bears over time for 1984-2011 (previous study period ended in 2004). The authors (Lunn et al. 2013:18) calculated a new estimate for the population at 2004 (previous count), using the same method they used for their new count in 2011; this generated an estimate of 742 (630-872) for 2004, vs. the 806 (653-984) estimated for 2011. This indicates that there has been no decline in population numbers since the last estimate was calculated in 2004.
In addition, Lunn and colleagues (see pg 15) found no significant trend in sea ice breakup or freeze-up dates over the period 2001-2010 (using a definition of 50% ice cover, rather than polar bear-relevant definitions of 30%/10% determined by Seth Cherry and colleagues in 2013, discussed in detail here). They also acknowledged that they did not cover a significant portion of the WHB population territory in their 2005-2011 mark-recapture surveys and this likely accounted for the difference between their estimate and the one calculated from an aerial survey in 2011.
As a consequence, the PBSG updated their population status table in late January 2015. They listed the WHB subpopulation estimate as “1030” and its trend as “stable,” in agreement with Environment Canada’s recent assessment.
Footnote 1. Sciullo’s supervisor is York University’s Faculty of Environmental Studies assistant professor Gregory Theimann (a former student of Andrew Derocher) who is also an IUCN Polar Bear Specialist Group (PBSG) member .
From her Polar Bears International bio page:
Luana Sciullo is a doctoral student in the Department of Biology at York University working under the supervision of Dr. Gregory Thiemann. She has earned a Specialized Honours undergraduate degree in Conservation Ecology from York University and completed a Master’s degree in Community Ecology at McMaster University. Currently, she is working in collaboration with researchers at Environment Canada to investigate long-term shifts in polar bear foraging ecology and body condition in relation to environmental change in Western Hudson Bay.
Footnote 2. In order to describe the body condition of polar bears, many researchers now use a “girth” measurement (e.g. Rode et al. 2012), which replaced a relative “condition index” (e.g. Stirling et al. 1999), which replaced actual weights (e.g. Derocher et al. 1992) or a subjective condition index (“1-5”) of thinnest to fattest (e.g. Amstrup et al. 2006:998). These changes make it virtually impossible to compare body condition over time or between subpopulations. Bottom line for body condition: Derocher et al. (1992:564) suggested that the critical weight for WHB females to successfully become pregnant and carry cubs to term was 189 kg (417 lbs) in the late summer.
References
Amstrup, S.C., Stirling, I., Smith, T.S., Perham, C. and Thiemann, B.W. 2006. Recent observations of intraspecific predation and cannibalism among polar bears in the Southern Beaufort Sea. Polar Biology 29, no. 11:997–1002. Pdf here.
Cherry, S.G., Derocher, A.E., Thiemann, G.W., Lunn, N.J. 2013. Migration phenology and seasonal fidelity of an Arctic marine predator in relation to sea ice dynamics. Journal of Animal Ecology 82(4):912-921.
http://onlinelibrary.wiley.com/doi/10.1111/1365-2656.12050/abstract
Derocher, A.E., Stirling, I., and Andriashek, D. 1992. Pregnancy rates and serum progesterone levels of polar bears in western Hudson Bay. Canadian Journal of Zoology 70:561-566. http://www.nrcresearchpress.com/doi/abs/10.1139/z92-084#.VVy3BEZmzs0
Lunn, N.J., Regehr, E.V., Servanty, S., Converse, S., Richardson, E. and Stirling, I. 2013. Demography and population assessment of polar bears in Western Hudson Bay, Canada. Environment Canada Research Report. 26 November 2013. PDF HERE
Obbard, M.E., Cattet, M.R.L., Moody, T., Walton, L.R., Potter, D., Inglis, J. and Chenier, C. 2006. Temporal trends in the body condition of southern Hudson Bay polar bears. Ontario Ministry of Natural Resources, Applied Research and Development Branch, Sault Ste, Marie, Canada. Climate Change Research Information Note 3. Available from http://sit.mnr.gov.on.ca
Obbard, M.E., McDonald, T.L., Howe, E.J., Regehr, E.V. and Richardson, E.S. 2007. Polar bear population status in southern Hudson Bay, Canada. Administrative Report, U.S. Department of the Interior- U.S. Geological Survey, Reston, VA.
Obbard, M.E., Middel, K.R., Stapleton, S., Thibault, I., Brodeur, V. and Jutras, C. 2013. Estimating abundance of the Southern Hudson Bay polar bears subpopulation using aerial surveys, 2011 and 2012. Ontario Ministry of Natural Resources, Wildlife Research and Monitoring Section, Science and Research Branch, Wildlife Research Series 2013-01. Peterborough, Ontario. Pdf here.
Ramsay, M.A. and Stirling, I. 1988. Reproductive biology and ecology of female polar bears (Ursus maritimus). Journal of Zoology London 214:601-624.
http://onlinelibrary.wiley.com/doi/10.1111/j.1469-7998.1988.tb03762.x/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. http://link.springer.com/article/10.1007/s10144-011-0299-9
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. http://arctic.synergiesprairies.ca/arctic/index.php/arctic/article/view/935/960
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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