Even though it is well known that subadult male polar bears (≤ 4 years old) continue to grow in mass and bulk as they mature – so that their thick necks get even larger – in recent years Andrew Derocher and his students at the University of Alberta potentially endangered the lives of many subadult males in the Southern Beaufort in the process of learning relatively little they didn’t already know.
Money quote from a just-accepted paper by Master’s student Jody Pongracz and supervisor Derocher (“Summer refugia of polar bears (Ursus maritimus) in the southern Beaufort Sea” Polar Biology, in press 2016):
“The number of bears tracked varied over time due to collar design, deployment, and both planned and unplanned collar retention.”
So, how much “unplanned collar retention” issues [collars that did not fall off as expected] went on during this 2007-2010 study? They don’t say.
Is this paper saying U of A researchers knew they had ‘collar retention’ issues as far back as 2010 but continued to deploy them on subadult males after that study was over? It seems so, because they had an issue with just such a bear last year.
The bear with an apparently tight collar that was photographed last fall (see photo above) went out onto the ice and no one knows what happened – there has been no more information on him since, although researchers have apparently been watching for him, updated just yesterday). The University of Alberta statement says (under the June 2 update):
“Ongoing research at the University of Alberta is shifting to ear tag radios as required”
So now they realize that putting collars on subadult males is not such a good idea. Brilliant!
CBC News (28 October 2015): “Photo shows polar bear injured by tight radio collar“. See previous posts here and here. In a Global News interview (23 November 2015), Derocher admitted his team had “likely” put the collar on that bear, prompting the University of Alberta to issue a “Q & A” statement on the incident – which continues to insist that failure of collars to release is “rarely seen.”
From the Pongracz and Derocher paper:
“A total of 64 collars were deployed on 60 different bears with 17 on solitary adult females, 5 on females with cubs-of-the-year, 15 on females with yearlings, 4 on females with two-year-olds, and 23 on subadults (≤4 years old) (12 females, 11 males). Four bears were recollared. The number of bears tracked varied over time due to collar design, deployment, and both planned and unplanned collar retention. One adult female collared in 2009 emigrated to the Chukchi Sea in Russia and was excluded from analyses.”
But look at the statement below: out of the 60 collars deployed on bears (not including the 4 re-dos), they ‘lost’ another 11 collars (either failed collars or collars that fell off) because they actually collected data from only 49 bears:
“Of the 49 different bears tracked throughout the summer, 13 (27 %) used land areas in Alaska: 33 % (5/15) in 2007, 22 % (2/9) in 2008, 26 % (6/23) in 2009, and 32 % (6/19) in 2010. Of these 13 bears, 9 were adult females, two were subadult females, and two were subadult males.”
That’s a hell of a failure rate for the stress they put the bears through to get the collars on (especially the 4 they had to do twice). But that failure rate was still less than another of Derocher’s studies: a just-published paper (Cherry et al. 2016:5) on Western Hudson Bay polar bears (work done 2004-2008) admits that collar failures reduced their sample size by more than half (from 56 bears to 20 with functioning collars).
Back to the paper at hand…where Pongracz and Derocher note:
“None of the bears observed on land along the Alaskan coast in 2010 visited Kaktovik. Instead of being concentrated around Barter Island (Kaktovik region), as in previous years, use during summer 2010 was concentrated just offshore and along the Barrier Islands. Moderate Resolution Imaging Spectroradiometer (MODIS) images of sea ice (https://earthdata.nasa.gov) revealed there was a large amount of broken sea ice in the nearshore region throughout the summer and autumn of 2010. Bears were likely taking advantage of hunting off the available sea ice during this time, rather than using anthropogenic-derived food sources as in previous years.”
So, in 2010 there was so much sea ice that satellites could not detect that it was more attractive to polar bears than the whale bone pile onshore.
Actually, there were a lot of times when the bears appeared to be on ice when sea ice maps show none: for virtually all months (but especially July-Sept), this Fig. 2 from Pongracz and Derocher shows polar bears on ice that is not detected by satellite images (using a 15% concentration threshold).
“Nonetheless, our results indicate that the majority of the SB population remained on sea ice during summer and autumn.”
Which is precisely what they knew before the study began. But clearly worth the risk of putting the lives of young bears in danger to clarify this knowledge more precisely./sarc
One of their final, concluding statements is this absolute gem:
“A recent study examining the trend of polar bear population dynamics in the SB identified a decrease in survival and abundance in the mid 2000s (2004–2007) to coincide with a period of heavy sea ice conditions (Bromaghin et al. 2015), highlighting the complexity of impacts related to sea ice dynamics an [sic] importance of monitoring metrics other than sea ice extent.”
Wise words – except no one has ever done this.
If polar bear biologists have actually monitored thick sea ice metrics for any subpopulation (either Southern Beaufort or Western Hudson Bay), they never reported them or included them in their predictive models of future survival, such as Amstrup et al. 2007 (basis of ESA ‘threatened’ listing); Wiig et al. 2015 (the IUCN Red List assessment); Atwood et al. 2016 (latest USGS predictive model).
References
Amstrup, S.C.,Marcot, B.G. andDouglas,D.C. 2007. Forecasting the rangewide status of polar bears at selected times in the 21st century. Administrative Report, US Geological Survey. Reston, Virginia.
Atwood, T. C., B. G. Marcot, D. C. Douglas, S. C. Amstrup, K. D. Rode, G. M. Durner, and J. F. Bromaghin. 2016. Forecasting the relative influence of environmental and anthropogenic stressors on polar bears. Ecosphere 7(6):e01370. 10.1002/ecs2.1370 http://onlinelibrary.wiley.com/doi/10.1002/ecs2.1370/full [Manuscript Received: 16 July 2015]
Bromaghin, J.F., McDonald, T.L., Stirling, I., Derocher, A.E., Richardson, E.S., Rehehr, E.V., Douglas, D.C., Durner, G.M., Atwood, T. and Amstrup, S.C. 2015. Polar bear population dynamics in the southern Beaufort Sea during a period of sea ice decline. Ecological Applications 25(3):634–651.
Cherry, S.G., Derocher, A.E., and Lunn, N.J. 2016. Habitat-mediated timing of migration in polar bears: an individual perspective. Ecology and Evolution. DOI 10.1002/ece3.2233 Open access. http://onlinelibrary.wiley.com/doi/10.1002/ece3.2233/full
Pongracz, J.D. and Derocher, A.E. 2016. Summer refugia of polar bears (Ursus maritimus) in the southern Beaufort Sea. Polar Biology. 08 July 2016
DOI 10.1007/s00300-016-1997-8 http://link.springer.com/article/10.1007/s00300-016-1997-8
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 [Date assessed: 2015-08-27]
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