Wrangel Island research team counted a record number of Chukchi Sea polar bears in 2020
Posted on September 21, 2021 | Comments Offon Wrangel Island research team counted a record number of Chukchi Sea polar bears in 2020
Many Chukchi Sea polar bears spend the summer on Wrangel Island and a survey there conducted by Russian researchers in 2020 reportedly collected data on a record 747 bears, well up from the 589 reportedly counted in 2017 by the same team (photo below is from 2015).
Note the latest survey of the Chukchi Sea estimated about 3,000 bears inhabit the region (AC SWG 2018; Regehr et al. 2018), at least 1,000 more that the figure of 2,000 used in recent IUCN assessments and survival predictions (Amstrup et al. 2007; Regehr et al. 2016; Wiig et al. 2015). Wrangel Island is the primary terrestrial denning area in the Chukchi Sea (Garner et al. 1984; Rode et al. 2014) and a recently published study showed that the body condition (i.e. fatness) and litter size of Chukchi Sea polar bears has not been negatively affected by low summer sea ice (Rode et al. 2021).
According to a short project report last week from polar bear specialist Eric Regehr (formerly at the US Wildlife Service, now University of Washington), filed on 14 September 2021 (‘Polar bears on Wrangel Island‘), Russian researchers at the Wrangel Island State Nature Reserve were able to continue work that began in 2016 as a joint American/Russian project. Covid-19 restrictions kept US researchers from participating in 2020 and again this year.
There were no details provided on the methodology of the study and no report on the work is yet available. But rest assured that if any signs of a population collapse or starving bears had been spotted, it would have been headline news around the world instead of a ‘good news’ story on the Polar Bears International website. On the contrary, the photo that accompanies Regehr’s article (below) appears to show a female with four cubs-of-the-year, a rare phenomenon also reported in 2017. In fact, it sounds like the Chukchi Sea subpopulation is still ‘productive and heathly’ as Regehr told the Daily Mail they were in 2017, despite markedly reduced summer sea ice since 2007.
Polar bear numbers on Wrangel Island since 2007
Although methods of counting and amount of the island surveyed might not be comparable between years (impossible to know at this point), here is what the reported counts have been year to year:
2020 747 bears (Regehr 2021)
2017 589 bears (Regehr, quoted in the Daily Mail 2017)
2012 ~200-300 bears (Ovsyanikov and Menyushina 2015)
2013 ~200-300 bears (Ovsyanikov and Menyushina 2015)
2007 ~550-600 bears (Ovsyanikov 2010)
Sea ice conditions
The number of bears taking refuge on Wrangel Island during the summer clearly varies year to year. This variability may be a function of local sea ice conditions, which also vary year to year, rather than reflecting the overall numbers of bears in the subpopulation. However, contrary to predictions that lack of ice year after year should cause population stress, counts of bears on Wrangel Island in ‘high-bear’ years have clearly increased since 2007 despite a corresponding decline in summer sea ice.
This year (at 19 September 2021), Wrangel Island is still almost surrounded by ice, as it was earlier this month, which may mean that fewer bears have spent the summer on the island. We won’t know until next year, when this summer’s survey results are released, if that has been the case or not.
In 2020 when the survey discussed above found record numbers of polar bears, the pack ice was well away from Wrangel Island on the same date (19 September), as shown below.
Similarly in 2017, when 589 bears were found on Wrangel, sea ice extent in the Chukchi Sea at mid-September (below) was more like 2020: far, far away.
In contrast, in 2012 (at 13 September, see closeup below) there was a patch of ice around Wrangel even though Chukchi Sea ice in general was at a very low extent, with only about 200-300 bears counted on the island. This is what suggests counts for 2021 may be similar: probably not as low as 2012 but lower than 2020. In high-ice years like 2021, pregnant females may make up the bulk of bears that spend the summer on Wrangel. Time will tell if that’s the case.
AC SWG 2018. Chukchi-Alaska polar bear population demographic parameter estimation. Eric Regehr, Scientific Working Group (SWG. Report of the Proceedings of the 10th meeting of the Russian-American Commission on Polar Bears, 27-28 July 2018), pg. 5. Published 30 July 2018. US Fish and Wildlife Service. https://www.fws.gov/alaska/fisheries/mmm/polarbear/bilateral.htm pdf here.
Amstrup, S.C., Marcot, B.G. & Douglas, D.C. 2007. Forecasting the rangewide status of polar bears at selected times in the 21st century. US Geological Survey. Reston, VA. Pdf here
Garner, G.W., Belikov, S.E., Stishov, M.S., Barnes Jr., V.G. and Arthur, S.M. 1984. Dispersal pattern of maternal polar bears from the denning concentration on Wrangel Island. International Conference on Bear Research and Management (now URSUS) 9(1):401-410.
Regehr, E.V., Hostetter, N.J., Wilson, R.R., Rode, K.D., St. Martin, M., Converse, S.J. 2018. Integrated population modeling provides the first empirical estimates of vital rates and abundance for polar bears in the Chukchi Sea. Scientific Reports 8 (1) DOI: 10.1038/s41598-018-34824-7 https://www.nature.com/articles/s41598-018-34824-7
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. http://rsbl.royalsocietypublishing.org/content/12/12/20160556
Rode, K.D., Regehr, E.V., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2014. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Global Change Biology 20:76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract
Rode, K.D., Regehr, E.V., Bromaghin, J.F., Wilson, R.R., Martin, M.S., Crawford, J.A. and Quakenbush, L.T. 2021. Seal body condition and atmospheric circulation patterns influence polar bear body condition, recruitment, and feeding ecology in the Chukchi Sea. Global Change Biology 27:2684-2701.
Ovsyanikov, N. 2010. Polar bear research on Wrangel Island and in the central Arctic Basin. In, Proceedings of the 15th meeting of the Polar Bear Specialists Group IUCN/SSC, 29 June-3 July, 2009, edited by Obbard, M.E., Theimann, G.W., Peacock, E. and DeBryn, T.D., pp. 171-178. Gland, Switzerland and Cambridge UK, IUCN. pdf here.
Ovsyanikov, N.G. and Menyushina, I. E. 2015. Demographic processes in Chukchi-Alaskan polar bear population as observed in Wrangel Island region. pg. 37-55, In: Marine Mammals of the Holarctic, Collection of Scientific Papers. Vol. 2. Moscow. pdf here.
Wiig, Ø., Amstrup, S., Atwood, T., Laidre, K., Lunn, N., Obbard, M., et al. 2015. Ursus maritimus. The IUCN Red List of Threatened Species 2015: e.T22823A14871490. Available from http://www.iucnredlist.org/details/22823/0 [accessed Nov. 28, 2015]. See the supplement for population figures.