Results from spring Norwegian fieldwork in the Svalbard region of the Barents Sea are in and they show that despite having to deal with the most extreme loss of summer sea ice in the Arctic, polar bears in this region continue to thrive.
Svalbard polar bear territory (managed by Norway) includes sea ice to the Russian boarder to the east as well as the area around the Svalbard archipelago: the map below is from Aars et al. 2017.
Observations were collected around Svalbard by a team lead by Jon Aars and Magnus Andersen of the Norwegian Polar Institutebetween March and May this year, and posted online 4 June 2019. Kudos to them for making their on-going observations and analysis available, in a timely manner for all to see.
Note that Svalbard is the western half of the ‘Barents Sea’ polar bear subpopulation: in recent years, most of the region’s polar bears have been living around Franz Josef Land in the eastern (Russian) sector where Norwegian researchers are not permitted to work.
Spring sea ice in the Barents Sea
Sea ice extent at end May 2019 (end of the 2019 Svalbard study field season):
Summer sea ice decline in the Barents Sea since 1979 has been the most profound across the Arctic (with a loss of 4.11 days of ice per year, from 1979-2014), shown below (far left) compared to the Chukchi Sea (middle) and Southern Hudson Bay, which had the least (a loss of 0.68 days of ice per year), all graphs from Regehr et al. (2016):
Body Condition of Male Svalbard Polar Bears (1993-2019)
Body condition index of adult male polar bears caught in spring (March-May) in the period 1993-2019. The lines in the middle of each box show the median value, and the box segments and lines above and below the median each cover ca 25% of the data points. There is no significant trend over time.
Number of Svalbard Cubs per Litter (1993-2019)
Average litter size (cubs of the year); data from the annual capture-recapture program 1993-2019. There is a statistically significant (p=0.04) weak trend of decreasing litter size over time (red line).
Number of Svalbard Cubs of the Year per Female (1993-2019)
Proportion of females with cubs of the year, based on data from the annual capture-recapture program 1993-2019. The red trend line shows a non-significant (p=0.069) linear trend in the proportion of females with COYs over time.
Svalbard Females with Cubs of Different Ages (1993-2019)
Proportion of females with cubs of the year (COYs) and yearlings, based on data from the annual capture-recapture programme in 1993–2019. The blue dotted line describes a non-significant (p=0.106) linear trend in the proportion of females with COYs over time. There is no significant trend over time in the proportion of females with yearlings (red dotted line). The observed interannual variation in the proportion of females with yearlings cannot be explained by time trend (p=0.764).
The results above (originals here) confirm the conclusion from previous few years that polar bears in the Svalbard region are doing well despite such a profound decline of summer and fall sea ice that it has prevented females from reaching traditional denning areas in the east for the last four consecutive years (Aars 2018; Aars et al. 2017).
However, there has been ample ice in the eastern Barents sea for hunting in the fall and abundant denning habitat exists around the Franz Josef Land archipelago for polar bear females (Aars 2015; Andersen et al. 2012): most bears previously living and denning around Svalbard appear to have shifted their allegiance to the sea ice east of Svalbard and the Russian portion of the subpopulation region.
These results also confirm that early spring sea ice – not summer ice – are what is required for polar bear health and survival (Crockford 2017, 2019a,b).
In contrast to summer sea ice last year, late spring sea ice in the Svalbard area this year at 28 June remains above average and the Barents Sea in general still has abundant ice, as the graph and map below show (from the Norwegian Ice Service). This has been true since late March. Whether this is enough to entice some bears (including pregnant females) to come ashore on islands in the north and north-east of the archipelago (to spend the summer on Norwegian soil and have their cubs there next winter), remains to be seen.
Aars, J. 2015. Research on polar bears at Norwegian Polar Institute. Online seminar (‘webinar”), January 14. pdf here.
Aars, J. 2018. Population changes in polar bears: protected, but quickly losing habitat. Fram Forum Newsletter 2018. Fram Centre, Tromso. Download pdf here (32 mb).
Aars, J., Marques,T.A, Lone, K., Anderson, M., Wiig, Ø., Fløystad, I.M.B., Hagen, S.B. and Buckland, S.T. 2017. The number and distribution of polar bears in the western Barents Sea. Polar Research 36:1. 1374125. doi:10.1080/17518369.2017.1374125
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
Andersen, M., Derocher, A.E., Wiig, Ø. and Aars, J. 2012. Polar bear (Ursus maritimus) maternity den distribution in Svalbard, Norway. Polar Biology 35:499-508.
Crockford, S.J. 2017. Testing the hypothesis that routine sea ice coverage of 3-5 mkm2 results in a greater than 30% decline in population size of polar bears (Ursus maritimus). PeerJ Preprints 19 January 2017. Doi: 10.7287/peerj.preprints.2737v1 Open access. https://peerj.com/preprints/2737/
Crockford, S.J. 2019a. State of the Polar Bear Report 2018. Global Warming Policy Foundation Report 32, London. pdf here.
Crockford, S.J. 2019b. The Polar Bear Catastrophe That Never Happened. Global Warming Policy Foundation, London. Available in paperback and ebook formats.
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