Reposted from Polar Bear Science
After being locked out last year, fieldwork monitoring polar bears in the Svalbard region of the Barents Sea resumed this spring. The results show that despite having to deal with the most extreme loss of summer sea ice in the entire Arctic, polar bears in this region continue to thrive. These facts show no hint of that impending catastrophic decline in population size we keep hearing is just around the corner. No tipping point here.
Svalbard polar bear territory is managed by Norway. It includes sea ice all the way to the Russian border in the east and the Svalbard archipelago: the map below is from Aars et al. 2017.
Svalbard polar bear management region. Fig 1, Aars et al. 2017.
Observations are usually collected around Svalbard by a team lead by Jon Aars and Magnus Andersen of the Norwegian Polar Institute between March and May every year and they post their results online in June. They deserve our admiration and respect for making their research results available in such a timely fashion and without fanfare. It’s something all good scientists should be able to do.
Note that Svalbard comprises only 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 (shown below) where Norwegian researchers are not permitted to work.
Spring sea ice in the Barents Sea
Shown below is sea ice extent at end May 2021 (end of the 2021 Svalbard study field season):
In general, 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): that’s six times as much summer ice loss as bears in the most southern-living subpopulation (Southern Hudson Bay, which had a loss of only 0.68 days of ice per year) according to calculations by Eric Regehr and colleagues (2016).
However, last summer Svalbard sea ice extent took a nose-dive to well below average levels (shown below at 18 Sept 2020). This condition of below-average ice persisted well into the fall (not shown): sea ice levels did not come back into the purple zone shown on the graph below until mid-December 2020. The ice chart below that for 15 September 2020 shows what that looked like.
According to polar bear specialist Andrew Derocher, this situation had disaster written all over it. In early November, the ice extent was the lowest it had been since 1967.
Poor conditions at Svalbard. Arrow shows Hopen Island. If the ice arrives in early November, 20+ denning females give birth to cubs there. In recent years, sea ice has arrived far too late for pregnant females to use the Island. 2020 doesn’t look good. https://t.co/CS7J50WRJE pic.twitter.com/rMdibACe0r— Andrew Derocher (@AEDerocher) November 9, 2020
However, that’s only because he and most of his colleagues still embrace the false premise (e.g. Amstrup et al. 2007) that summer sea ice is critical for polar bear health and survival, despite compelling evidence that spring ice conditions are the crucial environmental factor (Crockford 2017, 2019), which includes the data from Svalbard. They also have neglected to take into account the much greater primary productivity (i.e. more food for all ) that areas like the Barents Sea have experienced precisely because there has been less summer ice (summarized, with references, in Crockford 2021).
2021 Svalbard spring polar bear data
First up is body condition of adult male bears (1993-2021, 2020 data missing), which is down a bit from 2019 but this amount of year-to-year variance is normal. Some male bears were in much worse condition in the late 1990s and early 2000s (note the lowest ‘tails’ on the box plots) than they have been since 2015 and the analysis of the data, which does not include 2021, concluded: There is no significant trend over time.
And how about litter sizes? Below is the graph provided for number of cubs per litter (1993-2021, 2020 missing):
Litter size 2021 = 1.75. According to the analysis of the data without 2021, “There is a statistically significant (p=0.04) weak trend of decreasing litter size over time (red line).” Note that the litter size for 2019 was the highest it’s been since 1993.
Finally, there is the proportion of females that have cubs of the year (called ‘production of cubs’), which this year was 0.54 (well above what it was in 2019):
The analysis of the data without 2021, “shows a non-significant (p=0.069) linear trend [red line] in the proportion of females with COYs over time.”
This conclusion remains (@30 June 2021) at the bottom of the MOSJ webpage:
An aerial survey to estimate the size of the shared Norwegian-Russian Barents Sea subpopulation was carried out in 2004, and the resulting estimate was 2650 bears +/- ca 30%. A new survey of the Norwegian part of the population was conducted in August 2015, and the results do not show any sign of a reduction in population size.
Bottom line: Despite extremely low summer ice and record-breaking fall ice levels in 2020, on top of this region having the highest relative decline in summer sea ice of all polar bear subpopulations, there is no signature of impending disaster in the spring 2021 polar bear monitering data: no starving bears or large numbers of females without cubs. Last summer should have been the ‘tipping point’ for this population, according to the models. But adequate winter and spring ice developed and the bears are still thriving, as they were in 2015 (Aars 2018; Aars et al. 2017).
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
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. 2019. The Polar Bear Catastrophe That Never Happened. Global Warming Policy Foundation, London. Available in paperback and ebook formats.
Crockford, S.J. 2021. The State of the Polar Bear Report 2020. Global Warming Policy Foundation Report 48, London. pdf here.
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