Reposted by Polar Bear Science
After the lockdown last year, field work to monitor polar bears in the Svalbard region of the Barents Sea was resumed this spring. The results show that polar bears in this region continue to thrive throughout the Arctic, despite the most extreme sea ice loss in summer. These facts show no indication that the looming catastrophic population decline that we keep hearing about is imminent. No turning point here.
The polar bear area on Svalbard is administered by Norway. It includes sea ice as far as the Russian border in the east and the Svalbard Archipelago: the map below is from Aars et al. 2017.
Polar bear management region Svalbard. Fig. 1, Aars et al. 2017.
Observations are usually collected between March and May of each year by a team led by Jon Aars and Magnus Andersen from the Norwegian Polar Institute in Svalbard and posted online in June. They deserve our admiration and respect for making their research results available so promptly and without causing a stir. All good scientists should be able to do that.
Note that Svalbard comprises only half of the polar bear subpopulation of the “Barents Sea”: In recent years, most of the polar bears in the region around Franz Josef Land lived in the eastern (Russian) sector (see below), where Norwegian researchers did not are allowed to work.
Spring sea ice in the Barents Sea
Shown below is the extent of the sea ice at the end of May 2021 (end of the Svalbard study field season 2021):
In general, the summer sea ice decline in the Barents Sea has been the sharpest in the entire Arctic since 1979 (with a loss of 4.11 days of ice per year from 1979-2014): that’s six times as much ice loss in summer as bears in According to calculations by Eric Regehr and colleagues (2016), the Arctic is the southernmost subpopulation (Southern Hudson Bay, which lost only 0.68 days of ice per year).
However, the extent of the sea ice in Svalbard last summer fell to a significantly below average level (see below on September 18, 2020). This state of below-average ice persisted into autumn (not shown): the sea ice level only returned to the purple range shown in the graphic below in mid-December 2020. The ice map below for September 15, 2020 shows what that looked like.
According to polar bear specialist Andrew Derocher, the situation was marked by disaster. At the beginning of November the ice extent was lower than ever since 1967.
Bad conditions on Svalbard. Arrow points to Hopen Island. When the ice arrives in early November, 20+ Denning females will give birth there to young. In recent years, sea ice has come too late for pregnant females to use the island. 2020 is not looking good. https://t.co/CS7J50WRJE pic.twitter.com/rMdibACe0r— Andrew Derocher (@AEDerocher) November 9, 2020
However, this is only because he and most of his colleagues still hold the false premise (e.g., Amstrup et al. 2007) that summer sea ice is critical to polar bear health and survival, despite compelling evidence that spring ice conditions are the decisive environmental factor (Crockford 2017, 2019), which contains the data from Spitsbergen. They have also neglected the much higher primary productivity (i.e. more food for everyone) that areas like the Barents Sea experienced precisely because of the lower summer ice (summarized with references in Crockford 2021).
Polar bear data for Svalbard in spring 2021
In the first place is the body condition of adult male bears (1993-2021, data for 2020 missing), which has slightly decreased compared to 2019, but this variance from year to year is normal. Some male bears were in much worse shape (note the lowest “tails” on the box plots) in the late 1990s and early 2000s than they were since 2015, and analysis of the data, which does not include 2021, concluded: there are no significant trend over time.
And what about litter sizes? Below is the graph for the number of boys per litter (1993-2021, 2020 missing):
Litter size 2021 = 1.75. Analyzing the data excluding 2021, “there is a statistically significant (p = 0.04) weak trend in decreasing litter size over time (red line).” Note that litter size for 2019 was the highest since 1993.
Finally, there is the proportion of females who have young of the year (called “production of young”), which this year was 0.54 (significantly higher than in 2019):
The analysis of the data without 2021 “shows a non-significant (p = 0.069) linear trend” [red line] in the proportion of women with COYs over time. “
This conclusion remains (@ June 30th, 2021) at the bottom of the MOSJ website:
An aerial photograph to estimate the size of the shared Norwegian-Russian Barents Sea subpopulation was taken in 2004, and the resulting estimate was 2,650 bears +/- approximately 30%. A new survey of the Norwegian part of the population was carried out in August 2015 and the results show no signs of a decrease in population size.
Bottom line: Despite extremely low summer ice and record-breaking autumn ice levels in 2020, in addition to this region with the highest relative decline in summer sea ice of all polar bear subpopulations, there are no signs of an impending disaster in the spring of 2021 polar bear monitoring data: no starving bears or many females without Boy. According to the models, last summer should have been the “tipping point” for this population. But enough winter and spring ice developed and the bears are still thriving as they did in 2015 (Aars 2018; Aars et al. 2017).
Aars, J. 2018. Population changes in polar bears: Protected, but quickly losing their habitat. Fram Forum Newsletter 2018. Fram Center, Tromsø. Download PDF here (32 MB).
Aars, J., Marques, TA, Lone, K., Anderson, M., Wiig, Ø., Fløystad, IMB, Hagen, SB and Buckland, ST 2017. Number and distribution of polar bears in the western Barents Sea. Polar Research 36: 1. 1374125. doi: 10.1080 / 17518369.2017.1374125
Amstrup, SC, Marcot, BG & Douglas, DC 2007. Predicting the blanket status of polar bears at selected times in the 21st century. US geological survey. Reston, VA. PDF here
Crockford, SJ 2017. Testing the hypothesis that routine sea ice cover of 3-5 mkm2 leads to a decrease in the population size of polar bears (Ursus maritimus) by more than 30%. PeerJ Preprints January 19, 2017. Doi: 10.7287 / peerj.preprints.2737v1 Open Access. https://peerj.com/preprints/2737/
Crockford, SJ 2019. The polar bear disaster that never happened. Global Warming Policy Foundation, London. Available in paperback and e-book format.
Crockford, SJ 2021. The State of the Polar Bear Report 2020. Global Warming Policy Foundation Report 48, London. pdf here.
Regehr, EV, Laidre, KL, Akçakaya, HR, Amstrup, SC, Atwood, TC, Lunn, NJ, Obbard, M., Stern, H., Thiemann, GW, & Wiig, Ø. 2016. Conservation status of polar bears (Ursus maritimus) in relation to the predicted decline in sea ice. Biology Letters 12: 20160556. http://rsbl.royalsocietypublishing.org/content/12/12/20160556
Comments are closed.