It’s back: Bering Sea polar bear habitat has recovered from a low earlier this month

Fancy that! After a load of handwringing earlier this month, mobile pack ice in the Bering Sea has returned. Just like ice in the Barents Sea, Bering Sea ice is highly variable (Brown et al. 2011): it moves with winds and currents, so a ‘decline’ during the winter usually indicates redistribution, not melting.

Polar bear on Bering Sea ice 2007 USFWS

According to researcher Rick Thoman from the University of Alaska Fairbanks, quoted by the Canadian Press:

“Wind blew ice to Russian beaches in the west and to the south side of Norton Sound south of Nome but left open water all the way to Chukchi Sea north of the Bering Strait.”

Polar bears that venture into the Bering Sea are part of the Chukchi Sea subpopulation, which is known to be thriving (Crockford 2019; AC SWG 2018; Regehr et al. 2018; Rode and Regehr 2010; Rode et al. 2013, 2014, 2015, 2018).

What happened

Bering Sea courtesy Wikipedia. Light blue areas are shallow, continental shelf areas (not sea ice).

In late February, ice in the Bering Sea (south of the Bering Strait) receded rather rapidly. By early March, a number of folks were in full-blown panic mode:

The Bering Strait should be covered in ice, but it’s nearly all gone (Mashable, 4 March 2019, Mark Kaufman).

In the Middle of Winter, Bering Strait Sea Ice Is Disappearing (Bloomberg, 6 March 2019, Jeremy Hodges).

There’s open water where sea ice historically covers much of Bering Sea off Alaska’s west coast (Canadian Press/GlobalNews, 5 March 2019, Dan Joling).

You could almost see the ice streaming north into the Chukchi Sea by the 5 March:

5 March 2019

However, by 17 March it was all back:

17 March 2019

Here’s the recovery in graphic form, track the dark green line (to 17 March 2019):

Bottom line: The ice will retreat north as spring progresses, of course, so the current level shouldn’t be expected to remain static. Less ice near the Alaska coast may make it difficult for polar bear specialists to do their spring surveys but is unlikely to cause trouble for the bears themselves. The seals follow the ice as it moves in the spring: the bears follow the seals.

References

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.

Brown, Z.W., van Dijken, G.L. and Arrigo, K.R. 2011. A reassessment of primary production and environmental change in the Bering Sea. Journal of Geophysical Research 116:C08014. doi:10.1029/2010JC006766.

Crockford, S.J. 2019. State of the Polar Bear Report 2018. Global Warming Policy Foundation Report #32. London. pdf here.

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

Rode, K. and Regehr, E.V. 2010. Polar bear research in the Chukchi and Bering Seas: A synopsis of 2010 field work. Unpublished report to the US Fish and Wildlife Service, Department of the Interior, Anchorage. pdf here.

Rode, K.D., Douglas, D., Durner, G., Derocher, A.E., Thiemann, G.W., and Budge, S. 2013. Variation in the response of an Arctic top predator experiencing habitat loss: feeding and reproductive ecology of two polar bear populations. Oral presentation by Karyn Rode, 28^th Lowell Wakefield Fisheries Symposium, March 26-29. Anchorage, AK.

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(1):76-88. http://onlinelibrary.wiley.com/doi/10.1111/gcb.12339/abstract

Rode, K. D., R. R. Wilson, D. C. Douglas, V. Muhlenbruch, T.C. Atwood, E. V. Regehr, E.S. Richardson, N.W. Pilfold, A.E. Derocher, G.M Durner, I. Stirling, S.C. Amstrup, M. S. Martin, A.M. Pagano, and K. Simac. 2018. Spring fasting behavior in a marine apex predator provides an index of ecosystem productivity. Global Change Biology http://onlinelibrary.wiley.com/doi/10.1111/gcb.13933/full

Rode, K.D., Wilson, R.R., Regehr, E.V., St. Martin, M., Douglas, D.C. & Olson, J. 2015. Increased land use by Chukchi Sea polar bears in relation to changing sea ice conditions. PLoS One 10 e0142213.