Most Chukchi Sea ice in 20 years means no walrus feasts for polar bears at famous Russian cliffs

From Polar Bear Science

By Dr. Susan Crockford

After years of hype, including documentary over-reach by David Attenborough and his collaborators at WWF and Netflix, there has been relatively abundant ice in the Chukchi Sea this summer, particulary along the Russian coast and around Wrangel Island, which in recent years have been important summer refuge areas for polar bears and Pacific walrus.

This year, there has been nothing like the complete retreat of ice into the Arctic Basin as happened in 2007, 2012, and 2020. The chart below shows the ice extent at 11 October 2021:

Wrangel Island was surrounded by ice in 2000 and 2001, which made access to walrus haulouts on the island impossible (Kochnev 2004). Most of the walrus haulouts along the Chukotka coast were also ice-covered in September in those years, as were all of the western locations in 2021 – as the ice charts below show. The extra ice will have drastically affected the distribution of walrus this year, which in turn will have meant no walrus carcasses for polar bears to feast on as they have done for many years now.

Only the south coast of Wrangel Island was ice-free by early September, which may have made a few haulouts accessible for a few weeks at most. Cape Blossom, a sandy spit at the western tip, has historically been a particular favourite for walrus in summer but this year looks to have been largely unavailable.

As the recent (18 October 2021) ice chart from the NOAA’s Alaska Sea Ice Program below shows, that ice along the Russian shore is now showing up as second-year ice that did not melt this year (brown is multi-year ice), with new ice (light and dark purple) forming beyond it.

In recent years, the pattern for mixed herds of females, calves, and older juvenile Pacific walrus has been to use western-most haulouts like Cape Schmidt in September (with its famous cliff that polar bears use as a hunting aid) but many move east to Vankarem in October. By late October/early November, virtually the entire Chukchi herd migrates even further east to the beaches at Cape Serdtse-Kamen where there is room for more than 100,000 of them to congregate (Chakilev and Kochnev 2019).

With winter approaching, the herd then moves east and south to join male walrus at land haulout sites in the northern Bering Sea where they wait to intercept the Chukchi Sea ice as it pushes south (Fay 1982; MacCracken et al. 2017).

The mobile ice that usually occupies the northern Bering Sea in winter (January-March) is critical to the survival of Pacific walrus because they need a mix of ice and open water for mating and feeding. Mating occurs in the water between the broken ice floes in December/January and calves resulting from mating events the previous year are born on the ice in spring (March/April). Cows need access to open water to feed on the ocean floor while nursing newborn calves. The Chukchi Sea in winter is too consolidated with thick ice for these activities.

Even in 2018 and 2019 (but not 2020), when winter ice in the Bering Sea was at a very low extent in February, there was apparently enough suitable ice for walrus needs, whether that ice was north or south of the Bering Strait: if there had not been, we would have heard about it by now. Note that geological evidence indicates that there was no ice south of the Bering Strait in winter for an extended period during the Eemian Interglacial (Polyak et al. 2010) and yet Pacific walrus survived (Fay 1982).

You can see on the labeled map below of the 18 October ice chart that both Cape Schmidt and Vankarem would have been inaccessible to walrus the entire summer which means no accumulated walrus carcasses for polar bears at Cape Schmidt this year!

This year, as for previous years when ice was present in the Chukchi Sea, walrus herds would have been able to feed from the ice in the Chukchi or used land haulouts in the Bering Strait or northern Bering Sea that have traditionally been used in late fall while waiting for winter ice to arrive. See haulout sites in the diagrams below from Fischbach and colleagues (2017): the first shows historically-known sites and the second shows sites where large haulouts have been documents since 1980.

References

Chakilev, M.V. and Kochnev, A.A. 2019. Monitoring results of the Pacific walrus (Odobenus rosmarus divergens) haulout site at Cape Serdtse-Kamen (Chukchi Sea) in 2016-2017. In, Marine Mammals of the Holarctic, Papers of The Tenth International Conference (29 October-2 November 2018), Volume 1, pg. 381-391. Marine Mammal Council, Moscow. [Russian and English]

Fay, F.H. 1982. Ecology and biology of the Pacific walrus, Odobenus rosmarus divergens, Illiger. US Department of the Interior, Fish and Wildlife Service, North American Fauna, No. 74.

Fischbach, A.S., Kochnev, A.A., Garlich-Miller, J.L. and Jay, C.V. 2016. Pacific walrus coastal haulout database, 1852-2016 – Background Report. USGS Open-File Report 2016-1108. DOI: 10.3133/ofr20161108 PDF HERE, download here.

Kochnev, A.A. 2004. Warming of eastern Arctic and present status of the Pacific walrus (Odobenus rosmarus divergens) population. In, Marine Mammals of the Holarctic, Papers of The Third International Conference (11-17 October 2004), Belkovich, V.M. (ed.), pg. 284-288.  Marine Mammal Council, Moscow. [Russian and English]

MacCracken, J.G., Beatty, W.S., Garlich-Miller, J.L., Kissling, M.L. and Snyder, J.A. 2017. Final Species Status Assessment for the Pacific walrus (Odobenus rosmarus divergens). US Fish and Wildlife Service, Anchorage, Alaska.

Polyak, L., Alley, R.B., Andrews, J.T., Brigham-Grette, J., Cronin, T.M., Darby, D.A., Dyke, A.S., Fitzpatrick, J.J., Funder, S., Holland, M., Jennings, A.E., Miller, G.H., O’Regan, M., Savelle, J., Serreze, M., St. John, K., White, J.W.C. and Wolff, E. 2010. History of sea ice in the Arctic. Quaternary Science Reviews 29:1757-1778. http://bprc.osu.edu/geo/publications/polyak_etal_seaice_QSR_10.pdfd