Adult Female Walruses on Ice Floe with Young. US waters of the Eastern Chukchi Sea,
AK, USA. Captions and Photo source: S.A. Sonsthagen / USGS
Compared to the photogenic polar bear, the walrus makes an unlikely poster species for climate change. In the last week, environmental campaigners have cried that the mass walrus beaching in Alaska, first spotted last month, is another clear signal of our warming world. Climate-change skeptics insist that the event is nothing unusual, and have dug out records of previous mass walrus ‘haul-outs’ to support their case.
There is a simple way to tell this tale. Walruses spend much of their time out of the water, especially when they are rearing young. They prefer to perch on floating sea ice, which gives them access to the seabed, where most of their food lives. As sea ice retreats north — and this year provided the sixth-lowest extent of summer Arctic ice on record — more walruses have to haul themselves onto the coast. Since 2000, increasing numbers of Pacific walruses (the Atlantic population is less affected) have been forced onto the beaches around the Chukchi Sea; in October 2010, scientists counted a gathering of 120,000 at Cape Serdtse-Kamen in Russia.Walrus haul-outs on the coast tend to be dominated by adult males. The current event features substantial numbers of mothers and young, which makes it more worrying. A walrus stampede might sound unlikely, but it is a genuine risk. Spooked animals rush to the water and trample anything in their path. The demographics also suggest that something out of the ordinary is going on: female walruses usually recognize the risks of mass haul-outs, and leave the bulls to it.
The link between increased walrus haul-outs on Arctic beaches and the decreased availability of sea ice is clear-cut. The link to climate change is less so, at least in the short term. Sea-ice cover fluctuates with wind and currents from year to year, and the key for walruses is the position of the ice as much as its extent. They need ice over the continental shelf so that they can both rest and feed. In 2008, when remnant ice remained in the Chukchi Sea in the shallow waters of the shelf, walruses did not come ashore in significant numbers. Whether or not this particular haul-out of walruses in Alaska is a result of climate change is ultimately a moot point. Annual peaks and troughs — of animal movement and ice measurements — are symbolic, but the long-term trend is clear: the Arctic is warming, its ice is melting and the walrus’s traditional habitat is disappearing. The walruses of the Pacific Arctic face an uncertain future. They might be able to move, they might be able to adapt. Or they might be stuffed.
Copyright © 2014, Nature Publishing Group; Nature 514,140; doi:10.1038/514140a