An Ice-Dependent Existence
The Pacific walrus, Odobenus rosmarus divergens, is a massive pinniped perfectly adapted to life in the Arctic. Males can weigh more than 2,000 kilograms (4,400 pounds) and are exceeded in size among pinnipeds only by elephant seals. Their lives are tied to the seasonal advance and retreat of sea ice in the Bering and Chukchi Seas. This floating ice is a resting place; it is a platform for giving birth, nursing calves, and accessing the feeding grounds on the shallow continental shelf.
Walruses are benthic foragers, meaning they feed on the ocean floor. Using their highly sensitive whiskers, or vibrissae, they detect bivalve mollusks like clams, as well as marine worms, snails, and sea cucumbers. A walrus can consume between 3,000 and 6,000 clams in a single feeding session. They dive in the relatively shallow waters above the continental shelf, often less than 80 meters (262 feet) deep, to root for food in the soft sediment. Sea ice provides the ideal mobile base, allowing them to rest directly above these foraging areas without a long commute.
A Shoreline of Last Resort
As the Arctic warms at a rate twice the global average, the summer sea ice is rapidly diminishing. It retreats far north of the shallow continental shelf and over the deep Arctic Ocean basin, where walruses cannot feed. This forces tens of thousands of them, primarily females and their young, to swim to shore to rest between foraging trips.
This has led to the formation of immense coastal gatherings, known as haulouts, on the shores of Chukotka in Russia and across the strait in Alaska. These are not small assemblies; the haulout at Cape Serdtse-Kamen' in Chukotka has been observed to hold between 75,000 and 115,000 walruses. The density of so many enormous animals creates a perilous environment. The herds are easily startled by predators like polar bears, aircraft, or human activity, which can trigger a stampede. In the ensuing panic, the animals rush for the safety of the water, and calves or smaller walruses are often crushed. In one such event in 2007 along the Chukotka coast, up to 10,000 animals died.