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CENTER for BIOLOGICAL DIVERSITY Because life is good

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PACIFIC WALRUS (Odobenus rosmarus divergens)

RANGE: Bering and Chukchi seas.

With tusks like an elephant and weighing up 1660 kilograms (3650 pounds), the Pacific walrus is one of the most memorable Arctic inhabitants. Like the polar bear, it is heavily dependent on sea ice for survival. In winter, males and females gather on the sea ice of the Bering Sea to court, find mates and give birth. Females and their calves, which maintain a tight bond for two to three years, follow the sea ice year-round from the Bering Sea in winter, northward to the Chukchi Sea in summer, and back again. Since walruses cannot swim continuously, sea ice floes over their foraging grounds provide walruses with safe havens for resting between dives to the seafloor to feed on clams and mussels. Sea-ice floes are especially important for walrus calves. While the mother dives to the seafloor to suction up clams, the calf naps on the ice protected from predators.

Global warming is rapidly shrinking the summer sea ice over the walrus’s foraging grounds. In recent years, sea ice has retreated completely from the walrus’s feeding areas in the Chukchi Sea. With no ice floes for resting, females and calves are forced to abandon their food supply and come ashore. On the long journey to shore, walrus calves can drown from exhaustion or be separated from their mothers. [1] Once on land, calves are vulnerable to being attacked by predators or trampled to death. When alarmed by humans or predators, walruses will stampede to the water, and large males can easily crush calves in the chaos. An estimated 3,000 to 4,000 young walruses were killed in stampedes in Siberia in 2007, and 133 young walruses perished in a stampede in Alaska in 2009.

Shrinking sea-ice cover and rising temperatures are also threatening the walrus’s food. Sea ice in the northern Bering Sea is important for sustaining a high abundance of animal life on the seafloor, including the walrus’s clam and mussel prey. When sea ice in the Bering Sea melts in spring, nutrients released from the melting ice spark a bloom of small marine plants which rain down and enrich life on the ocean bottom. Without sea ice, the nourishing spring bloom does not happen, depriving life on the seafloor. As a result, the northern Bering Sea is shifting from an ecosystem rich in bottom-dwelling animals to a system dominated by pelagic fish. [2] On top of this, the rising acidification of Arctic waters is making it more difficult for the walrus’s clam and mussel prey to build their shells.

As sea ice melts, the walrus’s most important foraging grounds in the Chukchi Sea are also being opened up to oil drilling to extract more fossil fuels that will further accelerate the melting of the Arctic. Oil drilling and the proliferation of shipping routes in the increasingly ice-free Arctic threaten the Pacific walrus with the heightened risk of oil spills, rising noise pollution and human disturbance.


1. Cooper, L. W., C. J. Ashjian, S. L. Smith, L. A. Codispoti, J. M. Grebmeier, R. G. Campbell, and E. B. Sherr. 2006. Rapid seasonal sea ice retreat in the Arctic could be affecting Pacific Walrus (Odobenus rosmarus divergens) recruitment. Aquatic Mammals 32:98-102.
2. Grebmeier, J. M., J. E. Overland, S. E. Moore, E. V. Farley, E. C. Carmack, L. W. Cooper, K. E. Frey, J. H. Helle, F. McLaughlin, and S. L. McNutt. 2006. A major ecosystem shift in the Northern Bering Sea. Science 311:1461-1464.


Polar bear photo © Jenny E. Ross/ www.jennyross.com