WALRUS: Odobenidae

PHYSICAL CHARACTERISTICS

The walrus is the second largest pinniped, after the elephant seal. Walruses are 44 to 126 inches (112 to 320 centimeters) long and weigh 139 to 2,662 pounds (63 to 1,210 kilograms). Their streamlined, smooth, body allows for easy movement through water. They are sparsely covered with short, cinnamon brown hair, which is darker in young walruses. In older males, the hair is almost absent, giving a naked appearance. The wrinkled skin measures 0.75 to 2 inches (2 to 5 centimeters) thick. Adult males have large, coarse bumps on the neck and shoulders. Underneath the skin is a layer of blubber, or fat, about 0.4 to 6 inches (1 to 15 centimeters) thick, which protects against the cold and serves as storage for food energy.

Although its head is quite small compared to the rest of its body, the walrus has a powerful skull. If the seawater freezes while the walrus is underwater, it uses its skull like a sledge-hammer to break through the ice overhead, up to 8 inches (20 centimeters) in thickness. The walrus has no external ears, just small openings covered by a fold of skin. About 600 to 700 stiff whiskers form a mustache and act as antennas for detecting prey. The thickened upper lip is used to feel around for food in the muddy sediments of the ocean floor. Two air pouches in the throat extend to the shoulders. They can be inflated to function as life preservers, enabling the walrus to sleep or rest in an upright position with its head above water. Males produce bell-like sounds with these inflated air pouches when courting females.

Walruses have webbed flippers. The back flippers act as paddles for swimming, while the front flippers do the steering. On land or ice, walruses use their flippers the same way eared seals use theirs. The back flippers are turned forward and, together with the front flippers, are used for moving around. However, unlike eared seals, walruses cannot lift their enormous body off the ground. They walk by pushing off the ground with the help of the belly and flippers. The thick blubber helps cushion its underparts while walking.

The walrus is known for its long, ivory tusks, which are enlarged upper canine, dagger-like, teeth. The teeth first extend out of the mouth when they are about one year old. The tusks serve many functions. They are used for hauling out (getting out of the water) onto the ice. This is where the first part of the walrus's scientific name came from. The Greek word odobenus means "tooth walker" or "one who walks on his teeth." The tusks are also used to threaten rivals for breeding territories and for actual fights. Dominant males typically have larger tusks and use them as power displays. Walruses sometimes use their tusks to support their head while sleeping or resting on ice. They sleep or rest vertically in water with the tusks hooked over the edge of an ice floe, a large sheet of floating ice. The tusks grow with age. In adult males, they can grow up to 3 feet (1 meter) long and weigh about 12 pounds (nearly 5.5 kilograms) each.

GEOGRAPHIC RANGE

Walruses are found mainly in the coastal areas of the Arctic Ocean and adjoining seas. There are two populations of walruses. Pacific walruses are found in the Bering, Chukchi, and Laptev Seas. Atlantic walruses occupy the coastal regions of Greenland and northeastern Canada.

WHY DOES A WALRUS TURN WHITE THEN BRIGHT PINK?

In cold seawater, the walrus closes its blood vessels in the skin to prevent blood flow to that area, thus preventing heat loss. The absence of blood gives the skin a pale appearance. On land under the sun, the walrus's thick blubber makes it feel hot. To prevent overheating, blood vessels in the skin are opened to carry heat from inside the body and get rid of it through the skin, turning it pink.

HABITAT

Walruses live mainly in the sea, occupying pack ice, large pieces of ice frozen together, that floats on the continental shelf, the shallow part of the ocean floor that starts at the shoreline. Males haul out on sandy, cobble, or boulder beaches.

DIET

Walruses eat primarily bivalve mollusks, clams and mussels. They also feed on marine worms, crabs, shrimp, octopus, squid, and sea cucumbers. They occasionally eat fish and seals, including spotted, ringed, and bearded seals. The walrus squirts the muddy sediments on the ocean floor with water from its mouth, exposing the mollusks. Then it sucks the meat out of the shell. An adult walrus consumes about 4 to 6 percent of its total body weight daily. It can eat 3,000 to 6,000 clams per meal.

BEHAVIOR AND REPRODUCTION

Walruses socialize in groups called herds, although males and females keep to their groups except when mating in the winter. They travel and forage together in small groups, and several hundred may haul out on ice floes. Thousands of walruses congregate on beaches to molt, shed, or rest. They typically lie close together, oftentimes draped over one another. However, they can annoy one another, at which point they hit their neighbors with their tusks. Sometimes fighting occurs. However, walruses are supportive of one another. They will help a neighbor who is being attacked by a polar bear or attempt to get a dead animal off an ice floe into the water to get it away from a hunter.

Walruses follow the pack ice throughout the year. In spring, they migrate north toward the Arctic Ocean to feed. Males haul out onto beaches along the Alaskan and Russian coasts to molt and rest, while females migrate farther north. Females give birth on pack ice in the spring and summer. Unlike other pinnipeds, walruses do not mate right after giving birth.

In the fall, they follow expanding pack ice, this time heading south. In the winter, males follow herds of females and their young at sea. When the mother-offspring groups haul up on ice floes, the males remain in the water close by. The males go through a courtship display of producing bell-like sounds underwater, followed by whistles and teeth-clacking above the water. The males also fight for dominance, and only the winner will mate with the females of a certain herd. Mating occurs underwater, after which males rejoin their all-male group. This yearly migration north and south covers about 2,000 miles (3,000 kilometers), with walruses swimming or riding on moving ice.

Walruses spend about two-thirds of their lives in the water. They are slow swimmers, typically going up to 4.3 miles (7 kilometers) per hour, but can reach a speed of up to 22 miles (35 kilometers) per hour. They can stay underwater for 25 minutes, although they usually remain underwater for just 10 minutes because they forage on shallow ocean floors.

Pregnancy lasts fifteen months due to delayed implantation, during which the fertilized egg grows a little then waits four to five months before attaching to the uterus for further development. A single calf is born during the spring migration north. Nursing usually occurs in water, with the calf hanging upside down. The calf can swim at birth. Calves remain with their mothers for two years, although they forage for other food before being completely weaned from their mother's milk. Young females stay with female herds, while young males leave to join all-male herds. The long nursing period means that females do not give birth annually. Mothers are very protective of their young, fighting off intruders with their tusks. They carry their newborn on their back in the water. On land, they hold their calf close to their body with their front flippers when they perceive danger. Walruses have been known to guard one another's young and to adopt orphans.

WALRUSES AND PEOPLE

Native people of the Arctic have always associated the walrus with spiritual power. For thousands of years, they depended on walruses for subsistence, hunting them for food and fuel, as well as material for shelter, clothing, boats, sled, tools, and handicrafts. In the seventeenth century, Europeans first harvested walruses commercially, especially for their ivory tusks, eventually causing declining populations. Today, walruses are legally protected by the governments of the United States, Canada, and Russia. Only native people are allowed to hunt them.

CONSERVATION STATUS

Walruses are not a threatened species.

FOR MORE INFORMATION

Books:

Bonner, Nigel. "The Walrus." In Seals and Sea Lions of the World. New York: Facts on File, Inc., 1994.

Knudtson, Peter. The World of the Walrus. San Francisco: Sierra Club Books, 1998.

Nowak, Ronald M. "Walrus." Walker's Mammals of the World Online 5.1. Baltimore: Johns Hopkins University Press, 1997. http://www.press.jhu.edu/books/walkers_mammals_of_the_world/pinnipedia/pinnipedia.odobenidae.odobenus.html (accessed on July 7, 2004).

Patent, Dorothy Hinshaw. Seals, Sea Lions and Walruses. New York: Holiday House, 1990.

Reeves, Randall R., Brent S. Stewart, Phillip J. Clapham, and James A. Powell. Guide to Marine Mammals of the World. New York: Alfred A. Knopf, 2002.

Periodicals:

Fay, Francis H. "Odobenus rosmarus." Mammalian Species 238 (May 24, 1985): 1–7.

Lanken, Dane. "Grace Under Water." Canadian Geographic (March 2002): 48–53.

Rosing, Norbert. "Walrus: Giant of the Arctic Ice." National Geographic (September 2001): 62–78.

Schleichert, Elizabeth. "Giants of the North." Ranger Rick (November 1997): 4–11.

Web sites:

Alaska Science Center-Biological Science Office. "Pacific Walrus Research." U.S. Geological Survey. http://www.absc.usgs.gov/research/walrus/home.html (accessed on July 7, 2004).

Sea World Education Department. "Walrus." Sea World/Busch Gardens Animal Information Database. http://www.seaworld.org/infobooks/Walrus/home.html (accessed on July 7, 2004).

Vlessides, Michael. "In Search of the Tooth Walker." National Wildlife Federation. http://www.nwf.org/internationalwildlife/2000/walrusnd.html (accessed on July 7, 2004).