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| istockphoto/Pauline Mills |
| Tusks can reach one meter in length. |
The walrus (
Odobenus rosmarus) is the only member of the family Odobenidae. Walruses are a member of the order Pinnipedia (or pinnipeds), along with seals and sea lions. They are easily distinguished from the other pinnipeds by their tusks, whiskers and giant bulk of up to 4,500 pounds.
Walruses have a mix of seal and sea lion characteristics, one of the reasons the species stands alone in its own family. They can rotate their hind limbs forward to walk well on land like a sea lion, but do not have external ear flaps, like a seal. Male walruses even have their own built-in life preservers: air sacs in their necks which inflate and allow them to float.
There are two known sub-species of walrus, the Atlantic walrus (O. rosmarus rosmarus) and the Pacific walrus (O. rosmarus divergens). There is also thought to be a third sub-species in the Laptev Sea (O. rosmarus laptevi). The name walrus is said to have originated from the Danish word hvalros, meaning “sea cow” or “sea horse.”
Prey/Predators
Walruses prefer to hunt for food in shallower waters and can hold their breath for up to 30 minutes. While they most commonly dine on bivalves such as clams, they enjoy a diverse array of marine organisms including shrimp, crab, mollusks, sea cucumbers, and sometimes even parts of other pinnipeds. Their only natural predators are killer whales and polar bears, but these enemies attack at their own risk because walruses’ tusks can cause serious injury.
Habitat
Walruses are distributed in the Arctic Ocean and sub-arctic seas of the northern hemisphere. They generally inhabit coastal areas around shallow waters with rocky bottoms.
Reproduction
At 15 months, the walrus’s gestation period is among the longest for mammals. Once calves are born, the mothers usually nurse them for about two years. Males generally begin reproducing at about 15 years of age and females at about 10 years. Walruses can live a maximum of 35-40 years, making them the longest-lived pinniped.
Characteristics
The most prominent feature of the walrus is no doubt the tusks, which grow on both males and females and can reach one meter in length. Their tusks are actually long canine teeth, which are used to pull their huge bodies out of the water, to cut air holes in ice, or for use in the bulls’ aggressive displays to defend their territory and their groups of females, or cows. Their whiskers, meanwhile, help them locate food on the ocean floor.
Threats
Walruses have been targeted for many centuries for their meat, skin, tusks and bone. Increased hunting and commercial exploitation of their blubber and ivory in the 19th and 20th centuries left walrus populations depleted. They have since rebounded worldwide, although Atlantic and Laptev walrus populations remain low. Because accurate walrus numbers are still unknown, native subsistence hunting that is still taking place could be having a detrimental effect on the species.
Global climate change is also taking a toll on walrus populations as sea ice continues to melt. Walruses rely on the ice shelves that form over shallow waters as “haul-out” (or resting) areas and to keep their young safe as they dive for food. As the sea ice retreats, it has become more and more difficult for walruses to feed. In addition, increased crowding on ever fewer haul-outs can lead to mass injuries and even deaths if the animals stampede into the water (which they sometimes do when boats, helicopters, hunters, or natural predators startle them). The Alaskan Coast Guard has reported seeing more lone walrus calves stranded in the open ocean. This likely occurs when ice shelves on which they live with their mothers collapse.
Posted Jan. 30, 2008
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Sources:
Seal Conservation Society
U.S. National Park Service: Pacific Walrus
The Marine Mammal Center, The Pinnipeds: Seals, Sea Lions and Walruses
