| Walrus | ||||||||||||||||||
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 Pacific Walrus
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 Least Concern | ||||||||||||||||||
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| Odobenus rosmarus (Linnaeus, 1758) | ||||||||||||||||||
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O. rosmarus rosmarus |
The walrus is a large, semi-aquatic mammal that lives in the cold Arctic seas of the Northern Hemisphere and is the only non-seal pinniped (Pinnipedia) and the only pinniped with tusks. There is only one extant (living) species of walrus, Odobenus rosmarus, which is typically placed in its own pinniped family Odobenidae, although some classifications place walruses in the family Phocidae with the true (earless) seals (McKenna and Bell 1997, Tree of Life Web Project 2000). Like other pinnipeds, walruses have both front and hind limbs in the form of flippers and need to come on land (or ice) to give birth and raise their offspring.
There are six populations of walruses in the arctic and two or three subspecies exist. Four populations are in the Atlantic, of the subspecies Odobenus rosmarus rosmarus, one is in the Pacific, Odobenus r. divergens, and some consider the sixth population in the Laptev Sea to be a third subspecies, Odobenus r. laptevi. The Pacific walrus is slightly larger, with males weighing up to 1,900 kilograms (4,180 pounds), but Atlantic males top out at 1,600 kilograms (3,500 pounds).
With their plump body, bushy mustache, and peacefully sleepy expression, walruses are often depicted in Western cultural fiction as a happy, lovable, friendly animals, and at times comical. However, they play key roles in food chains, consuming crustaceans, fish, mollusks, echinoderms, and even seals and young whales, and being consumed by bears, orcas, and humans. Walruses have been utilized by indigenous people for thousands of years, being hunted for their meat, tusks, and skins.
The name walrus comes from Dutch, walrus, probably a folk-etymological alteration, via Dutch walvis, "whale," and ros, "horse"—of an older Scandinavian word related to Old Norse rosmhvalr, "red? whale" or "walrus." The compound Odobenus comes from odous (Greek for "tooth") and baino (Greek for "walk"), based on observations of walruses using their tusks to pull themselves out of the water. Divergens (the Pacific subspecies) in Latin means "turning apart," referring to the tusks.
The walrus should not be confused with the elephant seal, another large pinniped, and despite the etymology of its name it is not related to the whales.
Description
Walruses are the only pinnipeds that have tusks, which can grow up to one meter in length. Both male and female walruses have tusks, with larger tusks generally among the males. Both males and females also have bristles around the mouth that form a moustache. The Pacific walruses can have longer tusks and smaller noses than the Atlantic populations.
Walruses have thick skin, which can get to five centimeters (two inches) thick around the neck and shoulders of males. The underlying blubber may reach 15 centimeters.
The walruses live around 50 years.
Walruses spend about half their time in the water and half their time on beaches or ice floes, where they gather in large herds. They may spend several days at a time either on land or in the sea. Diving to depths of 90 meters (300 feet), they sometimes stay under for as long as a half hour. They use their pectoral flippers to move along out of water and can stand on all fours with an awkward gait when on rough surfaces.
In the sea, walruses sometimes catch fish, but generally graze along the sea bottom for clams, which they suck from the shell. Pacific walruses feed on more than 60 genera of marine organisms including shrimp, crabs, tube worms, soft coral, tunicates, sea cucumbers and other echinoderms, various mollusks, and even parts of other pinnipeds. Abrasion patterns of the tusks show that the tusks are dragged through the sediment but are not used to dig up prey and the upper edge of the snout is used instead. Walruses can also spit jets of water to look for clams. Clams and mollusks frequently form the large part of their diet. Large male walruses have been observed to attack seals if they cannot find any other food source.
Walruses have only three natural enemies: humans, orca, and the polar bear. Polar bears hunt walruses by rushing at them, trying to get the herd to flee, then picking off calves or other stragglers. Walruses have been known to kill polar bears and small whales.
The walruses use their long tusks (elongated canines) for fighting, dominance, and display and the males will spar with their tusks. They can also use them to form and maintain holes in the ice, or to anchor themselves with the ice.
The taxonomic group to which walruses and seals belong, Pinnipedia, has traditionally been seen as a suborder of the order Carnivora, but more recently is placed as a superfamily within the suborder Caniformia (doglike carnivores); some systematists consider Pinnipedia to be a separate order.
Life cycle
The males reach sexual maturity around ten years, although some do so as early as seven. They go into rut in January through April, increasing their food intake before the rut, but decreasing their food intake dramatically and eating only sporadically during the rut.
Females can begin ovulating as soon as four to six years old. Interestingly, the females are polyestrous, coming into heat both in late summer and also around February, yet the males are only fertile around February so the animals are in practicality monoestrous. It is unclear why the females have this second season of potential fertility. By ten years old, the females have reached maximum size and all are fertile by then.
Breeding takes place from January to March with peak conception in February, and perhaps have a delayed implantation for a few months (four to five) with total gestation lasting 15–16 months. Walruses mate in the water and give birth on land or ice floes. The males show off in the water for the females who view them from pack ice. Males compete with each other aggressively for this display space; the winners in these fights breed with large numbers of females. Older male walruses frequently bear large scars from these bloody but rarely fatal battles.
When a calf is born, it is over one meter (three feet) long and able to swim. The calves are born on the pack ice generally April to June and then generally nurse for 8–11 months before they begin eating fish on their own. They can spend three to five years with the mothers.
Distribution
About 200,000 Pacific walruses exist. Pacific walruses spend the summer north of the Bering Strait in the Chukchi Sea along the north shore of eastern Siberia; around Wrangel Island in the Arctic Ocean; in the Beaufort Sea along the north shore of Alaska; and in the waters between those locations. Smaller numbers of males summer in the Gulf of Anadyr on the south shore of the Chukchi Peninsula of Siberia and in Bristol Bay off the south shore of southern Alaska west of the Alaska Peninsula.
In the spring and fall, Pacific walruses congregate in the Bering Strait, adjacent to the west shores of Alaska, and in the Gulf of Anadyr. They winter to the south in the Bering Sea along the eastern shore of Siberia south to the northern part of the Kamchatka Peninsula, and along the southern shore of Alaska.
About 15,000 Atlantic walruses exist: they live in the Canadian Arctic; in the waters of Greenland; off of Svalbard in the Arctic Ocean, north of mainland Europe; and off of the western portion of the Russian Arctic. The Atlantic walrus once enjoyed a range that extended south to Cape Cod and occurred in large numbers in the Gulf of St. Lawrence.
Traditional hunting
Alaska Natives slaughter about three thousand walruses annually. Humans use ivory from the tusks for carving. The natives call the penis bone of males an oosik and use it in making knives. Although a male walrus's penis is completely internal, it has one of the largest bacula (penis bones) of the animal kingdom.
Federal laws in both the United States and in Canada protect walruses and set quotas on the yearly harvest. Only under rare circumstances may non-native hunters gain permission to kill a walrus legally. The law prohibits the export of raw tusks from Alaska, but walrus ivory products may come on the market if first sculpted into scrimshaw by a native craftsman.
Medical problems
Eye problems for the walrus are common and they sometimes experience intestinal disease. They sometimes get tusk infections, and in captivity they are prone to ingesting foreign objects. Also various fungus and bacteria sometimes cause minor infections. Trampling and tusk injuries occur during interactions and sometimes females are harassed and show bruises and laceration.
The Atlantic walruses show exposure to the bacteria Brucella and sometimes will show infection with Trichinella and also lice. Caliciviruses are thought to sometimes affect Pacific walruses causing skin lesions and they are thought to have a wide exposure to the viruses. These viruses are thought to interact between terrestrial and aquatic mammals, with marine mammals showing antibodies to many caliciviruses that affect land mammals. Herpesviruses can also be seen sometimes in the walrus population.
ReferencesISBN links support NWE through referral fees
- Dierauf, L., and F. Gulland. 2001. Marine Mammal Medicine. CRC Press. ISBN 0849308399
- Flynn, J., J. Finarelli, S. Zehr, J. Hsu, and M. Nedbal. 2005. “Molecular phylogeny of the Carnivora (Mammalia): Assessing the impact of increased sampling on resolving enigmatic relationships.” Systematic Biology 54(2): 317-337. Retrieved August 27, 2007.
- McKenna, M. C., and S. K. Bell. 1997. Classification of Mammals Above the Species Level. New York: Columbia University Press.
- Myers, P., and A. Poor. 2007. Carnivora. Animal Diversity Web. Accessed August 27, 2007.
- Nowak, R. M. 1999. Walker's Mammals of the World, 6th ed. Baltimore, MD: The Johns Hopkins University Press. ISBN 0801857899
- Seal Specialist Group. 1996. Odobenus rosmarus. In 2006 IUCN Red List of Threatened Species. Retrieved August 27, 2007.
- Tree of Life Web Project. 2000. Carnivora. Dogs, cats, bears, raccoons, weasels, mongooses, hyenas, seals, walruses, etc. Version 01 January 2000. Tree of Life Web Project.
- Wozencraft, W. C. 1992. Order Carnivora. In D. E. Wilson and D. M. Reeder (eds.), Mammal Species of the World: A Taxonomic and Geographic Reference, 2nd ed. Washington, DC: Smithsonian Institution Press.
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