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Kingdom
Animalia
Phylum
Chordata
Subphylum
Vertebrata
Class
Mammalia
Order
Carnivora
Suborder
Caniformia
Family
Odobenidae
Species
Odobenus rosmarus
Odobenus rosmarus
walrus
2010/02/07 04:07:08.425 US/Eastern
By Matt Carling
Species:
Odobenus rosmarus
Geographic Range
Walruses occupy a nearly circumpolar region of the Arctic. Three distinct subspecific populations are recognized: 1) Atlantic (
Odobenus rosmarus rosmarus
), which lives in the eastern Canadian Arctic and Greenland east to Novaya Zemlya; 2) Pacific (
O. r. divergens
), living in the Bering Sea and adjacent Arctic Ocean; 3) Laptev Sea (
O. r. laptevi
), occupying the Laptev Sea, north of Siberia. Some taxonomists do not recognize the Laptev Sea population as a separate subspecies. Unless otherwise specified, all walruses will be treated here as one population,
Odobenus rosmarus
(Jefferson et al. 1993; Nowak 1991; Parker 1990).
Habitat
Walruses prefer to inhabit areas with ice floes in the shallower regions near the coasts of Arctic waterways. Their seasonal migration patterns coincide with the changes in the ice. In the winter, walruses move south as the Arctic ice expands, and in the summer they retreat north as the ice recedes. This migration can cover distances of 3000 km. Individuals concentrate where the ice is relatively thin and dispersed in the winter. In the summer time, bulls may use isolated coastal beaches and rocky islets. Cows and young prefer to stay on ice floes in all seasons (Nowak 1991, Parker 1990).
Terrestrial Biomes:
icecap.
Physical Description
Mass
400 to 1700 kg
(880 to 3740 lbs)
The most obvious physical characteristic of the walrus is the presence of large tusks in both the male and female. These tusks, which are canines, can reach lengths of 1 meter (the average size is 50 cm), and are usually longer and heavier in the males (bulls) than in the females (cows). Accompanying the tusks are stiff beard bristles, called vibrissae, and although individual variation in length is great, the bristles can grow up to 30 cm long. The bristles are replaced yearly. In natural environments these bristles are often quite worn. Bulls are physically larger than the cows, growing to lengths of 3 m compared to 2.6 m for cows. Aside from the conspicous beards, both males and females appear almost completely bald. In fact, they are covered with short coarse hair that becomes less dense as the animal ages. Their skin, which lies in many folds and wrinkles, can be 4 cm thick. This tough skin is the thickest on the neck and shoulders of adult males. As walruses age their skin becomes paler. When the animals enter the water they become even paler as blood flow to the skin is restricted. Conversely, when walruses are warm their skin is flushed with blood and they appear to be very red, almost "sunburned." Walruses have no external ears and their eyes are small and piglike (Lawlor 1979, Nowak 1991, Parker 1990).
Reproduction
Because walruses breed during the harsh Arctic winters, little is known about their mating systems. The walrus mating system is believed to be a female-defense polygyny. Large mature males have exclusive access to a herd of females for 1-5 days at a time. Courtship behavior is described in the next section. Mating takes place in January and February, most likely underwater. Walruses are interesting because implantation of the blastocyst is delayed for 4 or 5 months, until June or July. Birth occurs 10-11 months later, from mid-April to mid-June, meaning that the total gestation period is 15-16 months. Females give birth to a single, precocial offspring. The calf is about 113 cm long and weighs approximately 63 kg. It is grey in color and can swim at birth. The social bond between the mother and calf is very strong, and cows are extremely protective of their offspring. Lactation generally lasts for 2 years, but calves are often able to find food before they are finally weaned. Young bulls become sexually mature at 8-10 years, but are often unable to compete successfully for females until they are at least 15 years old. Females become sexually mature at 6-7 years, and are full grown at 10-12 years old. Female fecundity is greatest when cows are 9-11 years old, and at this age they can produce a calf every other year. The interval between births is longer in older females. In the wild, walruses have been known to live for over 40 years (Sjare and Stirling 1996, Nowak 1991).
Key reproductive features:
gonochoric/gonochoristic/dioecious (sexes separate);
sexual
.
Behavior
Walruses are extremely gregarious. Often they haul out on land or ice floes in herds of up to several thousand individuals lying in close physical contact. During the nonbreeding season, these groups are sexually segregated, and there are dominance hierarchies based on both body and tusk size. When an individual hauls out of the water and seeks a resting spot occupied by a smaller animal, it may throw back its head and point its tusks at the smaller animal. If this does not scare the smaller walrus, the larger one may strike with their tusks, and frequently there is bloodshed. Apparently, walruses prefer to lie in the middle of these large congregations. Courtship behavior usually consists of several mature bulls competing for the exclusive mating rights to a herd of cows. Groups of males gather in large herds and use a variety of tactics to attract females. These tactics include extensive singing and vocal displays, as well as male-male combat. Males make a variety of clicking and bell-like sounds underwater. They also raise their heads above water and emit a series of sharp clucks and whistles. Occasionally, males engage in physical combat, trying to injure each other by stabbing their tusks into the neck region of the other. These fights generally do not last long and usually end with one bull leaving the area. Males successful in attracting females usually hold onto their position for 1-5 days, after which they are generally displaced by other males. Mating and birth are both presumed to occur underwater. When a female is almost ready to give birth, she often leaves her herd. After giving birth, she joins a group of other mothers and their young. Female offspring remain in their mothersO group, but young males disperse at around 2-3 years old to join a herd of males. Bulls provide no parental care for the young, but community care of offspring by other females has been observed. Adoptions of orphaned calves have also been documented (Nowak 1991, Parker 1990, Sjare and Stirling 1996).
Food Habits
Walruses feed on animals that reside on the surface of the bottom of the ocean, or in the sediments that coat the bottom. Their main diet includes mussels, snails, echinoderms, and crabs. Walrus foraging dives usually last 2-10 minutes at depths of 10-50 m. They swim headfirst along the ocean bottom, rooting about with their stiff beard bristles in a piglike fashion. Softbodied organisms are swallowed whole. Two theories on how walruses eat bivalves have been proposed, and it appears that walruses employ both methods. Walruses crack mollusk shells between their flippers and then eat the soft part. More often, walruses hold the shelled organisms in their lips and ingest the fleshy parts by powerful suction, discarding the shells. Occasionally, walruses also prey on fish, seals, and young whales. Walruses are capable of holding down seals and small whales with their flippers and tearing them apart with their tusks. In the winter, when accompanying the females and young, the bulls apparently eat very little. It was once believed that walruses used their tusks to dig up food, but this notion is false (Nowak 1991, Parker 1990).
Economic Importance for Humans: Negative
Aside from humans hunting them, walruses have little contact with people. Because of this, walruses have little negative impact on human economies (Jefferson et al. 1993).
Economic Importance for Humans: Positive
Walruses have been exploited by humans for many millenia. Native peoples have harvested them for their meat, skin (which they used for shelters and kayak coverings), and ivory for tools, weapons, and arts. In the early 10th century, Viking traders began taking large numbers, and this European decimation of walruses continued until the early 20th century. Walruses are now managed by governments but continue to be killed. Northern cultures are allowed to hunt walruses for subsistence living, but poachers continue to take walruses illegally, mostly for their ivory tusks (Jefferson et al. 1993).
Conservation Status
Although walrus populations had declined drastically by the early 20th century, management programs have resulted in the dramatic rebound of the Pacific population. Although the populations are not believed to be in danger of becoming extinct, the Atlantic and Laptev Sea populations still remain at low levels. Presently, estimates of the number of walruses in all populations is not known well enough to warrant an IUCN listing (Jefferson et al. 1993).
Other Comments
Walruses are among the strangest living mammals. Their large tusks make them unlike any other marine animal. These tusks are used in fighting as noted above, but they also serve other functions. Tusks can be used for cutting through ice, hooking over ice for stability while sleeping, and helping to pull the body out of the water. Walruses sometimes use their heads to break through ice up to 20 cm thick. Males possess a large baculum (penis bone), up to 63 cm in length, the largest of any mammal in both absolute and relative sizes. Walruses swim at an average speed of 7 km/hr, but can reach maximum speeds of at least 35 km/hr. The three subspecies differ slightly in physical characteristics (weight and body length) and in geographic distribution. Pacific walruses are a little larger than their Atlantic counterparts, and the Laptev Sea populations are of intermediate size. Another unusual feature of walruses is the presence of pharyngeal pockets that open on either side of the esophagus. These pockets can hold up to 50 liters of air and provide buoyancy to the animal when filled. This allows walruses to be able to sleep in an upright position. The pockets may even play a role as a resonating chamber and amplifier for the call they produce during mating season, which sounds like the ringing of a bell (Nowak 1991, Parker 1990).
For More Information
Find
Odobenus rosmarus
information at
Contributors
Matt Carling (author), University of Michigan.
References
Jefferson, T. A., S. Leatherwood, and M. A. Webber. 1993. Marine Mammals of the World. Food and Agriculture Organization of the United Nations, Rome.
Lawlor, T. E. 1979. Handbook to the Orders and Families of Living Mammals. Mad River Press, Eureka, California.
Nowak, R. M. 1991. Walker's Mammals of the World. Fifth Edition. Johns Hopkins University Press, Baltimore.
Parker, S. P. ed. 1990. Grzimek's Encyclopedia of Mammals. McGraw-Hill Publishing Company, New York.
Sjare, B., and I. Stirling. 1996. The breeding behavior of the Atlantic walruses, Odobenus rosmarus rosmarus, in the Canadian High Arctic. Canadian Journal of Zoology 74: 897-911.
2010/02/07 04:07:09.321 US/Eastern
To cite this page:
Carling, M. 1999. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed February 09, 2010 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html.
Disclaimer:
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written largely by and for college students
. ADW doesn't cover all species in the world, nor does it include all the latest scientific information about organisms we describe. Though we edit our accounts for accuracy, we cannot guarantee all information in those accounts. While ADW staff and contributors provide references to books and websites that we believe are reputable, we cannot necessarily endorse the contents of references beyond our control.
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Sponsored in part by the Interagency Education Research Initiative,
the Homeland Foundation and the
University of Michigan
Museum of Zoology
.
This material is based upon work supported by the
National Science Foundation
under Grants DUE-0633095 and DRL-0628151.
The ADW Team gratefully acknowledges their support.
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