Marine Species Identification Portal : Walrus

(Linnaeus, 1758) - Walrus

Distinctive Characteristics

Walruses are very large and bulky animals. Males are longer and heavier than females. Adults have a short coarse pelage that grows sparser in older males than in females. The skin is thick, rough, and heavily marked with creases and folds. Older males often have lumps or nodules on the neck and chest, giving them a warty appearance. The neck, chest, and shoulders are massive, and the body tapers towards the tail. The head, and especially the muzzle, are short, but very wide. The “bloodshot” eyes are small, somewhat protruding, and set far apart. The end of the muzzle is flattened and has large, fleshy, forward-facing mystacial pads sprouting several hundred short, stiff, whitish vibrissae. The nostrils are located on top of the muzzle. Walruses have no ear pinnae. The foreflippers are relatively short and squarish; in some ways they resemble otariid foreflippers, with longer first digits and shorter subsequent digits, each with a very weakly developed claw. The hindflippers are phocid-like, with longer first and fifth digits, and strong expandable webbing between the digits, each with a small claw. The tail is enclosed in a web of skin.

Walrus coloration varies with age and activity. Most walruses are greyish cinnamon-brown. Males become paler as they age; some old bulls look albinistic. When walruses enter cold water they become paler still, as blood flow to the skin is reduced. Conversely, when these animals are warm, the skin becomes flushed with blood and they acquire a rosy red “sunburned” colour. Subadult animals tend to be darker, with almost black skin.

The dental formula is I 1/0, C 1/1, PC 3/3. The upper canine teeth develop into tusks that grow throughout life;they are longer (up to 1 m total length) and thicker in males than in females (although they often are partially, or entirely, broken off in adults of both sexes). Tusks also tend to be less curved and more divergent at the tips in males. Walrus calves are born without tusks, but they erupt at an early age.

Can be confused with

Walruses are unmistakable, and should not be confused with any other animal.

Size

Males reach about 3.6 m and 1900 kg, females about 3 m and 1200 kg. Newborns are 1 to 1.2m and weigh 45 to 75kg.

Geographical Distribution

Walruses have a nearly circumpolar distribution in the Arctic. Three distinct subspecific populations are recognized: Atlantic, O. rosmarus rosmarus, from the eastern Canadian Arctic, and Greenland east to Novaya Zemlya; Pacific, O. r. divergens, in the Bering Sea and adjacent Arctic Ocean, and; O. r. laptevi, from the Laptev sea, north of Siberia (although this subspecies is not recognized by most taxonomists). Walruses are found in shallow water and coastal habitats, usuallyassociated with pack ice. They regularly haul out on sandy beaches, rocky shores, and ice floes to rest and moult.

Biology and Behaviour

Calves are born from mid-April to mid-June on pack ice. Courtship and mating has been little studied, because walruses mate in the harsh winter environment of the Arctic. It is believed that walruses are polygynous and that males may form a type of lek; they seem to establish small aquatic territories adjacent to females hauled out on ice floes, where they vigorously vocalize and display. There is also some intense male-male fighting at this time.

In most populations walruses generally follow the movements of the pack ice. However, some walruses summer far from the pack ice, such as on Round Island, Alaska. Walruses also haul out on shore, away from ice in years of reduced pack ice. Walruses are among the most gregarious of pinnipeds. Ashore they are regularly found in huddled masses; at sea they are often seen in groups of less than 10.

Tusks are used for hauling out, and in social interactions, not for digging up food, as previously thought. Walruses feed on a wide variety of prey, chiefly benthic invertebrates. Some of the favourite foods are clams, worms, snails, shrimp, and slow-moving fish. Some “rogues” regularly prey on seals and small whales.

Exploitation

Walruses have been severely exploited by humans. Like most Arctic pinnipeds, they have been hunted for millennia by native peoples who made wide use of the carcass for meat, skins for shelter and kayak coverings, and ivory for tools, weapons, and art. Europeans have taken vast numbers of these animals beginning with Viking traders in the 10th Century. Most populations were decimated in the 19th and early 20th Centuries. Although the Pacific population has recovered dramatically, the Atlantic and Laptev Sea populations are still at low levels. Subsistence catches are still important to northern cultures. These are managed by governments, but poaching continues to be a problem in most areas.

IUCN Status

Insufficiently known.

Images

O. rosmarus 1 (A full-color drawing of the habitus)
O. rosmarus dv skull (Dorsal view of the skull)
O. rosmarus vv skull (Ventral view of the skull)
O. rosmarus lv skull (Lateral view of the skull)
O. rosmarus dvm skull (Dorsal view of the mandible)
O. rosmarus 2 (A walrus on an ice-floe)
O. rosmarus map (Distribution map)

Audio

O. rosmarus track 1 , RUTTING WHISTLES OF A MALE PACIFIC WALRUS (Odobenus rosmarus divergens), Walruses are extremely social animals which use a number of sensory modalities to exchange information with conspecifics. The most conspicuous signals are in air sounds, but underwater sounds are also produced. One of the in air sounds is a 'rutting whistle', produced by male walruses in spring. Fay et al. (1984) describe walruses in the Bering Sea producing loud whistles when swimming alongside a herd of female walruses, which were hauled out on the ice in March. The bulls were diving and surfacing at short intervals (1 - 3 minutes). The females, however, seemed to pay little attention to the diving bulls, although the diving sometimes continued for 5 hours. Miller (1985) also describes Pacific walrus whistles. A bull, swimming close to a hauling ground, lifted its head out of the water and produced whistles through its pursed lips. Sometimes the signal had a noisy character, but at other times it was an almost pure tone.The frequencyof the rutting whistle fundamental varies between roughly 1 and 2 kHz. The whistle starts at 1184 Hz, sweeps down to 1056 Hz, keeps this frequency for 0.8 s and rapidly increases to 1952 Hz. The total duration of the whistle is approximately 1.8 seconds. Sometimes a 'false' tone, consisting of two fundamentals, is heard. The average Source Level in air is 120 dB re 1 pW. Using certain assumptions concerning the walrus hearing system and the propagation conditions, the range of the walrus' whistle signal, to be heard by conspecifics in their natural environment, is calculated to be 1100 (+/- 100) m (Verboom and Kastelein, 1995).The rutting whistle differs considerably from other Walrus in-air vocalisations, which are described as knocks, roars, clicks, grunts and a bell-sounds (the last two signals are emitted under water as well). The knock is a short, broadband pulse with a frequency contents of 100 - 4000 Hz. The sound seems to originate from deep out of the throat, without the animal moving the jaws. Roars are long, loud calls with most of the energy around 300 Hz. Grunts are brief calls, also with a low-frequency spectrum. How the bell-sound (pure tone around 500 Hz with harmonics) is produced is not clear (Schevill et al., 1966; Fay et al., 1984).

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Walrus (Odobenus rosmarus)