Walrus (Odobenus rosmarus)

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Young Atlantic walrus bull
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Walrus fact file

Walrus description

KingdomAnimalia
PhylumChordata
ClassMammalia
OrderCarnivora
FamilyOdobenidae
GenusOdobenus (1)

One of the largest and most distinctive of all pinnipeds, the walrus (Odobenus rosmarus) is renowned for its enormous tusks, which can reach an incredible one metre in length. Although both sexes have the distinctively prolonged upper canines, the much larger male has tusks which are considerably longer and thicker than the female’s (2) (4) (5). The foreflippers are short and squarish like those of a sea lion, while the rear flippers resemble those of true seals, but compared with other pinnipeds, the walrus’ bulky body is much less streamlined (4) (5), as it forages for sessile organisms (6). The blunt muzzle of the walrus is also highly distinctive, as is the dense protrusion of whiskers on the upper lip (2) (4) (5), which are used to detect and identify objects in the substrate (6). Walrus skin is remarkably thick and tough, an attribute that protects against injury from other walrus’ tusks, and from the rough rocks and sharp ice it lumbers over when hauling out (2) (7), and when ploughing through the substrate in search of food (6). Except on the flippers, walrus skin is also covered with short, coarse hair that gets sparser in adult males, particularly around the neck and chest. In older bulls, this area is characteristically covered with lumps and nodules that are thicker than the surrounding skin, and protect the tissues underneath from the tusks of competitors (2) (4) (7). Skin colouration varies with activity, appearing pale grey when in cold water, due to reduced blood flow to the skin, but becoming characteristically darker reddish-brown when warm and dry (2) (4) (5) (7). Males also become paler with age, such that some older bulls almost look albinistic (4).

French
Morse.
Spanish
MORSA.
Size
Male average length: 320 cm (2)
Female average length: 270 cm (2)
Male weight: 1200 - 1500 kg (2)
Female weight: 600 - 850 kg (2)
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Walrus biology

For an animal of such size, the walrus feeds on organisms that are relatively low in the food chain, preferring the small invertebrates that inhabit the ocean floor to the highly mobile fish and crustaceans taken by most other pinnipeds (2). By far the greatest proportion of its diet is comprised of bivalve molluscs such as clams, cockles, and mussels, but it will also take various shrimps, crabs, worms, octopuses, sea cucumbers, slow moving fish and, very rarely, seals (1) (2) (5) (7). In order for such a large, bulky animal to sustain itself on a diet dominated by relatively small organisms, it needs to be a highly efficient forager (2). Diving to depths of up to 180 metres for up to 24 minutes at a time, it uses its highly sensitive whiskers and snout to locate food, which it then excavates using the tough edges of its nose, and by squirting jets of water from its mouth (2) (5) (7), and creating water flow with its foreflippers (6).

Male and female walruses typically spend little time together outside of the breeding season, but being a highly gregarious species, both sexes haul out on land or ice in large numbers. In these largely sexually segregated herds, the animals lie in close physical contact, sometimes piled on top of each other (2) (8). Walrus society is extremely hierarchical, with the largest individual, with the largest tusks, commanding the best positions at the haul out sites. Usually the dominant walrus can displace subordinates with the minimal of posturing, but similar sized/tusked adults may put up a fight, in which case a stabbing duel may ensue, until one aggressor accepts defeat and retreats to less coveted territory (2) (7). Although these fights do take place between both sexes, the most violent encounters occur between bulls during the breeding season (4) (7).

In the harsh winter, males and females congregate for the mating season, between January and April (2) (4) (7). Whilst the females haul out on ice floes, the males compete for nearby aquatic territory through a combination of vocalisation, physical displays, and, if necessary, intense fighting (1) (4). The female chooses a mate from the competing males and usually copulates in the water, with the most dominant bulls siring offspring with multiple females (2) (4). After a gestation period that lasts 15 months, including a four to five month period of delayed implantation, the female gives birth to a single calf. The calf is able to swim immediately but is typically only weaned during its second year, and usually remains within the extremely protective care of its mother for several years (2) (5). While most females become sexually mature at 7 years of age, and give birth for the first time at around the age of nine years, most males only become sufficiently physically and socially mature to mate at around 15 years, despite reaching sexual maturity between 7 and 10 years (2) (7).

The seasonal movements of the walrus, and in particular of the females, calves and most of the juveniles in the Pacific, are typically governed by the movements of the pack ice. However, in the summer in the Atlantic, walruses of all sexes and ages commonly haul out on land relatively far from the pack ice (1) (4).

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Walrus range

The walrus has a nearly circumpolar distribution in the Arctic and sub-Arctic, with three recognised subspecies occupying different areas within its overall range. The Atlantic walrus (Odobenus rosmarus rosmarus) occurs from the eastern Canadian Arctic and Greenland, to the western Kara Sea; the Pacific walrus (O. r. divergens) occurs in the Bering Sea and the adjacent Arctic Ocean; and the Laptev walrus (O. r. laptevi) is found in the Laptev Sea, north of Siberia (1) (4). However the taxonomic status of the Laptev walrus is considered dubious, with recent genetic analyses indicating that it should be treated as the western most population of the Pacific walrus (1) (2) (4).

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Walrus habitat

Inhabits relatively shallow continental shelf areas, seldom occurring in deeper water (as it has to forage on the ocean floor) (6), and generally follows the movements of the pack ice (1) (2) (4). Sandy beaches, rocky shores and ice floes are all used as haul out sites (4).

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Walrus status

The walrus is classified as Data Deficient (DD) on the IUCN Red List (1) and Appendix III of CITES (3).

IUCN Red List species status – Data Deficient

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Walrus threats

As an important source of food and other materials, the walrus has been hunted by native peoples for thousands of years, however, it was from the 18th to mid-20th century that commercial hunters severely depleted the population (7). Although some walrus populations have since recovered significantly, there is little recent information on population sizes and trends and so the species is currently classified as Data Deficient on the IUCN Red List (1) (4).

Subsistence hunting continues through most of the walrus’ range, but it is regulated in all areas. However, poaching continues to be a problem in many parts (1) (4) (7). Climate change and the reduction in the extent of the sea-ice is expected to have a negative impact on the walrus, particularly in the Pacific (1). There is also concern that the loss of sea-ice will open commercial sea-lanes in previously isolated parts of the walrus’ range, which will likely lead to increased disturbance. The walrus is extremely sensitive to disturbance, and human activity at and around haul-outs can lead to populations abandoning sites. Other threats to this species include competition with shellfish fisheries, accidental by-catch, pollution, and habitat destruction through bottom trawling, resulting in walrus prey destruction (1) (2) (6) (7).

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Walrus conservation

In Canada, Russia and Greenland, walrus harvests are controlled by regulations, while Norway forbids all hunting at Svalbard (1) (2). In Alaska, native people are allowed to hunt the walrus for subsistence purposes, and while no quotas or limits have been established, all harvests must be conducted in a non-wasteful manner (1). Following a petition (and a subsequent lawsuit) submitted by the Center for Biological Diversity, the US Fish and Wildlife Service is currently reviewing the status of the Pacific walrus to determine whether it warrants inclusion on the Endangered Species Act, the highest level of protection afforded to wildlife in the US. It is the threat of the loss of sea-ice habitat in the face of global warming that is considered the main threat to the Pacific walrus, and the principal motivation for its elevated protection (9). If listed under the Endangered Species Act, the Pacific walrus can benefit from the compulsory development of a recovery plan, protection and restoration of critical habitat, scientific research and public education (9) (10) (11).

View information on this species at the UNEP World Conservation Monitoring Centre.
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Find out more

Find out more about the conservation of the Pacific walrus:

For more information on the walrus:

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Authentication

Authenticated (24/01/2011) by Dr R.A. Kastelein, Director of SEAMARCO (Sea Mammal Research Company)

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Glossary

By-catch
In the fishing industry, the part of the catch made up of non-target species.
Crustaceans
Diverse group of animals with jointed limbs and a hard chitinous exoskeleton characterised by the possession of two pairs of antennae, one pair of mandibles (mouthparts used for handling and processing food) and two pairs of maxillae (appendages used in eating, which are located behind the mandibles). Includes crabs, lobsters, shrimps and barnacles.
Gestation
The state of being pregnant; the period from conception to birth.
Invertebrates
Animals with no backbone, such as insects, crustaceans, worms, molluscs, spiders, cnidarians (jellyfish, corals, sea anemones), echinoderms, and others.
Molluscs
A diverse group of invertebrates, mainly marine, that have one or all of the following; a horny, toothed ribbon in the mouth (the radula), a shell covering the upper surface of the body, and a mantle or mantle cavity with a type of gill. Includes snails, slugs, shellfish, octopuses and squid.
Pinnipeds
Carnivorous, aquatic mammals belonging to the Pinnipedia, which includes the seals, sea lions and walruses. All have four limbs modified into flippers.
Subspecies
A population usually restricted to a geographical area that differs from other populations of the same species, but not to the extent of being classified as a separate species.
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References

  1. IUCN Red List (June, 2009)
    http://www.iucnredlist.org/
  2. Kastelein, R. (2008) Walrus. In: Perrin, W.F., Würsig, B. and Thewissen, J.G.M. (Eds) Encyclopedia of Marine Mammals. Academic Press, London.
  3. CITES (June, 2009)
    http://www.cites.org/
  4. Jefferson, T.A., Leatherwood, S. and Webber, M.A. (1993) FAO Species Identification Guide. Marine Mammals of the World. Food and Agriculture Organization of the United Nations, Rome.
  5. Burnie, D. (2001) Animal. Dorling Kindersley, London.
  6. Kastelein, R.A. (January, 2011) Pers. comm.
  7. Macdonald, D.W. (2006) The Encyclopedia of Mammals. Oxford University Press, Oxford.
  8. Nowak, R.M. (1999) Walker's Mammals of the World. Johns Hopkins University Press, Baltimore.
  9. Center for Biological Diversity (October, 2009)
    http://www.biologicaldiversity.org/news/press_releases/2009/pacific-walrus-09-08-2009.html
  10. Taylor, M.F.J., Suckling, K.F. and Rachlinski, J.J. (2005) The effectiveness of the endangered species act: a quantitative analysis. Bioscience, 55(4): 360-367.
  11. Clark, J.A., Hoekstra, J.M., Boersma, P.D. and Kareiva, P. (2002) Improving U.S. Endangered Species Act recovery plans: key findings and recommendations of the SCB Recovery Plan Project. Conservation Biology, 16: 1510-1519.
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Image credit

Young Atlantic walrus bull  
Young Atlantic walrus bull

© B. & C. Alexander

B. & C. Alexander
Alexander@arcticphoto.co.uk

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