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Lifespan, longevity, and ageing

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Observations: In the wild, walrus have been estimated to live over 40 years (Bernhard Grzimek 1990). Their longevity in captivity has not been studied in detail and hence information on ageing is limited. One wild born specimen was about 30.6 years old when it died in captivity (Richard Weigl 2005). Atherosclerosis was described in a 25 year-old captive animal (Gruber et al. 2002).
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Joao Pedro de Magalhaes
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Habitat

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Walruses inhabit areas in the Arctic that are largely made up of ice. Walruses prefer areas with shallow water so they can easily access food. This slow moving marine mammal spends the majority of its time in or around water. Females spend more time on ice opposed to the males, who spend more of their time on sand or boulder beaches. Walruses migrate north during the summer and south in the winter. The migrations ensure that the walruses can be where the most optimal ice is found. Optimal is defined as relatively thin ice but thick enough to hold the enormous weight of their bodies.

Habitat Regions: polar ; terrestrial ; saltwater or marine

Terrestrial Biomes: icecap

Aquatic Biomes: coastal

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Associations

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Walruses predators include killer whales and polar bears. Adults use their giant tusks as a weapon to defend themselves. The young walruses are more susceptible to predation. Humans are the main predator of walruses.

Known Predators:

  • killer whales (Orcinus orca)
  • polar bears (Ursus maritimus)
  • humans (Homo sapiens)
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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Morphology

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Walruses are one of the largest pinnipeds. The Pacific walruses tend to have a larger body mass than the Atlantic walruses. This animal is known for their massive tusks, which are really just enlarged canine teeth. These tusks can break through 20 cm of ice. They also assist walruses in climbing out of the water and onto the ice. The tusks can be used for the walruses to defend themselves from larger predators and are also a way to establish dominance and a hierarchy among walruses. Tusks can grow to a length of 90 cm but the average size is roughly 50 cm. Walruses have thick skin that ranges from a light grey to a yellowish brown color. Walrus pups skin color differs from the adult, because they are usually solid grey, while adults can range in colors. The skin thickness varies across the body but is usually 2 to 4 cm thick. The layer of blubber underneath the skin can be as thick as 25.4 cm.

Walruses have short fur in most areas of their bodies except their appendages. Walruses have whiskers to help them feel around on the ocean floor. They have relatively small eyes because they rely mainly on sense of touch to find food. They have short front flippers not only to swim but also to assist them on land. It uses its hind flippers as a motor to move its large body through the waters with the help of the front flippers to navigate which direction it will go in. Male have greater mass than females, weighing up to 1200 to 1500 kg and can be as long as 320 cm. Females of the same age can weigh 600 to 850 kg and grow to a length of 270 cm. Males also have longer and thicker tusks than females. Males usually have thicker skin than females as well.

Range mass: 600 to 1500 kg.

Average mass: 1000 kg.

Range length: 270 to 320 cm.

Average length: 300 cm.

Sexual Dimorphism: male larger

Other Physical Features: endothermic ; bilateral symmetry

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Melissa Whistleman, Radford University
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Life Expectancy

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The average lifespan for walruses is between 30 to 40 years in the wild. They have a high survival rate as calves due to the protection by the females. Lower life spans may be a result of poachers and hunters. In captivity, walruses have been recorded to live up to age 30. However, ingesting objects that are not meant for eating and tusk infection could prevent a long lifespan in captivity. Also, since they are in artificial surroundings, the behavior between mothers and calves may cause problems, such as malnutrition.

Range lifespan
Status: wild:
30 to 40 years.

Range lifespan
Status: captivity:
30 (high) years.

Typical lifespan
Status: wild:
30 to 40 years.

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Melissa Whistleman, Radford University
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Distribution

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Walruses (Odobenus rosmarus) are found in Arctic regions of the world. There are three subspecies. Pacific walruses (Odobenus roasmarus divergens) live primarily in the Bering Sea. In warm summer months it could travel as far the Beaufort Sea and the East Siberian Sea. Atlantic walruses (Odobenus rosmarus rosmarus) resides in the eastern and western Atlantic Ocean. Laptev walruses (Odobenus rosmarus laptevi) are found in the Laptev Sea. Laptev walruses are the smallest subspecies of walrus with only a few thousand living currently in the Laptev Sea and the least is known about them.

Biogeographic Regions: arctic ocean (Native ); atlantic ocean (Native ); pacific ocean (Native )

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Melissa Whistleman, Radford University
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Trophic Strategy

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Walruses mainly feed on small invertebrates, most commonly consuming bivalve mollusks. It is unknown exactly how walruses find them. however it is known that walruses use their hind fins to propel them forward, while their tusks, mouth, and whiskers drag the bottom of the ocean floor in search of food. Once the walrus has obtained a mollusk, it uses a suction method to ingest the inside after its mouth and tongue have opened the shell. Occasionally a different method is used to get shellfish open by crushing them open with their rounded teeth. Due to the walrus’s diet of small organisms, large quantities are required to sustain them. Each time a walrus dives down to eat, they can consume up to 60 clams. Their dives for food usually last 5 to 20 minutes. Walruses can dive to depths of approximately 70 m. Adults require 25 kg of small benthic organisms per day. Walruses occasionally eat bigger animals such as seals and some seabirds.

Animal Foods: birds; mammals; mollusks; aquatic crustaceans; other marine invertebrates

Foraging Behavior: stores or caches food

Primary Diet: carnivore (Molluscivore )

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Associations

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Walruses forage mainly on molluks and other benthic organisms. Sometimes the parasite Trichinella spiralis can get inside their intestines and the intestinal lining. In extreme cases this can cause death but usually it just causes pain, sickness, and organ damage. The parasite, Toxoplasma gondii, is found in walruses and is acquired when eating bivalves. This parasite can cause Toxoplasmosis and results in death. Brucellosis causing parasites (Brucella) result in reproductive problems for walruses. This can lead to stillbirths and can result in death to the parent, as well.

Commensal/Parasitic Species:

  • Trichinella spiralis
  • Toxoplasma gondii
  • Brucella
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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Benefits

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Walruses are extremely important to humans. Humans hunt them and use them for oil, ivory, and their hides. Many centuries ago, the natives of Alaska, Canada, and Russia hunted them for their meat and bones, which were used to make tools. Population sizes of walruses decreased greatly in the 18th century due to overhunting. Through the years, governments from various countries have put restrictions on walrus hunting. This has allowed the populations to rebound but they have never fully recovered.

Positive Impacts: food ; body parts are source of valuable material

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Conservation Status

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According to IUCN Redlist of threatened species, walrus conservation status is currently listed as data deficient. Walruses are threatened by hunters who use them for their bones, skin, and tusks. According to IUCN redlist, there are regulations on walrus hunting in Canada, Greenland, and in the Russian Federation. In Alaska, most natives use walruses in a non-wasteful way. Walruses are fully protected in Svalbard and the Russian Atlantic under the North Atlantic Marine Mammal Commission. Another threat to this species is global warming. There is a decrease of floating ice further out at sea, which reduces their feeding areas. CITES lists walruses in appendix III. This appendix includes general information on the walrus as well as information on the walrus population and conservation. Species are listed in Appendix III not because they are globally threatened, but because countries requested help in trade control and permitting for the species' import or export.

US Federal List: no special status

CITES: appendix iii

State of Michigan List: no special status

IUCN Red List of Threatened Species: data deficient

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Behavior

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Walruses have small eyes that are adapted to the cold environment. Some fat cells are in place to help keep the eyes warm. Some studies indicate that walruses can see in color, but the range of the color spectrum is unknown. Walruses has short-range vision and often cannot see when they are on the ocean floor scavenging for food. The whiskers, also called vibrissae, are used for feeling their way around the ocean floor. Walruses use their whiskers to help identify food or any other small objects. They can hear relatively well on land but under water, they use a system of tissue conduction to hear. This system closes their auditory meatus and only allows them to hear through their outer ear tube. Walruses are vocal mammals. They communicate during mating season, when they have mother and calf interactions, and when establishing dominance among other walruses. Walruses have a series of grunts and barks they will use in the situations described above. The Atlantic walrus and the Pacific walrus have slightly different vocalizations. A study showed that walruses could differentiate between the two different subspecies vocalizations.

Communication Channels: visual ; tactile ; acoustic ; chemical

Perception Channels: visual ; tactile ; acoustic ; chemical

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Benefits

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There are no known adverse effects of walruses on humans.

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Reproduction

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Walruses are polygynous, meaning that one male usually mates with many females. Males have many mating calls and noises they make to attract females during mating season and in order to mark their territory. Underwater, the males make bell whistling noises and thumping noises to get the attention of females. These noises, not only attract females, but also serve as a warning to other male walruses. These noises are meant to intimidate other walruses. When it comes to mating, usually the strongest, largest and oldest of the males get to mate with the females. Tusk fights occur between males over who gets to mate with a group of females either on land or in water. Sometimes these fights can be very gruesome and even fatal.

Mating System: polygynous

Female walruses sexually mature between the ages of 5 and 7. Males sexually mature around ages 7 and 10 but don’t mate until they are approximately 15 years old, when they are socially mature. During the winter and summer, both male and female walruses gather in the thousands to breed. Both sexes congregate in their haul-out sites, which are rocky or sandy beaches, to pick potential mates. However, mating is believed to take place in the water. Walruses produce offspring most of their lives. Females produce one calf every 3 years. The average gestation period for a female walrus is 15 months, which includes a 4 to 5 month delay in the egg implantation.

Because walruses breed between January and April, the baby walruses will be born the next year between April and June. The average weight of a walrus pup is about 60 kg with a length of 120 cm. When the calves are born, they immediately know how to swim. This, along with the mother’s protection, decreases the chance for predation. Before the calves are weaned, they live with the herd of female walruses. They are very dependent on their mothers for the first few years. At age two, they learn to scavenge for their own food and by age three, they are completely weaned. At this time, male walruses join the male herd and females stay in the female group but are independent from their mothers.

Breeding interval: Walruses breed once every 2 to 3 years.

Breeding season: Walruses breed between January and April.

Range number of offspring: 1 to 1.

Average gestation period: 15 months.

Range weaning age: 12 to 36 months.

Range time to independence: 2 to 3 years.

Average time to independence: 3 years.

Range age at sexual or reproductive maturity (female): 5 to 7 years.

Average age at sexual or reproductive maturity (female): 7 years.

Range age at sexual or reproductive maturity (male): 7 to 10 years.

Average age at sexual or reproductive maturity (male): 10 years.

Key Reproductive Features: seasonal breeding ; gonochoric/gonochoristic/dioecious (sexes separate); sexual ; delayed implantation

Average birth mass: 60000 g.

Average gestation period: 331 days.

Average number of offspring: 1.

Female walruses care for their pups until the pups reach three years of age. Male walruses have no part in raising their young.

Parental Investment: female parental care ; pre-weaning/fledging (Protecting: Female); pre-independence (Protecting: Female)

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Baker, H. 2013. "Odobenus rosmarus" (On-line), Animal Diversity Web. Accessed April 27, 2013 at http://animaldiversity.ummz.umich.edu/site/accounts/information/Odobenus_rosmarus.html
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Hillary Baker, Radford University
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Karen Francl, Radford University
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Kiersten Newtoff, Radford University
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Melissa Whistleman, Radford University
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Biology

provided by Arctic Ocean Biodiversity 2011
A massive circumpolar pinniped with large tusks
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Lloyd Lowry
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Bodil Bluhm

Comprehensive Description

provided by Arctic Ocean Biodiversity 2011
Gray-brown to cinnamon brown and sometimes pink; Robust, large body with Tusks
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Lloyd Lowry
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Trophic Strategy

provided by Arctic Ocean Biodiversity 2011
arrow range of prey which include Greenland halibut, squid, and polar cod; Echolocate prey with sonar
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Lloyd Lowry
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Bodil Bluhm

Life Cycle

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Size at birth 1.5m (15 feet); Sexual maturity at 5-7 years; Females have calves every 3 years; Longevity over 60 years, possibly more than 100; Behavior; Vocal and gregarious
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Lloyd Lowry
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Bodil Bluhm

Habitat

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Arctic, Atlantic waters of Canada and Greenland; Offshore and in deep water within dense sea ice
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Lloyd Lowry
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Bodil Bluhm

Brief Summary

provided by Ecomare
You can't miss the tusks of the walrus. Male walrusses can have tusks up to 1 meter long. Females also have tusks, but they are shorter. These long teeth may look awkward, but the walrus certainly knows how to put them to use. It uses them as an ice ax to help hoist itself onto slippery ice, or as pickax to loosen shellfish from the sea bottom. It also uses them as a weapon to fight rivals and as an ornament to attract females.
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Benefits

provided by FAO species catalogs
Conservation Status : 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: Insufficiently known.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Food and Agriculture Organization of the UN
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Diagnostic Description

provided by FAO species catalogs
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.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Food and Agriculture Organization of the UN
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Size

provided by FAO species catalogs
Males reach about 3.6 m and 1 900 kg, females about 3 m and 1 200 kg. Newborns are 1 to 1.2 m and weigh 45 to 75 kg.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Food and Agriculture Organization of the UN
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Brief Summary

provided by FAO species catalogs
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.
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Marine mammals of the world. Jefferson, T.A., S. Leatherwood & M.A. Webber - 1993. FAO species identification guide. Rome, FAO. 320 p. 587 figs. . 
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Food and Agriculture Organization of the UN
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Walrus

provided by wikipedia EN

Walrus cows and yearlings (short tusks)

The walrus (Odobenus rosmarus) is a large pinniped marine mammal with discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. It is the only extant species in the family Odobenidae and genus Odobenus. This species is subdivided into two subspecies:[2] the Atlantic walrus (O. r. rosmarus), which lives in the Atlantic Ocean, and the Pacific walrus (O. r. divergens), which lives in the Pacific Ocean.

Adult walrus are characterised by prominent tusks and whiskers, and considerable bulk: adult males in the Pacific can weigh more than 2,000 kilograms (4,400 pounds)[3] and, among pinnipeds, are exceeded in size only by the two species of elephant seals.[4] Walrus live mostly in shallow waters above the continental shelves, spending significant amounts of their lives on the sea ice looking for benthic bivalve molluscs. Walruses are relatively long-lived, social animals, and are considered to be a "keystone species" in the Arctic marine regions.

The walrus has played a prominent role in the cultures of many indigenous Arctic peoples, who have hunted it for meat, fat, skin, tusks, and bone. During the 19th century and the early 20th century, walrus were widely hunted for their blubber, walrus ivory, and meat. The population of walruses dropped rapidly all around the Arctic region. It has rebounded somewhat since, though the populations of Atlantic and Laptev walruses remain fragmented and at low levels compared with the time before human interference.

Etymology

Walrus, labeled Ros marus piscis, is depicted in а 16th-century map of Scandinavia (the Carta Marina)

The origin of the word walrus derives from a Germanic language, and it has been attributed largely to either the Dutch language or Old Norse. Its first part is thought to derive from a word such as Old Norse hvalr ('whale') and the second part has been hypothesized to come from the Old Norse word hross ('horse').[5] For example, the Old Norse word hrosshvalr means 'horse-whale' and is thought to have been passed in an inverted form to both Dutch and the dialects of northern Germany as walros and Walross.[6] An alternative theory is that it comes from the Dutch words wal 'shore' and reus 'giant'.[7]

The species name rosmarus is Scandinavian. The Norwegian manuscript Konungs skuggsjá, thought to date from around AD 1240, refers to the walrus as rosmhvalr in Iceland and rostungr in Greenland (walruses were by now extinct in Iceland and Norway, while the word evolved in Greenland). Several place names in Iceland, Greenland and Norway may originate from walrus sites: Hvalfjord, Hvallatrar and Hvalsnes to name some, all being typical walrus breeding grounds.

The archaic English word for walrus—morse—is widely thought to have come from the Slavic languages,[8] which in turn borrowed it from Finno-Ugric languages, and ultimately (according to Ante Aikio) from an unknown Pre-Finno-Ugric substrate language of Northern Europe.[9] Compare морж (morž) in Russian, mursu in Finnish, morša in Northern Saami, and morse in French. Olaus Magnus, who depicted the walrus in the Carta Marina in 1539, first referred to the walrus as the ros marus, probably a Latinization of morž, and this was adopted by Linnaeus in his binomial nomenclature.[10]

The coincidental similarity between morse and the Latin word morsus ('a bite') supposedly contributed to the walrus's reputation as a "terrible monster".[10]

The compound Odobenus comes from odous (Greek for 'teeth') and baino (Greek for 'walk'), based on observations of walruses using their tusks to pull themselves out of the water. The term divergens in Latin means 'turning apart', referring to their tusks.[11]

Taxonomy and evolution

The walrus is a mammal in the order Carnivora. It is the sole surviving member of the family Odobenidae, one of three lineages in the suborder Pinnipedia along with true seals (Phocidae) and eared seals (Otariidae). While there has been some debate as to whether all three lineages are monophyletic, i.e. descended from a single ancestor, or diphyletic, recent genetic evidence suggests all three descended from a caniform ancestor most closely related to modern bears.[12] Recent multigene analysis indicates the odobenids and otariids diverged from the phocids about 20–26 million years ago, while the odobenids and the otariids separated 15–20 million years ago.[13][14] Odobenidae was once a highly diverse and widespread family, including at least twenty species in the subfamilies Imagotariinae, Dusignathinae and Odobeninae.[15] The key distinguishing feature was the development of a squirt/suction feeding mechanism; tusks are a later feature specific to Odobeninae, of which the modern walrus is the last remaining (relict) species.

Two subspecies of walrus are widely recognized: the Atlantic walrus, O. r. rosmarus (Linnaeus, 1758) and the Pacific walrus, O. r. divergens (Illiger, 1815). Fixed genetic differences between the Atlantic and Pacific subspecies indicate very restricted gene flow, but relatively recent separation, estimated at 500,000 and 785,000 years ago.[16] These dates coincide with the hypothesis derived from fossils that the walrus evolved from a tropical or subtropical ancestor that became isolated in the Atlantic Ocean and gradually adapted to colder conditions in the Arctic.[16]

The modern walrus is mostly known from Arctic regions, but a substantial breeding population occurred on isolated Sable Island, 100 miles southeast of Nova Scotia and 500 miles due east of Portland, Maine, until the early Colonial period.[17][18] Abundant walrus remains have also been recovered from the southern North Sea dating to the Eemian interglacial period, when that region would have been submerged as it is today, unlike the intervening glacial lowstand when the shallow North Sea was dry land.[19] Fossils known from San Francisco, Vancouver, and the Atlantic US coast as far south as North Carolina have been referred to glacial periods [20]

An isolated population in the Laptev Sea was considered by some authorities, including many Russian biologists and the canonical Mammal Species of the World,[2] to be a third subspecies, O. r. laptevi (Chapskii, 1940), but has since been determined to be of Pacific walrus origin.[21]

Anatomy

Photo of several walruses, with prominently displayed white pairs of tusks
Young male Pacific walruses on Cape Pierce in Alaska, showing variation in the curvature and orientation of the tusks and the bumpy skin (bosses) typical of males.
Photo of walrus in ice-covered sea.
Walrus using its tusks to hang on a breathing hole in the ice near St. Lawrence Island, Bering Sea
Skeleton
Skull without tusk

While some outsized Pacific males can weigh as much as 2,000 kg (4,400 lb), most weigh between 800 and 1,700 kg (1,800 and 3,700 lb). An occasional male of the Pacific subspecies far exceeds normal dimensions. In 1909, a walrus hide weighing 500 kg (1,100 lb) was collected from an enormous bull in Franz Josef Land, while in August 1910, Jack Woodson shot a 4.9-metre-long (16 ft) walrus, harvesting its 450 kg (1,000 lb) hide. Since a walrus's hide usually accounts for about 20% of its body weight, the total body mass of these two giants is estimated to have been at least 2,300 kg (5,000 lb).[22] The Atlantic subspecies weighs about 10–20% less than the Pacific subspecies.[4] Male Atlantic walrus weigh an average of 900 kg (2,000 lb).[3] The Atlantic walrus also tends to have relatively shorter tusks and somewhat more flattened snout. Females weigh about two-thirds as much as males, with the Atlantic females averaging 560 kg (1,230 lb), sometimes weighing as little as 400 kg (880 lb), and the Pacific female averaging 800 kg (1,800 lb).[23] Length typically ranges from 2.2 to 3.6 m (7 ft 3 in to 11 ft 10 in).[24][25] Newborn walruses are already quite large, averaging 33 to 85 kg (73 to 187 lb) in weight and 1 to 1.4 m (3 ft 3 in to 4 ft 7 in) in length across both sexes and subspecies.[1] All told, the walrus is the third largest pinniped species, after the two elephant seals. Walruses maintain such a high body weight because of the blubber stored underneath their skin. This blubber keeps them warm and the fat provides energy to the walrus.

The walrus's body shape shares features with both sea lions (eared seals: Otariidae) and seals (true seals: Phocidae). As with otariids, it can turn its rear flippers forward and move on all fours; however, its swimming technique is more like that of true seals, relying less on flippers and more on sinuous whole body movements.[4] Also like phocids, it lacks external ears.

The extraocular muscles of the walrus are well-developed. This and its lack of orbital roof allow it to protrude its eyes and see in both a frontal and dorsal direction. However, vision in this species appears to be more suited for short-range.[26]

Tusks and dentition

Skull with tusks
Tooth

While this was not true of all extinct walruses,[27] the most prominent feature of the living species is its long tusks. These are elongated canines, which are present in both male and female walruses and can reach a length of 1 m (3 ft 3 in) and weigh up to 5.4 kg (12 lb).[28] Tusks are slightly longer and thicker among males, which use them for fighting, dominance and display; the strongest males with the largest tusks typically dominate social groups. Tusks are also used to form and maintain holes in the ice and aid the walrus in climbing out of water onto ice.[29] Tusks were once thought to be used to dig out prey from the seabed, but analyses of abrasion patterns on the tusks indicate they are dragged through the sediment while the upper edge of the snout is used for digging.[30] While the dentition of walruses is highly variable, they generally have relatively few teeth other than the tusks. The maximal number of teeth is 38 with dentition formula: 3.1.4.23.1.3.2, but over half of the teeth are rudimentary and occur with less than 50% frequency, such that a typical dentition includes only 18 teeth 1.1.3.00.1.3.0[4]

Vibrissae (whiskers)

Surrounding the tusks is a broad mat of stiff bristles ("mystacial vibrissae"), giving the walrus a characteristic whiskered appearance. There can be 400 to 700 vibrissae in 13 to 15 rows reaching 30 cm (12 in) in length, though in the wild they are often worn to much shorter lengths due to constant use in foraging.[31] The vibrissae are attached to muscles and are supplied with blood and nerves, making them highly sensitive organs capable of differentiating shapes 3 mm (18 in) thick and 2 mm (332 in) wide.[31]

Skin

Aside from the vibrissae, the walrus is sparsely covered with fur and appears bald. Its skin is highly wrinkled and thick, up to 10 cm (4 in) around the neck and shoulders of males. The blubber layer beneath is up to 15 cm (6 in) thick. Young walruses are deep brown and grow paler and more cinnamon-colored as they age. Old males, in particular, become nearly pink. Because skin blood vessels constrict in cold water, the walrus can appear almost white when swimming. As a secondary sexual characteristic, males also acquire significant nodules, called "bosses", particularly around the neck and shoulders.[29]

Native Alaskan woman dresses walrus skin

The walrus has an air sac under its throat which acts like a flotation bubble and allows it to bob vertically in the water and sleep. The males possess a large baculum (penis bone), up to 63 cm (25 in) in length, the largest of any land mammal, both in absolute size and relative to body size.[4]

Life history

Photo of five walruses on rocky shore
Walruses fighting
A herd of walruses on Northbrook Island, Franz Josef Land, Russia

Reproduction

Walruses live to about 20–30 years old in the wild.[32] The males reach sexual maturity as early as seven years, but do not typically mate until fully developed at around 15 years of age.[4] They rut from January through April, decreasing their food intake dramatically. The females begin ovulating as soon as four to six years old.[4] The females are diestrous, coming into heat in late summer and around February, yet the males are fertile only around February; the potential fertility of this second period is unknown. Breeding occurs from January to March, peaking in February. Males aggregate in the water around ice-bound groups of estrous females and engage in competitive vocal displays.[33] The females join them and copulate in the water.[29]

A walrus pup at Kamogawa Seaworld, Japan

Gestation lasts 15 to 16 months. The first three to four months are spent with the blastula in suspended development before it implants itself in the uterus. This strategy of delayed implantation, common among pinnipeds, presumably evolved to optimize both the mating season and the birthing season, determined by ecological conditions that promote newborn survival.[34] Calves are born during the spring migration, from April to June. They weigh 45 to 75 kg (99 to 165 lb) at birth and are able to swim. The mothers nurse for over a year before weaning, but the young can spend up to five years with the mothers.[29] Walrus milk contains higher amounts of fats and protein compared to land animals but lower compared to phocid seals.[35] This lower fat content in turn causes a slower growth rate among calves and a longer nursing investment for their mothers.[36] Because ovulation is suppressed until the calf is weaned, females give birth at most every two years, leaving the walrus with the lowest reproductive rate of any pinniped.[37]

Migration

The rest of the year (late summer and fall), walruses tend to form massive aggregations of tens of thousands of individuals on rocky beaches or outcrops. The migration between the ice and the beach can be long-distance and dramatic. In late spring and summer, for example, several hundred thousand Pacific walruses migrate from the Bering Sea into the Chukchi Sea through the relatively narrow Bering Strait.[29][38]

Ecology

Range and habitat

The majority of the population of the Pacific walrus spends its summers north of the Bering Strait in the Chukchi Sea of the Arctic Ocean along the northern coast of eastern Siberia, around Wrangel Island, in the Beaufort Sea along the northern shore of Alaska south to Unimak Island,[39] and in the waters between those locations. Smaller numbers of males summer in the Gulf of Anadyr on the southern coast of the Siberian Chukchi Peninsula, and in Bristol Bay off the southern coast of Alaska, west of the Alaska Peninsula. In the spring and fall, walruses congregate throughout the Bering Strait, reaching from the western coast of Alaska to the Gulf of Anadyr. They winter over in the Bering Sea along the eastern coast of Siberia south to the northern part of the Kamchatka Peninsula, and along the southern coast of Alaska.[4] A 28,000-year-old fossil walrus was dredged up from the bottom of San Francisco Bay, indicating that Pacific walruses ranged that far south during the last Ice Age.[40]

Commercial harvesting reduced the population of the Pacific walrus to between 50,000 and 100,000 in the 1950s-1960s. Limits on commercial hunting allowed the population to increase to a peak in the 1970s-1980s, but subsequently, walrus numbers have again declined. Early aerial censuses of Pacific walrus conducted at five-year intervals between 1975 and 1985 estimated populations of above 220,000 in each of the three surveys.[41][42][43][44][45][46][47][48][49]

In 2006, the population of the Pacific walrus was estimated to be around 129,000 on the basis of an aerial census combined with satellite tracking.[50][51] There were roughly 200,000 Pacific walruses in 1990.[52][53]

The much smaller population of Atlantic walruses ranges from the Canadian Arctic, across Greenland, Svalbard, and the western part of Arctic Russia. There are eight hypothetical subpopulations of Atlantic walruses, based largely on their geographical distribution and movements: five west of Greenland and three east of Greenland.[54] The Atlantic walrus once ranged south to Sable Island, Nova Scotia, and as late as the 18th century was found in large numbers in the Greater Gulf of St. Lawrence region, sometimes in colonies of up to 7,000 to 8,000 individuals.[55] This population was nearly eradicated by commercial harvest; their current numbers, though difficult to estimate, probably remain below 20,000.[56][57] In April 2006, the Canadian Species at Risk Act listed the population of the northwestern Atlantic walrus in Quebec, New Brunswick, Nova Scotia, Newfoundland and Labrador as having been eradicated in Canada.[58] A genetically distinct population existed in Iceland that was wiped out after Norse settlement around 1213–1330 AD.[59]

The isolated population of Laptev Sea walruses is confined year-round to the central and western regions of the Laptev Sea, the eastmost regions of the Kara Sea, and the westmost regions of the East Siberian Sea. The current population of these walruses has been estimated to be between 5,000 and 10,000.[60]

Even though walruses can dive to depths beyond 500 meters, they spend most of their time in shallow waters (and the nearby ice floes) hunting for food.[61][62]

In March 2021, a single walrus, nicknamed Wally the Walrus, was sighted at Valentia Island, Ireland, far south of its typical range, potentially due to having fallen asleep on an iceberg that then drifted south towards Ireland.[63] Days later, a walrus, thought to be the same animal, was spotted on the Pembrokeshire coast, Wales.[64] In June 2022, a single walrus was sighted on the shores of the Baltic Sea - at Rügen Island, Germany, Mielno, Poland and Skälder Bay, Sweden.[65][66][67] In July 2022, there was a report of a lost, starving walrus (nicknamed as Stena) in the coastal waters of the towns of Hamina and Kotka in Kymenlaakso, Finland,[68][69] that, despite rescue attempts, died of starvation when the rescuers tried to transport it to the Korkeasaari Zoo for treatment.[70][71]

Diet

Photo of walrus head in profile showing one eye, nose, tusks, and
Vibrissae of a captive walrus (Japan)
Photo of two walruses in shallow water facing shore
Walruses leaving the water

Walruses prefer shallow shelf regions and forage primarily on the sea floor, often from sea ice platforms.[4] They are not particularly deep divers compared to other pinnipeds; the deepest dives in a study of Atlantic walrus near Svalbard were only 31±17 m (102 ft)[72] but a more recent study recorded dives exceeding 500 m (1640 ft) in Smith Sound, between NW Greenland and Arctic Canada - in general peak dive depth can be expected to depend on prey distribution and seabed depth.[62]

The walrus has a diverse and opportunistic diet, feeding on more than 60 genera of marine organisms, including shrimp, crabs, tube worms, soft corals, tunicates, sea cucumbers, various mollusks (such as snails, octopuses, and squid), some types of slow-moving fish, and even parts of other pinnipeds.[73] However, it prefers benthic bivalve mollusks, especially clams, for which it forages by grazing along the sea bottom, searching and identifying prey with its sensitive vibrissae and clearing the murky bottoms with jets of water and active flipper movements.[74] The walrus sucks the meat out by sealing its powerful lips to the organism and withdrawing its piston-like tongue rapidly into its mouth, creating a vacuum. The walrus palate is uniquely vaulted, enabling effective suction. The diet of the Pacific walrus consist almost exclusively of benthic invertebrates (97 percent).[75]

Aside from the large numbers of organisms actually consumed by the walrus, its foraging has a large peripheral impact on benthic communities. It disturbs (bioturbates) the sea floor, releasing nutrients into the water column, encouraging mixing and movement of many organisms and increasing the patchiness of the benthos.[30]

Seal tissue has been observed in a fairly significant proportion of walrus stomachs in the Pacific, but the importance of seals in the walrus diet is under debate.[76] There have been isolated observations of walruses preying on seals up to the size of a 200 kg (440 lb) bearded seal.[77][78] Rarely, incidents of walruses preying on seabirds, particularly the Brünnich's guillemot (Uria lomvia), have been documented.[79] Walruses may occasionally prey on ice-entrapped narwhals and scavenge on whale carcasses but there is little evidence to prove this.[80][81]

Predators

Due to its great size and tusks, the walrus has only two natural predators: the orca and the polar bear.[82] The walrus does not, however, comprise a significant component of either of these predators' diets. Both the orca and the polar bear are also most likely to prey on walrus calves. The polar bear often hunts the walrus by rushing at beached aggregations and consuming the individuals crushed or wounded in the sudden exodus, typically younger or infirm animals.[83] The bears also isolate walruses when they overwinter and are unable to escape a charging bear due to inaccessible diving holes in the ice.[84] However, even an injured walrus is a formidable opponent for a polar bear, and direct attacks are rare. Armed with its ivory tusks, walruses have been known to fatally injure polar bears in battles if the latter follows the other into the water, where the bear is at a disadvantage.[85] Polar bear–walrus battles are often extremely protracted and exhausting, and bears have been known to break away from the attack after injuring a walrus. Orcas regularly attack walruses, although walruses are believed to have successfully defended themselves via counterattack against the larger cetacean.[86] However, orcas have been observed successfully attacking walruses with few or no injuries.[87]

Relationship with humans

Conservation

In the 18th and 19th centuries, the walrus was heavily exploited by American and European sealers and whalers, leading to the near-extirpation of the Atlantic subspecies.[88] As early as 1871 traditional hunters were expressing concern about the numbers of walrus being hunted by whaling fleets.[89] Commercial walrus harvesting is now outlawed throughout its range, although Chukchi, Yupik and Inuit peoples[90] are permitted to kill small numbers towards the end of each summer.

Traditional hunters used all parts of the walrus.[91] The meat, often preserved, is an important winter nutrition source; the flippers are fermented and stored as a delicacy until spring; tusks and bone were historically used for tools, as well as material for handicrafts; the oil was rendered for warmth and light; the tough hide made rope and house and boat coverings; and the intestines and gut linings made waterproof parkas. While some of these uses have faded with access to alternative technologies, walrus meat remains an important part of local diets,[92] and tusk carving and engraving remain a vital art form.

According to Adolf Erik Nordenskiöld, European hunters and Arctic explorers found walrus meat not particularly tasty, and only ate it in case of necessity; however walrus tongue was a delicacy.[93]

Walrus hunts are regulated by resource managers in Russia, the United States, Canada, and Greenland (self-governing country in the Kingdom of Denmark), and representatives of the respective hunting communities. An estimated four to seven thousand Pacific walruses are harvested in Alaska and in Russia, including a significant portion (about 42%) of struck and lost animals.[94] Several hundred are removed annually around Greenland.[95] The sustainability of these levels of harvest is difficult to determine given uncertain population estimates and parameters such as fecundity and mortality. The Boone and Crockett Big Game Record book has entries for Atlantic and Pacific walrus. The recorded largest tusks are just over 30 inches and 37 inches long respectively.[96]

The effects of global climate change are another element of concern. The extent and thickness of the pack ice has reached unusually low levels in several recent years. The walrus relies on this ice while giving birth and aggregating in the reproductive period. Thinner pack ice over the Bering Sea has reduced the amount of resting habitat near optimal feeding grounds. This more widely separates lactating females from their calves, increasing nutritional stress for the young and lower reproductive rates.[97] Reduced coastal sea ice has also been implicated in the increase of stampeding deaths crowding the shorelines of the Chukchi Sea between eastern Russia and western Alaska.[98][99] Analysis of trends in ice cover published in 2012 indicate that Pacific walrus populations are likely to continue to decline for the foreseeable future, and shift further north, but that careful conservation management might be able to limit these effects.[100]

Currently, two of the three walrus subspecies are listed as "least-concern" by the IUCN, while the third is "data deficient".[1] The Pacific walrus is not listed as "depleted" according to the Marine Mammal Protection Act nor as "threatened" or "endangered" under the Endangered Species Act. The Russian Atlantic and Laptev Sea populations are classified as Category 2 (decreasing) and Category 3 (rare) in the Russian Red Book.[60] Global trade in walrus ivory is restricted according to a CITES Appendix 3 listing. In October 2017, the Center for Biological Diversity announced they would sue the U.S. Fish and Wildlife Service to force it to classify the Pacific Walrus as a threatened or endangered species.[101]

In 1952, walruses in Svalbard were nearly gone due to ivory hunting over a 300 years period, but the Norwegian government banned their commercial hunting and the walruses began to rebound in 2006, making their population increase to 2,629.

Culture

Folklore

The walrus plays an important role in the religion and folklore of many Arctic peoples. Skin and bone are used in some ceremonies, and the animal appears frequently in legends. For example, in a Chukchi version of the widespread myth of the Raven, in which Raven recovers the sun and the moon from an evil spirit by seducing his daughter, the angry father throws the daughter from a high cliff and, as she drops into the water, she turns into a walrus – possibly the original walrus. According to various legends, the tusks are formed either by the trails of mucus from the weeping girl or her long braids.[102] This myth is possibly related to the Chukchi myth of the old walrus-headed woman who rules the bottom of the sea, who is in turn linked to the Inuit goddess Sedna. Both in Chukotka and Alaska, the aurora borealis is believed to be a special world inhabited by those who died by violence, the changing rays representing deceased souls playing ball with a walrus head.[102][103]

Most of the distinctive 12th-century Lewis Chessmen from northern Europe are carved from walrus ivory, though a few have been found to be made of whales' teeth.

Literature

Because of its distinctive appearance, great bulk, and immediately recognizable whiskers and tusks, the walrus also appears in the popular cultures of peoples with little direct experience with the animal, particularly in English children's literature. Perhaps its best-known appearance is in Lewis Carroll's whimsical poem "The Walrus and the Carpenter" that appears in his 1871 book Through the Looking-Glass. In the poem, the eponymous antiheroes use trickery to consume a great number of oysters. Although Carroll accurately portrays the biological walrus's appetite for bivalve mollusks, oysters, primarily nearshore and intertidal inhabitants, these organisms in fact comprise an insignificant portion of its diet in captivity.[104]

The "walrus" in the cryptic Beatles song "I Am the Walrus" is a reference to the Lewis Carroll poem.[105]

Another appearance of the walrus in literature is in the story "The White Seal" in Rudyard Kipling's The Jungle Book, where it is the "old Sea Vitch—the big, ugly, bloated, pimpled, fat-necked, long-tusked walrus of the North Pacific, who has no manners except when he is asleep".[106]

See also

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Walrus: Brief Summary

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Walrus cows and yearlings (short tusks)

The walrus (Odobenus rosmarus) is a large pinniped marine mammal with discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. It is the only extant species in the family Odobenidae and genus Odobenus. This species is subdivided into two subspecies: the Atlantic walrus (O. r. rosmarus), which lives in the Atlantic Ocean, and the Pacific walrus (O. r. divergens), which lives in the Pacific Ocean.

Adult walrus are characterised by prominent tusks and whiskers, and considerable bulk: adult males in the Pacific can weigh more than 2,000 kilograms (4,400 pounds) and, among pinnipeds, are exceeded in size only by the two species of elephant seals. Walrus live mostly in shallow waters above the continental shelves, spending significant amounts of their lives on the sea ice looking for benthic bivalve molluscs. Walruses are relatively long-lived, social animals, and are considered to be a "keystone species" in the Arctic marine regions.

The walrus has played a prominent role in the cultures of many indigenous Arctic peoples, who have hunted it for meat, fat, skin, tusks, and bone. During the 19th century and the early 20th century, walrus were widely hunted for their blubber, walrus ivory, and meat. The population of walruses dropped rapidly all around the Arctic region. It has rebounded somewhat since, though the populations of Atlantic and Laptev walruses remain fragmented and at low levels compared with the time before human interference.

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Diet

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Bivalves, polychaetes, fish

Reference

North-West Atlantic Ocean species (NWARMS)

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Distribution

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circumpolar in the Arctic

Reference

van der Land, J. (ed). (2008). UNESCO-IOC Register of Marine Organisms (URMO).

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Distribution

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North America

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North-West Atlantic Ocean species (NWARMS)

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Morphology

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Distinguishing characteristics: long tusks, stout whiskers, large size, square face, colour of skin is brown with sparse red hair. May appear white or red at times.

Reference

North-West Atlantic Ocean species (NWARMS)

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