In the northern cold seas amazing giants dwell. They are huge, tender, good-natured and clumsy, have thick and bristly “beard” and huge tusks, their body is pink in the sunlight. The whales and elephant seals are the only marine mammals that can be larger than the walrus.
These amazing animals are walruses.
Scientific classification
Order – Pinnipedia
The name derives from the Latin “the one that walks on flippers”. And now they are called pinnipeds.
The order includes 3 families:
Family of the true seals (Phocidae) consists of 18 species.
Family of the eared seals (Otariidae) includes fur seals and sea lions and consists of 14 species. The eared seals obtain external earflaps compared to true seals.
Family of Odobenidae is represented only by walruses. As the true seals they have no external earflaps, but have ears itself and also good hearing. The name “odobenus” derives from the Greek “the one walks on teeth”. Such name was given to walruses because of the way they haul themselves up onto the ice: their tusks are acting as a counter-balance and ice-picks to climb and take hold on ice float.
Even in the 16 century Albert Magnus describes how “they climb at the tops of cliffs using their teeth as a ladder”.
Walruses spend about two-thirds of their lives in the water. They inhabit coastal areas where the water is no more than 80 m deep and prefer a gravelly bottom.
Walruses are well adapted to a habitat of sea ice and prefer snow-covered moving pack ice or ice floes to land. They haul out on small rocky islands when ice is not present.
But they are not found at the areas where ice covers 80% of the sea surface.
Walruses spend most time on ice floats where the air temperature is about -15° to +5°C. When it’s possible, they laze in the sun. Lying in the sun, a walrus may overheat, that’s why blood flushes to the skin surface, increasing heat exchange. In these moments the skin appears pink, thus, their scientific name is odobenus rosmarus. When they return in water, blood runs away from the skin surface. The skin than becomes pale-gray again.
Population
Walruses inhabit arctic and sub-arctic seas, but the area of their distribution is not continuous. Total world walrus population is about 250 000 animals. According to the area of distribution, walruses are divided into 3 subspecies: Pacific, Atlantic and Laptev. The biggest one is pacific population – more than 200 000 animals. Pacific walrus live in the Bering Sea, Chukchee Sea, East Siberian Sea. Atlantic walrus colonies inhabit coastal areas of Hudson Bay, Ellesmere Islands, Greenland, Spitsbergen, and Barents Sea. Each population has its own geographical habitat, that’s why interbreeding between them is almost impossible. The Pacific walrus has a wider skull and larger tusks. At one time this population was almost exterminated, but recently it had recovered and started to increase. Without the proper concern and care from human, walrus population may disappear. In the recent past walruses were endangered because of their commercial importance. Nowadays walrus commercial hunting is banned. After the latest population depletion, which began in the 1930s, walruses were given protection by Russia, the State of Alaska, and the USA. This protection led to the recovery of the Pacific walrus population. Walruses reoccupied long-abandoned rookeries.
Laptev walruses form the smallest and the little-studied population on Laptev Sea.
Migration
At the end of summer walruses leave their rookeries and drift to the ice-regions where they stay till spring. Walruses migrate primarily by swimming, but they may also ride ice floes.
The walruses' migration follows the extent of the pack ice. Throughout the year, they occur primarily in or near the southern periphery of the pack ice. Pacific walruses winter in the central and south Bering Sea and summer in the Chukchi Sea. Migration of the Canadian population is less well known. They seem to remain in the same general vicinity all year. Some walruses migrate more than 3000 km each year. Pacific walrus adult females and young walruses are more migratory than adult males. Some researchers have suggested that the hormones that control sperm development may also influence migration of adult males.
Physical characteristics
Size
The whales and elephant seals are the only marine mammals that can be larger than the walrus.
Adult male Pacific walruses weigh about 800 to 1700 kg and are about 2.7 to 3.6 m long. Female Pacific walruses weigh about 400 to 1250 kg and are about 2.3 to 3.1 m long.
Atlantic walruses are slightly smaller. Males weigh about 908 kg and are about 2.4 m long.
Walrus males weigh a lot mostly due to their body thickness: the girth of their body may be more than the length.
Body shape
A walruses have a rounded, fusiform body
Coloration
Usually walruses are light-brown. They appear quite pale in the water. After a sustained period in very cold water, they may appear almost white. They are pink in warm weather when tiny blood vessels in the skin dilate and circulation increases. This increased skin circulation sheds excess body heat.
Calves at birth are ash gray to brown. Within a week or two, calves become sandy-brown. The coloration pales with age. In general, younger individuals are darker than adults.
Flippers
Limbs are modified into fins or flippers. Flippers are skin webs covering bones and muscles. Flippers double up in elbow easily. They are flexible enough to scratch a walrus neck by hind limbs’ claws. Leaning on the flippers, walrus can lift hindquarters and easily move on land.
The foreflippers, or pectoral flippers, have all the major skeletal elements of the forelimbs of land mammals, but are shortened and modified.
Each foreflipper has five digits of about equal length. Each digit has a small claw. Flippers are hairless. The skin on the soles of flippers is thick and rough, providing traction on land and ice.
While swimming, a walrus uses flippers for steering. On land, a walrus uses its foreflippers as a support for walking.
Walruses have triangular-shaped hind flippers. Hind flippers have five bony digits. Claws on the three middle digits are larger than those on the two other digits.
Like sea lions, walruses can rotate their hind flippers. In water they use hind flippers for steering.
Head
A walrus's head is square and broad with conspicuous teeth and whiskers. A head appears to be disproportionately small because of the tick fat layer and skin folds on shoulders and neck.
The most notable walrus’s features are tusks and vibrissae – thick and elastic whiskers. Vibrissae grow on thick and pulpy pads on the upper lip and may be longer and denser at mouth corners achieving 10-12 cm. A walrus has about 400 to 700 vibrissae in 13 to 15 rows. Vibrissae transfer tactile information in brain through nerves.
Walruses use their vibrissae combing through the bottom to find food. Observers say that walrus gathers dig out shellfishes and rolls into a ball using vibrissae. Vibrissae are worn due to dragging on the bottom. Vibrissae of very old walruses even fall out baring rough and wrinkly skin. In capture, where it is not necessary to forage, vibrissae may reach 30 cm.
Most walruses have 18 teeth. Canine teeth in the upper jaw are modified into long ivory tusks. Two tusks are overgrown canine teeth sticking out of mouth. Both males and females have tusks. The tusks of males tend to be longer, straighter, and stouter than those of females.
Tusks erupt during a calf’s first summer or fall. Abrasive wear of enamel begins from the top.
The primary functions of the tusks are establishing of social dominance and hauling out onto ice or shore.
Tusks can grow to a length of 100 cm in males and 80 cm in females. Tusks grow up to 15 years, although they may continue to grow longer.
Walruses use tusks to break holes in ice, kill and carve sea dogs, attack other walruses and white bears, dig sea bottom searching for shellfish, and foster the rising generation. Tusks are very important in walrus’s life. While sleeping, they have to slant their head as tusks grow downward slightly turning at the ends. They can even put them on their neighbors.
Eyes are small and located high on the sides of the head.
Ears, located just behind the eyes, are very small with no external earflaps.
Paired nostrils are located above the vibrissae. In the resting state nostrils are closed.
Walrus’s brain weighs up to 1 kg.
Tongue is short, broad on the back end and narrow and rounded on the front end.
Walruses’ tail is almost invisible.
Skin and hair
A walrus's skin is thick and tough. It may reach a thickness of 2 to 4 cm. It is skin thickness on the neck and shoulders of adult males. The skin is highly wrinkled and thick, up to 7 cm, around the neck and shoulders of males. The blubber layer under the skin is 4 to 12 cm thick. Such thick skin protects vital organs against jabs in fights with other males. The skin of males often has large nodules which are absent in females. The nodules appear at the time of puberty, some researchers consider them to be a secondary sex characteristic.
Walruses retained remains of hair-covering common for other mammals. Adult female’s hair is usually brown and male’s is reddish-brown. Hair is densest on juveniles and becomes less dense with age. As walruses age, their hair-covering becomes dull and pale. Hair is about 7 to 12 mm long over the whole body. It is shorter on the face and absent on the flippers.
Molting
An annual molt for most walrus takes place from June to August. Females molting is more prolonged. Molting in walruses is gradual, lost hairs are replaced by new ones.
Calves shed a fine prenatal coat, called lanugo, about two to three months before they are born. They molt again at the age of 1 to 2 months.
Senses
Eyesight
Rolling eyes of walrus are located high on skull and protruded out of eye-pits. To see any object, walruses turn not a head, but the eyes which are rather movable. Because walruses search shellfish on the sea bottom, probably acute vision is not necessary for them.
Taste
Little is known about walrus’s sense of taste. However walruses usually show strong food preferences in dolphinariums and zoos.
Smell
Walruses have well-developed sense of smell. It helps them to scent danger, for instance approaching white bear – the main (except for human) enemy of walrus. By means of smell mother and calf are able to find each other in a crowd of other walruses.
Hearing
Acoustic foramen is small, 1 to 2 mm in diameter. Auditory muscles tightly close it to prevent penetration of water while swimming and diving.
Walruses have good hearing both in water and in the air.
The same as seals walruses do not have external ear, but still have sharp hearing. Observations suggest that walrus’s hearing is almost the same as humans’.
Eskimos imitate walrus sounds and obtain a response from walruses 1.6 km away.
Mother hears calf’s calls for help at a distance about 2 km.
Walruses also have well-developed and expressive voice.
Communication
Walruses produce diverse sounds. According to scientist there are 3 types of sounds which walruses produce under water with closed mouth and nostrils. The bell-like sounds which are produced by pharyngal air sacs acting as resonant cavity, short rasps and clicks. The sounds produced out of water are more diverse.
Some scientists believe that walruses produce sounds mainly not to lose contact with the pod. Males’ and female’ voices are almost the same. Walruses cough, gurgle, and roar. Kane writes: “A walrus may lie and listen to itself for hours. The sounds they produce are something in between cow’s bellow and low barking of mastiff, it’s something deep and full-toned”.
Swimming
Normal swimming speed for walruses is about 4 to 4,5 km/h. They are capable to swim on short distances up to 35 km/h.
Most propulsion comes from alternate strokes of the hind flippers. Foreflippers also work with the hind flippers for maneuvering
Diving
Usually walruses dive at depth no more than 80-90 m. They can stay submerged for about 5 to 10 minutes and then come up at the surface to breathe for 3 to 4 minutes before diving again.
According to the scientific observations there were dives of 113 and submersion time of 25 minutes.
A walrus dives downmost to the bottom spreading its flippers. The depth of diving depends on how strong an animal pushed off by the hind flippers. The stronger a walrus pushes, the deeper it dives.
Respiration
External respiration of walruses had changed as a result of diving. Respiratory rate and paused, breathing organs structure had changed. The nostrils became flexible and are able no close tightly while diving. Nostrils slightly open while exhaling and wide open while inhaling.
Thermoregulation
Temperature of walrus’s core body is constant and 36-37° C, but in may change in external coverings and tissues. Skin’s temperature always stays 1-3° C warmer than the water.
Effective thermoregulation is achieved by means of skin-fat sac, under-skin fat stores, dense blood supply in skin and flippers, changing intensity of blood circulation.
There is an under-skin blubber layer which may achieve about 10 cm. fat has a low thermal conductivity and, thus, conserve heat.
In cold water, blood is shunted inward as blood vessels in the skin constrict, reducing heat loss to the environment. The skin appears pale, almost white. When walruses are lying in the sun, blood is driven to flippers, releasing heat into the environment. The skin appears pink.
From about -20° to 15°C a walrus's metabolism doesn't change, and the temperature doesn't appear to affect the walrus.
Walruses can withstand even cooler temperatures up to -35°C.
Adaptation to water life
Walrus’s body is streamlined, fusiformed and well-adapted to life in water and fast swimming. Their neck is thick and flows smoothly into body. The limbs have transferred into flippers and are more suitable for swimming than for moving on land or ice.
Walruses seem clumsy on land, but water environment change them. They are perfect swimmers and divers.
Many people think that walruses have higher lung volume than land mammals. But marine mammals’ lung volume is higher only by a third than land mammals’. Marine mammals use oxygen more efficiently than land mammals. Red blood cells have high content of hemoglobin. The oxygen is stored not only in blood; walrus’s muscles contain mioglobin – a protein similar to hemoglobin that accumulates oxygen used for muscles work.
When diving, blood flows toward the most-important organs where oxygen is needed, such as the heart and brain. The heart rate slows down from 150 to 4-15 beats per minute, temperature reduces by 4 degrees. However, marine mammals are able to stay submerged only for limited time period and have to come up for breathing.
Walruses are able to stay in water during several days due to under-skin fat layer which is about 25% of the total body weight. A pair air sacs closed by esophagus muscles activity fulfills a function of floating ring and allows walruses to hold vertically in the water while sleeping.
A life of each animal depends on the conditions in which it dwells. Walruses inhabit the seas where they can find banks with shellfish they prey on. The banks should lie at the depth no more than 75-90 meters as it is the depth limit walruses can dive on. That is why the most walruses inhabit the shallow waters of the Bering and Chukchi Sea.
Diet
Walruses inhabit the seas where they can find banks with shellfish they prey on. Usually feeding banks lie at the depth 10 to 50 meters. The basic diet of walruses consists of mussels and other shellfish, but they also feed on worms, sea cucumbers, starfish, shrimps and craw fish. Observations indicate that adult walruses feed twice a day eating 3000 to 6000 shellfish in a single feeding.
Walruses forage moving backward, they drag through the bottom by tusks digging shellfish and use their vibrissae to detect prey among kelp forest or between rocks. They chafe shells by the foreflippers picking out mollusk then remove shells and eat flesh.
Some observers say that walrus gathers dig out shellfishes and rolls into a ball using their unique vibrissae.
Adult walruses eat about 4% to 6% of their total weight per day. They eat more on their migration in cold waters.
Social structure
Walruses are the most gregarious animals. They live in herds throughout the year numbering in hundreds.
For most of the year males and females live in separate herds meeting only for mating. Many males live separately from females with calves during each season, especially in summer. They migrate in different areas or males do not migrate at all. But mixed herds are also indicated at different seasons. Mixed herd include small groups of females, their calves of different age, and females.
Dominance is well established in herds and subgroups. Usually dominance in herds is established by the largest and the most aggressive walrus with the longest tusk, weight. Smaller and less aggressive walruses with smaller tusks have a lower social ranking.
Social behavior
Walruses demonstrate their tusks to display social status and their weapon. Hierarchy is based on the right of the strongest. Adult males behave aggressively towards the younger males.
One male demonstrate its tusks to the other one as a symbol of dominance. Such showdowns often result in injuries. Despite of its weight, a male may be very maneuverable if it’s necessary. Raising up, male moves surprisingly fast sending its body forward. He hits an opponent on neck and shoulders very fast during fighting. Walruses easily turn their necks and slickly hit upward, downward and sideward.
New scars appear on the back of adult males after the breeding season. Frequently they compete for the most favorable haul-out sites.
Vocalization is also important in male’s behavior display.
Reproduction
Male walruses are sexually mature at about 8 to 10 years. Successful reproduction, however, occurs only at 15 years old when a male attains full physical size and is able to compete for females. Most females are sexually mature at about 6 to 8 years. Successful reproduction begins at about 10 years.
Mating season of the Pacific walruses occurs from the end of April till the middle of June. Mating takes place on the ice during migration. Mating of the Atlantic females occurs in the early spring. Gestation lasts more than a year, about 15-16 months.
Calves are often born on the ice, far from land when walruses migrate to the summer banks.
Females generally give birth to only one calf.
Newborn calves weigh about 45 to 75 kg and are about 0,9 to 1,2 m long. They are born with thick skin folds covered by dense and long (up to 1 cm) silver-gray fur which in one or two months is changed by shorter, harsher and thin brown fur.
Four mammary nipples are hidden in skin folds of a mother. Walrus milk is about 30% fat, 5 to 10% protein and 60% water. A calf is nursed on the ice or upside-down in the water.
When a calf is not sleeping or crawling upon its mother, it may sleep on her back – the safest place among a crowd of adults.
Adult walruses and calves lie back-to-back to each other. If adults are startled, they may stampede to the sea pushing and stepping on each other. Calves and young walruses may die being trampled.
Walrus females are considered to be one of the most attentive mothers among mammals. Lying on the ice, a mother keeps an eye on calf, if any walrus approaches to a calf, she immediately attacks. Many hunters had seen how a mother saved her baby rushing into water and grasping baby with her flippers, and then swam on back supporting the calf. There are evidences of hunters and Eskimos that females protect orphans in case of danger. If a calf’s mother died, other females “adopt” him.
During first 3 months calves grow about 10-15 cm in length each month. At 1year they achieve 1,5 length and weigh 200 kg. Males and females grow similar up to 3 years old until they achieve about 2 meters length and weigh more than 300 kg. Then male grow faster.
At 1 year old calves start to wander away from mothers. But females nurse calves up to 2 years, obviously, because a walrus can prey on shellfish only using its tusks which achieve a minimal length of 7-10 cm necessary for food digging only to the end of the second years.
Calves have no innate tendency to water. Mothers push calves into the water, and they swim whining until mothers get them back. However by the age of 1-2 weeks calves swim and dive well copying their mother. But even then calves continue to ride on mother’s back holding with their flippers, or mothers carry them taking to chest.
Only after more than two years calves leave mothers and try to forage themselves. Walruses become adult at 5-7 years, but grow up to 20 years old.
Longevity
Age can be estimated by a sliced section of tusk. End of calves tusks are covered dental enamel which abrades in two years. A tusk consists of dentin which grows layer by layer each year. At a sliced section of a tusk is a range of annual growth layers of bone tissue. The number of layers shows the age of walrus.
According to scientists walruses live of about 16 to 39 years.
According to reports some walruses achieves 40-year old age. Probably they can live even longer, but exact age is almost impossible to estimate due to growth layers loss as a result of tusk abrasion. The exact longevity of walruses in nature is still unknown.
The highest number of walruses dies for various reasons in infancy.
About 4% to 8% of adult walrus’s annual deaths are caused by human.
Predators
There are only two predators in Arctic strong enough to prey on walruses.
Killer whale is a dangerous enemy able to rip across sea swine or fur seal. But young walruses are more often fall prey to the white bears. The white bear is the world biggest predator. Besides habitats of white bears and walruses are almost the same. But bears pose dangerous mainly for young walruses and females with calves. Attack of a big walrus male is very troublesome and unfavorable.
Conservation
For a long time walruses have been killed on the rookeries mainly by American hunters within the Pacific Ocean, at Chukchi Sea and Bering Sea. Not only walrus population was harmed, but also kalan was almost depopulated, number of fur seals decreased strongly. To the end of the 20th century number of walruses was so low that soviet zoologists opened a question of complete prohibition of hunting. Commercial hunting of walruses had been prohibited.
Nowadays walruses’ population increases every year. Walruses inhabit the rookeries being empty for a long time.
Today walruses are hunted in Russia, USA, Norway and Canada only for purposes of indigenous Arctic peoples.
Copyright belongs to N.D. Grechishkina. Any use of the text is only with consent of the author.
