~Explore Biology~

ORDER - PINNIPEDIA
FAMILY - ODOBENIDAE
GENUS, SPECIES - ODOBENUS ROSMARUS
DISTRIBUTION
1. Walruses are circumpolar, but they are concentrated in geographically separated areas, with little or no chance of interbreeding.
• 
Pacific walruses inhabit the Bering, Chukchi, and Laptev Seas.
• Atlantic walruses inhabit coastal areas of northeastern Canada and Greenland.Pacific walruses inhabit the Bering, Chukchi, and Laptev Seas, while Atlantic walruses are found in coastal areas of northeastern Canada and Greenland.
HABITAT
1. 
Most walruses live where the air temperature is about -15º to +5ºC (5º - 41ºF)  
2. 
Walruses are generally found where the water is no more than 80 m (262 ft.) deep. They prefer a habitat with a gravelly bottom. Walruses spend about two-thirds of their lives in the water.  
3. 
Walruses haul out to rest and bear their young.
• 
Walruses are 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.
• Eskimos call a traditional walrus haul-out area an ooglit.
MIGRATION
1. 
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. 
2. 
Walruses migrate primarily by swimming, but they may also ride ice floes. 
3. 
Some walruses migrate more than 3,000 km (1,863 miles) each year.  
4. 
Pacific walrus adult females and young walruses are more migratory than adult males.
• 
Pacific walrus calves are born on the northward migration to the Chukchi Sea.
• Several thousand Pacific walrus bulls remain in the south Bering Sea during the summer. When the ice melts, these bulls haul out on islands.
POPULATION
1. 
Total world walrus population is about 250,000 animals.
2. 
The Pacific walrus population is currently unknown but was last estimated at more than 200,000 animals in 1990.
• 
The Pacific walrus population has been hunted to depletion and allowed to recover several times.
• After the latest population depletion, which began in the 1930s, Pacific walruses were given protection by Russia, the State of Alaska, and the U.S. federal government. This protection led to the eventual recovery of the Pacific walrus population. Walruses reoccupied areas where they had not been seen for several years.
• By the early 1980s, walruses appeared leaner. They increased their consumption of alternate foods such as fishes. Natural mortality increased, and birth rates decreased. This evidence supports the theory that the Pacific walrus population may have approached the carrying capacity of its environment.
• As the Pacific walrus population grew, annual subsistence catches by indigenous Arctic peoples ranged from about 3,000 to 16,000 walruses per year until about 1990, and then decreased to an average of 5,789 animals per year from 1996 to 2000. Some scientists predict that, without long-term management, natural and human-related mortality factors could rapidly reduce the population once more.
• Currently the US Geological Survey (USGS) and the Russian Knipovich Polar Research Institute are jointly undertaking a walrus population study. Using infrared imaging they locate walrus groups hauled out on sea ice. High resolution digital photography allows researchers to estimate group numbers. They also use satellite telemetry to estimate the percentage of the population visible during counts.
PYSICAL CHARACTERTISRICS
SIZE
1. 
Male Pacific walruses weigh about 800 to 1,700 kg (1,764-3,748 lb.) and are about 2.7 to 3.6 m (9-12 ft.) long.   
2. 
Female Pacific walruses weigh about 400 to 1,250 kg (882-2,756 lb.) and are about 2.3 to 3.1 m (7.5-10 ft.) long.   
3. 
Atlantic walruses are slightly smaller: males weigh about 908 kg (2,000 lb.) and reach lengths of 2.4 m (8 ft.).
4. 
The northern and southern elephant seals are the only pinnipeds that, when full-grown, can be larger than the walrus.

BODY SHAPE
A walrus has a rounded, fusiform body.
COLORATION
1. 
Generally, walruses are cinnamon-brown overall. 
2. 
Walruses 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. 
3. 
Calves at birth are ash gray to brown. Within a week or two, calves become tawny-brown. The coloration pales with age. In general, younger individuals are darkest
FLIPPERS

1. 
Limbs are adapted as flippers. 
2. 
Flippers are hairless. The skin on the soles of a walrus's flippers is thick and rough, providing traction on land and ice.
3. 
The foreflippers, or pectoral flippers, have all the major skeletal elements of the forelimbs of land mammals, but are shortened and modified.
• 
A walrus's foreflippers are short and square. Each foreflipper has five digits of about equal length. Each digit has a small and inconspicuous claw.• While swimming, a walrus holds its foreflippers against its body or uses them for steering.
• On land, a walrus positions its foreflippers at right angles to the body for walking.
4. 
Walruses have triangular-shaped hind flippers. Hind flippers have five bony digits. Claws on the three middle digits are larger than those on the outer two digits.
• 
Walruses use alternating strokes of the hind flippers to propel themselves in water.
• Like sea lions, walruses can rotate their hind flippers under their pelvic girdle, enabling them to walk on all fours.
HEAD
A walrus's head is square and broad with conspicuous tusks and whiskers. 
A walrus has about 400 to 700 vibrissae (whiskers) in 13 to 15 rows on its snout. Vibrissae are attached to muscles and are supplied with blood and nerves.
3. 
Most walruses have 18 teeth. The two canine teeth in the upper jaw are modified into long ivory tusks.
• 
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.
• Tusks can grow to a length of 100 cm (39 in.) in males and 80 cm (31.5 in.) in females. Tusks grow for about 15 years, although they may continue to grow in males.
• The primary functions of the tusks are establishing social dominance and hauling out onto ice or rocky shores.
4. 
Eyes are small and located high and toward the sides of the head.
 5. 
Ears, located just behind the eyes, are small inconspicuous openings with no external ear flaps.
6. Paired nostrils are located on the snout above the vibrissae. Nostrils are closed in the resting state.
SKIN AND HAIR

1. 
A walrus's skin is thick and tough. It may reach a thickness of 2 to 4 cm (0.79-1.6 in). It is thickest on the neck and shoulders of adult males, where it protects the animal against jabs by the tusks of other walruses.
2. 
The skin of males often has large nodules; these are absent in females. Because the nodules appear at the time of puberty, they are presumed by some researchers to be a secondary sex characteristic.
 3. 
Hair is about 7 to 12 mm (0.3-0.5 in.) long over most of the body. It is shortest on the face and absent on the flippers.  
4. 
Hair is densest on juveniles and becomes less dense with age. 
5. 
Molting.
• 
An annual molt (hair-shedding) for most males takes place from June to August. Females molt over a more prolonged period. Molting in walruses is gradual - individual hairs fall out and are replaced.
• Calves shed a fine prenatal coat, called lanugo, about two to three months before they are born. They molt again at about one to two months.
Diet & Eating Habits
1. 
Walruses prefer molluscs - mainly bivalves such as clams. They also eat many other kinds of benthic invertebrates including worms, gastropods, cephalopods, crustaceans, sea cucumbers, and other soft-bodied animals. Walruses may occasionally prey on fishes such as polar cod.   
2. 
Walruses may eat the carcasses of young seals when food is scarce.
3. 
There are some rare but habitual seal-eating walruses. Their diet consists mainly of ringed and bearded seals. These are usually male walruses, recognizable because they are usually larger than other males, with powerful shoulder and chest muscles. Their skin may become grease-stained from the blubber of the seals they prey on.

FOOD INTAKE

1. 
Adult walruses eat about 3% to 6% of their total weight per day.
2. 
Adults may eat as many as 3,000 to 6,000 clams in a single feeding session.  
3. 
Observations of feedings indicate that walruses usually fill their stomachs twice daily. 
4. 
In the summer months, and during the southward migration in the fall, walruses spend most of their day foraging. They eat less on their northward migration in the spring. Food intake for mature male walruses dramatically decreases during the breeding season and probably for a shorter time for females in estrus. Pregnant females increase food consumption about 30% to 40%.
METHODS OF COLLECTING FOOD
1. 
Walruses usually forage on the bottom within 80 m (262 ft.) of the surface. Most feeding probably takes place between 10 and 50 m (33-164 ft.).   
2. 
Because visibility is poor in deep and murky waters, walruses rely on their vibrissae to locate food. A walrus moves its snout along the bottom, rooting through the sediment and using its vibrissae to help detect prey. Abrasion patterns of the tusks show that they are dragged through the sediment, but are not used to dig up prey.  
3. 
In addition, researchers have seen foraging Atlantic walruses rapidly waving a foreflipper to uncover prey from the sediment. The walruses that were observed, preferentially used their right flipper when foraging this way. 
4. 
Evidence shows that walruses may take in mouthfuls of water and squirt powerful jets at the sea floor, excavating burrowing invertebrates such as clams.  
5. 
Walruses do not chew their food, but they do sometimes crush clam shells.
• 
Soft-bodied invertebrates are usually not crushed or torn. A walrus sucks off the foot and the fleshy siphon of a clam and swallows it whole.
• The cheek teeth do get worn, but this is probably from abrasion by minute particles of sand that walruses inadvertently take into their mouths and not from crushing clam shells.   
6. Researchers have found numerous pebbles and small stones in the stomachs of walruses. These are thought to be ingested while feeding.
Reproduction
SEXUAL MATURITY
1. 
Most male walruses are sexually mature at about eight to ten years. Successful reproduction, however, probably doesn't occur until 15 years when a male attains full physical size and is able to compete for females.   
2. 
Most females are sexually mature at about five to six years. Successful reproduction probably begins at about ten years.

MATING ACTIVITY

1. 
Only a portion of the female population mates each year, as some are pregnant from the year before. Non-pregnant females may go into estrus some time between December and June and most ovulate in February.   
2. 
In the Pacific, female herds meet male herds as they move south into the central and south Bering Sea in January. Estrous females gather in herds separate from pregnant females and are attended by males displaying nearby in the water. 
3. 
Most mating probably occurs from December through March, when most sexually mature males produce viable sperm. Mating takes place off the pack ice, underwater and remote from shore; breeding locations are thus largely inaccessible for observation.   
4. 
Each herd of estrous females is attended by one or more large adult males. According to one study, the ratio of males to females averaged 1 to 23.
5
Males display visually and vocally from the water while the females rest. A display occurs both at and below the surface and lasts about two to three minutes. The males' displays include clanging bell-like sounds, pulses, and clicks under water, and teeth clacking and whistles at the surface.
GESTATION
1. 
Total gestation is 15 to 16 months.   
2. 
Gestation includes a period of delayed implantation. The fertilized egg divides into a hollow ball of cells one layer thick (blastocyst), and then it stops growing and remains free-floating in the uterus for four to five months. The blastocyst then implants on the uterine wall and continues to develop.  
3. 
Delayed implantation allows the mother time to recover from her last pregnancy and devote her energy to nursing and caring for her calf. It also ensures that the calf will be born when environmental conditions are optimal for its survival.