Walrus

## Description

The walrus (Odobenus rosmarus) is a large flippered marine mammal with a discontinuous distribution about the North Pole in the Arctic Ocean and subarctic seas of the Northern Hemisphere. The walrus is the only living 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. Walruses are relatively long-lived, social animals, and they are considered to be a "keystone species" in the Arctic marine regions. They have also played a prominent role in the cultures of many indigenous Arctic peoples, who have hunted walruses for their meat, fat, skin, tusks, and bone.

## Appearance

The walrus has a short muzzle, a broad head, small eyes, whiskers, tusks, and flippers. Their large front flippers each have five digits. Males and females both have large tusks used for defense, getting out of the water, and cutting through ice. 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). 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. Males also acquire significant nodules, called "bosses", particularly around the neck and shoulders. Walruses have an air sac under their throats which acts like a flotation bubble and allows them to bob vertically in the water and sleep.

## Distribution

Walruses live throughout the Pacific and northern Atlantic Oceans on rocky coastlines and ice floes. They spend most of their time in shallow waters (and the nearby ice floes) hunting for food. Despite suiting freezing northern conditions, walruses have ventured further south to Central Canada and the United Kingdom, even near the Spanish coast.

## Behavior

Walruses are extremely sociable animals, living in large herds of up to thousands in number, mainly females with their young, and some dominant males. Male walruses fight with their tusks to compete for females and establish dominance. They make a variety of sounds including loud bellows produced via two pouches of air that are in their necks. These animals are diurnal. When not in the water, they feed and rest on sea ice. Walruses prefer shallow shelf regions and forage primarily on the seafloor, often from sea ice platforms. They are not particularly deep divers compared to other pinnipeds but can dive to depths beyond 500 meters. When feeding on their favorite mollusks, walruses find them by grazing along the sea bottom, searching and identifying prey with their sensitive vibrissae, and clearing the murky bottoms with jets of water and active flipper movements.

## Diet

Walruses are carnivores (molluscivores) and hunt other animals to survive. They eat clams, snails, worms, octopuses, squid, and some types of slow-moving fish. They will eat young seal carcasses when food is scarce.

## Reproduction

Walruses are polygamous meaning that males mate with more than one female. Breeding occurs between January and March. After the gestation period of about 15 months, females give birth to a single pup is produced. Calves weigh 45 to 75 kg (99 to 165 lb) at birth and are able to swim. The females nurse their young for over a year before weaning, but calves can spend up to 5 years with their mothers. They drink only their mother's milk for 6 months and then start to eat solid foods. Young females can reproduce at about 6 or 7 years but males not until they are 10, though 5 years later when they have proved their dominance might be more successful.

## Population

### Population threats

Humans are a threat, hunting them for their hides, bones, tusks, and oil. Water pollution is also a threat in certain areas. Potential threats are climate change and global warming causing changes and loss of suitable habitats and an increase in shipping and development of oil and gas fields.

### Population number

According to IUCN, the overall population of the walrus is likely greater than 225,000 individuals, comprising about 25,000 Atlantic walruses and 200,000 Pacific walruses. Currently, this species is classified as Vulnerable (VU) on the IUCN Red List.

### Ecological niche

Walruses are considered to be a "keystone species" in the Arctic marine regions. They feed on large numbers of organisms and their foraging has a large peripheral impact on benthic communities. When foraging walruses disturb the seafloor, releasing nutrients into the water column; this way they encourage the mixing and movement of many organisms and increase the patchiness of the benthos.

## Fun Facts

Walrus tusks are their large teeth, which never stop growing.

Walruses pull themselves onto land with their tusks.

Walruses are able to hold their breath for as much as 30 minutes under the water.

Walruses stampede toward open water when startled, sometimes crushing calves as they do so. This is perhaps why females form separate herds with their calves.

Walruses have an excellent sense of smell and hearing but poor eyesight.

Walruses dig out clams, shellfish, and other food by squirting jets of water out of their mouths.

A walrus will break the ice by hitting its head against it. Its tusks are then used to increase the size of the hole.