Walrus

Walruses are the only extant species of the family Odobenidae, recognized by their long elephant-like tusks and a prominent mustache of grizzly whiskers. These pinniped mammals inhabit the shallow waters of the Arctic and sub-Antarctic regions, feasting on their favorite bivalve mollusks like clams. Though they love basking under the sun on ice floes, they are surprisingly agile on land, sometimes running as fast as humans on all four flippers.

Due to commercial overhunting, they were once a threatened species in the 18^th and 19^th centuries and are still vulnerable to extinction. 

Subspecies

There are two subspecies of walruses.

• The Atlantic Walrus (O. r. rosmarus)
• The Pacific Walrus (O. r. divergens)

Description

Length: 

Body: Male – 3.2 m (125 inches), Female – 2.7 m (106 inches); Tusk: 1 m (3 ft 3 inches)

Weight: 

Male – 1200 kg to 1500 kg (2645 lbs to 3300 lbs), Female – 600 kg to 850 kg (1320 lbs to 1874 lbs)

Body and Coloration:

They have brown or light gray, wrinkled hides under which is a thick layer (up to 15 cm or 6 inches) of fatty ‘blubber.’ Their skin is covered with short, reddish hair that appears cinnamon to rosy pink under the sun on hot days. 

Apart from the striking pair of long white canines, these pinnipeds also possess a broad mat of grizzly whiskers, making them look mustached. They have small eyes, capable of short-range vision, and often find it challenging to observe the ocean floor while foraging.

The Pacific walruses usually have larger body mass than their Atlantic counterparts.

Distribution

They are spread widely across the snow-capped Arctic regions of the world. 

The Pacific walruses spend their summers north of the Bering Strait, often traveling as far as the Beaufort Sea and the East Siberian Sea. During spring and fall, they congregate in the Bering Strait, extending from the western coast of Alaska to the Gulf of Anadyr. They winter in the Bering Sea, along Siberia’s eastern coast and Alaska’s southern coast.

Atlantic walruses reside in the Atlantic Ocean, ranging from the Canadian Arctic across Greenland to the west of Arctic Russia.

Habitat

These marine mammals prefer living in shallow waters for easy access to food. Though they haul themselves onto ice floes to bask, they rarely venture too far from the shoreline or margins of ice shelves. Females spend more time on ice than males, who prefer sand or boulder beaches.

Pacific walruses migrate in large groups from the Bering Sea to the Chukchi Sea through the Bering Strait in search of warmth. 

Diet

They feed on almost 60 genera of marine organisms, including crabs, shrimps, soft corals, tubeworms, and sea cucumbers. Benthic bivalve mollusks are their preferred food source, but they also take in sea mollusks such as snails, squids, and octopuses. Though rare, walruses also prey upon seals and narwhals if readily available.

Sometimes, parasites like Trichinella spiralis, Toxoplasma gondii, and Brucella sp. can accidentally enter their body along with bivalves, causing pain, sickness, organ damage, and even stillbirths. 

Behavior

• Walruses are extremely sociable and characteristically vocal and communicate through distinct grunts and barks while asserting dominance over competing males or seeking mates.
• When grazing the ocean floor for prey, they move their hind flippers to swim forward, using their tusks and whiskers to drag the floor. If a walrus feeds on clams, it sucks the meat out of them by sealing its lips to the shell and withdraws its tongue rapidly into its mouth, creating a vacuum. Sometimes, they also crush the shells using their powerful, rounded teeth.
• During late spring and early summer, thousands of Pacific walruses aggregate in large groups and migrate from the Bering Sea to the Chukchi Sea through the narrow Bering Strait to ensure the availability of optimum thickness of ice for survival. On average, they swim at about 7 kph (4 mph) but can upgrade to 35 kph (22 mph) if necessary.

Lifespan

On average, walruses can live up to 40 years in the wild, while they have been recorded living up to 30 years in captivity.

Reproduction and Life Cycle

Walruses are polygynous, with each male mating multiple females per breeding season. Males begin to mature at seven, but reaching full maturity takes about 15 years. The females begin ovulating at around four to six years of age. Mating occurs from January to April, peaking in February.

Males and females live in separate groups, gathering only when they are about to mate. The males aggregate around ice-bound herds of estrous females, engaging in competitive vocal displays and fighting with their tusks. The females then join the superior male and copulate in water. The average gestation period in females is around 15 to 16 months, including a 3 to 4-month delay in implantation. 

The calves are born during migration in spring from April to June. They weigh about 45 to 75 kg (99 to 165 lb) at birth and have an average length of 120 cm (47 inches). They typically learn to find food by age two and are fully weaned by three. Although they are good swimmers from birth, they continue to stay with their mothers for up to 5 years for protection against enemies.

Walruses have the lowest reproductive rate of all pinnipeds because their ovulation is suppressed until the calf is fully weaned. Because of this low birth rate, the mothers dedicatedly invest in parental care to ensure the survival of their calves.

Predators

They are only preyed upon by the orca (killer) whales and polar bears. In addition, they are often hunted by indigenous peoples, such as the Inuit, the Yupik, and the Chukchi, for their skin, fins, and tusks.

Adaptations

1. The thick layer of blubber below the skin insulates against the extreme cold and chilly winds of the Arctic. The blubber also acts as a reserve energy source when prey availability is low. Some fat cells are also present around the eyes to keep them warm.
2. The prominent tusks help form breathing holes in chunks of ice (up to 20 cm or 8 inches) for aeration, besides aiding them in climbing out of the water onto ice slabs.
3. The presence of extraocular muscles and the simultaneous lack of an orbital roof allows a walrus to protrude its eyes and observe in both frontal and dorsal directions. 
4. While the long hind flippers propel its giant body, the short front flippers help navigate on both land and water. 
5. The mat of whiskers called ‘mystacial vibrissae’ around their tusks are highly sensitive organs that help them to differentiate shapes and identify food and other objects on the ocean floor. Their prey, particularly shellfish, are found near the dark ocean floor, where they use these whiskers as detection devices. 
6. Even though they lack ears, specialized tissue conduction ensures efficient hearing underwater, allowing sound to pass through the outer ear tube while the auditory meatus remains closed.
7. Walruses have an air sac under their throat, which helps them float in the water while sleeping. They can also voluntarily slow their heartbeats to withstand the extreme polar temperatures.

Conservation Status

According to the IUCN Red Data List, walruses belong to the ‘Vulnerable’ category. Their Pacific and Atlantic subspecies belong to the ‘Least Concern’ category. CITES lists these pinnipeds under Appendix III.

During the 18th and 19th centuries, this animal was exploited by whalers and sealers for commercial sale of its skin, tusk, oil, and bones. Though regulated by law, some indigenous ethnic groups are still permitted to kill walruses in restricted quantities by the end of every summer, adding to their population decline.

However, the recent cause of concern is global warming and the subsequent melting of pack ice. The gradual thinning of the ice layer over the Bering Sea has reduced their resting habitat near feeding grounds, causing overcrowding along shores and increased deaths by stampede.