Walruses

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Walruses

The walrus (Odobenus rosmarus) is one of the largest seals, suborder Pinnipedia. Although similar in many respects to other seals, particularly the eared seals, the walrus is sufficiently different to merit being placed in its own family, Odobenidae. It is the sole member of that family, with only a few subspecies. The genus name is derived from the Greek words for “tooth” and “I walk”—thus, “tooth walker,” which refers to the walrus’s use of its tusks to haul out on ice floes. The species name is derived from the Scandinavian word for walrus.

Walruses are found along the coast of the Arctic Ocean, where they spend most of their time on the seasonal pack ice. (If ice is unavailable, they will gather on land.) They have bred as far south as Nova Scotia, the Aleutians, and the White Sea, and stray individuals have been recorded in more temperate waters, including coastal Massachusetts, Ireland, southern England, France, and even northern Spain.

Among the seals, the walrus is second in size only to the elephant seal. It varies in size according to location; the smallest walruses are found in Hudson Bay, the largest in the Bering and Chukchi Seas. Hudson Bay

males average 9.5 ft (2.9 m) in length and weigh about 1,750 lb (795 kg), and the females are about 8.2 ft (2.5 m) long and weigh 1,250 lb (565 kg). In the Bering Sea population, the adult males are about 10.5 ft (3.2 m) long and weigh 2,670 lb (1,210 kg) and the females are 8.9 ft (2.7 m) long and 1,830 lb (830 kg).

It is impossible to mistake a walrus for anything else. Its distinctive tusks are present in both sexes. Tusk length, like body size, varies among populations, but can exceed 39 in (100 cm) in males and 32 in (80 cm) in females. The tusks are derived from the canine teeth, and they grow throughout life. The tusk is almost purely dentine (ivory); this has made the walrus a target of hunting. Although fearsome weapons, the tusks are mostly used as ice axes, when the animal hauls itself out of the water onto an ice floe. They are also used as a social signal, much like the antlers of deer. The size and shape of tusks differs between males and females, so it is likely that walruses use these clues to determine sex and age.

The body of a walrus is massive. The head, which appears to be set directly on the animal’s trunk, is round and the skull is thick. A walrus may use its head as a battering ram to break through ice up to 8 in (20 cm) thick. The deeply folded skin is 1.2-1.6 in (3-4 cm) thick, and is underlain by a 4 in (10 cm) layer of blubber. In females and young males, the skin is covered with coarse hair about 0.4 in (1 cm) long, which gives them a soft, velvety look. Older males are nearly hairless, and their thick, folded skin is bare on their neck and shoulders. When an old male hauls himself out of the Arctic water, he may be nearly white; but as the sun warms him, his skin will turn a rosy shade of pink. The skin is particularly thick on the male’s neck, where it can be up to 2.4 in (6 cm). Males also have a pair of pouches extending from the pharynx. When inflated, these pouches produce a distinctive bell-like sound, and help the male float.

The walrus has four flippers, each with five digits. The flippers are thick and cartilaginous. All the flip-pers have a bare, warty sole that provides good traction on ice. Like the eared seals, the walrus can rotate the flippers forward and use them to walk. In the water, however, the walrus propels itself almost entirely with its hind flippers, using the fore-flippers only to steer. They swim at an average speed of about 4.3 mph (7 km/h), and can reach 22 mph (35 km/h). However, they are generally not great migrators, and seem to prefer to hitch rides on ice floes that drift with the current. Dives last about 2-10 minutes; the depth is typically 32-164 ft (10-50 m), but the deepest known dive was 262 ft (80 m).

The eyes are small, and the external ears are mere folds of skin. While these senses may not be particularly good, there is an excellent sense of touch using the distinctive moustache, used to find food. The moustache, found in both sexes, is composed of about 450 sensitive whiskers.

The whiskers help the walrus detect the bottom-dwelling organisms on which it feeds. Bivalve mollusks such as clams comprise the bulk of the typical diet. Once a walrus noses a mollusk out of the mud (an old wives’ tale suggests that walrus use their tusks to dig up mollusks), it sucks the creature out and spits the shell back into the mud. Thousands of mollusks may make up a meal. The diet also includes crabs, octopus, sea cucumbers, polychaete worms, tunicates, fish, and occasionally, birds. Some individuals have been known to hunt other seals and even whales.

Walruses are gregarious animals. They seem to enjoy nothing more than sunbathing in great agglomerations called haul-outs. The haul-outs are generally all-male or all-female during the non-breeding season, and within them several thousand walruses may lie close together. Within a haul-out there is a social hierarchy, with the largest animals with the largest tusks at the top. A dominant animal need just show its tusks to a subordinate and the latter will generally move along; sometimes there is violence, but generally there is no lasting injury.

Mating occurs during January and February, in the water, and the female can delay implantation of the fertilized egg until July. The calf is born 10-11 months later, about 140 lb (63 kg) in weight, 45 in (113 cm) in length, and tuskless. Mothers and calves share a strong bond, and the mother is very protective. Unlike in the eared seals, walrus mothers do not leave their calf for long periods. However, females will “babysit” each other’s young, and even adopt orphans. Calves remain with their mother for two years. Females are sexually mature between the ages of six and seven; males mature later, at around eight to 10, but they generally cannot compete for females until they reach their full growth at around age 15. Females are full-grown at 10-12 years old. Walruses can live about 40 years.

Walruses have been hunted for thousands of years by aboriginal Arctic peoples, who used all parts of the animal—skin, fat, meat, and bones—for clothing, fuel, food, tools, and boat-skins. Then Europeans realized the walrus was an easy-to-kill source of oil, ivory, and skins. By the mid-1800s, the Atlantic sub-species (O. r. rosmarus) had vanished at southern locations they had traditionally used, such as Sable Island and the Magdalen Islands off eastern Canada. This subspecies has never recovered from the onslaught; about 30,000 North Atlantic walruses remain, but they occur much farther to the north than in former times. During the nineteenth century, western hunters turned their attention to the Pacific subspecies (O. r. divergens), and tens of thousands of those animals were killed. On the Pribilof Islands alone, hunters took 35,280 lb (16,000 kg) of walrus ivory. The walrus of the Laptev Sea, O. r. laptevi, is considered rare, as it numbers only between 4,000-5,000 animals.

Although both the United States and Russia have prohibited hunting except by native peoples, some conservationists contend that this “subsistence” hunting is now primarily commercial. Poaching has increased since an international moratorium on international trade of elephant ivory was enacted (walrus ivory is a good substitute for many purposes). Between poaching and the legal killing of 10,000-15,000 walruses in the eastern and western Arctic each year, the population of all walruses is likely to decrease greatly.

Other than human beings, walruses have few natural enemies; they include polar bears, but walruses are quite good at fending off these predators.