Seals belong to the order Pinnipedia, which is made up of the three families of finfooted marine mammals: Phocidae (true seals, or hair seals), Otariidae (fur seals and sea lions, or eared seals), and Odobenidae (walruses). There are six species of pinnipeds (five seals and the walrus) that can often be seen in Svalbard. The pinnipeds are found primarily in cold oceanic regions such as the Arctic and the Antarctic, although some species inhabit tropical regions (especially such areas which are affected by cold water currents). Unlike the whales, however, pinnipeds are still linked to land, or ice, in their seasonal breeding, preening, and molting procedures.
All pinnipeds are carnivorous, and except for the fact that their feet are flipperlike to accommodate an aquatic life style, they are very similar to members of the order Carnivora, which includes the cats, dogs, otters, skunks, bears, etc. The Pinnipedia and Carnivora orders are obviously closely related, but scientists are still unsure of that relationship. One theory holds that all pinnipeds evolved from a single strain of early carnivores somewhere in the north Atlantic region, from which one branch later migrated to the north Pacific and gave rise to the eared seals and walruses. A second theory speculates that the pinnipeds evolved from two different groups of carnivores: the eared seals and walruses originated from bearlike ancestors in the north Pacific region, and the true seals developed from primitive otterlike ancestors in Asia. Recent genetic studies have indicated the first theory is more likely the true scenario.
The pinnipeds make their living from the sea, and as expected they have evolved many different mechanisms to assure their success in a marine environment. They contain an enormous amount of blood in relation to their body size (about twice the amount found in a comparablysized human). A larger content of blood obviously holds more dissolved oxygen and carbon dioxide, and the animal can therefore survive for longer periods of time without breathing. Also, the presence of myoglobin in the blood reduces the problem of lactic acid buildup in the muscles. This gives them the ability to spend a great deal of time under water searching for food. During a dive the heartbeat rate slows from perhaps 100 beats per minute to as few as four or five beats per minute. Pinnipeds have a venal shunt system which allows the blood to bypass muscles and organs which do not need a constant supply of oxygenated blood, and circulate the blood instead to critical organs such as the heart, brain, and spinal cord. They normally exhale before they dive below the surface, but their lungs are dorsally located so as to give them extra stability when they are buoyant at the surface.
Many species migrate long distances during different seasons of the year, but they accumulate in and around the pack ice and/or shorelines during Summer months in order to breed. The females only give birth to one young per season. Gestation for most species is about nine months, and because they scatter after the short breeding season, mating must take place soon after parturition. The next year's pup is born almost exactly one year later, which means the pregnant female must have some physiological method by which she delays the development of the fertilized egg, or its implantation in the uterus. This technique is called delayed implantation.
Being mammals, the babies suckle milk from their mothers. The milk contains about 45% fat and 10% protein (compared to about 4% fat and 2% protein in cow's milk), and the offspring grow very quickly. Most species are weaned in about two months. The males have little or nothing to do with the raising of their offspring. There is tremendous variation in life styles and food preferences among the species, which makes it difficult to give simple generalizations.
As well as describing the pinnipeds in general as a group, it is also important to explain the differences within the group. The two families Otariidae and Odobenidae are closely related, and many of the following descriptions given for the eared seals also hold true for the walruses of the Northern Hemisphere (except walruses have huge tusks and are nearly hairless). Eared seals have external ears, their hind feet can be positioned beneath the body in order to walk or hop on land, the fore limbs are long and broad and provide the main power stroke for locomotion in water (because of this, much of the muscle mass is centered around the pectoral girdle and thoracic region), the soles of their flippers are naked, they have claws only on the middle three digits of each flipper, and there is extreme sexual dimorphism. Males are much larger than females…males are often more than four times the mass of the females.
The true seals have no external ears, their hind limbs stick straight back in line with the body forcing the animals to crawl (rather like an inch worm) when on land, the fore limbs are short and the hind limbs provide the means for locomotion in water, the flippers are completely covered with fur, there are claws on all digits, and except for a few species which form harems, the sexes are fairly similar in size.
Of all the differences, however, the most important is the makeup of the fur. The fur seals are aptly named for they have dense, luxurious coats. Their fur consists of two different types of hairs, guard hairs and under fur, which are arranged in bundles. Each long guard hair is surrounded by up to 70 short under fur hairs, and this gives the animal a highly efficient protective layer of insulation against cold temperatures both in the water and on land. Unfortunately, it also gives them a pelt which is highly valued by mankind. The true seals, on the other hand, rely primarily on a thick layer of subcutaneous oil-rich fat, or blubber, to insulate their bodies from the intense cold. Therefore, their fur is not nearly so thick or luxurious. True seals also have both guard hairs and under fur, but on average there are only two to five under fur hairs associated with each guard hair. It was the expanding search for fur seals which led to the discovery of Antarctic continent in the early 19th century.
The harp seal is a piebald animal which grows to a length of 1.8 meters (6 feet). The male is white or creamcolored, with a dark face and circle, or horseshoe shape, on the back. The female and young are gray with similar pale brown marks on the face and back. This species inhabits open water and pack ice, and is seldom encountered close to land. Their breeding areas are found in large fields of loose pack ice. The females arrive first and give birth in late February and early March, at which time the males arrive and mating then takes place. The pup has a soft, woolly, pure white coat for about three weeks, and then it changes to gray. The pups take to the water at about the time of their first molt.
The ringed seal is small and fat, and has a roundshaped head. It grows to about 1.8 meters (6 feet), and the sexes are similar with a graybrown coloration covered with dark spots (often edged in white) which are more densely concentrated on the back. This is the commonest and most widespread of the Arctic seals, and is often found on inshore ice. The Svalbard population is estimated to be about 100,000 individuals. They are not as colonial as most other seals, and females usually den in ice caverns or hollows in ice fields to give birth in March. This affords them much protection, but polar bears still manage to find them and dig them out. Ringed seals maintain breathing holes which allows them to remain among the sea ice throughout the Winter. They feed on large crustaceans and small fish, and can dive to at least 106 meters (350 feet). Ringed seals are the favorite prey of both polar bears and human subsistence hunters.
The hooded, or bladdernose, seal is the largest Arctic seal, growing to a length of 3.6 meters (12 feet). Typically, the coat is dark silvergray, sometimes suffused with brown, and the face and flippers are darker than the rest of the body. The male has an extraordinary proboscis which can be inflated as a threat display when the males gather in the breeding areas. Actually, this involves blowing air into one of the nostrils so that a skin flap inflates and protrudes outside of the nose like a red balloon…creating a startling effect. They are seldom found inshore, but spend their lives far out to sea where they feed on plankton and surface fish among the ice floes. They gather to breed in March and April, and pair off soon after the pups are born. Mating usually occurs three weeks after parturition, and the family groups disperse after another three weeks.
The bearded seal is a large species which grows to 3 meters (10 feet) in length. It has plain fur (sometimes with very faint spots), with a light brown colored back and grayish or yellow flanks and belly. Found usually in shallow coastal areas among moving ice, this animal feeds on the rich sea beds. Like all seals, it has long, sensory facial vibrissae, but these are considerably longer and thicker proportionally this species…hence the name bearded. The vibrissae are used to detect crustaceans and mollusks on the muddy sea beds. The shellfish diet tends to wear down the teeth of older animals. This species is relatively solitary, and the pups are born scattered across the pack ice in April and May. The pups spend an inordinate length of time with mother, compared to other seals, and the females breed only every other year. It is an especially curious animal, and often can be approached quite closely by small boat.
The common, or harbor, seal is a fat little animal with a round head. It grows to a length of 1.8 meters (6 feet), and its coloration varies from a leadengray with dark spots to dark gray with light spots, and everything in between including brownish tints. The world’s northernmost population of common seals is found in Svalbard, comprising approximately 1,000 animals. This species is quite shy, and usually is encountered in shallow, sandy bays and estuaries, and on coastal ice floes. It rarely comes ashore, but when it does, the preferred hauling out sites are places exposed only at low tide, i.e. sand bars, low rocky ledges, and shoaling, pebble beaches. Breeding groups gather in protected waters from Spring through late Summer, and in the more northerly areas pups are born during March and April (mostly on ice floes). The courtship rituals are quite impressive, with the animals cavorting around and leaping out of the water like fish. The pups can swim alongside their mothers within a few hours after birth, and are weaned in about six weeks.
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