seal

seal

, in zoology

seal, carnivorous aquatic mammal with front and hind feet modified as flippers, or fin-feet. The name seal is sometimes applied broadly to any of the fin-footed mammals, or pinnipeds, including the walrus, the eared seals (sea lion and fur seal), and the true seals, also called earless seals, hair seals, or phocid seals. More narrowly the term is applied only to true seals. The so-called performing seal of circuses is actually a sea lion.

Characteristic Features of All Seals

Pinnipeds have streamlined bodies, rounded in the middle and tapered at the ends, with a thick layer of fat beneath the skin. Their limbs are short and their feet are long and webbed, forming flippers. The sea lions and fur seals (family Otariidae) and the walrus (family Odobenidae) are able to turn their hind flippers forward for walking on land; they swim chiefly by a rowing action of the long front flippers. The true seals (family Phocidae) are unable to rotate the hind flippers. They progress on land by wriggling on their bellies, pulling themselves with the short front flippers; in the water they are propelled by a side-to-side sweeping action of the hind flippers.

Nearly all pinnipeds are marine, and most inhabit cold or temperate regions. Some spend most of the year in the open ocean, while others inhabit coastal waters and spend varying amounts of time on shores, islands, or ice floes. Occasionally they ascend rivers. All pinnipeds leave the water at least once a year, at breeding time. In nearly all species the females give birth a year after mating, so that the births take place on land, just before breeding begins. The pups are nursed during the period, usually of several months duration, spent on land. Some species spend most of the year far from their breeding grounds; the northern fur seals make particularly lengthy migrations each year. Most pinnipeds have diets of fish and shellfish; many are bottom feeders, with physiological adaptations for deep diving. They have acute hearing and some, if not all, make use of echolocation (sonar) for underwater navigation.

True Seals

True seals are called earless seals because they lack external ear projections; they have functional inner ears. They have short, coarse hair, usually with a close, dense undercoat. Their color and pattern vary with the species; many are spotted. The pups of most species have fluffy coats of a light color. True seals are generally polygamous and gregarious, but most do not form harems at breeding time, as do the eared seals. Some species have definite migrations, but in most the seals spread out after breeding, singly or in groups, over a wide area of ocean. Some polar species migrate in winter to avoid the advancing ice; members of other species winter under the ice, surfacing through holes to breathe.

Most true seal species fall into one of three geographical groups: northern, antarctic, and warm-water species. Nearly all are marine, but the Baykal seal (Pusa siberica) is confined to the freshwater Lake Baykal of Siberia, and the Caspian seal (P. caspica) to the brackish Caspian Sea. In addition several populations of the normally marine harbor seals and ringed seals are found in freshwater lakes. The northern seals include two species of temperate coastal waters: the common seal, or harbor seal, of the N Atlantic and N Pacific, and the larger gray seal of the N Atlantic. The former is the only seal frequently seen off U.S. coasts. The Greenland seal, or harp seal, is found in the arctic Atlantic; the ribbon seal in the arctic Pacific. The small ringed seal and the larger bearded seal are circumpolar arctic species. Antarctic seals include the voracious leopard seal, which feeds on penguins and other sea birds, and the Ross, Weddell, and crabeater seals. The warm-water seals are the Mediterranean, Caribbean, and Hawaiian species of monk seal. A fourth group includes the elephant seal and hooded seal. There are two elephant seal species, one of the Northern and one of the Southern Hemisphere. They are distinguished by their immense size and trunklike snouts. The hooded seal, distinguished by an inflatable bladder over the snout, is found in the arctic Atlantic.

Sealing

Seals have been used by the Eskimo and other northern hunting peoples for food, oil, and hides. Commercial sealing has been largely confined to a few species, most notably the fur seal. Commercially important species of true seals are the harp seal, whose pups are valued for their fluffy white coats, and the ringed seal. The hunting of these seals is regulated by international treaties, and they are not in danger of extinction. The elephant seals were formerly hunted for oil and almost exterminated, but they are now protected and are stabilized or increasing in numbers. The monk seals have been greatly depleted by hunting in past centuries and their survival is threatened, although they are no longer of commercial importance. The Caribbean monk seal is believed by some authorities to be extinct. The ribbon seal and Ross seal are not much hunted; estimates of their populations have varied considerably, but they are not thought to be endangered.

Classification

Seals are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Carnivora, suborder Pinnipedia.

Bibliography

See B. Davies, Savage Luxury: The Slaughter of the Baby Seals (1971); V. B. Scheffer, The Year of the Seal (1972); J. E. King, Seals of the World (2d ed. 1983); R. L. Gentry and E. L. Kooyman, Fur Seals (1986).

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seal

, stamp

seal, stamp made from a die or matrix of metal, a gem, or other hard substance that yields an impression on wax or other soft substance. The use of seals is very ancient, examples of great antiquity occurring in China, Egypt, Greece, Rome, and other places. The most common form was the seal ring, of which the gem formed the seal. Ecclesiastical seals, used in the 9th cent., reached their highest perfection in the 13th and 14th cent. The use of seals with emblematic designs antedates the development of the escutcheon and is therefore important in the history of heraldry. Edward the Confessor was the first English king to adopt a Great Seal for the kingdom. Heraldic or emblematic seals are in wide use by national, state, and local authorities, by institutions of all kinds, and in the certification of legal documents. A committee was appointed by the Continental Congress on July 4, 1776, to prepare a device for the Great Seal of the United States (see United States, Great Seal of the).

The Columbia Electronic Encyclopedia™ Copyright © 2022, Columbia University Press. Licensed from Columbia University Press. All rights reserved.

The following article is from The Great Soviet Encyclopedia (1979). It might be outdated or ideologically biased.

Seal

 

(also gland), a device to provide hermetic sealing in machine connections between rotating and stationary parts. This is accomplished using sealing rings, flanges, or other parts placed on the shaft or by means of various packings, such as asbestos, asbestos-wire, or fabric-reinforced rubber, embedded in the recesses or cavities of covers, housings, and similar parts.

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Seal

 

any one mammal of the order Pinnipedia, which comprises the families Phocidae (true seals) and Otariidae (eared seals). The true seals probably descended from primitive Mustelidae, whereas the eared seals apparently are descendants of primitive bearlike creatures. True seals lack external ears, and both pairs of limbs are modified into clawed flippers. The hind limbs of seals are directed backward and serve for locomotion in water; they do not bend forward on dry land and cannot support the heavy body. There are about 20 species, belonging to 12 genera. Seals are widely distributed but are particularly numerous in polar latitudes. Most species form rookeries on the ice during the mating and molting period. The waters of the USSR are inhabited by nine species (in six genera), of which the harp seal, Caspian seal, ringed seal, Pacific harbor seal, and bearded seal are of commercial significance.

The Great Soviet Encyclopedia, 3rd Edition (1970-1979). © 2010 The Gale Group, Inc. All rights reserved.

seal

[sēl]

(engineering)

Any device or system that creates a nonleaking union between two mechanical or process-system elements; for example, gaskets for pipe connection seals, mechanical seals for rotating members such as pump shafts, and liquid seals to prevent gas entry to or loss from a gas-liquid processing sequence.

A tight, perfect closure or joint.

(vertebrate zoology)

Any of various carnivorous mammals of the suborder Pinnipedia, especially the families Phoridae, containing true seals, and Otariidae, containing the eared and fur seals.

McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.

seal

seal, 4

1. A device usually consisting of an impression upon wax or paper, or a wafer, or the inscription of the letters L.S. (locus sigilli), sometimes used in the execution of a formal legal document such as a deed or contract. In some states, the statute of limitations applicable to a contract under seal is longer than that for a contract not under seal; in most states, the seal has been deprived by statute of some or all of its legal effect.

2. An embossing device or stamp used by a design professional on his drawings and specifications as evidence of his registration in the state where the work, 1 is to be performed.

McGraw-Hill Dictionary of Architecture and Construction. Copyright © 2003 by McGraw-Hill Companies, Inc.

seal

¹

RC Church the obligation never to reveal anything said by a penitent in confession

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seal

²

1. any pinniped mammal of the families Otariidae (see eared seal) and Phocidae (see earless seal) that are aquatic but come on shore to breed

2. any earless seal (family Phocidae), esp the common or harbour seal or the grey seal (Halichoerus grypus)

3. sealskin

Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005

SEAL

Semantics-directed Environment Adaptation Language.

ftp://ftp.cwi.nl/pub/gipe/0092b.ps.Z.

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