Phocidae: Seal Family
Often known as earless seals because they lack external ears, the 19 species in this family have made the most complete transition from terrestrial to aquatic way of life of all the pinnipeds. Their hind flippers cannot be turned forward like those of other pinnipeds. They move on land by dragging themselves forward with the foreflippers. They are skilful swimmers and divers, moving with undulatory movements of the hind portion of the body and the hind flippers. Seals have sophisticated mechanisms to enable them to dive deeply for food and to stay underwater for long periods. During a dive, the heart rate may drop from 120 to about 4 beats a minute, but without any drop in blood pressure. This is achieved by the restriction of the blood supply to the muscles of the heart and to the brain, thus reserving the blood oxygen for only the most vital organs.
The body of a seal is typically torpedo shaped, thick layers of fatty blubber under the skin accounting for much of its weight. The flippers as well as the body are furred, and the seals undergo an annual molt.
In some species, males are much bigger and heavier than females, but in others, females are the larger sex. Some are monogamous, but others, such as the elephant seals, are gregarious and polygamous. In most species there is a delay between fertilization and the actual start of gestation - delayed implantation. This ensures that birth and mating can be accomplished within the short period while the seals are on land.
Size: 1.6 m (5.25 ft); 70 - 95 kg (155 - 209 lb).
The ribbon seal is found off the coasts of the northern Pacific. The largest populations occur in the Bering Sea, between Alaska and Siberia. Ribbon seals rarely come to land. They raise their pups on the ice floes that extend southward in winter. In summer, they feed voraciously to prepare for the next winter on the ice. This species gets its name from its four ribbon-like stripes. One encircles the neck, another wraps around the body, and the remaining two ring the foreflippers.
Size: 1.4 - 1.5 m (4.5 - 5 ft); 65 - 95 kg (143 - 210 lb).
Ringed seals are the most common seal inside the Arctic Circle. They spend the winter on and under the thick ice floes that form on the Arctic Ocean. When under the floes, they breathe via air holes that they maintain in the ice. During the long, sunless Arctic winter, ringed seals hunt in the darkness for Arctic cod, using their sensitive whiskers to detect currents caused by these slow-moving fish. In spring, the seals gather in groups on the ice. Females give birth to pups in April, and mating takes place about a month later.
Size: 2.5 - 3.3 m (8.25 - 10.75 ft); 400 - 450 kg (880 - 990 lb).
This species lives around Antarctica. It is named after the Weddell Sea, a large bay in the Atlantic coast of Antarctica. Weddell seals are most often found occupying ice floes. They feed at night, hunting for squid and fish, and will even attack prey as large as the Antarctic toothfish, which grows to about 50 kg (110 lb).
This is the only one of 33 species of seal and sea lion that lives exclusively in fresh water. It has one of the most restricted distributions of all the pinnipeds, only being found in Lake Baikal in south-central Siberia.
In winter the lake is entirely covered in a thick layer of ice. During this period, the seals spend most of their time under the ice, coming up to breathe through access holes which they keep open by scratching with the claws on their front flippers and by abrading the edges with their teeth and heads.
The long whiskers are very sensitive to touch and are probably very important for locating prey in the dark conditions under the winter ice.
Baikal seals dive for about 25 minutes when foraging for fish, but can remain submerged for an hour if frightened. During the breeding season in May, successful males gain access to harems of several females. Mating occurs underwater, and the pups are born in late winter or early spring. Females construct a chamber in the snow, where they give birth to and suckle their young.
Distribution: Lake Baikal.
Habitat: Fresh water.
Food: Fish and aquatic invertebrates.
Size: 1.1 - 1.4 m (3.5 - 4.75 ft); 50 - 130 kg (110 - 260 lb).
Maturity: 6-7 years.
Breeding: Usually 1 pup, but occasionally twins.
Life span: 55 years.
Status: Near threatened.
Size: 1.3 - 1.5 m (4.25 - 5 ft); 55 kg (121 lb).
The Caspian seal lives in the Caspian Sea on the border of Europe and central Asia. It is one of only two seals to live in landlocked waters. Being a relatively small body of water, the Caspian Sea varies in temperature a great deal throughout the year. This variation impacts on the behaviour of the seals. In winter, when the northern part of the Caspian freezes, the seals live in large colonies on the ice. In summer, however, the ice melts and the seals migrate to the deeper water in the south, which remains cooler.
Caspian seals eat fish and crabs. Water pollution has killed much of the seals' food supply as well as making many seals infertile. As a result, Caspian seals are vulnerable. Hunting has also been a problem for the seals. For centuries the people have relied on the seals for oils, skins and meat.
Range: Arctic Ocean.
Habitat: Shallow waters; breeds on ice floes.
Size: 6 3/4 - 7 3/4 ft (2.1 - 2.4 m).
Numerous long bristles on the snout are the identifying feature of the bearded seal and the source of its common name. It is a robust, heavily built species, in which females are slightly longer than males. Bottom-dwelling invertebrates, such as crustaceans and mollusks, and fish are its main foods.
During the breeding season the males call underwater. The female gives birth to 1 pup each year from the age of about 6 years. The pup, which can swim immediately, suckles for between 12 and 18 days, during which time the female usually mates again.