Seals is a common name for marine mammals, uniting representatives of two families: true and eared seals. Rather clumsy on land, they are excellent swimmers underwater. Their traditional habitat is coastal zones of southern and northern latitudes. The species of seals that exist in nature are very different, but at the same time, there are many similarities in their appearance, habits and lifestyle.
Origin of seals
It is known that the ancestors of pinnipeds once freely walked the earth. Later, perhaps due to the deterioration of climatic conditions, they were forced to sink into the water. At the same time, most likely, real and eared seals originated from different animals.
Scientists believe that the ancestors of the real, or ordinary, seal were creatures similar to otters that were found in the North Atlantic fifteen million years ago. The eared seal is more ancient - its ancestors, dog-like mammals, lived in the northern latitudes of the Pacific Ocean twenty-five million years ago.
Body differences
The unrelated origin of these two groups of seals is confirmed by a significant difference in the structure of their skeleton. Yes, common sealalmost helpless on land. On the shore, he lies on his stomach, his front flippers stick out on his sides, and when moving, his back flippers drag along the ground, like a fish tail. To move forward, the beast is forced to constantly bounce, moving its very heavy body.
The eared seal, unlike him, firmly rests on all four limbs. At the same time, its front flippers have sufficiently powerful muscles that allow it to withstand a fairly solid body weight, and the hind flippers do not drag behind, but are turned forward and located under the belly. Usually this animal goes "waddling", using all flippers in the process of walking, and if necessary, it can "waddle" at a very decent speed. So, a fur seal is able to run along a rocky shore even faster than a person.
How seals swim
The front flippers of true seals are much smaller than the back flippers. The latter are always stretched back and do not bend at the heel joint. They are unable to serve as a support when moving on land, but in the water the animal swims precisely thanks to them, making powerful strokes.
The eared seal moves differently in the water. He swims like a penguin, sweepingly working with his forelimbs. Its rear flippers only serve as a rudder.
General Description
Different types of seals differ significantly in length (from almost one and a half to six meters) and in body weight (males - from seventy kilograms to three tons). The largest among common seals are elephant seals, and the smallest are ringed seals. earedseals are usually not that big. The largest of them, the sea lion, can grow up to four meters and weigh a little over a ton. The smallest, Kerch fur seal, is a seal, weighing only about a hundred kg and reaching a length of one and a half meters. Seals have developed sexual dimorphism - their males significantly outnumber females in weight and body size.
The body shape of seals is ideally adapted to comfortable movement in the water. All of them have an elongated body, a long and flexible neck, a short but well-defined tail. The head is usually small, and the auricles are clearly visible only in otarid seals; in real ones, the hearing organs are small holes on the sides of the head.
All seals are united by the presence of a thick layer of subcutaneous fat, which allows them to retain heat well in cold water. Pups of many species are born covered with thick fur, which they wear for no more than three weeks (its color is usually white). The real seal (adult) has a coarse hairline that does not have a pronounced down, and the seals are completely devoid of it almost completely. As for eared seals, their downy down, on the contrary, can be quite dense, while fur seals retain a thick fur coat even in adulthood.
Lifestyle
Most seals live in coastal areas - where undercurrents from the bottom rise masses of water, teeming with microscopic creatures. There are a lot of small aquatic fauna in these places. She, in turn, is eaten by fish,which serve as food for seals.
This is a carnivore. The seal has a tooth structure similar to that of carnivorous mammals. He prefers to hunt by diving into the depths. In addition to fish, seals feed on crayfish, crabs, and cephalopods. The leopard seal sometimes attacks penguins and other smaller seals.
These creatures are perfectly adapted to low temperatures. They lead a predominantly aquatic lifestyle, getting out to land for sleep and during periods of molting and breeding. When a seal dives, its nostrils and auditory openings close tightly, preventing water from getting inside. Most seals have poor eyesight, but their eyes are adapted to observe movement in the water in low light.
Reproduction
During the breeding season, most species of true seals form pairs. Of these, only seals and long-snouted seals are polygamous. The female's pregnancy lasts from 280 to 350 days, after which one cub is born - already sighted and fully formed. The mother feeds him with fatty milk from several weeks to one month, stopping feeding already when the seal is still unable to get food on its own. Babies starve for a while, surviving on accumulated fat stores.
Due to the thick white fur covering the skin and almost invisible against the background of snow, the newborn seal was nicknamed "White". Seals, however, are not always born white: baby bearded seals, for example, are olive brown. As a rule, females try to hide babies in "burrows" made of snow between icyhummocks, which contributes to their better survival.
Eared seals during the breeding season gather in fairly large herds on secluded coastal areas and islands. The first to appear on the shore are males, who, trying to capture larger areas, arrange fights with each other. Then females appear on the rookery. After some time, each of them gives birth to a cub, and soon after that again mates with the male, who continues to guard his territory. The aggression of male eared seals fades with the end of the breeding season. Then these animals begin to spend more and more time in the water. In colder latitudes, they migrate to winter where it is a little warmer, and in more favorable conditions they can stay near their rookeries all year round.
The most famous species of true seals
In the family of real seals, according to various sources, it consists of eighteen to twenty-four species.
These include:
- monk seals (white-bellied, Hawaiian, Caribbean);
- seals (northern and southern);
- Ross seal;
- Weddell seal;
- crabeater seal;
- leopard seal;
- lahtak (sea hare);
- Khokhlacha;
- common and spotted seals;
- seals (Baikal, Caspian and ringed);
- long-faced seal;
- harp seal;
- lionfish (striped seal).
All types of seals of this family are represented in the fauna of Russia.
Earedseals
Modern fauna includes fourteen to fifteen species of eared seals. They are combined into two large groups (subfamilies).
The first group includes fur seals, including:
- northern (the only species of the same name);
- southern (South American, New Zealand, Galapagos, Kerguelen, Fernandes, Cape, Guadalupe, Subantarctic).
Second group formed by sea lions:
- sea lions (northern);
- California;
- Galapagos;
- Japanese;
- southern;
- Australian;
- New Zealand.
In the waters of Russia, seals of this family are represented by the sea lion and northern fur seal.
Protected seal species
As a result of active human intervention in the life of nature, many species of animals, including seals, are now on the verge of extinction.
Thus, several varieties of seals are listed in the Red Book of Russia at once. This is a sea lion that lives on the Kuril and Commander Islands and in the Kamchatka region. The spotted seal, or spotted seal, which lives in the Far East, is also called rare. Currently, the gray long-faced seal, or tevyak, is considered to be protected. It is found in the B altic Sea and on the Murmansk coast. The ringed seal, a valuable Far Eastern commercial seal, is on the verge of extinction.
The Red Book of Ukraine contains an entry about a monk seal. The conservation status of this species is listed as "lost". This isan exceptionally shy animal has a low reproductive potential and does not withstand the close presence of a person at all. Only about ten pairs of monk seals live in the Black Sea, and today their number in the world is no more than five hundred individuals.
Common seal
Common seal is quite widespread on the coasts of the northern seas of Europe. This species lives relatively sedentary, usually choosing rocky or sandy areas of the coastal zone, islets, shoals and spits in bays and estuaries. Its main food is fish, as well as aquatic invertebrates.
The cubs of these seals are usually born on the shore in May-July, and a few hours after birth they go into the water. They feed on mother's milk for about a month and manage to gain up to thirty kilograms on this nutritious diet. However, due to the fact that a large amount of heavy metals and pesticides get into the milk of a female seal due to the fish she eats, many cubs get sick and die.
Despite the fact that this species is not listed as protected, like the spotted seal or ringed seal, for example, it also requires careful treatment as its numbers are inexorably declining.
Crab-eating seal
The Antarctic crabeater seal is considered today the most numerous species of seal in the world. According to various estimates, its number reaches from seven to forty million individuals - this is four times more than the number of all other seals.
The size of adults is up to two and a half meters, they weigh two hundred to three hundred kilograms. Interestingly, the females of this species of seals are somewhat larger than the males. These animals live in the Southern Ocean, drifting near the coast in summer, and migrating north with the onset of autumn.
They feed mainly on krill (small Antarctic crustaceans), this is facilitated by the special structure of their jaws.
The main natural enemies of crabeater seals are the leopard seal and killer whale. The first poses a threat mainly to young and inexperienced animals. Seals escape from killer whales by jumping out of the water onto ice floes with incredible dexterity.
Leopard seal
This sea seal is not in vain the "namesake" of a formidable predator from the cat family. An insidious and ruthless hunter, he is not content only with fish: penguins, skuas, loons and other birds become his victims. Often he even attacks small seals.
The teeth of this animal are small, but very sharp and strong. There are known cases of attacks of sea leopards on humans. Like the "land" leopard, the marine predator has the same spotted skin: black spots are randomly scattered on a dark gray background.
Along with the killer whale, the leopard seal is considered one of the most important predators of the southern polar region. The seal, reaching more than three and a half meters in length and weighing more than four hundred and fifty kilograms, is able to move along the edge of drifting ice with amazing speed. It usually attacks its prey in the water.
The leopard seal is the only seal whose diet is based on warm-blooded creatures.
