There happens to be over thirty-five species of seals worldwide spanning three families, the Phocidae family, Odobenidae family, and the Otariidae family. The Phocidae family of seals are considered to be true seals whereas the fur seals and sea lions belong to the Otariidae family. The walrus is the only surviving species of the Odobenidae family. Seals that are in the order Pinnipedia have two distinctive groups, eared and earless.
The largest seal is the Elephant Seal weighing in at 4 tons and measuring up to 20 feet long. The Elephant Seal is split up in two species: The Northern Elephant Seal and the Southern Elephant Seal. The Northern Elephant Seal is found in the Pacific Ocean of the Northern Hemisphere and is smaller than the Southern Elephant Seal found in the Pacific Ocean of the Southern Hemisphere.
The smallest of the seal species is the Ringed Seal weigh only 140 pounds and measuring a mere 4 feet in length. They can be found around the Arctic Ocean.
Seals are designed to live most of their lives in the water. Their bodies are streamlined so their flippers can propel their bodies through the water with ease. Although they do spend most of their lives in the water, they are mammals. Their respiratory system is specially adapted to life in the water. They can go for 40 minutes, diving to depths of over 2,000 feet, before they must return to the surface for another breath. Because they are rather clumsy and tend to move too slowly on dry land, many seals only return to dry land, or packed ice in some cases, to breed, give birth, or simply to bask in the sun.
Seals can be found in the oceans of both hemispheres. Although some seal are known to be migratory, a few species of seal have been known to stay in one area. For example there are four true seal species that stay in the Antarctic. These are the Crabeater Seal, Leopard Seal, Ross Seal, and the Wendell Seal.
The social structure of seals varies from species to species. Some seal species are known for their monogamy where as other species are polygamous. There are even some seals that are solitary. Depending upon what type they are seems to determine how many different vocalizations they have. Solitary seals have 10 different vocalizations, polygamous seals have up to 35 different vocalizations, and seals that are monogamous only have one vocalization.
Male seals are called bulls and female seals are called cows. Cows reach sexual maturity between 3-4 years. When a cow becomes pregnant she will spend long periods of time at sea building up fat reserves. Seals have a long gestation period of 12-months and usually only have one pup. The cow's milk is 50 percent fat allowing the pup to grow by 3 pounds per day up until they are weaned at 3-weeks old. The natural life-span of a seal varies. Bulls can live anywhere from 20-30 years, whereas a cow can live 30-35 years.
Many seals have diet that consists of crustaceans, mollusks, octopus, squid, and a variety of fish. Many times this is determined by location and availability. Some scientist believe that some seals use sonar to aid in locating food, but that is still just a theory.
Seals have a few natural predators to watch out for. Some predators include polar bears, orcas (killer whales), sharks, wolves, and wolverines. However, humans are high on the list of predators for seals. In fact, due to humans there are approximately twenty-eight species of seals that are on the endangered list. Although seal hunting is outlawed in many countries, humans still continue to pollute the waters, take over their habitat and poach seals. If you are interested in adopting a seal, you can visit the Marine Mammal Center website. By doing so, you could help save an injured seal and help aid research in marine mammal diseases.