Monday, November 28, 2011

Life of Northern Elephant Seal

Life of Sea | Northern Elephant Seal (Mirounga angustirostris) | The Northern elephant seal is one of the two species of elephant seal (the other is the Southern elephant seal). It is a member of the family Phocidae ("true seals"). Elephant seals get their name from their large size and large trunk of the man. The Northern elephant seal seal is the only mammal with a bi-annual migratory pattern. The first migration comes after winter breeding season, and the second after the summer moult. They are mostly underwater, diving to depths of about 1330-800 m for 20-30 minutes with only short breaks to the surface. They are rarely seen at sea for this reason. While on land, they prefer sandy beaches. Northern elephant seals can be found on the coast and offshore islands of California and Baja California. They migrate twice a year from California to Mexico and the men migrate to feeding grounds in the North Pacific Ocean, the Gulf of Alaska, and near the eastern Aleutian Islands.
Scientific classification
Kingdom:     Animalia
Phylum:     Chordata
Class:     Mammalia
Order:     Carnivora
Family:     Phocidae
Genus:     Mirounga
Species:     M. angustirostris

Northern elephant seals are characteristic long noses giving them their common name. Both adult and young elephants are bar-skin and black for the moult. After moulting they generally have a silver-gray to dark brown coat that fades to yellow and brown. Adult males have bare neck and chest mottled with pink, white and light brown. Pups are usually black at birth and molt into a silver-gray after weaning. The eyes are large, round and black. The width of the eyes and a high concentration of low light pigments suggests that the eye plays an important role in capturing the prey. Like all seals, elephant seals have shrunk back legs whose underdeveloped ends form the tail and tail fin.
The much larger Northern elephant seal males. The pectoral fins are rarely used while swimming. While the hind limbs are unsuitable for locomotion on land, sea elephants use their fins to support their body to drive. They are able to quickly propel themselves in this way for short-distance trips, returning to the water, catching up with a female or chase an intruder. Like other seals, elephant seals have adapted to the cold blood, in which a mixture of small veins surrounding arteries to absorb heat from them. This structure is present in the extremities, such as the hind legs.
The Northern elephant seal returns to its terrestrial breeding in December and January, with the bulls arriving first. The bulls usually attract insulated or otherwise protected beaches on islands or the mainland very remote locations. It is important that these beach areas, protection from the winter storms and high waves waves to offer. The bulls participating in battles of supremacy to determine which few bulls will result in a harem. Cephalopods are an important part of the Northern elephant seal diet. Other prey includes Pacific whiting, rays, sharks, and pelagic red crabs.Northern elephant seals prey by great white sharks, a major cause of mortality in young seals, and sometimes by orcas (killer whales).
After the male arrived to the beach, the females come to give birth. Females fast for 5 weeks and nurse their single pup for 4 weeks in the last few days of lactation, the females come in pairs and loops. However, dominant males often break off a mate to drive rivals. While the battles are usually not among the dead, they are brutal and often with considerable bloodshed and damage, but in many cases the wrong opponents, the younger, less capable males are simply chased away, often into upland dunes. The majority of copulations in a colony are made by only a few men with less than one third of the bulls to mate with a female. Pups are sometimes crushed in battle between bulls.
Once thought to be extinct from the commercial seal hunt in the 1800s, the population began to grow steadily in the early 1900s. Although a full population census of Northern elephant seal is not possible because all age classes are not ashore at the same time, the most recent estimate of the California breeding stock was approximately 124,000 people. Entanglement in marine debris, fisheries interactions, and ship collisions are their main threats.

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