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Elephant seals
 are large, oceangoing earless seals in the genus Mirounga. The two species, the northern elephant seal (M. angustirostris) and the southern elephant seal (M. leonina), were both hunted to the brink of extinction by the end of the 19th century, but numbers have since recovered.

The northern elephant seal, somewhat smaller than its southern relative, ranges over the Pacific coast of the U.S., Canada and Mexico. The most northerly breeding location on the Pacific Coast is at Race Rocks, at the southern tip of Vancouver Island in the Strait of Juan de Fuca. The southern elephant seal is found in the Southern Hemisphere on islands such as South Georgia and Macquarie Island, and on the coasts of New Zealand, South Africa, and Argentina in the Peninsula Valdés, which is the fourth-largest elephant seal colony in the world. Fossils of an as yet unnamed species of Mirounga have been found in South Africa, and dated to the Miocene epoch.

Elephant seals breed annually and are seemingly faithful to colonies that have established breeding areas.

Elephant seals take their name from the large proboscis of the adult male (bull), which resembles an elephant's trunk. The bull's proboscis is used in producing extraordinarily loud roaring noises, especially during the mating season. More importantly, however, the nose acts as a sort of rebreather, filled with cavities designed to reabsorb moisture from the animals' exhalations. This is important during the mating season when the seals do not leave the beach to feed, and must conserve body moisture as they have no incoming source of water. These animals are colossally large in comparison with other pinnipeds, with southern elephant seal bulls typically reaching a length of 16 ft (4.9 m) and a weight of 6,600 lb (3,000 kg), and are much larger than the cows, with some exceptionally large males reaching up to 20 ft (6.1 m) in length and tipping the scales at 8,800 lb (4,000 kg); cows typically measure about 10 ft (3.0 m) and 2,000 lb (910 kg). Northern elephant seal bulls reach a length of 14 to 16 ft (4.3 to 4.9 m) and the heaviest weigh about 5400 lbs (2455 kg).

Elephant seals spend upwards of 80% of their lives in the ocean. They can hold their breath for more than 100 minutes – longer than any other noncetacean mammal. Elephant seals dive to 1,550 m beneath the ocean's surface (the deepest recorded dive of an elephant seal is 2,388 m (7,835 ft) by a southern elephant seal). The average depth of their dives is about 300 to 600 m (980 to 1,970 ft), typically for around 20 minutes for females and 60 minutes for males, as they search for their favorite foods, which are skates, rays, squid, octopuses, eels, small sharks and large fish. Their stomachs also often contain gastroliths. While excellent swimmers, they are also capable of rapid movement on land.

Elephant seals are shielded from extreme cold by their blubber, more so than by fur. The animals' hair and outer layers of skin molt in large patches. The skin has to be regrown by blood vessels reaching through the blubber. When molting occurs, the seal is susceptible to the cold, and must rest on land, in a safe place called a "haul out". Northern males and young adults haul out during June to July to molt; northern females and immature seals during April to May.

Elephant seals have a very large volume of blood, allowing them to hold a large amount of oxygen for use when diving. They have large sinuses in their abdomens to hold blood and can also store oxygen in their muscles with increased myoglobin concentrations in muscle. In addition, they have a larger proportion of oxygen-carrying red blood cells. These adaptations allow elephant seals to dive to such depths and remain underwater for up to two hours.

Milk produced by elephant seals is remarkably high in milkfat compared to other mammals. After an initially lower state, it rises to over 50% milkfat (human breast milk is about 4% milkfat, and cow milk is about 3.5% milkfat).

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