Definitions

elephant seal

elephant seal

elephant seal or sea elephant, a true seal of the genus Mirounga. It is the largest of the fin-footed mammals, or pinnipeds, exceeding the walrus in size. There is a northern species, Mirounga angustirostris, along the Pacific coast, and a larger southern species, M. leonina, that breeds on sub-Antarctic islands. Males commonly reach a length of 18 ft (5.5 m) and a weight of 5,000 lb (2,270 kg); the female may measure 10 ft (3 m). A hollow, flabby snout about 15-18 in. (38-45 cm) long on the male gives these seals their name. During the 3-month breeding season the largest bulls stake out territories and try to attract and hold as many females as possible. When a bull is sexually excited or angry it snorts air from the proboscis into the throat, producing sounds heard miles away. Bulls do not eat during breeding, but females without pups feed on squid, fish, crabs, and other organisms that compose their main diet. These earless seals are graceful in water, diving to 2,275 ft (700 m) for food. Seal hunters, who extracted oil from blubber, pushed the northern species to the edge of extinction in the 19th cent. In 1911 the Mexican government extended protection to the single remaining M. angustirostris colony on Guadalupe Island off Baja California; the United States eventually followed suit. By the early 1990s an estimated 60,000 animals were found on island rookeries off Baja and central California. Elephant seals are classified in the phylum Chordata, subphylum Vertebrata, class Mammalia, order Carnivora, suborder Pinnipedia, family Phocidae.

See W. N. Bonner, Seals and Man (1982); B. LeBeouf, Elephant Seals (1985); F. Trillmich, ed., Pinnipeds and El Niño (1991).

Elephant seal bull (Mirounga)

Either of the two largest pinniped species: the northern elephant seal (Mirounga angustirostris), of coastal islands off California and Baja California, or the southern elephant seal (M. leonina), of sub-Antarctic regions. Both are gregarious earless seals. The male has an inflatable, trunklike snout. The northern species is yellowish or gray-brown, the southern species blue-gray. Males of both species reach a length of about 21 ft (6.5 m) and a weight of about 7,780 lbs (3,530 kg) and are much larger than the females. Elephant seals feed on fish and squid or other cephalopods. During the breeding season, bulls fight to establish territories along beaches and to acquire harems of up to 40 cows.

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The Northern Elephant Seal (Mirounga angustirostris) is one of two species of elephant seal (the other is the Southern Elephant Seal). It is a member of the Phocidae ("true seals") family. Elephant seals derive their name from their great size and from the male's large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating competition. There is a great sexual dimorphism in size, with the males (bulls) reaching five meters in length, much bigger than the females (cows), who average about three meters. The males average and , while the females average . Correspondingly, there is a highly polygynous mating system, with a successful male able to impregnate up to 50 females in one season.

Description

The southern elephant seal is slightly larger than the northern species. A northern elephant seal can grow long and weigh up to .

Range and habitat

The Northern Elephant Seal lives in the Eastern Pacific Ocean, migrating as far north as Alaska, British Columbia, and as far south as the shores of California and Baja California, where they come ashore to breed, give birth and molt, mostly on offshore islands. While the pelagic range covers an enormous span, there are only about seven principal breeding areas, four of which are on islands off the coast of California. Recently increasing numbers have been observed in the Gulf of California. Colonies can be observed at Año Nuevo State Reserve, Piedras Blancas Lighthouse, and Morro Bay State Park.

History and status

Beginning in the 1700s Northern elephant seals were hunted extensively almost to extinction by the end of the 19th century, being prized for oil that could be made from their blubber, and the population may have fallen as low as 100 to 1000. Finding refuge in Mexican waters, by the turn of the century, there was only a sole surviving rookery, on Guadalupe Island, Mexico; and this colony was granted protection by the Mexican government. Since the early 20th century, they have been protected by law in both Mexico and in the United States. Subsequently the U.S. protection was strengthened after passage of the Marine Mammal Protection Act, and numbers have now recovered to over 100,000.

Nevertheless, there is a genetic bottleneck in the existing population, which could make it more susceptible to disease and pollution. In California, the population is continuing to grow at around 25 percent per year, and new colonies are being established; they are now probably limited mostly by the availability of haulout space. However, numbers can be adversely affected by El Niño events and the resultant weather conditions, and the 1997-98 El Niño may have caused the loss of about 80 percent of that year's pups. Presently the Northern elephant seal is protected under the Federal Marine Mammal Act and under California law has a fully protected status.

Populations of rookery sites in California have exploded during the past half-century. At Año Nuevo State Park, for example, there were no individuals observed whatsoever until the 1950s; the first pup born there was observed in the early 1960s. Currently, thousands of pups are born every year at Año Nuevo, on both the island and mainland. The growth of the site near San Simeon has proved even more spectacular; there were no animals there prior to 1990. Currently, the San Simeon site hosts more breeding animals than Año Nuevo State Park during winter season.

Feeding and behavior

The Northern Elephant Seal feeds on a wide range of over 30 fish and cephalopods, including squid, octopus, hagfish, ratfish and small sharks. They are nocturnal deep pelagic feeders famous for the long time intervals they remain underwater (Morejohn, 1970). This species dives to great depths while feeding, typically between and , and males can dive as deep as ; moreover, the Northern elephant seal will generally not feed in depths of less than (Condit, 1984). Average dive times are correspondingly long, around 20 minutes for males, less for females, and they require about three minutes on the surface between dives. The deepest dive records are held by female elephant seals and is currently at 1603 meters (nearly a mile) with a time of 119 minutes. Typically this species is observed singly in its pelagic environment, although on land there may be thousands in almost tangent harems. Northern elephant seals, especially juveniles, are preyed on by great white sharks and sometimes also by orcas (killer whales). While at sea from late spring to early winter, the Northern elephant seal stores vast amounts of food as blubber and also water oxidatively produced in fat stores to prepare for his long fast on land (Ortiz, 1978).

In the summer, elephant seals undergo a "catastrophic moult" that lasts about one month, during which they lose much of their fur and skin. They spend this time on beaches to preserve body heat while they wait for the new fur to grow. During this time, elephant seals can be observed at a number of preserves on the California coastline, such as the Año Nuevo State Park and the Point Reyes National Seashore. Observers must have a permit and be very cautious because over short distances bulls can move faster on land than a person can run, despite their ungainly appearance. Elephant seals have no interest in attacking humans but are oblivious to objects blocking attacks on rival males.

Life cycle

The Northern elephant seal returns to its terrestrial breeding ground in December and January, with the bulls arriving first. The bulls haul out on isolated or otherwise protected beaches typically on islands or very remote mainland locations. It is important that these beach areas offer protection from the winter storms and high surf wave action (Riedman, 1982). The bulls engage in dramatic fights of supremacy to determine which few bulls will achieve a territory and harem. While fights are not usually to the death, they are brutal and often with significant bloodshed and injury; however, in many cases of mismatched opponents, the younger, less capable males are simply chased away, often to upland dunes, where they will rest up and contemplate their martial strategy for the next year.

After the males have secured their territorial position on the beach, the females arrive and somehow select an alpha bull for housekeeping. In this polygynous culture, a bull will typically have a harem of 30 to 100 cows. To assist him is the runner up in battle, the beta bull, who typically keeps watch at the perimeter of the harem for any belated challenges to the alpha bull's supremacy. In a lifetime an alpha bull could easily sire over 500 pups, whereas most bulls will never mate, due to the hierarchy established by combat. The lifetime reproduction potential of a female is about ten pups.

After arrival on shore males fast for three months, and females fast for five weeks during mating and nursing of her single pup. The gestation period is approximately eleven months. Pups nurse about four weeks and are weaned abruptly approximately two months before departing on their first journey to sea.

Notes

Footnotes

General references

  • Marine Mammal Center - Northern Elephant Seal
  • C.L. Ortiz, D. Costa and B.J. LeBoeuf, Water and energy flux in elephant seal pups fasting under natural conditions, Physiol. Zool. 51:166-178
  • California Wildlife, Volume III, Mammals, ed, by David C. Zeiner, William F. Laudenslayer and Kenneth E. Meyer, published by the California Department of Fish and Game, Apr., 1990.
  • G.V. Morejohn and D.M. Beltz, Contents of the Stomach of an Elephant Seal, J. Mammal 51:173-174
  • M.L. Riedman and B.J. LeBoeuf, Mother-pup separation and adoption in northern elephant seals, Behav. Ecol. Sociobiol. 11: 203-213
  • R. Condit and B.J.LeBoeuf, Feeding Habits and Feeding Grounds of the Northern elephant seal, J. Mammal, 65:281-290

External links

  • http://www.pinnipeds.org/species/nelephnt.htm
  • http://www.racerocks.com/racerock/eco/taxalab/ashleyc.htm
  • http://animaldiversity.ummz.umich.edu/site/accounts/information/Mirounga_angustirostris.html
  • http://ourworld.compuserve.com/homepages/jaap/elepseal.htm
  • http://essp.csumb.edu/eseal/noESlinks.html
  • http://www.elephantseal.org/
  • Elephant Seal Research Group - http://www.eleseal.it

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