Northern Elephant Seal
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| Missing image Northern_Elephant_Seal.jpg Northern Elephant Seal | ||||||||||||||
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| Mirounga angustirostris (Gill, 1866) |
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 get their name from their great size (the Southern Elephant Seal is the larger of the two species) and the fact that the adult males have a large proboscis, which is used in making extraordinarily loud roaring noises, especially during the mating season. There is a great sexual dimorphism in size, with the males, reaching 5m in length, very much bigger than the females (they are called bulls and cows), who average about 3m. Correspondingly, there is a highly polygynous mating system, with a successful male able to impregnate up to 50 females in one season.
The Northern Elephant Seal lives in the Eastern Pacific Ocean, migrating between northern waters as far north as Alaska and the shores of California and Baja California, where they come ashore to breed, give birth and moult, mostly on offshore islands. There are a number of places on the Californian coast where colonies can be observed. Recently increasing numbers have been observed in the Gulf of California.
Northern Elephant Seals were hunted almost to extinction in the 19th century (they were prized for the oil that could be made from their blubber), and it is thought that the population numbers may have fallen as low as 100 to 1,000, finding refuge in Mexican waters. By the turn of the century, they had just one surviving rookery, on Guadalupe Island, Mexico, and this was granted protection by the Mexican government. Since the early 20th century, they have been protected by law in both Mexico and the United States, and numbers have now recovered to (it is thought) 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. Numbers can however be badly affected by El Niņo events and the resultant weather conditions, and the 1997-98 El Niņo is thought to have caused the loss of about 80 percent of pups born that year.
The Northern Elephant Seal feeds on a range of fish and cephalopods, including squid, octopus, hagfish, ratfish and small sharks. Much of their prey comes from deep water, and the seals are famous for the very long periods of time they can stay underwater. They dive to great depths while feeding, typically between 300 and 800m (females, which are smaller, do not usually go to the very greatest depths), and they can dive as deep as 1500m. Average dive times are correspondingly long, around 20 minutes (again a little less for females), and they require very little time on the surface between dives (about 3 minutes). The deepest dives are over 1,500m deep and can last up to 2 hours.
Northern elephant seals, especially juveniles, are preyed on by great white sharks and sometimes also by orcas.
In the summer, elephant seals undergo a "catastrophic moult," lasting 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, for example the Aņo Nuevo State Park and the Point Reyes National Seashore. However, observers must have a permit. This is because despite their ungainly appearance, elephant seals can move faster on land than a human being can run. As generations of researchers have discovered the hard way, being charged by one is like being hit by a small car.
External links
- http://www.sealexperience.com
- 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