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 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. Correspondingly, there is a highly polygynous mating system, with a successful male able to impregnate up to 50 females in one season.
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[edit] Range and Habitat
The Northern Elephant Seal lives in the Eastern Pacific Ocean, migrating as far north as Alaska and 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. There are two places on the California coast where colonies can be legally observed including Ano Nuevo State Park. Recently increasing numbers have been observed in the Gulf of California.
[edit] 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.
[edit] 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 300 and 800 meters, and males can dive as deep as 1500 meters; moreover, the Northern elephant seal will generally not feed in depths of less than 200 meters (Condit, 1984).
Average dive times are correspondingly long, around 20 minutes (again less for females), and they require very little time on the surface between dives (about three minutes). The deepest dive records are surprisingly 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. 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," 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 Año Nuevo State Park and the Point Reyes National Seashore. However, observers must have a permit. This is because despite their ungainly appearance, bulls can move faster on land than a human being can run (for short distances). As generations of researchers have discovered the hard way, being charged by one is like being hit by a car; the elephant seal has no interest in attacking humans, but rather he is oblivious to an object blocking his attack on a male rival.
[edit] 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.
[edit] Opportunities to view the species
One elephant seal colony, about 7500 strong, makes a year-round home at Piedras Blancas, a short drive up the coast from San Simeon, California. Fenced observation areas give visitors a chance to get a safe, close-up view of the animals. A smaller colony of about 2000 exists at Ano Nuevo State Park, where guided walks take one within ten meters of elephant seals with no barriers. Docents are on hand at both locations to explain elephant seal behavior and the status of the local population. In the case of Ano Nuevo, most of the access is by a guided tour, where visitors will hike approximately one mile to visit the breeding areas. There is considerable on-going research being done on behavior of these animals, including significant amounts at UCSC.
[edit] References
- Seal Specialist Group (1996). Mirounga angustirostris. 2006 IUCN Red List of Threatened Species. IUCN 2006. Retrieved on 09 May 2006.
- Mirounga angustirostris (TSN 180672). Integrated Taxonomic Information System. Accessed on 18 March 2006.
[edit] Bibliography
- C.L. Ortiz, D. Costa and B.J. LeBoeuf, Water and energy flux in elephant seal pups fasting under natural conditons, 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
[edit] 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
- http://www.elephantseal.org/
- Elephant Seal Research Group - http://www.eleseal.it
