Origins and Discovery: Elephant seals were in California 100-130 thousand years ago (Miller, 1971), about the time of the beginning of the last glaciation. When the ice regressed the northern species became separated spatially from its southern hemisphere congener by about 8,000 km and there is no evidence of intermingling. The earliest reports of northern elephant seals in modern times was by sealers hunting them along the west coast of North America in the early 1800s, along with sea otters, whales and fur seals (Scammon, 1874). The population was decimated by hunting during the first three decades of the 19th century and the species was considered extinct at times during the latter part of the century. In 1892, the species was "rediscovered" at Isla de Guadalupe, Mexico (Townsend, 1912), and the population began a long period of recovery that continues today.
Nomenclature: The name for the genus, Mirounga, is from miouroung, an old Australian Aboriginal name for elephant seals. Macrorhinus, or big nose, would have been more appropriate and was proposed but an insect had priority. The species name, angustirostris, or narrow nose, was proposed to differentiate them from leonina in the Antarctic (Gill, 1866). Calling adult males "bulls" and adult females "cows" and newborns "pups" is the legacy of sealers, so too are the terms "rookeries" for breeding grounds and "harems" for groups of breeding females.
Order: Carnivora
Sub-order: Pinnipedia
Family: Phocidae
Genus: Mirounga
Size, shape and distinctive characteristics
Size and Shape: Elephant seals are the largest of the seals; the northern species is second in size to its southern relative. Elephant seals are extremely sexually dimorphic, fully grown adult males may be up to ten times larger than adult females. Adult males weighing 2300 kg have been recorded (Deutsch et al., 1990); most adult females have a post-partum mass ranging from 360 to 710 kg (Deutsch et al., 1994). Adult males have distinctive secondary sexual characteristics besides size that females lack - an enlarged proboscis and thick, ruddy, rugose skin on the sides and underside of the neck. The pelage is short and the color is brown, black, gray or silver depending on animal age and time of year. The body is fusiform and has been modified to reduce drag while moving in the water, e.g., the penis and mammary glands are internalized when not in use. At certain times of the year, body composition approaches 50% blubber.
Geographic Distribution: The northern elephant seal breeding range consists of 14 island and mainland rookeries with sandy beaches ranging from Isla de Guadalupe, Mexico, to Point Reyes, California (Condit et al., in press; Stewart et al., 1994). The feeding range extends throughout a large part of the northeastern Pacific from 40 to 60 ° N Latitude to 172.5 ° E Longitude. Males forage close to islands off the coast of Oregon, Washington and Alaska as far west as the Aleutian Islands; females forage in the open ocean (Le Boeuf et al., 2000).
Ecology and Behaviour
Ecology: The year of the elephant seal is divided into two terrestrial periods and two aquatic periods. Breeding occurs in winter from early December to mid-March. Breeding is followed by foraging at sea, then a return to the rookery to molt the pelage, which lasts a month, then a second foraging trip to sea before returning to the rookery to breed again. Adult females spend more time at sea foraging (10 months) than adult males (8 months).
Behavior and Breeding: Adult males arrive on the rookery a few weeks before pregnant females. They are belligerent and fight with each other to establish dominance. When females arrive and gather together in a harem, the most dominant bull aggressively prevents other males from gaining access to females. He monopolizes mating when the harem contains fewer than 100 females. If the harem exceeds this number he select an area of the harem that he prevents males from entering; this affords the males ranked immediately below him access to females. Access to females translates to mating when females come into estrus, which is what all the fighting and threat posturing is about. A few males dominate mating and mating success is directly related to social rank; a male may dominate breeding for four continuous years and sire up to 200 pups in a lifetime (Le Boeuf, 1974). Most males die before reaching breeding age; even some that live to breeding age and old age do not succeed in mating (Le Boeuf and Reiter, 1988). Studies of DNA analysis reveal a high and positive relationship between mating success and paternity (Hoelzel et al., 1999). Females give birth for the first time at 2-5 years of age. Within six days after arrival, a female gives birth, and then nurses her pup daily for about four weeks. She fasts throughout lactation never leaving the rookery until weaning her pup by embarking on the post-partum foraging trip. During the last few days of lactation, she copulates with one or more males (Le Boeuf et al., 1972).
Life History
Growth, Development and Longevity: Pups average 38 kg at birth and 132 kg at weaning; standard length increases from 1.24 m at birth to 1.45 m at weaning (Deutsch et al., 1994) Both sexes do not gain mass during the first year but the muscle/blubber ratio increases. Female growth approaches an asymptote at age 6. Females may give birth for the first time at age 2 but most do so at age 4; thereafter, females give birth annually until death. Some females live to more than 20 years of age. Males reach puberty at 5-6 years of age, at which time a growth spurt is observed, but few succeed in mating before age 8, the beginning of adulthood. The peak of life for males is 11 or 12 years of age, as reflected by dominance rank and mating success. At age 13, males are "over the hill", and prevented from entering harems, and none survive to age 14 (Le Boeuf and Reiter, 1988).
Foraging, migration and diet: Adult males migrate twice a year to focal foraging areas along the continental margin from coastal Oregon to southern Alaska to the western Aleutians, a maximum distance of over 5,000 km from rookeries in California. The direct route and diving pattern suggests little or no feeding en route but gorge feeding around the clock upon reaching their destination. In contrast, adult females range across a wider area of the northeastern Pacific exploiting patches of prey in the water column over deep water (Le Boeuf et al., 2000). Their diving pattern is consistent with feeding on vertically migrating prey in the deep scattering layer. Observations and prey remains from elephant seal stomachs show that they feed on a variety of epi- and mesopelagic, bioluminescent cephalopods, teleosts such as Pacific Hake, Merluccius productus, crustaceans, elasmobranchs, cyclostomes, and tunicates. Limited observations, combined with sex-specific diving records, suggest that females feed mainly on squids and Hake and males feed principally on benthic prey such as elasmobranchs and cyclostomes (Antonelis et al., 1987; Antonelis et al., 1994).
Predators: The principal predators of elephant seals, besides humans, are white sharks, Carcharodon carcharias, and killer whales, Orcinus orca. White shark predation on elephant seals of both sexes and all ages is well documented (Ainley et al., 1981; Klimley et al., 2001; Le Boeuf et al., 1982); killer whale predation has been observed but infrequently.
Growth, Development and Longevity: Pups average 38 kg at birth and 132 kg at weaning; standard length increases from 1.24 m at birth to 1.45 m at weaning (Deutsch et al., 1994) Both sexes do not gain mass during the first year but the muscle/blubber ratio increases. Female growth approaches an asymptote at age 6. Females may give birth for the first time at age 2 but most do so at age 4; thereafter, females give birth annually until death. Some females live to more than 20 years of age. Males reach puberty at 5-6 years of age, at which time a growth s
Diet
see above
Global Abundance
Population Trend and Abundance: The northern elephant seal population has made a remarkable recovery from near extinction in the late 1890s, a time when fewer than 30 seals may have lived and the entire population was restricted to a small volcanic island far off the coast of Mexico (Hoelzel et al., 1993). As the seals recovered, the breeding range first extended out from Isla de Guadalupe to islands near the coast of Baja California, Mexico, then north to the Channel Islands in southern California in the 1930s and to central California islands in the 1960s and 1970s. In 2009, there are four major rookeries in Mexico and 10 in California. Growth on the major rookeries in Mexico ceased in the early 1970s, at which time San Miguel and San Nicolas Islands in southern California became the major pup-producing rookeries. But by 2005, San Miguel became crowded and the seals colonized new rookeries at nearby Santa Rosa Island and along the mainland coast at Piedras Blancas. Although the population continues to grow, there are signs of slowing down. The growth rate of 3.8% per year from 1991 to 2005 was half that of the 8.9% per year observed from 1977 to 1991. It is estimated that 43,000 total pups were produced in 2005 and that 172,000 total northern elephant seals were living (Condit et al., in press; Stewart et al., 1994).
IUCN status
Least concern.
Genetic Diversity: Northern elephant seals are genetically depauperate (Bonnell and Selander, 1974). All measures of molecular genetic variation reveal such low levels that paternity analysis using DNA fingerprinting is not feasible. Genomic diversity was evidently reduced significantly because of one or more extreme population bottlenecks experienced as a result of hunting (Hoelzel, 1999; Hoelzel et al., 1993). The effect of low genetic variation on adaptability is not clear.
Burney Le Boeuf, University of California Santa Cruz leboeuf@ucsc.edu
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Mirounga angustirostris
