Northern elephant seal - Mirounga angustirostris

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Northern elephant seals are huge and imposing. Significant sexual dimorphism exists in size and secondary sexual characteristics. In both sexes, the body is long and robust, and the neck very thick. The eyes are large, widely-spaced, and have a forward orientation that is especially noticeable in females and subadult males. The vibrissae are beaded, short to medium length, and black. In addition to the mystacial clusters, there are one to two vibrissae on the bridge of the nose, and several in prominent supra-orbital patches above and slightly behind each eye. Each fore flipper digit bears a large blackish-brown nail. The nails on the hind flippers rarely emerge, but there is a vestigial nail beneath a small opening located above the end of each hind flipper digit.

In females, young subadult males, and juveniles the head, muzzle, and lower jaw are all proportionately large and conspicuously broad. The mystacial area and nose are thick, full and rounded across the top, when viewed from the front. In profile, the bridge of the nose forms an arc ending in the terminally placed nostrils, and there is a downward droop to the end of the nose.

Adult males are unmistakable because of their great size, heavily scarred and cornified chest and neck, and large inflatable fleshy nose, called a proboscis. When relaxed, the proboscis hangs down in front of the mouth. When inflated, it resembles a foreshortened elephant trunk, thus the species' common name. The chest shield is made up of thickened, creased, hardened nearly hairless skin, and accumulated scars. Chest shield and neck become increasingly pink over large areas as the male ages. In old bulls the chest shield can completely ring the neck. Fighting, which occurs when bulls are ashore during the breeding season, adds more red coloration from raw open wounds and patches of dry crusted blood caked on the shield. Wounds and scars accumulate all over the back, sides, and head of males during their lives, and as these heal the scars are tan to lighter gray on the darker pelage. The proboscis can be left bloody, torn, and ragged from fighting, and is also often marked with pinkish skin and scars. As subadult males grow their proboscis lengthens so that it may extend 15-25 cm below the lower lip. A male ashore, asleep on his chest and chin, is readily identified as an older bull when his proboscis is long enough to touch the ground and be bent backwards or off to the side. In addition to their much longer and larger body size, males also have larger canines that are both considerably longer and thicker than those of adult females.

Northern elephant seal coloration varies from uniformly dark charcoal gray or dark brown to light gray or tan, with coloration fading as time progresses from the end of the last annual molt. With the exception of adult males, most northern elephant seals are lightly to moderately countershaded, being darker above and paler with a yellowish tinge below. Adult males are typically dark brown to charcoal overall, with the already noted coloration of chest shield, neck, proboscis and body scarring. Northern elephant seals are multicolored and ragged looking during their annual molt, when they shed their fur and epidermis together in patches, starting in the axillary region and progressing around the body. During this time they have varying amounts of darker more richly colored fur appearing as the faded duller fur is lost.

Pups are born in a long woolly black lanugo coat that is shed without the epidermis starting at about 3 weeks and usually lasting several weeks until after the pup is weaned. After molting, the newly weaned juvenile’s coat is made up of short hairs like those found on adults, and they are countershaded dark gray above and silver gray below.

Sexual dimorphism is significant in this species with males being three to four times heavier, and nearly 1.5 times the length of adult females. Adult males reach 4.2 m in length and a maximum weight of 2,500 kg. Mean length is 3.85 m and mean weight is 1,844 kg. Maximum weight is seen when the bulls are newly arrived for the breeding season after a summer and fall largely spent feeding. The mean length of adult females is 2.65 m, and they can reach a length of 2.82 m. Mean mass is 488 kg, with a maximum recorded of 710 kg, both values are from shortly after females give birth. Newborn pups are about 1.25 m long and weigh 30-40 kg.

Body weight fluctuates dramatically due to the demands of fasting during the breeding season. Adult females can lose almost half their mass during lactation, when they take their single pup from birth to weaning in approximately 28 days. The situation is similar for breeding males, which also lose about half their mass while ashore for periods that may exceed three months.

The dental formula is: I 2/1, C1/1, PC 5/5.

The great size of northern elephant seal bulls makes them virtually unmistakable. The massive head and the large fleshy proboscis are unique for animals within their range. Only one other phocid, the harbor seal, regularly shares the range of the northern elephant seal, and it is much smaller, being only as large as a juvenile northern elephant seal and has a spotted coat. Even female and subadult male elephant seals can be distinguished from other vagrant seals within their range by a combination of features including: large body size, large size and shape of the head and muzzle, pelage coloration and the lack of spots, blotches or bands of contrasting color, prominence and all black color of vibrissae, and the large size of the eyes.

Northern elephant seals are found in the eastern and north central North Pacific. Breeding takes place on offshore islands and at a few mainland localities from central Baja California to Northern California. Northern elephant seals migrate to and from their rookeries twice a year, returning once to breed from December to March, and again later for several weeks to molt, at different times depending on sex and age. They also show up at additional coastal sites as far north as southern Oregon for molting. Their post-breeding and post-molt migrations take most seals north and west to oceanic areas of the North Pacific and Gulf of Alaska twice a year. Adult males tend to travel further north and west than adult females. Wanderers have been found as far away as Japan and Midway Island.

Northern elephant seals are highly polygynous, but not territorial. Males compete for access to females by ranking themselves in a hierarchy. There is much male-male fighting, vocalizing, and displaying during the breeding season, when bulls may be ashore for months at a time. One of the most impressive displays occurs when a male rears up on his hindquarters, thrusts one half to two-thirds of his body upward, and produces a distinctive clap threat vocalization as a challenge to other bulls. The sound is a rolling, resonant, metallic-sounding series of backfire like sounds punctuated with pauses (it has been described as sounding like someone farting in a trash can).

Females give birth within a few days of coming ashore, from late December to March, and wean their pups in 28 days on average. Females have a throaty sputtering growl, made with the mouth wide open and used as threat gesture. Females and pups have a warbling scream call that they use to call to each other, and in the case of the pup, when disturbed. Mother and pup form a strong bond immediately after birth, and females aggressively bite other pups that approach them, occasionally killing them with bites to the head. Bulls also cause pup mortality by crushing them as they charge through aggregations of mothers and pups to chase off or fight males approaching females or challenging their status. Occasionally, they suffocate pups by stopping on top of them and not moving again soon enough.

Great white sharks and killer whales are predators on northern elephant seals. Recent work at the Farallon Islands off of central California has revealed that large great white sharks aggregate around the islands in the fall when juvenile elephant seals return for their annual molt. Seals that swim at or near the surface as they are approaching or departing the islands are particularly vulnerable to ambush attacks by fast-rising sharks that patrol near the bottom in seven to ten meter deep waters.

Northern elephant seals hold the record as the deepest-diving pinniped. Time-depth recording devices have documented dives to an astounding 1580 m by an adult male. They also have extreme breath holding ability and have been recorded to dive for as long as 77 minutes. Rest intervals at the surface are usually short, lasting only several minutes between routine dives that last 20-30 minutes and reach 300 to 800 m in depth. After leaving the rookeries, most of these seals spend 80-90% of their time underwater, helping explain why they are infrequently seen at sea.

Fifty-three species of prey have been identified in the diet of northern elephant seals. More than half of these species are squid. Other prey includes various fishes, such as Pacific whiting, several species of rock fish, and a variety of small sharks and rays. They have also been reported to feed on pelagic red crabs. The habitat of 70% of their prey is open ocean and included species from surface, mid and deep water zones.

The northern elephant seal was hunted to the brink of extinction in a surge of commercial exploitation in the late 1800s. Much speculation exists on the numbers of animals that survived this population bottleneck. Some estimates are as low as 50 animals or less. Fortunately, for the species, their pelagic nature and the fact that most seals spend 80% or more of their lives at sea, and that they all do all not return to their rookeries at the same time, ensured that enough seals were at sea to support continuation of the species when sealers undertook wholesale slaughters at rookery sites. Following a slow recovery in the early 1900s, northern elephant seals began to recolonize former sites throughout the 1980s, and the population was estimated to have reached more than 120,000 by 1991. The current estimate of 150,000 suggests that the population is continuing to increase, although there has not been a recent range-wide survey to confirm this figure.

Northern elephant seals are fully protected on their Mexican and US rookeries, and incidental take in fisheries is low. Most of the prey of the northern elephant seal is either of low commercial value or minimally harvested in fisheries. If the population continues to expand there will likely be new rookeries on mainland beaches, and there will be additional challenges to keep conflicts with humans and domestic animals to a minimum. The risk of transfer of diseases, such as morbillibivirus from domestic animals to northern elephant seals, is unknown.

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DeLong, R.L. and B.S. Stewart. 1991. Diving patterns of northern elephant seal bulls. Marine Mammal Science 7(4):369-384.

Deutsch, C.J., D.E. Crocker, D.P. Costa and B.J. Le Boeuf. 1994. Sex- and age-related variation in reproductive effort of northern elephant seals. pp. 169-210 in B.J. Le Bouef and R.M. Laws (eds.), Elephant seals, University of California Press.

Hindell, M.A. 2002. Elephant seals Mirounga angustirostris and M. leonina. pp. 370-373 in W.F. Perrin, B. Würsig and J.G.M. Thiewissen (eds.), Encyclopedia of marine mammals. Academic Press.

McGinnis, S.M. and R.J. Schusterman. 1981. Northern elephant seal-Mirounga angutirostris Gill, 1866. pp. 329-349 in S.H. Ridgway and R. Harrison (eds.), Handbook of marine mammals, Vol. 2: Seals. Academic Press.

Stewart, B.S., P.K. Yochem, H.R. Huber, R.L. DeLong, R.L. Jameson, W.J. Sydeman, S.G. Allen and B.J. Le Boeuf. 1994. History and present status of the northern elephant seal population. pp 29-48 in B.J. Le Bouef and R.M. Laws (eds.), Elephant seals, University of California Press.

Stewart, B.S. and H.R. Huber. 1993. Mirounga angustirostris. Mammalian Species No. 449:1-10, 4 figures. American Society of Mammalogists.

Stewart, B.S. and R.L. DeLong. 1995. Double migrations of the northern elephant seal, Mirounga angustirostris. Journal of Mammalogy 76(1):196-205.