(Gill, 1866) - Northern elephant seal
Distinctive Characteristics
Northern elephant seals are huge and imposing. Significant sexual dimorphism exists in size and shape. In both sexes, the body is long and robust, and the neck very thick. The head, muzzle, and lower jaw are broad. The mystacial area and nose are fleshy and rather pointed on females and young subadult males. The eyes are very large, a feature that is noticeable in females and subadult males. The mystacial vibrissae are beaded, short, and black; they are accompanied by 1 or 2 nose or “rhinal” whiskers, as well as several prominent vibrissae above each eye.
Adult males are unmistakable, because of their great size and large, fleshy nose, called a proboscis. This proboscis is inflatable and, when relaxed, hangs down in front of the mouth. When inflated, it resembles the trunk of an elephant, thus the species' common name. Another feature of bulls is the chest shield, a thickened area of heavily scarred, creased and cornified skin, which on old bulls, completely rings the neck. Each foreflipper digit bears a large blackish brown nail.
Northern elephant seals are uniformly grey, tan, or brown; colour generally fades after the annual moult. Many bulls become pale in the face, proboscis, and head with increasing age; the chest shield and areas of the face and proboscis are often pink. Adults and subadults undergo an epidermal moult that usually starts in the axillary region and progresses around the body. Pups are born in a long woolly black lanugo that is shed at about 3 weeks of age to reveal a silver-grey coat, similar to that of adults.
The dental formula is I 2/1, C 1/1, PC 5/5.
Can be confused with
The great size and massive head and large fleshy proboscis of northern elephant seal bulls makes them virtually unmistakable. Only 1 other phocid, the harbour seal, regularly shares the range of the northern elephant seal, and is much smaller with a spotted coat. Even female and subadult male elephant seals can be distinguished from other vagrant seals within their range by body size, size and proportions of the head, pelage coloration, prominence and colour of vibrissae, and relative size of the eyes.
Size
Adult males reach almost 5 m in length and an estimated 1800 to 2200 kg; however, few have been weighed. Adult females are up to 3 m in length and 400 to 800 kg in weight. Newborn pups are about 1.2 m and 30 to 40 kg.
Geographical Distribution
The eastern and central North Pacific forms the range of the northern elephant seal. Breeding takes place on offshore islands and a few mainland localities from central Baja California to northern California. Nearly all seals migrate to and from their rookeries twice a year, once to breed (December to March) and later to moult (different times for each age/sex class). Post-breeding and post-moult migrations take most seals north and west to oceanic areas of the North Pacific and Gulf of Alaska. Wanderers have been found as far away as Japan and Midway Island.
Biology and Behaviour
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-to-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 some two-thirds of his body upward, and produces a distinctive threat vocalization as a challenge to other bulls. Females give birth within a few days of coming ashore, from late December to March.
Northern elephant seals hold the record as the deepest-diving pinniped. Time-depth recording devices haverecorded dives of an amazing 1580 m and 80 minutes. Rest intervals at the surface are very short, usually only a few minutes. After leaving the rookeries, most of these seals spend 80 to 90% of their time underwater, accounting for the fact that they are infrequently seen at sea. Prey consists mostly of squids, small sharks, and deep water fishes.
Exploitation
Intensive commercial sealing in the 19th Century greatly reduced the population and these seals have recovered in this century. Sealers were after the great volume of high quality oil that could be obtained from these seals, especially from the bulls. They were thought to be extinct by the turn of the century, but a small number survived the carnage and gave rise to the present burgeoning population.
IUCN Status
Insufficiently known. |
