Southern elephant seal
Introduction to Southern Elephant Seals
|Adult male southern elephant seal at
Royal Bay, South Georgia
The southern elephant seal (Mirounga leonina) is the world's largest seal and the largest member of the order Carnivora, which includes all seals, cats, dogs, foxes, wolves, bears, raccoons, hyenas, weasels and civets, among others. Southern elephant seals are "true"” or "earless" seals and are named for the male's trunk-like proboscis (nose) and for the seal's massive size. The species was hunted almost to extinction in the 19th and 20th centuries and, on South Georgia, their blubber was rendered into oil as late as 1964. Since that time, the southern elephant seal population has recovered to about 700,000 individuals, and sightings by travelers on TravelWild Expeditions voyages in the Southern Ocean are common.
Distribution and Migration of Southern Elephant Seals
The southern elephant seal spends most of the year at sea (9–10 months), migrating anywhere from sub-Antarctic waters to nearly as far north as the Tropic of Capricorn in search of food. Seasonal distribution is poorly known, but males are believed to forage in the waters close to the Antarctic continental shelf while females circulate farther into more distant open waters.
During the breeding season (August–November), individuals go ashore on the sub-Antarctic islands. Males arrive in late August to claim and fight for territory, and females arrive late September through early October, giving birth just after arrival. Southern elephant seals also go ashore and fast during the molting season, which lasts three to five weeks during January and February.
South Georgia is home to the largest population of southern elephant seals, hosting more than half of the world’s population. Other notable populations are found at Macquarie Island, Heard Island, the Falkland and the Kerguelen Islands, and at widespread islands near the Antarctic Peninsula. Elephant seals return annually to the same place for breeding, birthing and molting, and probably to the same hunting areas of the open ocean.
Identifying Southern Elephant Seals—Physical Characteristics
Southern elephant seals are enormous—the largest of all seals. Males can be over 20 feet (6m) long and weigh up to 8,800 pounds (4,000kg) or more. A species with extreme sexual dimorphism, males are typically five to six times larger than the females, who weigh 880–2,000 pounds (400–900kg). Males are fully grown by their eighth year.
|Bull elephant seal bellowing|
Southern elephant seals have large blocky heads, strong front flippers used to steer while they swim, and rear flippers used for propulsion. Complementing their tremendous bulk is the inflatable trunk-like proboscis of the bull. The southern elephant seal’s large eyes indicate that vision is important for hunting in the dark ocean depths.
When onshore, seals of all sexes and ages display a snotty-looking discharge from their noses (much to the chagrin of many photographers). This discharge is actually the method by which excess salt, from ingested seawater, is eliminated from their bodies. To avoid predation, young southern elephant seals have darker backs and lighter bellies. This allows camouflage by blending in with the lighter water when viewed from below and with the darker water when seen from above. Orcas and great white sharks are their principal predators—mostly preying on inexperienced young at sea.
Pups are born with dark brown-black fur that is not adapted for extended periods in the cold water. Most of the time pups stay on land in their black “lanugo” pelage, unless they are forced into the water. After weaning, the pup’s coat molts and the “weaner” starts to learn to swim and hunt. Young “weaners” are often mistaken by inexperienced nature travelers for other species of seals—mostly Weddell seals. Adult skin, after molting, is silvery-brown—but on land it is usually browner from staining by the mud and excrement that fills the “wallows” in which the seals often congregate while on the shore.
Southern elephant seals are closely related to northern elephant seals that look remarkably similar, although the northern is noticeably smaller. Northern elephant seals are found in the eastern Pacific along the west coast of North America from the Baja Peninsula to Alaska. Their range does not overlap with southern elephant seals.
Southern Elephant Seal Habitat
When going ashore to breed or molt, the southern elephant seal seeks rocky island shores and smooth sandy beaches. The rest of the year is spent entirely at sea replenishing their layer of blubber.
Southern Elephant Seal Breeding and Mating
Southern elephant seals give birth and breed September to November. The larger males arrive at the breeding beach a month before the females and the smaller/younger males in order to fight for dominance and the right to breed with a harem of females.
On shore, the males start to form beach colonies. The strongest bulls—the alpha males—establish harems of several dozen females, with the biggest males occupying the beach real estate most desirable for attracting females. Beta males have smaller harems. The least successful males have no harems, but may try to seduce another male’s females. An elephant seal must stay in his territory to defend it, which can mean fasting for up to three months, living off stored blubber. During this time the male can lose as much as 40% of his body weight. As the mating season progresses the biggest dominant bulls can acquire a harem of up to 50 females or more. Occasionally, the number of breeding females in a harem can exceed 100 seals.
|Male and female southern elephant seals:
Note size disparity
The amount of time spent ashore by males during the breeding season varies greatly; some breeding males spend more than 60–90 days on shore—the females spend 25–30 days.
The female gives birth 0–10 days after coming ashore and does not leave the beach to feed until her pup is weaned. During this time she depends on her stored fat reserves to sustain her and loses an average of 35% of her body weight, a weight loss of 17 lbs (8kg) per day.
Pups weigh about 88 pounds (40kg) at birth and reach 260–290 pounds (120–130kg) by the time they are weaned. The nursing period lasts an average of about 23 days and the pup puts on weight very quickly during this period as the mother’s milk contains as much as 52% fat. Pups can gain 7–9 pounds (3.5–4kg) per day. The mother mates up to 5 days before her pup is weaned and upon weaning she abandons her pup and returns to the sea. By this time, the pups have quadrupled their weight.
The pup leaves the beach about 3–8 weeks later to begin the process of learning to find food. Suitable food may not be located near its birth beach, so the pup relies on its stored body fat to get it through this lean time—an important aspect for its survival. The weaned size of pups is variable and some are three times the weight of others.
Many pups die on the crowded breeding beaches—some crushed by the giant males, others abandoned by their mothers.
Most females reach sexual maturity at 2–4 years of age. Males may reach sexual maturity at 3–6 years of age but few breed until 10 years of age.
Southern Elephant Seal Diet
Southern elephant seals feed exclusively at sea. The main sources of food are fish and squid. Prey is captured both near the surface and very deep underwater. The seals have been known to eat bottom dwelling fish from the ocean’s darkest depths. Southern elephant seals locate prey with their vision; their large eyes are an adaptation allowing them to take advantage of the bioluminescence of some prey. While they do not use echolocation, it is believed that their vibration-sensitive whiskers also aid them in locating prey.
Southern Elephant Seal Social Behavior
During the foraging months, southern elephant seals spend 90% of their time underwater, surfacing approximately every 20–30 minutes for a short rest of 2–3 minutes. They are swift and powerful swimmers and can dive further and longer than any other seal. A physiological adaptation allows them to store oxygen and simultaneously reduce its consumption while diving. They can lower their heart rate to as little as a single beat per minute. The recorded diving record for the seal is nearly two hours underwater and more than 4,200 feet (1,400m) in depth. At sea, they are usually solitary animals.
|Southern elephant seals swimming|
During breeding and molting, they are more social, gathering in large colonies along their natal beaches. Males defend their breeding territories through a series of specific behaviors. An interloper will vocally (their large proboscis amplifies their bellows) and physically challenge the alpha male, who in turn will rise up on its chest and respond in kind. If this does not drive away the challenger, vicious and bloody fights can break out, with the winner keeping or claiming the territory and local females as his own. Subordinate males will exhibit a flattened posture without inflating their proboscis when near another male’s harem to demonstrate that they are not a threat.
Colonies form again in January and February when the southern elephant seals go through a molting process of shedding their fur and the outer layer of skin. After three to five weeks, they grow new fur and return to the sea. Southern elephant seals are known to live up to 23 years.
For more information on Southern Elephant Seals
“Elephant Seals: Population Ecology, Behavior, and Physiology,” edited by Burney J. Le Boeuf and Richard M. Laws