Mirounga leonina
southern elephant seal

Mirounga leonina (southern elephant seals) are found along the coast of Antarctica and on sub-Antarctic islands when breeding or molting. However, before human exploitation they were more common farther north. The largest present population occurs on the island of South Georgia, in the South Atlantic Ocean. Southern elephant seals are also common on Macquarie Island, Heard Island, Kerguelen Island, and the Peninsula Valdez in Argentina. When at sea, M. leonina often journey thousands of miles from their breeding grounds. Despite the occasional sighting, not much is known about their range outside of the breeding season. ()

When southern elephant seals are on land, they are typically found along the coast of sub-Antarctic islands on smooth beaches of sand or small rocks. Although they used to breed well into temperate regions, M. leonina are now only found farther south. They are found on land during the breeding season, from August to November, and the molting season, which lasts 3 to 5 weeks in the spring. The rest of the year is spent entirely at sea. During this time they can be found from sub-Antarctic waters to almost as far north as the equator, often venturing thousands of kilometers from their breeding grounds. While males typically forage on the Antarctic continental shelf, females travel farther into open waters. During their time at sea, southern elephant seals can sustain dives for up to two hours, but most dives last only around thirty minutes. Amazingly, they only spend 2 to 3 minutes on the surface between dives. During most trips at sea, they are underwater for 90% of the time, day and night. While most dives are only between 300 and 800 m, dives of over 1500 m have been recorded, nearing depths only surpassed in mammals by sperm whales. ()

Male southern elephant seals are the largest pinnipeds, larger even than northern elephant seals, Mirounga angustirostris, their closest relatives. Mirounga leonina males have been documented reaching over six meters long and weighing over 4000 kg. This is in sharp contrast to females, which are rarely over 800 kg or four meters long. In fact, both species of the genus Mirounga are more sexually dimorphic than any other mammal. This dimorphism stretches beyond just size. Males also have a large, inflatable proboscis, which enhances vocalizations used to challenge other males for mating rights. The southern elephant seal proboscis is slightly smaller than the proboscis of northern elephant seals, overhanging the mouth by only about 10 centimeters compared to 30 centimeters in their northern relatives.

Breeding populations vary in size. In the South Georgian population, males average 450 cm in length and weigh 4,000 kg. Females average 280 cm and weigh 900 kg. The seals from Macquarie Island population are somewhat smaller, with males averaging 420 cm in length and 3,000 kg and females averaging 260 cm and 400 kg. ()

Despite the large difference in size, male and female southern elephant seals do share many physical traits. They have a similar body type. This includes short front flippers used primarily for steering in the water, and very strong, fully webbed, rear flippers that can propel them through the water with remarkable speed and agility. They also have a layer of short, stiff hair covering their bodies. At birth this fur is very dark in color, but lightens after the first molt. New fur after a molt is typically a dark gray/brown with lighter underside and lightens over the course of the year. It is also common for the bodies of both sexes to have scars, usually around the neck, from fighting and mating. ()

There is little known about lifespan in southern elephant seals. This is largely due to the lack of substantial information concerning the periods of the year when they are at sea. Average life expectancy in the wild, as seen during the breeding season, is about 23 years. However, about 30% of pups die in their first year. Captive M. leonina have lived to 15 years of age. Not much is known concerning the deaths of these mammals but, in addition to predation, weather and disease may play a large role in limiting their lifespan. ()

Southern elephant seals have both solitary and social seasons. During breeding and molting, large colonies gather along the same beaches where they were born. Alpha males defend breeding territories in these colonies through a series of specific behaviors. First the outsider vocally challenges the alpha male. The alpha male rises up on his rear fins and responds in kind. If this does not scare off the challenger, vicious fights can break out with the winner claiming the territory as his own. Colonies reform in the spring when M. leonina go through a molting process that involves the shedding of all fur and the outer layer of skin. In the next 3 to 5 weeks they grow new fur and return to the ocean. ()

Other than the time spent on land for breeding and molting, southern elephant seals live a solitary life in the waters of the southern oceans. Their time at sea is spent diving for food to replenish their weight lost during fasts when on land. Dives occur all day long, with perhaps some times spent resting. Mirounga leonina are amazing divers and will usually spend at least thirty minutes underwater, come up for a brief two-minute period, and then return underwater for another thirty minutes. Some dives can reach depths of over 1500 m and can last well over an hour. Some researchers think they may enter a sleep-like state when diving. Not very much is known about the habits of foraging southern elephant seals due to the solitary nature and the extreme depths to which they dive. ()

Home Range

Mirounga leonina remain on small portions of breeding beaches the entire time they are on land. It is unknown whether they maintain home ranges while foraging at sea. ()

When at sea, Mirounga leonina rarely encounter each other and thus have no need for communication. The only time communication is used is during breeding. Males use their large proboscis as a sound chamber for amplifying their bellows. These sounds are made to establish territories and challenge males for established harems. Upright posturing often accompanies these vocalizations and males are known to visually assess their competitor before fighting. Lesser males will also exhibit a flattened posture without inflating their proboscis when near another male’s harem to demonstrate that they are not threats.

A threat vocalization is a low-pitched harsh vocalization. While the seal is doing this it will raise its head and forequarters off of the ground, supporting itself without fore flippers. A lunge from an animal is a rapid movement of the head towards an opponent or invader. This is done with an open mouth. A high rear is the raising of the front half of the body then delivering blows to another animal with the neck or chin. A bite may also be used, mainly from a low rear or a high rear position.

Females are known to communicate with newborn pups through vocalizations. Females and pups recognize each other through these vocal cues and through their individual smells. ()

Southern elephant seals feed exclusively when they are at sea. For this reason not much is known about what they eat. The main known sources of food are squid, crabs, shrimp, fish, and sharks. This prey is obtained both near the surface and also during very deep dives. They have been known to eat bottom dwelling fish. ()

Knowledge of predation of M. leonina is limited due to their deep ocean habitat. Known predators include large sharks, specifically great white sharks, and killer whales. Leopard seals are also known to prey on pups. In order to avoid predation, southern elephant seals have dark dorsal surfaces with lighter undersides. This allows some camouflage by blending in with the lighter water when viewed from below and the darker water when seen from above. ()

Not much is known of the roles of southern elephant seals while they are at sea. However, they are known to be important to their ecosystem as predators of fish, sharks, squid, crabs, and shrimp and as prey for large sharks, killer whales, and leopard seals. Another important role they play in the ecosystem is as a host for many kinds of parasites. Some of the known parasites include tapeworms, acanthocephalans, and the louse Lepidophthirus macrorhini. ()

Southern elephant seals may occasionally compete with some fisheries, but this is unlikely. Southern elephant seals live in remote regions where they have few interactions with humans. ()

In the past, southern elephant seals were hunted for their blubber that was boiled down into oil. A typical male could produce about 350 liters of oil. Some aboriginal people also hunted them for food and skins. This activity has ceased and killing is now controlled by the Convention for the Conservation of Antarctic Seals. The only use of M. leonina to man today is for purely scientific purposes. ()

Although once hunted by humans, southern elephant seals were never near extinction like northern elephant seals. This is largely because most of the breeding grounds of M. leonina were out of reach of hunting boats. Hunting did have some impact, but numbers have recovered since hunting has ceased. Some populations are are experiencing declines. This may be normal population fluctuations, however. ()

During the Quaternary, it is thought that elephant seals spread north across the equator from the southern oceans. However, as ice ages ended, northern populations were separated from southern populations. The rewarming of the ocean waters forced both populations in different directions. Now these two populations have been separated by 8,000 km for thousands of years, forming two different species; M. angustirostris, northern elephant seals, and southern elephant seals, M. leonina. ()