Mirounga leoninasouthern elephant seal

Geographic Range

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. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Carroll, 2002; "Southern Elephant Seal (Sea Elephant)", 1997; Gaskin, 1972; Bradshaw, et al., 2003; Nowak, 2003; Rice, 1998; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

Habitat

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. ("Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Carroll, 2002; Gaskin, 1972; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

  • Range depth
    1500+ to surface m
    to ft
  • Average depth
    300-800 m
    ft

Physical Description

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. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; "Southern Elephant Seal", 2003; Anderson, 2003; Briggs and Morejohn, 1976; "Southern Elephant Seal (Sea Elephant)", 1997; "The Elephant Seals page", 2002; Gaskin, 1972; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002; Van Der Toorn, 1999)

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. ("Elephant Seals", 1983; Anderson, 2003; Briggs and Morejohn, 1976; "Southern Elephant Seal (Sea Elephant)", 1997; Gaskin, 1972; Nowak, 2003; "Southern Elephant Seal", 2001; Van Der Toorn, 1999)

  • Sexual Dimorphism
  • male larger
  • sexes shaped differently
  • ornamentation
  • Range mass
    300 to 4000 kg
    660.79 to 8810.57 lb
  • Average mass
    2000 (male) 500 (female) kg
    lb
  • Range length
    260 to 600 cm
    102.36 to 236.22 in
  • Average length
    500 (male) 300 (female) cm
    in

Reproduction

Male southern elephant seals arrive at breeding grounds several weeks before females and, through vocalizations, body positions, and occasional fighting, claim territories on the beach. The best and largest territories go to the largest and strongest males. These “alpha” males become the head of a harem when the females arrive, often mating with up to 60 females in their harem. If harems exceed this size, additional “beta” males may be present, each claiming as many females as they can. Females become a part of a harem simply through their position on the beach and may move from one harem to another incidentally.

In addition to their mating duties, alpha males are responsible for keeping unwanted males away from the harems. This is done through the same vocalizations and aggressive body postures that were used originally to claim their harem. Males must remain on their territory to defend it and, therefore, go for periods of months without eating. This, and the stress of aggressive encounters with other males and the energy expense of mating with multiple females, can take a significant toll on male physical condition. Only males in the best physical condition at the beginning of breeding season will successfully defend their territory and breed with multiple females. Subordinate males attempt to copulate with females on the edges of territories or in the surf as they leave the beach.

Females that were pregnant from the previous year’s mating give birth to one pup shortly after arriving on land. A period of lactation follows the birth. Then, several days before the pups are weaned from their mother’s milk, females enter estrus and mate with the alpha male or a successful beta male. Shortly following mating, males return to sea. Females return to the sea immediately after the pups are weaned. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Baldi, et al., 1996; Englehard, et al., 2002; "The Elephant Seals page", 2002; Galimberti, et al., 2003; Gaskin, 1972; Le Boeuf and Petrinovich, 1974; McCann, 1980; McCann, 1982; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

Once a year, from August to November, southern elephant seals return to land to breed. Amazingly, most return to the very same breeding grounds on which they were born. Five to seven days after pregnant females arrive on the beaches, they give birth to one pup. Occasionally twin pups are born but one typically dies soon afterwards. The mothers then nurse their young for about 23 days. Females may nurse longer if their energy reserves allow them to do so. During their time on the breeding grounds females eat little or not at all. Towards the end of this time, females enter estrus and mate with a male. Shortly after mating, females wean their young. At this point, they abandon their young and return to the ocean. Pups then forage on their own for several weeks before venturing out to sea in small groups. Female southern elephant seals typically reach sexual maturity by the age of 3 and participate in the annual breeding cycle by age 6. Males reach sexual maturity by age 5 or 6, but rarely are developed enough to compete for mates until they reach 10 to 12 years of age. The gestation period of female M. leonina is about eight months. There is a period of several weeks during late October when all mature females mate. In order to maintain the yearly birthing cycle with an eight-month gestation period, there is delayed implantation of the fertilized egg for about three months. After the three-month delay, the egg implants and begins to develop to become mature enough for birth during the next breeding season. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Englehard, et al., 2002; "The Elephant Seals page", 2002; Gaskin, 1972; Le Boeuf and Petrinovich, 1974; McCann, 1980; McConell, et al., 2002; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002; Van Der Toorn, 1999)

  • Breeding interval
    Southern elephant seals mate once each year.
  • Breeding season
    Breeding season lasts from August to November.
  • Range number of offspring
    1 to 2
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    9 to 7 months
  • Range weaning age
    20 to 35 days
  • Average weaning age
    23 days
  • Range time to independence
    20 to 25 days
  • Average time to independence
    23 days
  • Range age at sexual or reproductive maturity (female)
    2 to 4 years
  • Range age at sexual or reproductive maturity (male)
    5 to 6 years
  • Average age at sexual or reproductive maturity (male)
    6 years

Female southern elephant seals are the sole caregivers for their young from the moment of conception until weaning, a period that lasts around one year. After delayed implantation, which follows mating, the nine-month gestation period of the pregnancy begins. During this time, the pup develops inside the mother as she is diving and feeding in sub-Antarctic waters. Shortly after coming to land, females give birth to their pups, typically weighing between 25 and 50 kg at birth. Following birth, mothers bond vocally and through smell with their pup. For the next 20 to 25 days (sometimes as long as 35 days) mothers are responsible for providing milk and protecting pups. Mothers are typically less than one-meter from their pups during the stage of suckling, regardless of tide, the position in the harem, or the time in the breeding season. A pup might get separated from its mother due to male harassment and herding of females. This can result in an abandoned pup. Once a pup is separated from its mother the results are fatal. Alien suckling (nursing between unrelated cows and pups) isn't tolerated in this species. If an orphan pup attempts to steal milk from a sleeping or resting cow, it usually is bitten and will succumb to starvation or the effects of the bites. The most dire threat to young pups is adult males who crush pups as they travel and fight on beach territories. During lactation, mothers do not return to the water to feed and instead live on fat reserves built up during the previous foraging season. At weaning pups weigh from 120 to 130 kg, a weight gain of as much as 105 kg in a few weeks! ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Baldi, et al., 1996; Englehard, et al., 2002; "The Elephant Seals page", 2002; Gaskin, 1972; Hindell, et al., 1999; McCann, 1980; McCann, 1982; McConell, et al., 2002; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

Immediately following weaning, female southern elephant seals return to sea, leaving their pups alone on the beach. Eventually the pups begin to get hungry and find their way to the ocean, learning to feed and swim on their own. After weaning, there is no interaction between parents and pups. Approximately 30% of these pups will not live through their first year. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Baldi, et al., 1996; Englehard, et al., 2002; "The Elephant Seals page", 2002; Gaskin, 1972; Hindell, et al., 1999; McCann, 1980; McCann, 1982; McConell, et al., 2002; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

  • Parental Investment
  • no parental involvement
  • precocial
  • female parental care
  • pre-fertilization
    • protecting
      • female
  • pre-hatching/birth
    • provisioning
      • female
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female
    • protecting
      • female
  • pre-independence
    • provisioning
      • female
    • protecting
      • female

Lifespan/Longevity

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. ("Elephant Seals", 1983; "Southern Elephant Seal", 2003; Anderson, 2003; "Southern Elephant Seal", 2001)

Behavior

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. ("Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; "The Elephant Seals page", 2002; Galimberti, et al., 2003; Gaskin, 1972; McCann, 1980; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

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. ("Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; "The Elephant Seals page", 2002; Gaskin, 1972; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

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. ("Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; "Southern Elephant Seal (Sea Elephant)", 1997; "The Elephant Seals page", 2002; Gaskin, 1972; Nowak, 2003; Rice, 1998; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

Communication and Perception

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. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Southern Elephant Seal", 2003; Anderson, 2003; Gaskin, 1972; Nowak, 2003)

Food Habits

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. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Southern Elephant Seal", 2003; Anderson, 2003; "Southern Elephant Seal (Sea Elephant)", 1997; Bradshaw, et al., 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002; Slip, 1995)

  • Animal Foods
  • fish
  • mollusks
  • aquatic crustaceans

Predation

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. ("Elephant Seals", 1983; Gaskin, 1972; "Southern Elephant Seal", 2001)

  • Anti-predator Adaptations
  • cryptic

Ecosystem Roles

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. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Southern Elephant Seal", 2003; Anderson, 2003; "Southern Elephant Seal (Sea Elephant)", 1997; Gaskin, 1972; Bradshaw, et al., 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

Commensal/Parasitic Species

Economic Importance for Humans: Positive

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. ("Elephant Seal", 2002; "Elephant Seals", 1983; "Elephant Seals", 2002; Anderson, 2003; Nowak, 2003; "Southern Elephant Seal", 2001; Slip and Clippingdale, 2002)

  • Positive Impacts
  • body parts are source of valuable material
  • research and education

Economic Importance for Humans: Negative

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. ("Elephant Seals", 2002; Gaskin, 1972; Bradshaw, et al., 2003)

Conservation Status

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. ("Elephant Seal", 2002; Anderson, 2003; "Southern Elephant Seal (Sea Elephant)", 1997; Nowak, 2003; "Southern Elephant Seal", 2001)

Other Comments

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. (Le Boeuf and Petrinovich, 1974)

Contributors

Derek Block (earlier author), University of Wisconsin-Stevens Point, Chris Yahnke (editor), University of Wisconsin-Stevens Point, Nancy Shefferly (editor), Animal Diversity Web, Tanya Dewey (editor), Animal Diversity Web.

Philip Meyer (author), University of Michigan-Ann Arbor, Phil Myers (editor, instructor), Museum of Zoology, University of Michigan-Ann Arbor.

Glossary

Antarctica

lives on Antarctica, the southernmost continent which sits astride the southern pole.

Atlantic Ocean

the body of water between Africa, Europe, the southern ocean (above 60 degrees south latitude), and the western hemisphere. It is the second largest ocean in the world after the Pacific Ocean.

World Map

Pacific Ocean

body of water between the southern ocean (above 60 degrees south latitude), Australia, Asia, and the western hemisphere. This is the world's largest ocean, covering about 28% of the world's surface.

acoustic

uses sound to communicate

bilateral symmetry

having body symmetry such that the animal can be divided in one plane into two mirror-image halves. Animals with bilateral symmetry have dorsal and ventral sides, as well as anterior and posterior ends. Synapomorphy of the Bilateria.

carnivore

an animal that mainly eats meat

chemical

uses smells or other chemicals to communicate

coastal

the nearshore aquatic habitats near a coast, or shoreline.

cryptic

having markings, coloration, shapes, or other features that cause an animal to be camouflaged in its natural environment; being difficult to see or otherwise detect.

delayed implantation

in mammals, a condition in which a fertilized egg reaches the uterus but delays its implantation in the uterine lining, sometimes for several months.

diurnal
  1. active during the day, 2. lasting for one day.
dominance hierarchies

ranking system or pecking order among members of a long-term social group, where dominance status affects access to resources or mates

endothermic

animals that use metabolically generated heat to regulate body temperature independently of ambient temperature. Endothermy is a synapomorphy of the Mammalia, although it may have arisen in a (now extinct) synapsid ancestor; the fossil record does not distinguish these possibilities. Convergent in birds.

female parental care

parental care is carried out by females

fertilization

union of egg and spermatozoan

intertidal or littoral

the area of shoreline influenced mainly by the tides, between the highest and lowest reaches of the tide. An aquatic habitat.

iteroparous

offspring are produced in more than one group (litters, clutches, etc.) and across multiple seasons (or other periods hospitable to reproduction). Iteroparous animals must, by definition, survive over multiple seasons (or periodic condition changes).

molluscivore

eats mollusks, members of Phylum Mollusca

motile

having the capacity to move from one place to another.

natatorial

specialized for swimming

native range

the area in which the animal is naturally found, the region in which it is endemic.

nocturnal

active during the night

nomadic

generally wanders from place to place, usually within a well-defined range.

oceanic islands

islands that are not part of continental shelf areas, they are not, and have never been, connected to a continental land mass, most typically these are volcanic islands.

pelagic

An aquatic biome consisting of the open ocean, far from land, does not include sea bottom (benthic zone).

polar

the regions of the earth that surround the north and south poles, from the north pole to 60 degrees north and from the south pole to 60 degrees south.

polygynous

having more than one female as a mate at one time

saltwater or marine

mainly lives in oceans, seas, or other bodies of salt water.

seasonal breeding

breeding is confined to a particular season

sexual

reproduction that includes combining the genetic contribution of two individuals, a male and a female

sexual ornamentation

one of the sexes (usually males) has special physical structures used in courting the other sex or fighting the same sex. For example: antlers, elongated tails, special spurs.

social

associates with others of its species; forms social groups.

solitary

lives alone

tactile

uses touch to communicate

terrestrial

Living on the ground.

territorial

defends an area within the home range, occupied by a single animals or group of animals of the same species and held through overt defense, display, or advertisement

visual

uses sight to communicate

viviparous

reproduction in which fertilization and development take place within the female body and the developing embryo derives nourishment from the female.

young precocial

young are relatively well-developed when born

References

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