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Mirounga angustirostrisnorthern elephant seal

By Karen Warburton

Geographic Range

Northern elephant seals are found in the coastal waters of the Pacific Ocean from the Gulf of Alaska down to Baja California. Foraging migrations by males and females are made seperately, two times yearly. Males journey north to the Aleutian Islands and the Gulf of Alaska. Females don't travel as far north, but instead migrate further west to more open ocean. The total linear distances migrated by these animals each year has been recorded at 21,000 km. Seals can be seen on shore most often from December through March, during the mating season and again beginning in April and continuing through August as they haul out for moulting. (Feldhamer, et al., 1999; Le Boeuf, et al., 2000; McConnaughey and McConnaughey, 1997; Reeves, et al., 1992)

Habitat

Northern elephant seals reside terrestrially on the sandy, rocky or muddy shores of the coastline, particularly on offshore islands. They typically aggregate in large groups while on land. These animals spend only 10% of their time on land, during reproduction and moulting. The other 90% is spent in the water, diving and foraging for food, and only 11% of this time in the water is spent at the surface. This means that an extraordinary 85-90% of their time is spent at sea and under water. These mammals can dive exceptionally deep, to 500 to 600 meters (almost 1 mile) on average and to record depths of over 1500 meters for extended periods of time (20 to 70 minutes). (Andrews, et al., 2000; Bonner, 1990; Davis, et al., 2001; Delong and Stewart, 1991; Lawlor, 1979; Le Boeuf, et al., 2000)

  • Range depth
    1000 (high) m
    3280.84 (high) ft
  • Average depth
    500-700 m
    ft

Physical Description

Northern elephant seals are generally brown in color, however there are variations to this coloration. Males are usually a darker brown, while females are a light tan color. Hair is reduced on adult males and females and is completely absent for a short time after moulting. Newborns have hair that is black in color until successfully weaned, when they shed their black coat and it is replaced by a lighter one. Countershading is a feature to all adults and newly weaned youngsters, displaying a darker color dorsally and a lighter color ventrally. They possess two, lobed hind flippers. Pinnae are absent, giving the ear the appearance of being flush with the skin. The most conspicuous feature to the male body is the inflated proboscis that adorns his face. This feature is absent in females and is larger than that of their slightly larger close relatives, southern elephant seals. Young males begin development of the proboscis at 2 years of age, but it is not fully developed until the animal reaches its 8th year of maturity. These mammals are among the largest of the group comprising aquatic carnivores in the Northern Hemisphere. Females typically weigh 600 to 900 kg and males, which outweigh females by 3 to 10 times, can top out at 2300 kg. Females reach a length of 3.1 m on average and males usually extend from 4.0 m to 5.0 m. Newborns typically weigh about 47 kg at birth. They weigh about 147 kg and measure about 1.5 m between 24 and 28 days old, when they are weaned. Teeth are dimorphic in the sexes with males having considerably enlarged canines that are used in fighting. (Bonner, 1990; Ingles, 1965; Le Boeuf, et al., 2000; McConnaughey and McConnaughey, 1997; Reeves, et al., 1992)

  • Sexual Dimorphism
  • male larger
  • sexes shaped differently
  • ornamentation
  • Range mass
    600 to 2300 kg
    1321.59 to 5066.08 lb
  • Range length
    3.0 to 5.0 m
    9.84 to 16.40 ft

Reproduction

There is a definitive hierarchy structure to the mating system of these animals because they are polygynous and they aggregate in colonies on land during the breeding season. Each dominant male controls access to mating opportunities with a group of females. Bonner (1990) calls this mating system "female defence polygyny". Less dominant males are restricted to the fringes of a colony and continually try to gain access to females, resulting in battles between males and aggressive charges by the dominant male. Sub-dominant males usually run away but occasionally a male will challenge the dominant male in an attempt to take over the harem. Females release an audible "bawling" sound when a non-dominant male tries to mate with her. This results in a defense attempt by the dominant bull, who chases the less dominant male away. Occasionally the less dominant male becomes defiant and this can result in spectacular displays of threats and sometimes violent fighting. When a male wants to mate, he throws a flipper over the side of a female, grips her neck in his teeth and begins copulation. Resistance by a female only results in the male moving his large and heavy body on top of the female so she is unable to move. Aggressive interactions among males often result in elephant seal pups being killed by trampling. (Bonner 1990) (Bonner, 1990)

Northern elephant seals haul out for birthing and breeding from December to March. The females come into heat only 19 days after giving birth. They remain receptive for about four days, during which mating occurs. Females become sexually mature at 2 years of age, but usually begin giving birth in the 4th year of life. Males are sexually mature at the age of 6 or 7, but only occasionally are allowed to mate before they reach the age of 9 or 10 because of the hierarchy system of mating exhibited by these animals. (Reeves, et al. 1992; Bonner 1990) These animals display a phenomenon in their development cycle called delayed implantation. Delayed implantation lasts for about 3 months, resulting in a total gestation time of nearly one year. This allows both birthing and mating to occur in the same time frame, during the short period of the year when these animals are aggregated in terrestrial colonies. Interestingly, the embryo is never actually implanted, by definition of most mammals. Instead, it attaches only outwardly to the uterine wall throughout its development. (Bonner 1990; Mathews 1952) (Bonner, 1990; Matthews, 1952; Reeves, et al., 1992)

  • Breeding interval
    Females may breed as often as once yearly.
  • Breeding season
    Breeding and birthing occurs from December to March.
  • Range number of offspring
    1 to 2
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    10 to 12 months
  • Range weaning age
    23 to 27 days
  • Range age at sexual or reproductive maturity (female)
    2 to 10 years
  • Average age at sexual or reproductive maturity (female)
    9 years
  • Range age at sexual or reproductive maturity (male)
    2 to 10 years
  • Average age at sexual or reproductive maturity (male)
    9 years

The pregnancy will ultimately last just under one year, as a result of delayed implantation. Parturition, which results in one offspring per year (although there have been occurrences of twins), will occur the following winter and lactation will follow for about 27 days before the pup is weaned. Pup weight gain during the period of lactation is phenomenal, the milk is extremely high in fat. During weaning the pup remains close to the mother until such a time that the mother leaves the pup behind to return to sea. Young pups left alone form groups or "pods", which remain on shore for up to 12 weeks without parental care. They learn to swim in the surf and eventually swim further out to sea for a short time to feed. An interesting phenomenon displayed by young male pups left to fend for themselves is that of "milk stealing". An attempt to nurse from lactating females still on the beach raising their young can give the successful pup a significant advantage in survival and higher ranking later on in his life by increasing his weight and overall health. (Bonner, 1990; Reeves, et al., 1992)

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

Lifespan/Longevity

Because these animals spend such an extraordinary amount of time in the water, there are many gaps in how much we know about them. It is difficult to discern lifespans of these animals and what might be defined as a "natural" cause of death. Estimates of survival of reproductive females is represented in percentages with the probability of survival decreasing with each year of life. In the first year of life, a female's chances of survival are 35%, at 2 years, 30%, and at 3 years, 20%. Adult males live an average of 11 to 13 years old. Young pups are quite vulnerable to death, particularly by predation and trampling. Trampling usually happens as a result of a large male defending its females, crushing the pup under his weight as he tries to quickly move toward an intruder. By some estimates as many as 10% of the young pup population may perish this way annually. (Bonner, 1990; Klimley, et al., 2001; Reeves, et al., 1992)

  • Range lifespan
    Status: wild
    18 (high) years
  • Average lifespan
    Status: wild
    9 years
  • Typical lifespan
    Status: wild
    13 (high) years
  • Average lifespan
    Status: wild
    6.5 years
  • Average lifespan
    Status: captivity
    15.0 years
    Max Planck Institute for Demographic Research

Behavior

Northern elephant seals are probably solitary in nature while in the water, but aggregate during mating season on the shore. They are on the move for most of their lives, migrating while foraging for food. A social hierarchy exists during mating season, but the males are less aggressive toward each other when they haul out for moulting. One of the most extraordinary features to these animals is their dive behavior during foraging migrations. The extended period of time in which these animals stay under water is not brought about by their ability to hold their breath. Air is dispelled from the lungs before these seals dive, and throughout the 20 to 70 minutes the animal is under water, the oxygen they require is obtained from their blood and tissues. Northern elephant seals possess blood that is rich with hemoglobin and tissues rich in myoglobin, thus increasing their oxygen storing abilities. Another feature of this diving behavior that has perplexed researchers is the lack of rest or sleep for such an extended period of time. Recordings have indicated that these animals conduct dive after dive, 24 hours a day, sometimes for months at a time. It is thought that the dive activity may be a form of sleeping for the seals because their metabolic rate is very low.

(Le Boeuf, et al. 2000; Bonner 1990) (Bonner, 1990; Le Boeuf, et al., 2000)

Communication and Perception

Food Habits

Northern elephant seals spend 90% of their lives in the water in order to feed. During their foraging migrations, they dive into the water repeatedly and continuously to find food, never stopping to rest or sleep for months at a time. Females and males feed separately from each other. Males travel north, remain closer to land, and tend to return to the same locations to feed year after year. Females migrate away from the land, west to the open ocean, and are less accurate in returning to the same places each year. Male foraging behavior is characterized by benthic dives to the sea floor. By contrast, females exhibit pelagic diving while foraging which is defined by a trip to the floor, a partial ascent, another trip to the floor, a partial ascent, etc. There is some speculation as to the reason why male size is so extreme in relation to female size and some suggestions indicate that food type may be a contributing factor. Males are more likely to eat food sources that are dense in mass such as sharks and skates, while females eat foods that are less dense such as squid. These differences in foods is a likely occurence to the different locales in which they are foraging. This resource partitioning is likely to be the result of differences in body size. Males are less vulnerable to predators and are thus safer foraging in areas with more predators. Females are more vulnerable to predators and thus must forage in areas with fewer predators.

While elephant seals are on land they are fasting. They go for extended periods of time without food while they are reproducing and moulting. During this time, all nutrition and energy is broken down from fat that is stored on their bodies as blubber. It is believed that these animals never drink water. Their source of water comes from food sources and broken down fats. In addition they have developed physiological methods to retain water, such as producing a concentrated urine. Another interesting phenomenon about these mammals is the behavior of eating stones before coming ashore. The true purpose of this behavior is not known. The stones are eliminated when they re-enter the water for migration, so it has been suggested that this phenomenon is in response to the long period of fasting.

Foods eaten include: cephalopods, skates, small sharks, and fish. (Bonner, 1990; Le Boeuf, et al., 2000)

  • Animal Foods
  • fish
  • mollusks

Predation

Northern elephant seals try to feed by diving deep when in the water because the animals that view them as prey typically feed near the surface. Females migrate to the open ocean to feed in order to avoid predators as much as possible. (Bonner, 1990; Le Boeuf, et al., 2000)

Ecosystem Roles

Northern elephant seals are important as predators on octopus, squid, small sharks, skates, and fish. In this way they impact the populations of these animals. They are also important as food for animals which prey on them, such as great white sharks and orcas. (Bonner, 1990; Le Boeuf, et al., 2000)

Economic Importance for Humans: Positive

Northern elephant seals are a huge attraction for tourists to the Año Nuevo State Reserve in California. Here visitors can watch these magnificent animals from a safe distance, during breeding season. Northern elephant seals were once hunted for their blubber, which was refined to use as oil.

Elephant seals are the only known animals capable of filling collapsed lungs. Their lungs collapse during dives. The surfactant/lubricant responsible for this ability is being researched at the Scripps Institute in San Diego for the potential benefit to premature humans with immature lungs.

Northern elephant seals have also been used in research related to the effect of weightlessness on bone density because they spend 90% of their time in a neutrally buoyant environment. NASA has used this research in their efforts to counteract the effect of weightlessnes on bone density in astronauts.

Because northern elephant seals can dive to extreme depths it has been suggested that they can greatly aid human efforts to explore and map the deep oceans once instruments that can withstand extreme pressures are developed. (Hill, 1996)

  • Positive Impacts
  • ecotourism
  • research and education

Economic Importance for Humans: Negative

Northern elephant seals may consume some fish and other prey that are important to the fishing industry. However, their impact is probably exaggerated.

Conservation Status

Northern elephant seals are not presently endangered. At one time, however, this species was thought to have been hunted to extinction. They were presume extinct by the 1880's, after being exploited by hunters and whalers seeking to use the animals' thick layer of blubber as an oil source. A few animals were then discovered in 1892 which were captured and killed for scientific study. Eventually, it was discovered that a population of about 20 to 100 individuals had survived. Studies have shown that all individuals of the current population, which has grown to over 175,000, are relatives of these few survivors. The population bottleneck that occurred during this time is of concern because genetic variation is reduced, creating the possibility for the population to be vulnerable to disease or reproductive failure. (Bonner, 1990; Weber, et al., 2000)

Contributors

Allison Poor (editor), University of Michigan-Ann Arbor.

Karen Warburton (author), Humboldt State University, Brian Arbogast (editor), Humboldt State University.

Glossary

Nearctic

living in the Nearctic biogeographic province, the northern part of the New World. This includes Greenland, the Canadian Arctic islands, and all of the North American as far south as the highlands of central Mexico.

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.

World Map

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.

colonial

used loosely to describe any group of organisms living together or in close proximity to each other - for example nesting shorebirds that live in large colonies. More specifically refers to a group of organisms in which members act as specialized subunits (a continuous, modular society) - as in clonal organisms.

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.

desert or dunes

in deserts low (less than 30 cm per year) and unpredictable rainfall results in landscapes dominated by plants and animals adapted to aridity. Vegetation is typically sparse, though spectacular blooms may occur following rain. Deserts can be cold or warm and daily temperates typically fluctuate. In dune areas vegetation is also sparse and conditions are dry. This is because sand does not hold water well so little is available to plants. In dunes near seas and oceans this is compounded by the influence of salt in the air and soil. Salt limits the ability of plants to take up water through their roots.

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

ecotourism

humans benefit economically by promoting tourism that focuses on the appreciation of natural areas or animals. Ecotourism implies that there are existing programs that profit from the appreciation of natural areas or animals.

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.

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).

migratory

makes seasonal movements between breeding and wintering grounds

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

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).

piscivore

an animal that mainly eats fish

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.

solitary

lives alone

tactile

uses touch to communicate

temperate

that region of the Earth between 23.5 degrees North and 60 degrees North (between the Tropic of Cancer and the Arctic Circle) and between 23.5 degrees South and 60 degrees South (between the Tropic of Capricorn and the Antarctic Circle).

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

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

Andrews, R., D. Costa, B. Le Boeuf, D. Jones. 2000. Breathing frequencies of northern elephant seals at sea and on land revealed by heart rate spectral analysis. Respiration Physiology, 123: 71-85.

Bonner, W. 1990. The Natural History of Seals. New York, NY: Facts On File, Inc..

Davis, R., L. Fuiman, T. Williams, B. Le Boeuf. 2001. Three-dimensional movements and swimming activity of a northern elephant seal. Comparative Biochemistry and Physiology Part A, 129: 759-770.

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

Feldhamer, G., L. Drickamer, S. Vessey, J. Merritt. 1999. Mammalogy: Adaptation, Diversity, and Ecology. Boston: McGraw Hill.

Hill, A. 1996. "Get Outside! the Bay Area...naturally" (On-line). Accessed November 11, 2001 at http://www.sfgate.com/getoutside/1996/feb96/elephantseals.html.

Ingles, L. 1965. Mammals of the Pacific States. Stanford, California: Stanford University Press.

Kastak, D., R. Schusterman. 1999. In-air and underwater hearing sensitivity of a northern elephant seal (*Mirounga angustirostris*). Canadian Journal of Zoology, 77 (11): 1751-1758.

Klimley, A., B. Le Boeuf, K. Cantara, J. Richert, S. Davis. 2001. Radio-acoustic positioning as a tool for studying sit-specific behavior of the white shark and other large marine species. Marine Biology, 138: 429-446.

Lawlor, T. 1979. Handbook to the Orders and Families of Living Mammals. Eureka, California: Mad River Press.

Le Boeuf, B., D. Crocker, D. Costa, S. Blackwell, P. Webb. 2000. Foraging ecology of northern elephant seals. Ecological Monographs, 70 (3): 353-382.

Matthews, L. 1952. Sea Elephant: The Life and Death of the Elephant Seal. London: MacGibbon & Kee.

McConnaughey, B., E. McConnaughey. 1997. Pacific Coast. New York: Alfred A. Knopf, Inc..

Reeves, R., B. Stewart, S. Leatherwood. 1992. The Sierra Club Handbook of Seals and Sirenians. San Francisco: Sierra Club Books.

Weber, D., B. Stewart, J. Garza, N. Lehman. 2000. An empirical genetic assessment of the severity of the northern elephant seal population bottleneck. Current Biology, 10: 1287-1290.

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