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Leptonychotes weddelliiWeddell seal

By Omari J. Bayi

Geographic Range

Weddell seals are found throughout the Antarctic continent as well as on fifteen small neighboring islands (Stirling 1971).

Habitat

Leptonychotes weddellii live in Antarctic regions on fast ice areas and in the sea. They don't migrate and local movements are caused by changes in ice conditions. Underwater swimming occurs under natural ice cracks or under ice areas thin enough so that the seals can chew breathing holes using canine teeth. Ice areas where these seals dwell are usually flat icy plains (Stirling, 1970).

  • Terrestrial Biomes
  • icecap

Physical Description

Adult Weddell seals have a dark gray coat that is marked with black and lighter gray areas. Males are 2.5 to 2.9 meter in length and females reach up to 3.5 meters. They weigh between 400 and 600 kg.

  • Sexual Dimorphism
  • female larger
  • Range mass
    400 to 600 kg
    881.06 to 1321.59 lb
  • Range length
    2.5 to 3.5 m
    8.20 to 11.48 ft

Reproduction

Reproductive behavior occurs underwater. The female is mounted by the male from behind while her sides are held by his foreflippers. Quite often she is bitten on her neck while copulation occurs. Male-male fighting occurs, which suggests that mating systems are polygynous.

From mid-September to late December active spermatogenesis occurs. In late November to mid-December females are impregnated and about mid-January implantation occurs (Stirling 1971). Gestation last 9 to 10 months. Young pups are born with their permanent dentition. Birth occurs onto the sea ice, which often results in a change of external temperature in newborn pups. Pups are usually born singly, and the time of birth usually varies with latitude from early September at latitude 60 degrees south to late October at latitude 78 degrees south (Stirling 1971). Weddell seal pups weigh about 29 kg at birth. They have a gray lanugo, which after 3 to 4 weeks turns to a dark coat. Weaning takes place at 6 weeks of age and maturity at 3 years. First breeding of females may be denied for 1 or 2 years under some population conditions and males usually don't mate until 6 to 8 years of age because of social pressures (Stirling 1971).

  • Breeding season
    In late November to mid-December females are impregnated and about mid-January implantation occurs.
  • Average number of offspring
    1
  • Average number of offspring
    1
    AnAge
  • Range gestation period
    9 to 10 months
  • Average weaning age
    6 weeks
  • Average time to independence
    6 weeks
  • Range age at sexual or reproductive maturity (female)
    3 to 5 years
  • Range age at sexual or reproductive maturity (male)
    6 to 8 years
  • Parental Investment
  • precocial
  • pre-fertilization
    • provisioning
  • pre-hatching/birth
    • protecting
      • female
  • pre-weaning/fledging
    • provisioning
      • female

Behavior

The majority of the behavior occurs under water during the night. Weddell seals move in slow humping motion on land as well as on ice. They swim at a speed of about 5 to 7 knots, using their fore and hind flippers. Diving has been measured at depths of 600 m, and they can remain under for up to an hour (Stirling 1971). Drinking sea water as well as eating snow helps this seal meet its water consumption requirements. Eating occurs underwater. Fighting consists of continual chest contact, but is ceased when striking of chest, neck, or other areas occurs. Weddell seals sleep in the same position on the stomach or back for hours, but lying on their sides is most common. To maximize the sun's thermal benefits, seals often lie perpendicular to the sun (Stirling 1971). Play fighting occurs commonly with subadults. The nails of the foreflipper are used for grooming the head, neck, upper sides, and chest. Other areas are groomed by rubbing back and forth against the ice.

Communication and Perception

The eyes of Leptonychotes weddellii are well developed for low light visibility. This is an adaptive feature of this creature which assists it in locating breathing holes in the ice (Stirling 1971). Vocalization occurs underwater for communication. Overlapped calls are longer than solitary calls, which constitute the varied repertoire of vocal communication in the Weddell seal (Terhume 1994).

Food Habits

The diet of Leptonychotes weddellii consists of notothenid fishes, squids, and crustaceans, although they have been witnessed attacking Dissostichus mawsoni (Antarctic toothfish) as large as 54 kg in weight (Stirling 1971). These seals can dive up to 600 meters in search of food and are stealthy hunters, able to sneak attack fish from close range. They also use a method of disturbing fish from ice cracks by blowing bubbles into them and preying on the fish that emerge.

  • Animal Foods
  • fish
  • mollusks

Predation

Weddell's seals can be preyed on by orcas (Orca orcinus) or, occasionally, leopard seals (Hydrurga leptonyx).

Ecosystem Roles

These seals are heavily infested with worms and often reguritate them as a means of expulsion. The louse, Antarctophthirus ogmorhini, attacks the hind quarters as well as the penile orifice of these seals. Lice also infest subadults.

Commensal/Parasitic Species

Economic Importance for Humans: Positive

Leptonychotes weddellii are often killed and used as dog food. Their dead bodies are also of benefit to those studying worms and parasite infestation since these occur so often in this species. Study of their vocal abilities has advanced our attempt to communicate with animals, similar to the vocal communication studies performed with dolphins (Terhune 1994).

Conservation Status

Other Comments

These seals are named after Sir James Weddell, commander of British sealing expeditions into the sea which is also named after him, the Weddell Sea.

Contributors

Omari J. Bayi (author), 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.

World Map

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.

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.

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.

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.

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).

piscivore

an animal that mainly eats fish

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

solitary

lives alone

tactile

uses touch to communicate

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

Stirling, I. 1971. Leptonychotes weddelli. Mammalian Species. No. 6. The American Society of Mammalogists.

Terhune, J. M. 1994. Bioacoustics. Vol. 5. pp. 223-6. The International Journal of Animal Sound and its Recording. Great Britian.

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