Last modified: Thursday September 24th, 1999

Antarctic seals


Weddell seal

Leptonychotes weddelli (Lesson, 1826)

Appearance

Males of this species are 250 cm long and females 260 cm. They can weigh upto 400 kg. Pups measure 120 cm and weigh 22-25 kg. This seal has a dark dorsal and is laterally and ventrally mottled. Pups are born with a grey to dark grey lanugo and moult after 6 weeks.

Distribution

This seal lives on fast ice close to land. They are found in a circumpolar distribution around the Antarctic Continent. Breeding areas are South Georgia, South Shetlands and South Orkneys.

Feeding

They feed on fish, primarily Dissostichus, Trematomus and Pleurogramma.

Population dynamics and life history

Females become mature when they are 3-6 years old and males when they are 7-8 years. They pregnancy rate is 70-80%. Gestation lasts 11 months, including a delay of implantation of 2 months. Longevity is 25 years. Male mortality is 30-50% and female mortality 13-18%.

Trophic relations

There is no obvious competition. Predators of the Weddell seal are the leopard seal, Hydrurga leptonyx, and the killer whale.

Interactions

None.

Population size

The total population is estimated to be larger than 750,000 seals.

Exploitation

There is no exploitation currently, although there has been some harvest for dog food. There are no regulation concerning possible harvests. These should be implemented, since harvest in the breeding area can be detrimental for the population.

Threats to the population

Currently none. Future mineral exploitations on the Antarctic Continent may have detrimental effects on the seals and the ecosystem.

References

Bonner, W.N. (1982)
Seals and Man. A study of interactions. University of Washington Press, Seattle, 170pp.
DeMaster, D.P. (1979)
Weddell Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 130-134
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Kooyman, G.L. (1981)
Weddell Seal Leptonychotes weddelli, Lesson, 1826. in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 2: Seals, pp. 275-296, Academic Press Inc., Ltd, London

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Ross seal

Ommatophoca rossi (Gray, 1844)

Appearance

Males are 168-208 cm long and weigh 129-216 kg. Females are 196-236 cm long and weigh 159-204 kg. Pups measure 105-120 cm and weigh 27 kg. The dorsal of these seals is dark to chestnut coloured with a silvery white ventral and dark striped from the chin to the chest, along the neck.

Distribution

The Ross seal is found along the Antarctic pack ice and near smooth floes. Its distribution is circumpolar, but it is most abundant in the Ross Sea and the King Haakon VII Sea.

Feeding

Squid makes up 47% of its diet, fish 34% and invertebrates 19%.

Population dynamics and life history

Only the age at maturity is known for this species: 3-4 years for females, 2-7 years for males.

Trophic relations

There are no likely competitors or predators, because of its isolated way of life.

Interactions

None.

Population size

The population is very difficult to estimate but is probably somewhere around 150,000-220,000.

Exploitation

This species is not exploited. It is protected under the Convention for the Conservation of Antarctic Seals.

Threats to the population

Currently none. Possible future mineral exploitation may have negative effects.

References

Bonner, W.N. (1982)
Seals and Man. A study of interactions. University of Washington Press, Seattle, 170pp.
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Laws, R.M., Hofman, R.J. (1979)
Ross Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 120-124
Ray, G.C. (1981)
Ross Seal Ommatophoca rossi, Gray, 1844. in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 2: Seals, pp. 237-260, Academic Press Inc., Ltd, London

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Crabeater seal

Lobodon carcinophagus (Hombron and Jacquinot, 1842)

Appearance

Males can be upto 257 cm long and weigh 224 kg. Females can be 262 cm long and weigh 227 kg. Pups are 120 cm at birth and weigh 20 kg. This seal has a uniform light grey coat. Pups are born with light gray lanugo. After moult they have a dark grey mottled coat. Crabeater seals have special premolars and molars which serve as a filter when feeding on krill.

Distribution

This seal has a circumpolar distribution and can be found near the Antarctic pack ice and broken "cake-type" ice. This seal is most abundant in the Ross Sea and West of Graham Land, in the Weddell Sea.

Feeding

The crabeater seal feeds predominantly on euphasiids. They fast for about one month. In the other 11 months they consume about 7% of their body weight of krill per day.

Population dynamics and life history

The crabeater seal becomes mature at 2-6 years of age. Gestation lasts 11 months, including a 2-3 month delay of implantation. Longevity is about 33 years. The overall mortality rate is 20%. For seals of 8 years and older this is 14.5%.

Trophic relations

The crabeater seal competes for food with the leopard seal, baleen whales, the Adelie penguin and other seabirds and fish. Leopard seals and killer whales are its main predators.

Interactions

Currently none. Future krill harvests will affect the crabeater seal, as it will the whole Antarctic ecosystem. Future mineral ansd oil exploitation can have negative effects on the seals and the ecosystem.

Population size

The total population is estimated at 15 million. In the Weddell Sea alone there are 9-11 million crabeater seals.

Exploitation

There is no commercial exploitation. Only a few seals are taken for dog food. There is no legislation concerning this species.

Threats to the population

None. Future krill exploitation will affect this seal and the rest of the Antarctic ecosystem.

References

Bonner, W.N. (1982)
Seals and Man. A study of interactions. University of Washington Press, Seattle, 170pp.
King, J.E. (1983)
Seals of the world, 2nd edition. British Museum (Natural History), London and Oxford University Press, Oxford, 240pp.
Kooyman, G.L. (1981)
Crabeater Seal, Lobodon carcinophagus (Hombron and Jacquinot, 1842). in: Ridgway, S.H. and Harrison, R.J. (eds.): Handbook of Marine Mammals, vol. 2: Seals, pp. 221-235, Academic Press Inc., Ltd, London
Laws, R.M. (1979)
Crabeater Seal. in: Mammals in the Seas, volume II: pinniped species summaries and report on sirenians. FAO Fisheries Series No. 5, Vol II, pp. 115-119

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