| Last modified: Thursday September 24th, 1999 |
Antarctic seals
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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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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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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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