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5.4 Seals
Sub-Antarctic and Antarctic seals have adapted to their habitat, allowing them to hold their breath and swim under water for much longer periods than we can.
Weddell seal pup
Photo: S. Wickes
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Have students weigh themselves and work out how many individuals are needed to equal the weight of each seal. The students could also measure their height and compare the length of children to each type of seal. The male elephant seal is obviously the big 'daddy' of them all.
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Elephant seals are much better at holding their breath and swimming under water than we are. Their blood/oxygen adaptations have clearly evolved to enhance their underwater performance. The following activity helps students understand this and how it compares to humans.
It has been reported in scientific papers that approximately 21.2% of an adult elephant seal is blood. Assuming 1 g = 1 ml, the students could work out the litres of blood in an average male elephant seal of 3500 kg. It would be interesting to compare the percentage blood in the elephant seal to the percentage in humans and calculate how much that is in litres. A child weighing 30 kg has 2.4 L of blood approximately, and an adult man of 70 kg has 5.0 L. Women have slightly less blood as they tend to be smaller. They usually have around 4.5 L unless they are pregnant, when this figure rises. - Students could research the amount of blood in humans, or the teacher could give them some of the above data and ask them to work out the percentage of blood in adult males and females as well as children. This can also be related to the fact humans can only hold their breath under water about three minutes, while elephant seals can hold their breath for as long as two hours.
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Students can investigate how the sub-Antarctic and Antarctic seals have adapted to their habitat - warmth, movement, food gathering, protection from predators. What is the role of each species of seal in the food web?
Leopard Seal
(Hydrurga leptonyx).Photo: Christo Baars - Suppose that you wanted to investigate the depths to which seals are able to dive. What methods would you use?
- To what extent are sub-Antarctic and Antarctic seals harvested now? Students can discuss the international agreement that protects seals.
There are a number of articles on the Australian Antarctic Division website. These include:
- general information about seals
- a summary of information on elephant seals; southern seals: aquatic performers
- the international agreement that ensures the protection of seals from any possible future re-introduction of sealing activities. To find out how we study whales and seals, have a look at Applied Marine Mammal Ecology.
Further information:
Aerodynamics of Animals' marine animals adapting to their environment to become masters of 'flight' and speed under the water (particularly seals, dolphins and whales).
Background information on Antarctic seals and sealing is available from the Antarctic and Southern Ocean Coalition.
For statistics relating to the annual Norwegian seal harvest, see the following table:
Norwegian seal-hunt 1980-2002
Source: The Directorate of Fisheries, Norwegian Ministry of Fisheries and Coastal Affairs' website.
West Ice East Ice Year Hooded seal Harp seal Harp seal Total 1980 9,768 9,983 15,202 34.953 1985 338 557 19,007 19,902 1990 423 5,508 9,522 15,453 1995 1,301 8,206 6,842 16,349 2001 3,820 2,992 5,200 12,012 2002 7,116 1,227 2,348 10,691