whale

whale, the most charismatic of marine mammals. Whales are a popular tourist attraction and to see a whale breaching is an exciting moment. They belong to the order Cetacea, which consists of about 76 species of whales, porpoises, and dolphins. There are two main groups, baleen whales (Mysticeti) and the toothed whales (Odontoceti).

There are twelve species of baleen whales belonging to four families, and includes the largest of all animals on earth, the blue whale (Balaenoptera musculus). A new species, a small species similar to a fin whale (Balaenoptera physalus), was recognized in 2003 by Japanese scientists using molecular techniques. Baleen whales are characterized by having flexible horny plates with hairy fringes hanging from their upper jaws. The plates consist of a protein called keratin, which is the structural element of human hair. The whales take huge mouthfuls of water and use their tongues to squirt the water through the plates; they sieve out krill, plankton, and small fish. The whales undertake extensive migrations, moving into polar waters to exploit the rich populations of plankton that develop in the spring and summer. In winter they migrate into warm tropical seas to conserve energy and stop feeding. Calving tends to occur when they are in warm waters, so the newborn calves can use the energy from their mother's milk for growth rather than for keeping warm.

The toothed whales comprise ten families and include dolphins, beaked whales, the porpoise and the narwhal (Monodon monoceros), and the beluga (Delphinapterus leucas) or white whale. The male narwhal, which has one of its teeth developed into a long tusk, gave rise to the medieval myth of the unicorn. Belugas are also known as sea canaries, because of the loud chirping noises they produce when hunting under pack ice in the Arctic. The largest toothed whale is the sperm whale (Physeter macrocephalus), which feeds mainly on squid.

Whales are totally aquatic, although still dependent on the atmosphere for their oxygen. Their fusiform bodies are well insulated with fatty tissue known as blubber, which when rendered down was the source of the whale oil which created the whaling industry. They have tail flukes that are horizontal and beat vertically, and on the top of the head is the blowhole through which they inhale. They exhale or ‘blow’ before they dive or ‘sound’. Most dives last a few minutes, but the deeper-diving species, like the sperm whale and beaked whales (e.g. Ziphius spp.), can stay submerged for over an hour and can reach depths well in excess of 1,000 metres (3,000 ft). All species are highly vocal, using sound both to communicate between themselves and as sonar to detect their prey.

Whale populations are still threatened by whaling, but the biggest current threat is the use of powerful sonars by navies which are thought to disorient the whales' own sonar system. There have been several mass strandings of whales since the 1980s, which have coincided with NATO naval exercises. In 2002 fourteen beaked whales stranded themselves just four hours after new powerful sonars were switched on by warships exercising in the vicinity. Another potential threat is increases in the occurrences of red tides of the toxic algae (Alexandrium fundyense) which produces a poison, saxitoxin.

Bibliography

Evans, P. , The Natural History of Whales and Dolphins (1987).
Perrin, W.,, Wirsig, B.,, and and Thewissen, J. , Encyclopaedia of Marine Mammals (2002).

M. V. Angel