A whale is a marine mammal of the order Cetacea. A suborder, Odontoceti, includes most smaller whales and all dolphins and porpoises. Whales are unique among mammals in that they live entirely in water.
Many members of Odontoceti have teeth. They feed on fish and invertebrates such as squid. The Odontoceti include the white whale, the killer whale, the pilot whale and the sperm whale.
The male sperm whale can grow to a length of 18.3 metres. The remainder of the large whales are the baleen whales. They include the blue whale, the grey whale and the humpback whale.
Teeth have been replaced in baleen whales with large baleen plates that hang in their hundreds like vertical strip-blinds from the upper jaw. The whale feeds by swimming with its mouth open, engulfing plankton and sea water by the tonne. Then, shutting its enormous mouth, the whale presses its tongue against the back of the baleen plates, forcing the water out of its mouth and trapping the plankton in the overlapping plates.
It appears that the whale is descended from an ancient, hoofed land mammal that lived about 50 million years ago. It is not known why this mammal returned to the sea.
The body of the whale ancestor was streamlined by evolution into a fish-like shape. The front legs were modified into paddle shaped flippers whose bone structure still resembles leg and toe bone outline. The hind limbs were lost entirely. A thick layer of blubber envelops the body. This is a buoyancy aid and an energy store, and it preserves body heat.
The whale has lungs and breathes through a nostril (blowhole) on the top of the head. The "spout" emitted from the nostril contains water vapour from the lungs and some water from the depression around the blowhole, which is blown into the air when the whale exhales.
Whales can dive deep and stay underwater for long periods. Sperm whales can stay submerged for 75 minutes and reach depths of 460 metres in search of their prey, the giant squid. This is facilitated by a number of physiological adaptations.
Inhaled oxygen is used to burn glucose in body cells so as to produce energy. Carbon dioxide is an unwanted by-product and must be exhaled. The involuntary breathing response of most mammals is triggered by a build-up of carbon dioxide.
However, whales have a remarkable resistance to the build-up of carbon dioxide. Whales can also rebalance blood flow during a long dive so that essential organs like heart and brain are not damaged by oxygen deprivation.
MATURE whales (six to 13 years old) go through a courtship and then copulate belly to belly. Depending on the species, the pregnant female carries the unborn young for nine to 16 months when, usually, a single well-developed calf is born.
Baby whales are weaned somewhere between eight months and two years of age, but the age at which they leave the mother is unknown for many species. During the long childhood, adults teach the young - and play is a typical pastime. Young killer whales appear to remain in the family pod, which numbers five to 12 animals. Sperm whales live up to 70 years and baleen whales up to 80 years.
The sea is murky, and sight and smell are of limited usefulness in the ocean depths. So evolution developed a superb sense of sound in whales. At least two kinds of sounds are produced by whales, echolocation and vocalisations. Echolocation works like a biological sonar, while vocalisation seems to be a means of communication.
Some of the whale vocalisations are called "songs". They range over a broad range of frequencies, down to well below the range of the human ear. A typical song lasts about 15 minutes and the longest about one hour. Often the members of the whale group sing the same song together. No one knows what the whales are singing (talking) about.
Finback whales emit very loud sounds at a low frequency. These low-frequency sounds are scarcely absorbed by water and it has been calculated that using this sound, two whales could communicate with each other anywhere in the world. Of course this was possible only before the advent of modern background noise from shipping. Nowadays a realistic distance across which whales can communicate is probably a few hundred kilometres.
Whales are intelligent, social animals. The information content of the humpback whales' songs is about the same as contained in the Iliad. The brain of an adult sperm whale weighs nine kilograms; the average adult human brain weighs 1.35 kilograms.
Whales are hunted commercially for their oil, bone, meat and various by-products. Most of the commercially valuable species are endangered. Whaling is now greatly restricted, but is still practised by some countries.
It seems particularly inappropriate to hunt these wonderful, intelligent creatures. We would be much better employed trying to understand them.
William Reville is associate professor of biochemistry and director of microscopy at UCC.