Whales, Dolphins and Porpoises:
Whales were once known as ‘great fish’. This was because both fish and whales spend all their lives in the water, but they are not related in any way. Both have streamlined bodies but whereas a fish swims by wagging its tail from side-to-side, a whale swims by wagging its tail up-and-down.
Another important difference between whales and fishes is that whales, because they are mammals, are warm-blooded and fishes are cold=blooded. Yet both live all their lives in water and would die if they left the water to come onto land. Although the water is cold, whales are able to keep warm because they have a thick layer of oily blubber under their very thin skin. They have no hair except a few bristles on the snout and these are usually found only in the young.
Many millions of years ago whales lived on land. They ten had four legs. We know tis because all whales have tiny hip bones and very occasionally a whale is born with small hind legs.
Although their front legs have changed to flippers, the bones in them are very like those in your arms and hands.
A whale has no neck but it still has seven neck bones – the same number as most mammals. Another thing that marks a whale as a mammal is that its young is born alive and is fed with its mother’s milk. As soon as a baby whale is born it swims to the surface to take its first gulp of air to fill its lungs. Often the mother will help it by putting her snout under it to lift it to the surface. Then the baby swims beside its mother.
The mother whale has no teats. Instead she has two slits in her abdomen through which she squirts milk into her baby’s mouth as it swims close to her.
Whales are divided into two groups. These are the toothed whales and the whalebone whales. Toothed whales feed on squid and fish. They have peg-like teeth which in the sperm whale may be 20cm long. Whalebone whales have no teeth. Instead they have plates of whalebone hanging down from the roof of the mouth. These are used to strain small fish and small prawns, known as krill, from the sea. The blue, fin and humpback whales all belong to this group.
The largest whale is the blue whale. It may reach a length of 30cm or more and may weigh 142 tonnes. It is the largest animal that has ever lived. The smallest whale is the La Plata dolphin that lives in the estuary of the Rio de la Plata, in South America. It is only 1,60m long.
The small whales are called dolphins and porpoises. Most whales live in the sea, but some of the dolphins live in the large rivers. The home of the Chinese river dolphin, for example, is in Tung Ting Lake, nearly 1000km up the Yangtze river valley.
The blue whale, the largest animal that has ever lived, is a whalebone whale. The plates of whalebone can be seen hanging from its upper jaw. Whalebone whales swim through shoals of drill near the ocean’s surface, with their mouths open, straining the krill from the water:
The back of a fin whale breaks the ocean surface. Fin whales belong to the group of whales known as the whalebone or baleen whales:
Dolphins are strong swimmers, their stream-lined shape and smooth flexible skin help to reduce water resistance to a minimum:
Close-up of a dolphin’s blow-hole, as it comes to the surface to breathe. Under the water, the blow-hole is closed by a special muscle to stop water from entering:
Animals are the closest and most devoted friends of a person. They are more sensitive and loyal to people. They are ready to be from the very beginning, and some of us do not understand this ... and the animals are on the street.