Whales

No one can fail to be impressed by the great size of some whales (they include the largest animals ever known on Earth), but more striking than size alone are the features of their anatomy and physiology which makes them so wonderfully adapted to lead their entire life in water. Perhaps the most obvious of these is their fish-like appearance, the head is long and, though there are 7 neck vertebrae as in other mammals, there is no distinct neck extrenally between the head and the streamlined body. The forelimbs are modified as paddles and the tail terminates in large, forked, horizontal expansions called the flukes. Some species have a fin on their back but this has no skeleton, and the skeleton of the forelimbs is quite unlike that of a fish's paired fins. The hind limbs have been lost in all whales and a pari of small bones is all that remains internally of the hip girdle.

The tail fin of a fish is vertical and moved from side to side to drive the fish forward, but the wahle is thrust forward by the vertical movement of the horizontal tail flukes. This structure and the dorsal fin are though folds of skin.

Like all other mammals, whales are warm-blooded. They breathe air by means of lungs, and suckle their young. The skin, however, is smooth and hairless, except for a few bristles around the mouth in some species. The lack of hair heps to keep the amount of friction to a minimum as the animal moves through the water. The loss of body heat is reduced by a blubber - the thick layer of fatty tissue beneath the skin _ which acts as an insulator. Blubber also increases the whale buoiyancy, and the fat, besides being a food store, is likely a source of water when it is burned to provide energy. Since whales breathe air they must come to the surface periodically to obtain fresh supplies. A characteristic sign of this is the "blow" which is now thought to consist of exhaled air in which are suspended fine droplets of oil. It is not due to merely to the hot breath condesing in the colder air, for the "blow" is visible in the tropics as well as in polar regions. It has a characteristic fetid smell.

The nostrils open on top of the head, an adaptation which means that a whale needs only to raise the top of its head out of the water to obtain air. IN various parts of the body there are elaborate networks of blood vessels - the retia mirabilia. besides the oxygen taken into the lungs an extra supply is available during dives from the store in these vessels. The muscles, too, store large amounts of oxygen.



Hearing is the main sense of whales, vision and smell are less acute. The brain is very large (much larger than our own) and they are very intelligent. Many whales make elaborate noises - and these seem to be a form of speech by which they communicate with each other.

Harbor Porpoise
Harbor Porpoise
bbc.co.uk

There are two main groups of whales: the toothed whales or Odontoceti, and the whalebone whales or Mysticeti. The odontocetes from the largest group and include the sperm whale, bottle-nosed whale, narwhal, white whale, pilot whale or blackfish, killer whale and the dolphins and porpoises.

The sperm whale is the larges of them, reaching in length of 60 feet and weighing as much as 50 tons. It lives mainly in warm water. Its head is an enormous blunt-ended structure, the snout of which forms a reservoir of oil or spermaceti. These whales feed mainly on squids. They often search along the sea floor scooping up their prey with the lower jaw. The killer whale, or grampus, is the fiercest of whales. It moves about in groups or schools feeding principally on seals and porpoises - though several will make vicious attacks on another (much larger whale). Many captured sperm whales have been found badly wounded, with one or both of the front paddles and other parts of the body torn off.

The porpoises and dolphins often travel in schools. The common porpoise reaches a length of about 5 feet. They feed mainly on fish. The Mysticeti or whalebone whales possess teeth only when they are very young. These are absorbed and in the upper jaw the long horny plates of balees are developed. They are used to strain plankton from the water. The whales move along with the mouth open. It is then closed, the tongue and floor of the mouth are raised and water is forced out through the sides of the mouth, leaving the tiny planktonic organisms behind on the baleen.

Humpback Whale
Humpback Whale
Megaptera novaeangliae
source: dpiw.tas.gov.au

The blue whale is the larges animal ever known to inhibit the Earth. It may reach 100 feet in length and weigh over 120 pounds. Blue whales feed on tiny shrimp-like creatures called euphausids - known as krill. Other whalebone whales include humpback whale, fin whale, sei whale and lesser rorqual. Another group of whalebone whales are the right whales, so named because they were recognised by whale fishermen as being easier to catch and of greater value. The whale's age is determined by the number of layers of wax in the whale's ear. Whales are slow-breeding animals and they have been overfished to such an extent that several species are now extinct and other face probable extinction.

Many whales migrate from the polar regions towards the equator at the end of the polar summer during which they have built up a large reserve of body fat. It is during this migration that the young are born. Pregnancy lasts for about a year in the lue whale, fin whale and humpback whale. Normally only 1 youngster is born at a time. A young blue whale is about 24 feet long at birth and the period of suckling is about 7 months. A blue whale is able to breed when it is 2 years old and it is then about 85 feet long.






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