Dolphins Essay, Research Paper

The mammalian dolphins are small, streamlined whales, usually with

a well-defined, beaklike snout. They are often called porpoises, but

that name is usually reserved for similar, but beakless, whales of the

family Phocoenidae (see porpoise). Dolphins are popularly noted for

grace, intelligence, playfulness, and friendliness to man. The most

widely recognized species are the common and bottle-nosed

dolphins (Delphinus delphis and Tursiops truncatus; see photograph);

both are of the family Delphinidae and are widely distributed in warm

and temperate seas. These are probably the species of dolphins mentioned in the

works of Aristotle, Aesop, Herodotus, the Plinys, and other early writers, often as a

child’s mount or the rescuer of someone lost in the sea.

The family Delphinidae contains 14 genera and about 32 species of dolphins

distributed throughout the world oceans. Most are gray, blackish, or brown above and

paler below, and most are about 1 to 4 metres (3 to 13 feet) long. Risso’s dolphin

(Grampus griseus), found in tropical and temperate seas throughout the world, is

grayish in colour and lacks a beak. Teeth are usually lacking in the upper jaw. The pilot

and killer whales, also members of this family, are much larger and, because of their

size, are not usually thought of as dolphins.

The majority of the delphinids feed primarily on fish, and most of them are gregarious,

appearing in groups of a few to several hundred. A number of species are attracted by

moving ships, often accompanying them or leaping alongside and sometimes riding the

wave created by the moving bow. The bottle-nosed dolphin, characterized by a

“built-in smile” formed by the curvature of its mouth, has become a familiar performer

in oceanaria. It has also become the subject of scientific studies because of its

apparent intelligence and its ability to communicate with its kind through a range of

sounds and ultrasonic pulses. It adapts to captivity better than the common dolphin,

which is timid.

The Platanistidae, or river dolphins, comprise four genera and species of small, mainly

freshwater dolphins found in South America and Asia. They have long, slender beaks,

reduced eyes, and poor vision. The Stenidae, or long-snouted dolphins, comprise three

genera and eight species of little-known dolphins, also with long, slender beaks. They

are found in tropical rivers and oceans and are sometimes included in the family

Delphinidae.

The fish commonly known as a dolphin (Coryphaena hippuras), also called mahimahi and

dorado, is a popular food and sport fish. Famed for the rapid changes undergone by its

bright blue and gold coloration as it dies, this dolphin inhabits tropical and temperate

waters throughout the world. It has a large, blunt head, a tapered body, and a

slender, forked tail. The male, considerably larger than the female, may attain a length

and weight of about 1.5 m and 30 kilograms (70 pounds). A swift carnivorous fish, this

dolphin lives alone or in schools and feeds on invertebrates and other fishes. It and

the similar, though smaller, pompano dolphin (C. equiselis) are the only living members

of the family Coryphaenidae.