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 t
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.