Dusty DolphinThe majority of small tooth whales are called dolphins.  They are mammals of the order Cetacea and the families Plantanistidae and Delphinidae and include about 50 species.  All have a beak like snout and sharp, conical teeth.  The term porpoise is sometimes applied to many of the same species, but porpoises, are members of the family Phocaenidae and have a blunt snout and spade or chisel shaped teeth.  The dolphin fish, is neither a dolphin nor a porpoise.  It is a sport fish related to the mackerels.

Most dolphin species are about 6 ft in length, the males averaging 4 to 8 in longer than females.  The largest is the killer whale, which can be 19-22ft long and weigh between 8000-10000lbs.  One of the largest dolphins is the bottle-nose dolphin which can reach over 9ft in length and weigh 440 lbs.  The smallest species is the buffeo, found in the Amazon River.  The buffeo rarely grows over 3.9 ft in length and 66 lbs in weight, really smalled compared to the bottle_nose.

Dolphins feed on live food and are predators, except when trained otherwise in captivity.  The primary food is fish, mostly things like herring, mackerel, and sardines.  Some species seem to prefer squid, occasionally, shrimp and other crustacean are consumed, and even mollusk shells have been found in their stomach contents.  Food consumption is estimated at about 66 lb a day for an individual about 8.2 ft in length and 220 lb in weight.
 
 

Physiology
Reproduction
Communication
Intelligence
Range
Dolphins and Humans

Pacific White Sided DolphinPhysiology

The body is sleek and smooth and the hairless skin is rubbery to the touch.  Most species have jaws that protrude into a beak like snout.  Above the upper jaw is a large mass of fat and oil-containing tissue forming the so-called "melon" that looks much like a bulging forehead.

The anterior appendages contain the skeletal remnants of five digits that form the flippers, which the animal uses primarily as stabilizers, although occasionally in an oar like fashion.  The hind appendages are virtually absent and consist of a pair of small pelvic bones, deeply embedded in the connective tissue at the base of the tail.  The dorsal fin is formed from subcutaneous dermal tissue and is not movable by muscle action.  The caudal, or tail, fin is also primarily dermal in origin, rather than skeletal, and consists of a pair of horizontally extending flukes.  The locomotion of dolphins is typical of the whale.   The main thrust comes from vertical oscillations of the tail and flukes, and most species tested are capable of sustained swimming speeds of up to 18.6 mph and they jump at this high speeds travelling 30 ft or more.  Their normal "cruising speed" is about 23 to 25 mph, and if they are bow riding, they have been known to get up to 30mph.  Bow riding is when the dolphin rides teh bow of a wave produced by a ship.

Because dolphins are mammals, they must breathe air and maintain a high body temperature.  The  internal temperature, between 97.9 deg to 99 deg F, is acheived by a thick layer of blubber under the skin.  Air is breathed through blowhole, situated almost directly on top of the head.  The dolphin normally comes to the surface to breathe about every two minutes,  and each breath consists of a short, almost  explosive exhalation, followed by a slightly longer inhalation.  Dolphins can hold their breath for up to several minutes and are capable of rapid and deep dives of more then 1,000 ft.

Dolphins once were hunted commercially, especially for the small quantity of valuable oil extracted from parts of the head and used to lubricated delicate watch mechanisms.  Cheaper oils have now been found from other sources, and dolphins are no longer hunted for this reason.   Many dolphins, however, become accidentally trapped and drowned in tuna nets.  Between the years 1959 and 1972 an estimated 4.8 million dolphins died this way.   Because of the pressure from animal rights activists and United States consumers, both domestic and international tuna canners have refused to accept shipments from fishing fleets that do not protect dolphins.  The Marine Mammal Protection Act of 1972, amended in 1988 and 1992, was passed to prevent exploitation of dolphins and related aquatic animals. The National Marine Fisheries service is the principal regulatory agency.
 

Reproduction

Captive dolphins, mostly the bottle-nose dolphin, has provided us with the reproductive behavior studies.  Mating normally occurs during the spring months, like with most animals, with the male-female pair exhibiting courtship for some time prior to the actual mating.  A female dolphin has to carry her baby (calf) for 11-12 months.  The calf is delivered normally tail first, and the newborn is capable of swimming and breathing within the first minutes.  Some mothers have been observed raising the calf to the surface, as if to help it, but dolphins apparently play in this fashion with a variety of objects, living or not.  This kind of play may have helped the stories heard round the world of how dolphins have helped humans when they have been lost at sea, helping them get to the surface and to stay there.

The calf will follow its mother closely, and suckling takes place frequently, with the mother tolling slightly and the calf nuzzling the mammary area.  The dolphin's two mammary glands open into a pair of sacs on either side of the anal opening, and the calf's beak fits into the openings on the sacs.  The nipple is grasped between the upper jaw and the tongue, and muscular contractions by the mother literally squirt mil into the calf's mouth.  Nursing may continue for as long as 12 to 18 months after birth, although weaning is probably slowed or inhibited in captive animals.

White Beaked Dolphin

Communication

Dolphins are extremely and almost constantly vocal.  They are capable of two kinds of sounds.  A specialized mechanism in the nasal passages just below the blow-hole enables them to emit short, pulse-type sounds.  These sounds, called clicks, can be produced in such rapid succession as to sound like a buzz or even a duck like quack.   The clicks are used as a form of sonar, in which echoes of sounds from surrounding objects enable the animals to detect obstacles, other dolphins, fish, and even tiny bits of matter in the water.  The military uses dolphins and this ability to help them find water minds.  This ability is termed ECHOLOCATION.  Some Scientists have speculated that dolphins also use the sounds to deliver an acoustic shock for stunning of killing small prey.

Deeper in the respiratory system--presumably in the larynx--dolphins produce another type of sound: a high pitched whistle of squeal, which is capable of rapid pitch changes.  The whistles differ from the clicks in being essentially single tones.  Apparently the dolphin used the whistles to communicate a particular emotional state and thus influence the behavior of other dolphins.  Typically, the squeals denote alarm or sexual excitement.
 

Intelligence

Because dolphins are highly social and vocalize among themselves with a wide range of sounds, it has been conjectured that they might possess and almost human like intelligence.  In the 1950s and '60s the American neurologist John Lilly conducted well publicized experiments based on this concept, in which he attempted to communicate with dolphins in their own "language," but other scientists have rejected his work as poorly documented and lacking scientific validity.

Because of the ability of dolphins to learn and perform complex tasks in captivity, their continuous communications with one another, and their ability, through training, to approximate the sounds of a few human words, some investigators have suggested that the animals might be capable of learning a true language and communicating with humans.

Most researchers agree that dolphins exhibit a level of intelligence greater then that of dogs and even comparable to that of some primates--but not human beings.  Research into dolphin intelligence continues at centers such as Hawaii's Kewalo Basin Marine Mammal Laboratory (The Dolphin Institute).

Spinner DolphinRange

Dolphins can be found in virtually all the seas and oceans of the world.  Some species are sharply restricted, but many, like the common dolphin, Delphinus delphis, or the bottle nose dolphin, are found worldwide.  Several species are found in fresh water, notably the Ganges River dolphin, Platanista gangetica; the rivers of South America are the home of the long-snouted dolphin, Inia geoffrensis, and the small, graceful Sotalia fluviatilis, occasionally seen as far as 1,553 miles up the Amazon River.

Dolphins are quite abundant in some areas of the world.  Off the coast of Japan, for example, populations of the white-sided dolphin, are estimated at 30,000 to 50,000 individuals.  In many species, schools of up to 1,000 travel together, while some species, such as the bottle-nose dolphin, tend to be found in smaller groups of less than 100.
 
 

Dolphins and Humans

Dolphins adapt well to human companionship and are readily trained.  Bottle-nose dolphins have become well known performers in may aquariums; they are capable of spectacular tricks and may mimic the sounds of a few human words.
 
 

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This page was created by Kelly Gilby
Last updated 02/03/03