Dolphin Facts and Interesting
Information
The
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, strictly speaking, are members of the family
Phocaenidae and have a blunt snout and spade or chisel
shaped teeth. The dolphin fish, on the other hand, is
neither a dolphin nor a porpoise. It is a sport fish related
to the mackerels.
Most dolphin species are about 2 m (6 ft) in length, the
males averaging 10 to 20 cm (4 to 8 in) longer than females.
The largest is the bottle-nose dolphin. This species may
reach over 3 m (9 ft) in length and 200 kg (440 lb) in
weight. The smallest species is the buffeo, found in the
Amazon River; the buffeo rarely grows over 1.2 m (3.9
ft) in length and 30 kg (66 lb) in weight.
Dolphins are predators and feed on live food, except when
trained otherwise in captivity. The primary food is fish,
mostly open water types such as 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 30 kg (66 lb) a day
for an individual about 2.5 m (8.2 ft) in length and 100
kg (220 lb) in weight.
Physiology
The general form of dolphins is
a classic example of streamlining. The body is sleek and
smooth; 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 30 km/h (18.6 mph). In shorter
bursts dolphins can attain a speed of 37 to 40 km/h (23
to 25 mph), and in a few instances a speed of 48 km/h
(30 mph) has been reported. Shipboard observers commonly
see dolphins swimming in the bow wave of a moving vessel.
The animals seem to rest motionless but actually ride
the bow wave by using the trust of the ship.
Because dolphins are mammals, they must breathe air and
maintain a high body temperature. The maintenance of internal
temperature, which had been measured at 36.5 deg to 37.2
deg C (97.9 deg to 99 deg F), is aided by a thick layer
of dense fat (blubber) under the skin. Air is breathed
through a specialized single nostril, or 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 300
m (1,000 ft). The respiratory system is specially modified
to avoid the BENDS.
Reproduction
Reproductive behavior is known
mostly from studies on captive individuals, primarily
the bottle-nose dolphin. Copulation normally occurs during
the spring months, with the male-female pair exhibiting
courtship for some time prior to copulation. Gestation
in the species studied is between 11 and 12 months, after
which a single calf is produced. Delivery is 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. Such play may
have provoked the stories of drowning persons being helped
to shore by dolphins.
After birth, the calf follows 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.
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 beamed forward, with the oily melon
serving as an acoustic lens and the bony forehead as a
reflector. 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. This ability
is termed ECHOLOCATION and is found in a few other animal
groups, most notably the insect eating bats. 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.
It has been suggested by several noted scientists that
dolphins may be able to create acoustical holographic
images from the interlacing of their sonic output.
It
is well known that dolphins can see inside the bodies
of their fellow dolphins, and other animals in the water.
This is because dolphin
sonar evolved to pass through water and does not reflect
until it hits something like bone or air sacs. Since animal
bodies are more than 50% water, their sonar enables them
to literally "see" inside other animals. It
is possible that dolphins can read the emotion of other
dolphins and "see" through the bodies of other
animals due to their "x-ray" vision.
Dolphins
have a well-developed tactile sense. They are often in
contact with traveling companions. Body contact is an
important component in communication, and is accomplished
through rubbing, petting, and hitting among other forms
of touch. Some examples include the contact between a
mother/calf pair, pectoral fin to pectoral fin rubbing,
swimming while remaining in contact with another, and
rubbing bodies. Mutual pectoral fin rubs may be exchanged
by two dolphins that have just come together. These may
be a sort of greeting, similar to a handshake or hug between
two people. Or, sometimes dolphins swim a distance and
one individual rests its pectoral fin along the side of
a second individual. This behavior, called contact position,
may be a signal to others that these two are close friends.
It could also mean that the first dolphin wants a favor,
so to speak, from the second.
Body contact
is often modified by the posture of the dolphins involved.
Direct or perpendicular approaches are usually observed
during aggressive exchanges, while approaches from behind
or at oblique angles seem to be less threatening. We should
remember this when we swim among dolphins! Visual cues,
such as body coloration or posture, are also important
avenues for communication among dolphins. All these signals
combine in various ways to communicate vital information
such as age, gender, sexual responsiveness, identification
and activity.
Social Structure
Dolphins
are social animals with groups ranging in size from two
to 15 animals, and often containing more. Many studied
dolphin communities seem to be "matrilineal",
consisting of females and their accumulated offspring,
or sisters and other females. Calves within these groups
will often develop stable relationships with each other
over a period of years.
Subadult
males will usually leave these groups and form "bachelor"
groups that often remain together. Sexually mature males
may form partnerships or coalitions with other males and
seem to move throughout the female groups. There is no
evidence for strong social bonds between male and female
pairs.
Play is an integral part of social relations for dolphins.
They are frequently seen riding the bow wave or stern
wake of boats and "surfing" on waves. Both juvenile
and adult dolphins often chase each other and toss things
to one another, such as seaweed. Jumping from the water's
surface and breaching can also indicate excitement. Play
is often an extremely important mechanism for learning
and for practicing skills that assist a dolphin in survival.
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.
Most researchers agree that dolphins exhibit a level of
intelligence greater then that of dogs and even comparable
to that of some primates.
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.
Range
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 2,500 km (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, Lagenorhynchus obliquidens, 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, or even just a small family group.
Solitary individuals are, however, rare.
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. Dolphins
are also being studied by scientists and the military
for possible use in undersea operations, but the U.S.
Navy has dropped plans to use them to guard nuclear submarines.
Dolphins
at one time were hunted commercially. Some flesh and blubber
were used, but the main product obtained was a fine quality
oil that was extracted from the lower jaw of the dolphin.
Although the oil remains highly prized as a lubricant
for delicate watch mechanisms, similar and cheaper products
are available from other sources, and commercial dolphin
fishing is virtually nonexistent. Many dolphins have been
destroyed inadvertently by commercial tuna fishers using
purse nets. A tuna boycott pushed U. S. tuna canners to
agree in 1990 to buy tuna only from boats that fish in
areas where the dolphins and tuna swim separately.
Here are some
other dolphin facts that you may find interesting...
Dolphins tend to live for about
twenty years, but some have been known to live for about
forty years
When dolphins sleep, they sleep in a semi-alert state
by resting one side of their brain at a time
If need be, dolphins can hold their breath for 5-8 minutes
at a time
Dolphins can dive as deep as 200m (that's 650ft)
A dolphin sheds its outer layer of skin every two hours
Dolphins will help sick or injured dolphins as much as
they can
Dolphins work as a team if danger is near by
Every dolphin has its own signature whistle to distinguish
itself from its companions
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