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DOLPHINS AND PORPOISES
Delphinidae and Phocoenidae
People have long been fascinated with dolphins and porpoises.
They have been celebrated in art and literature since ancient
Greek times. Even today, dolphins and porpoises are among
the most popular animals. Few people would forget an encounter
with dolphins, especially one in which a group of wild dolphins
comes over to a boat to bowride (surf the wave that the boat
makes as it travels through the water).
Dolphins and porpoises are cetaceans, which are mammals in
the whale family. Dolphins and porpoises are considered to
be small whales. All dolphins and porpoises are toothed whales,
or odontocetes. However, dolphins and porpoises differ in
the type of teeth they have. Dolphins have sharp conal teeth,
while porpoises have teeth that are spade or shovel shaped.
In fact, scientists generally use tooth shape as a way of
classifying an animal as a dolphin or a porpoise. Dolphins
generally tend to have a pointy mouth or "beak"
and a curved dorsal fin, but there are exceptions.
All dolphins and porpoises use echolocation, which is something
like the sonar used on ships. Dolphins and porpoises produce
a sound in the air passages in their heads, which they then
send from the front of their heads. There, an oil-filled organ
called the melon, focuses or directs the sound. A sound wave
might hit an object, such as a fish, and the sound wave then
bounces, or echoes back to the dolphin or porpoise. They can
use this echo to tell what kind of fish or other object it
hit, how large it is, and much more information about their
environment. It is like seeing with their ears, but in some
ways even better!
Dolphins and porpoises tend to be very social animals, living
in groups. Sometimes thousands of individuals are seen together.
Dolphin and porpoise mothers generally take care of their
calves for one to two years until they are old enough to survive
on their own. Like all mammals, they provide milk to their
young.
Dolphins and porpoises are found in virtually all oceans
and major seas of the world. One family, the river dolphins,
is even found in large freshwater rivers such as the Amazon
in South America and rivers in China and India. Dolphins and
porpoises range in size from the Orca (killer whale) at a
maximum of 30 feet (9.5 m) in length and a weight of up to
eight tons, to the small vaquita, five (1.5m) long and weighing
less than 200 pounds (90 kg).
In the Pacific off the California Coast, several species
of dolphins and porpoises are found. They include the beautiful,
fast, black and white Dall's porpoise, the numerous but shy
harbor porpoise, the gregarious and friendly Pacific white
sided dolphin, common dolphins, and the deep diving Risso's
dolphin.
Large numbers of dolphins and porpoises are a sign of the
health and vitality of our oceans. But unfortunately, tens
of thousands of porpoises and dolphins are dying every year
due to problems caused by people. Many accidentally get caught
in fishing nets and drown. Others get entangled in old nets,
which are loose and floating freely. Many near-shore dolphins
and porpoises are exposed to pollution and toxins that can
make them sick. In recent years, large numbers of sick and
dying bottlenose dolphins have washed up on the East Coast
of the United States. In some places, people still catch and
eat dolphins and porpoises for food or to use as fishing bait.
Many scientists are concerned that dolphins and porpoises
now need to be protected in the same way that people worked
to save and protect large whales from hunting in the recent
past. You can help dolphins and porpoises by keeping informed
on current issues, by writing to government officials about
your concerns, and by supporting laws that protect dolphins
and their ocean home. You can also recycle your trash and
use less plastic (which is dangerous to these animals), buy
products that are dolphin safe, and participate in beach clean
ups.
Let's all work together to help protect these beautiful animals
and their ocean home.
May be reprinted for scientific and educational purposes
Revised 2/02
Learn more about the following:
Humpback
Whale
Blue Whale
Orca/Killer
Whale
Gray Whale
Beluga Whale
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Dolphins
& Porpoises