All dolphins, porpoises, and whales belong to the order Cetacea. They are often called cetaceans. Scientists group most dolphins (31 species) in the family Delphinidae, part of the suborder Odontoceti, or toothed whales. Delphinids include such well known dolphins as bottlenose dolphins and common dolphins as well as killer whales and pilot whales.
Another cetacean family, Plantanistidae, contains the river dolphins: small-eyed, long-snouted dolphins that live in fresh water. Porpoises belong to their own family, Phocoenidae. Porpoises are different than dolphins. They have shorter snouts, trangular tops fin, and spade-shped teeth. This fact sheet focuses on dolphins in the family Delphinidae.
A dolphin has streamlined body parts that help it swim easily through the water. The dorsal fin, located on the center of its back, is made of dense fibrous connective tissue - there is no bone inside. The dorsal fin acts as a keel, giving the dolphin some stability as it swims.
Each lobe of a dolphin's tail is called a fluke. Like the dorsal fin, flukes have no bone or muscle inside. A dolphin uses the powerful muscles along its back and tail stalk to move its flukes up and down. This motion moves the dolphin forward through the water.
As it swims, a dolphin uses its pectoral flippers to steer and, with the help of the flukes, to stop. Pectoral flippers are a dolphin's forelimbs. If you looked at an X-ray picture of a dolphin's pectoral flipper, you would see what looks like finger bones! Dolphins have no hind limbs, only ver small hip bones buried deep in the pelvic muscle and tissue.
A dolphin breathes through a single blowhole, located on top of its head. A muscular flap covers the blowhole, making a watertight seal when dolphins dive. To take a breath, dolphins contract the muscular flap. When dolphins relax the muscles, the flap stays tightly closed.
Dolphins live in all oceans of the world. While some inhabit one particular geographical area of an ocean, others like killer whales are found worldwide. Coastal, or inshore, dolphins live close to land and are often seen by people on beaches and boats. Oceanic, or offshore, dolphins live farther out at sea. Many dolphins have a homerange, an area where they tend to stay.
Some dolphins, like these Commerson's dolphins, swim in shallow coastal waters.
All dolphins are carnivores, or meat eaters. Many eat fishes and squids, while some, like killer whales, also catch seals, sea lions, walruses, and other dolphins. A dolphin grasps and tears food with its cone-shaped teeth. All dolphins swallow their food whole or in large chunks.
Although they sometimes feed by themselves, dolphins most often hunt in groups. Dolphins that live in the open ocean may swim in tight circles around a school of fish and take turns dashing in to catch a bite to eat. Closer to shore, a group of dolphins often herds fish into shallow water, keeping them trapped while group members feed.
Dolphins live and travel in groups called pods, often family groups. In some species, individual dolphins enter and leave the pod over time. But others, like killer whales, have a stable group. Sometimes, several pods may join together to form a temporary herd. Several hundred individuals have been seen traveling in a single herd.
These social mammals commuicate by squeaking, grunting, trilling, and moaning. They also send messages through body language by leaping, breaching, smacking their tails against the water, butting heads, and jaw-snapping. Within each pod, some dolphins are more dominant than others.
Sharks are a dolphin's main predator. Dolphin remains are often found in the stomachs of tiger sharks, dusky sharks and bull sharks. On occasion, killer whales may feed on some species of dolphins.
In some parts of the world, humans hunt certain types of dolphins for food. Yet even where they're not hunted, dolphins are threatened by some human activities.
Toxic chemicals that pollute nearshore waters may contaminate the fish on which dolphins feed. Scientists believe these chemicals might affect the health of dolphins and cause tumors. Pollution may have contributed to the deaths of dolphins that have washed up on beaches in recent years.
In the eastern tropical Pacific ocean, tuna travel under dolphin pods. When tuna fishermen set their nets around the dolphins to catch the tuna, the dolphins are trapped too. To help save dolphins, many tuna fishermen now use special nets and techniques to release the dolphins. From 1972 to 1994, dolphin deaths from purse seine fishing in the eastern tropical Pacific dropped more than 99%, from 423,678 to 4,095 individuals.
A more deadly type of fishing is done with gill nets. These nets stretch for miles across the ocean and extend deep under water. Once the fishermen have set the nets, they leave and return a few days later to haul them in. They remove the fish they were hoping to catch and discard all other animals that have died in the nets. Thousands of dolphins and other marine creatures drown in these huge nets each year.
What You Can Do for Dolphins
SeaWorld/Busch Gardens Animal Information Database
www.seaworld.org / www.buschgardens.org
©2002 SeaWorld, Inc.
All Rights Reserved.