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.