Dolphins

All dolphins belong to the group of Cetacean, or rather whales. The dolphins are divided in the Delphinidae family (toothed whales).

Habitat
Dolphins live in all oceans. There are dolphins almost everywhere in the world. Some live in a specific area of an ocean. Others, like the orca, appear world wide. Coastal dolphins live near the land and, are often seen by people often, while oceanic dolphins live farther in the oceans. Many dolphins have a territory of the ocean were they stay their whole life.
Dolphins live and travel in groups, called shoals. Dolphins which live in a specific shoal are often related to each other. Sometimes different shoals join together and form a herd. Shoals of more than hundred dolphins have been seen.

How dolphins move and breath

A dolphin has a streamlined body, which helps him to move through the water quickly. His backfin will keep him in balance, which gives him stability during swimming. There are no bones or muscles in the dolphin1.jpg - 13 K

flaps or tail. A dolphin uses the strong muscles in his back and tail to move the flaps of his tail up and down. This move makes a dolphin get on through the water. The dolphin uses his breast

flippers to coordinate and, his tail helps him to stop. A dolphin breaths through a hole in the middle of his head. This hole is closed by a muscled flap which makes the hole watertight while submerged. The flap opens to breath when above the water.

Food
Dolphins are carnivores, or meat eaters. A lot of dolphins eat mainly fish and arrow cuttle-fish. Other dolphins, like the orca, hunt and kill seals, walruses, and even other dolphins. They all swallow their prey entirely or in big pieces.

Enemies of dolphins
Sharks are dangerous enemies for a dolphin. Remains of dolphins have been found in the stomachs of sharks (but also in orcas).

Mankind may be the biggest enemy of the dolphin. In some countries, dolphins are caught or killed for food. Pollution is another threat caused by man. Poisonous chemicals which pollute the oceans or seas may infect the fish which serve as food for the dolphins. Scientific research has proven that these chemicals also have affected the health of dolphins and developed tumours. Pollution has been the cause of death of many dolphins which have stranded on our beaches.

Saving dolphins by scaring them
Every year tens of thousands to hundreds of thousands of dolphins die in fishing nets as unintended catch. Some of these deep drift nets are more than a mile long. No wonder that they are sometimes called "curtains of death". Dolphins do not recognize the fish net as a danger. They may try to get some of the fish or they may swim into the net by accident. Once they get tangled, they panic, and a fight for life begins. If they cannot free themselves and surface to breathe, they will suffocate and die. If a dolphin is lucky and free himself, some of the net may stay attached to his body and hinder him in his movements. Or he may swim away with injuries; sometimes serious cuts. In the fight for life and death, the tangled dolphin may cause considerable damage the nets. For the fisherman it also means much work to get the dead dolphin out.

A Dutch company recently came up with a technical solution for the problem: they developed the "Pinger".

Dolphins are very smart but also very curious. The idea was to develop an ultrasonic sound that would scare dolphins. Small transmitters could be attached to the fish nets. The scaring noise could keep the dolphins at a distance from the nets. The transmitter was named "Pinger".

The Pinger consists of a specially developed ceramic crystal (transducer-element) that transmits a high-frequency sound. A rechargeable battery pack provides the energy. It is all molded in plastic able to resist any pressure. The transmitter starts working immediately when it makes contact with salt water.

The determination of appropriate sound was not a simple task. There are many types of dolphins who may react in different ways to different impulses. Eventually, an ultrasonic whistle tone was found that scares enough dolphins and other mammals.

For every kilometre of net, four pingers are needed to cover the right range to keep the nets clear. The transmitters are very simple to use. They are relatively cheap. Fisherman worldwide could use them without any problems. It saves the costs of damaged nets. It saves the life of hundreds of thousands of dolphins.

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