1. Dolphins are marine mammals that are closely related to whales and porpoises.

2. Dolphins are part of the family of toothed whales that includes orcas and pilot whales. They are mammals and breathe through a blowhole on the top of their head.

3. They vary in size from 4 feet (1.2 meters) and 90 pounds (40 kilograms) for Maui's Dolphin and up to 30 feet (9.5 meters) and 10 tons for Orca or Killer Whale.

4. There are almost forty species of dolphin, and they are found worldwide, mostly in the shallow waters along the continental shelves. Five species live in river.

5. Dolphins are carnivores, mostly eating fish and squid. Dolphins live in social groups of five to several hundred. They use echolocation to find prey and often hunt together by surrounding a school of fish, trapping them and taking turns swimming through the school and catching fish. Dolphins will also follow seabirds, other whales and fishing boats to feed on the fish the birds scare to the surface or discard.

6. Dolphins are considered to be amongst the most intelligent of . The are friendly and extremely playful. They are also easy to train. These qualities have made them a favorite of many people. Scientists believe that dolphins conserve energy by swimming alongside ships, a practice known as bow-riding.

7. Dolphin vary in color, but they are generally gray with darker backs than the rest of their bodies.

8. Most dolphin species have a long lifespan. It is estimated that some may have lived for more than 100 years.

9. Dolphins mate throughout the year. Gestation lasts from 9 to 17 months depending on the species. They usually have only one baby. When it is time to give birth, the female will distance herself from the pod, often going near the surface of the water. As soon as the calf is born, the mother must quickly take it to the surface so it can take its first breath. The calf will nurse from 11 months to 2 years, and after it is done nursing it will still stay with its mother until it is between 3 and 8 years old.

10. Dolphins are at risk because the oceans are being polluted. They are also losing their habitats and many countries still allow dolphins to be hunted. Fishing nets also pose a problem for the dolphin population as does the increase in boating traffic.