Dolphins are small toothed aquatic mammals with superb hearing that live in saltwater and freshwater environments. Dolphins communicate with many different vocalizations, such as clicks and whistles, have advanced hearing that works underwater or above water, and can track prey using echolocation. The smallest dolphin, the Maui Dolphin, is only about 6 feet (1.82 m) in length while the largest dolphin, the Orca, can grow up to 31 feet (9.5 m) long. While mostly found in saltwater oceans, some dolphin species live in rivers, while others are kept in captivity and trained to perform tricks. Sleek and playful, the dolphin can reach speeds of over 18 miles an hour and are known to enjoy leaping out of the water and playing in the wake of a passing boat.
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