Dolphins can be found in virtually all the seas and oceans of the world. Some species are sharply restricted, but many, like the common dolphin, Delphinus delphis, or the bottle-nose dolphin, are found worldwide. Several species are found in fresh water, notably the Ganges River dolphin, Platanista gangetica; the rivers of South America are the home of the long-snouted dolphin, Inia geoffrensis, and the small, graceful Sotalia fluviatilis, occasionally seen as far as 2,500 km (1,553 mi) up the Amazon River.

Dolphins are quite abundant in some areas of the world. Off the coast of Japan, for example, populations of the white-sided dolphin, Lagenorhynchus obliquidens, are estimated at 30,000 to 50,000 individuals. In many species, schools of up to 1,000 travel together, while some species, such as the bottle-nose dolphin, tend to be found in smaller groups of less than 100, or even just a small family group. Solitary individuals are, however, rare.

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