River dolphins can be distinguished from ocean-dwelling dolphins by their smaller brains and more limited interactions with each other. Their eyes can detect light but do not form an image. As with dolphins, social interaction among porpoises is common. However, porpoises do not form enormous schools like some of the dolphins, generally remaining in coastal areas in small schools of two to four. Because porpoises do not survive as well in captivity, less is known about their biology and social behavior than that of some dolphins.
Porpoises share with dolphins the ability to produce a wide variety of underwater sounds.
It occurs in the north temperate regions of the Atlantic and Pacific Oceans, being sighted frequently along the coasts of Europe and North America. In some species, such as the pilot whales, several individuals will become stranded at the same time. Harbor porpoises, however, are usually alone. Dall's porpoises are noted for swimming playfully around ships or small boats. It is a shiny golden and blue color with deep blue spots.