Porpoises: Phocoenidae

Except for the finless porpoise on the Yangtze (yang-see; or Chang) River in China, which seems to have become used to heavy boat traffic, porpoises tend to avoid boats. This makes them difficult to study. They rise to the surface to breathe quietly without showing much of their bodies. Rarely do they leap above the surface of the water. Generally porpoises live in small groups of no more than ten individuals. When larger groups occasionally gather, it may be to feed or follow schools of fish.

Very little is known about the reproduction of vaquita and spectacled porpoises. Other porpoises become mature at three to five years, and have a single calf every year after that. Pregnancy lasts about eleven months and mothers nurse their young, feed them breast milk, for more than a year. Porpoises live about fifteen years.