"Dall’s porpoises are highly acrobatic and are often seen swimming at high speed, darting to and fro, riding the bow waves of boats and engaging in slow rolls at the surface. Because they are black and white, boaters sometimes misidentify them as killer whales. They are small cetaceans, with robust bodies and small heads, flukes, and flippers. Reproductively, they differ from many cetaceans by breeding annually, calving in June or July and mating soon thereafter. This means females are nursing young while pregnant with next year’s offspring. A calf often stays with its mother until the next one is born. Females favor certain areas of the ocean for calving; at calving time, most males, juveniles, and females without offspring stay farther south. Dall's porpoises have very tiny teeth: each tooth is about the size of a grain of rice. They feed on a great variety of prey, from squid to deepwater fish to small schooling fish, which they swallow whole."

Links:
Mammal Species of the World
Click here for The American Society of Mammalogists species account