The species usually swims near the surface, rising to the surface to breath about every 25 seconds. It does not present a very playful attitude, ignoring boats and rarely jumping out of the water. When diving for food this porpoise stays down for an average of 4 minutes, and is believed to be able to dive as deep as 200m. Although schools of up to 100 individuals may sometimes be seen, P. phocoena is usually seen in pairs or in groups of 5-10. When the larger groups do occur, it is usually because a number of smaller groups have joined together while following a rich food source.
Mothers bring newborn calves to secluded coves to nurse.
Some populations are known to migrate, but when they return to their regular waters they are territorial, patrolling certain areas. In the Western Atlantic, they also move far out to sea near the end of summer and reappear in spring. Other regional populations move south or farther away from shore to avoid ice buildups. Although fishing of P. phocoena is now illegal in most areas, the species is still in danger. Deliberate and accidental deaths still occur because modern fishing nets are almost undetectable to porpoises.