Behavior 
Porpoises are generally less active, slower swimmers than dolphins, traveling in small groups, rarely showing much of themselves above the surface and tending to stay away from boats. The exception to the rule is Dall’s Porpoise, a fast swimmer which travels in groups of several hundred or more, and loves to bow or wake ride. Dall’s Porpoises produce a great deal of spray when they swim along the surface -- this behavior is called rooster tailing.