A "shoal" is any group of fish engaged in similar behavior, while a "school" is a shoal that swims together in a coordinated manner. Many species of fish engage in schooling behavior for at least some part of their lives. Smaller fish often school for protection, since it is more difficult for a predator to pick out an individual target when faced with a coordinated, swirling mass. Similarly, larger fish may school for increased efficiency in finding or attacking prey. Other possible adaptive advantages of schooling include greater hydrodynamic efficiency for swimming, and greater ease in finding a mate.