Sperm whales subsist on squid, octopuses, deep-sea fishes, and a variety of other fishes. Yankee sperm whalers sometimes confirmed that they had arrived on the whaling grounds by noting pieces of squid floating on the sea surface. The basic social unit of sperm whales is the mixed school, which contains up to 50 or more individuals. Adult females accompanied by their offspring, including young whales of both sexes, are found in such schools. Bachelor schools formed by maturing males remain apart from the mixed schools, and adult males travel alone or in small, loosely associated bands.
Large males associate with mixed schools during part of the year, presumably for breeding purposes.
This segregated social structure allows sperm whales to partition the food resources on which they depend. Females and juveniles rarely venture north of about 50 N latitude except in areas influenced by warm currents. Bulls, on the other hand, migrate during summer into subarctic and even arctic regions, where their foraging efforts are not in direct competition with those of the females and young. Length at sexual maturity is about 9 m for females and 12 m for males. Breeding can occur any time between late winter and late summer, but generally peaks during late spring or summer.