Females cannot dive with their nursing calves, who are too young to hold their breath long enough to stay submerged with their mothers. At about one year of age, a young sperm whale begins feeding on its own. Its mother is never very far away, though, and responds defensively if a calf is threatened by a shark or killer whale. Male whales, called bulls, leave the pod when they are five years old, either to live alone or join bachelor pods of other young males. For the next 50 to 80 years, male adults live apart from the complicated social organization of females and children.
Younger males live in small groups, while older bulls lead solitary lives.
Males mingle with females only when it is time to mate. THE REAL MOBY DICK explains that beneath the water's surface, sperm whales reinforce social bonds by rubbing against each other. Once collected, the samples are sent to a lab for genetic analysis. Sperm whales' relatively peaceful lifestyle is fairly new, for they were heavily hunted by humans until 1987. In previous centuries, whale oil was used to light lamps and lubricate machines, and a single whale head can yield more than 600 gallons of pure oil.