The species is protected by the International Whaling Commission moratorium, and is listed as vulnerable by the International Union for Conservation of Nature. Sperm whaling was a major industry in the 19th century, depicted in the novel Moby-Dick. Beachcombers look out for ambergris as flotsam. Ambergris, a solid waxy waste product sometimes present in its digestive system, is still highly valued as a fixative in perfumes, among other uses. Spermaceti (sperm oil), from which the whale derives its name, was a prime target of the whaling industry, and was sought after for use in oil lamps, lubricants, and candles. It has the largest brain on Earth, more than five times heavier than a human's. The sperm whale uses echolocation and vocalization as loud as 230 decibels (re 1 µPa m) underwater. Plunging to 2,250 metres (7,382 ft), it is the third deepest diving mammal, exceeded only by the southern elephant seal and Cuvier's beaked whale. Mature males average 16 metres (52 ft) in length but some may reach 20.7 metres (68 ft), with the head representing up to one-third of the animal's length. A mature sperm whale has few natural predators, although calves and weakened adults are sometimes killed by pods of killer whales (orcas). Females give birth every four to twenty years, and care for the calves for more than a decade. The females cooperate to protect and nurse their young. Females and young males live together in groups, while mature males (bulls) live solitary lives outside of the mating season. The sperm whale is a pelagic mammal with a worldwide range, and will migrate seasonally for feeding and breeding. It is the only living member of the genus Physeter and one of three extant species in the sperm whale family, along with the pygmy sperm whale and dwarf sperm whale of the genus Kogia. The sperm whale or cachalot ( Physeter macrocephalus) is the largest of the toothed whales and the largest toothed predator. Physeter australasianus Desmoulins, 1822.