The sperm whale is the largest toothed predator on Earth. Adult males grow to 16-18 meters (52-60 feet) and can weigh 45-57 tonnes, while females reach about 11 meters (36 feet) and 15 tonnes. The enormous square head makes up a third of the body and holds the spermaceti organ, a mass of waxy oil that helps focus the whale's sounds and may help control buoyancy.
Sperm whales have the biggest brain of any animal, weighing up to 8 kg (18 lbs). Their skin is dark grey and wrinkled like a prune, and the single blowhole sits at the front left of the head, producing a bushy blow that angles forward. The narrow lower jaw carries 18-26 pairs of large teeth; the upper jaw has almost none.
They live 60-70 years or more. Females give birth every four to six years after a pregnancy of 14-16 months.
Sperm whales live in deep water in every ocean, from the edge of the polar ice to the equator. They prefer areas more than 1,000 meters (3,300 feet) deep, especially near underwater canyons, continental slopes and seamounts where squid are plentiful.
Females and young stay in tropical and temperate waters all year, while adult males travel to the cold waters of the Arctic and Antarctic to feed, returning to warmer seas to breed.
Sperm whales feed mainly on squid, from small species to the giant and colossal squid, whose suckers leave round scars on the whales' heads. They also eat deep-sea fish, octopus and sharks. An adult can eat about a tonne of food a day.
To find this food they make some of the deepest dives of any mammal, routinely reaching 600-1,000 meters (2,000-3,300 feet) and sometimes more than 2,000 meters (6,500 feet), staying down for up to 90 minutes.
Females and their young live in stable family groups of 10-20 that stay together for decades, babysitting each other's calves at the surface while mothers dive. Young males leave to form bachelor groups and the largest bulls spend much of their lives alone.
Sperm whales communicate with patterns of clicks called codas, and their echolocation clicks are the loudest sounds made by any animal. They rest by hanging motionless in the water, often in a vertical position. When threatened by orcas, a group forms a tight circle with their tails facing outward.
Physeter macrocephalus is the only living member of its genus; its small relatives, the pygmy and dwarf sperm whales, belong to a separate family. The name "sperm whale" comes from spermaceti, the oil in its head that early whalers mistook for something else entirely. This is the whale of Herman Melville's Moby-Dick.
Sperm whales were hunted for their oil for more than two centuries, and hundreds of thousands were killed before commercial whaling ended in the 1980s. The IUCN lists the species as Vulnerable, with a population thought to be in the low hundreds of thousands and recovering slowly.
Today's threats include collisions with ships, entanglement in fishing gear, swallowed plastic, chemical pollution and underwater noise.
