Sperm Whales: Physeteridae

Physical characteristics: Sperm whales, sometimes called giant sperm whales to distinguish them from the smaller members of this family, are the largest toothed whales. They can reach 60 feet (18.3 meters) in length and weigh 125,000 pounds (57,000 kilograms). Males are much larger than females, who reach only about 36 feet (11 meters) and 33,000 pounds (15,000 kilograms). Although these whales are usually dark gray, they can also be black or white (albino). An albino sperm whale is famous as the monster great white whale in Herman Melville's story Moby Dick.

Sperm whales, especially males, have huge square asymmetrical heads that take up about one-third the length of their body. They have the largest brain of any mammal, larger even than the brain of the giant blue whale, the largest mammal on earth. Their brain weighs an average of 20 pounds (9.2 kg). For comparison, the average adult human brain weighs less than 3 pounds (1.3 kilograms). The spermaceti organ can contain more than 500 gallons (1,900 liters) of spermaceti

Sperm whales can dive to depths of more than a mile (2.2 kilometers), and stay underwater an hour before coming to the surface to breathe. (© François Gohier/Photo Researchers, Inc. Reproduced by permission.)

oil. Their blubber can be almost 14 inches (35 centimeters) thick. Sperm whales have about thirty-five to fifty large cone-shaped teeth in their lower jaw only. When the whale closes its mouth, these teeth fit into pockets in the roof of the mouth. These teeth were prized by sailors who carved pictures on them in an art form known as scrimshaw.

Geographic range: Giant sperm whales are found in every ocean of the world.

Habitat: These whales live in deep water and are often found near underwater features such as seamounts (underwater mountains that do not rise above the surface of the ocean) and sharp drop-offs.

Diet: Sperm whales hunt their prey by echolocation deep in the ocean where there is no sunlight. They mainly eat squid, including the giant squid that can be over 50 feet (15 meters) long. Many whales have scars on the head made by the suckers of these squid as they battle the whale. They also eat smaller squid, fish, and sharks.

Behavior and reproduction: Giant sperm whales are champion divers and are able to dive deeper than any other whale. They can dive to depths of more than a mile (2.2 kilometers), and stay under water for an hour. Some scientists believe that they may be able to dive to depths of 10,000 feet (3,000 meters). More typically, these whales dive to depths of 1,000 to 2,600 feet (300-800 meters) and remain under water for thirty to forty-five minutes. They then rest at the surface for about ten minutes before diving again. Females do not dive as deep as males and may spend more time at the surface with their calves. These whales swim at about 6 miles per hour (10 kilometers per hour) but can reach speeds of 19 miles per hour (30 kilometers per hour) when hunting or avoiding danger.

Females become sexually mature and able to reproduce when they are about eight years old. Males may be capable of reproducing earlier, but usually do not do so until they are nineteen or twenty years old. Females give birth every five to seven years. The mother-calf bond is strong and socially important. Mothers may continue to nurse their young for up to thirteen years. Mothers and calves form groups of about twenty to forty individuals (although one group of 3,000 to 4,000 animals was seen off the coast of South America) that appear to stay together and assist each other. For example, since calves cannot make deep dives, some females will take turns staying at the surface guarding the young from killer whales while their others dive for food.

As the young mature, the males leave the group and swim with other young males in groups of about twelve to fifteen individuals. As they grow older, they split off into smaller and smaller groups. It is common for an old male to swim alone. Males tend to move toward the poles and come back to warmer water where the female groups stay when it is time to breed. The males fight for the right to breed, which is why young males rarely start reproducing until age twenty. Once mating has occurred, the males leave the group of females and calves and go off on their own again. Sperm whales are thought to live about seventy years.

Sperm whales make a wide variety of sounds with the help of specially modified nasal passages and air sacs. The sounds they make are loud and carry well over long distances. It appears that each whale has a signature "song" to identify it to other whales. They also make clicks for echolocation and ringing sounds that may be involved in attracting a mate.

Sperm whales and people: Sperm whales have been hunted since the early 1700s, with peak whaling activity between 1880 and 1930 and 1950 to 1975. They are valued for their spermaceti, oil, and ambergris (AM-bur-gris), a waste product used in manufacturing perfumes. Whale meat is also eaten in some countries such as Japan.

Conservation status: Sperm whale hunting stopped in 1985. However, in 2000, Japan resumed hunting for what they called "scientific research" and has continued to kill between five and ten sperm whales each year. Sperm whales are considered Vulnerable. Because it takes them so long to mature and they have calves only every five to seven years, it will take a long time for their populations to recover from hunting. They are also at risk from collisions with ships and accidental entanglement in fishing nets and transatlantic communication cables. ∎