Marine mammals: sperm whales and beaked whales

The sperm and beaked whales are some of the largest toothed whales, but their offshore lifestyle and long dive times have made their study relatively difficult. Many beaked whale species appear externally similar and several species have only recently been identified. These whales are the basal odontocetes and diverged from the ancestral lineage c. 15–25 Ma. Beaked whales are characterized by the presence of a beak, while sperm whales were named for their spermaceti organ, a fatty structure containing oil thought to resemble semen, used in sound production. Sperm whales and some beaked whales were taken in large numbers during whaling operations in the last centuries. Much of what we know about them stems from the study of dead animals, but today live animals are also being studied at sea. Sperm and beaked whales are found in deep water in all oceans. These are some of the deepest mammalian divers, often feeding a kilometer underwater for their squid prey. However, difficulties studying such relatively shy animals mean that, except for the sperm whale, little is known of the social dynamics of most other species. Their most significant threats today are from fisheries, shipping, contaminants, and particularly increasing levels of underwater noise, especially military sonars.