Historically, whaling was the dominant threat to sperm whales. Sperm whales were killed in two massive hunts, the Moby Dick whalers who worked mainly between 1740-1880, and the modern whalers whose operations peaked in 1964, when 29,255 were killed. Most recent estimates suggest a global population of about 360,000 animals, down from about 1,100,000 before whaling. Today they are threatened by ship strikes, entanglements in fishing gear (although these are not as great of a threat to sperm whales as they are to more coastal cetaceans), disturbance by anthropogenic noise notably in areas of oil and gas activities or where shipping activity is high, pollutants (e.g. polycholorobiphenyls (PCBs), chlorinated pesticides (DDT, DDE, etc.), polycyclic aromatic hydrocarbons (PAHs), and heavy metals). The potential impact of coastal pollution may be an issue for this species in portions of its habitat, though little is known.
Natural threats to sperm whales include killer whales, which have been documented killing at least one sperm whale in California. Typically, however, it is believed that most killer whale attacks are unsuccessful. Large sharks and giant squid may also be a threat, especially for young sperm whales. Sperm whales are also protected under the Marine Mammal Protection Act of 1972.