Sperm whales are hard to count because they spend long periods under water and can be missed during sightings. Scientists have found ways around that, and these are the tools they use.

One tool is a digital tag. Scientists used digital tags to study 198 foraging dives by 37 sperm whales in the Atlantic Ocean, the Gulf of Mexico and the Ligurian Sea. In that study, an average dive cycle was a 45-minute dive followed by a 9-minute surface interval.

In the same tagging study, the maximum dive depth averaged for each whale was 985 m in the Atlantic, 644 m in the Gulf of Mexico and 827 m in the Ligurian Sea.

A suction-cup time-depth tag on a female sperm whale off Japan recorded her repeatedly diving for 30 to 45 minutes down to 400 to 1,200 m. A sperm whale can stay underwater for an hour or more, and its deep dives last about 45 minutes on average.

Sperm whales are usually found in water at least 1,000 metres deep. A sperm whale's ribcage is flexible, so its lungs can collapse safely under the water pressure of a deep dive, and its muscles hold extra myoglobin, a protein that stores oxygen.

Sound is another tool. Sperm whales make clicking sounds and use echolocation to find food. In echolocation, an animal makes a sound that travels through the water, bounces off an object and comes back as an echo.

Scientists pinpoint sperm whales by towing a hydrophone array and measuring the tiny time differences when a click arrives at each hydrophone.

The sperm whale is the largest of the toothed whales, but the blue whale and other large rorquals are bigger. An adult male is 49 to 59 feet (15 to 18 metres) long and can weigh up to 45 tons, and an adult female is up to about 40 feet long.

Female sperm whales and their young travel together in groups, and the females help look after the young together. They stay in warm tropical waters all year, and females become adults between the ages of 7 and 13 years.

Adult male sperm whales usually live alone, except in the breeding season, and young males leave their family groups and live with other young males. Males often do not take part in breeding until their late twenties.

Sperm whale hunting reached two peaks, one in the 1840s and one in the 1960s. Commercial whaling from about 1800 to the 1980s greatly reduced sperm whale numbers around the world, and the International Whaling Commission placed a moratorium on commercial whaling in 1986.

Underwater noise from human sources can interrupt the normal behavior of sperm whales, which rely on sound to communicate. Sperm whales can become entangled in many different types of fishing gear, including trap lines, pots and gillnets. Between deep dives, they spend long periods at the surface, typically up to 10 minutes, which makes them more open to collisions with ships.

As of November 2026, the sperm whale is listed as endangered under the Endangered Species Act in the United States. NOAA says sperm whale populations are still recovering and their numbers are likely increasing.

Words to know

• hydrophone: underwater microphone
• foraging: looking for food
• echolocation: finding by sound
• moratorium: official pause
• entangled: caught up