The sperm whale (Physeter macrocephalus) is the champion diver of mammals, staying submerged as long as 2 hours at a depth of up to 6,560 feet. Within the whale's head is a cavity that holds up to 5 tons of sperm oil. As the whale dives deeper, the oil hardens and becomes heavier, helping the animal descend. As the whale surfaces, the oil softens into a liquid, making the whale more buoyant.
Each day a sperm whale eats 2,000 pounds of giant squid, octopus, and cuttlefish. This diet maintains the whale's body: 60 feet in length and weighing as much as 140,000 pounds (70 tons). The sperm whale was once hunted to near extinction. Currently the world's population of sperm whales is about 500,000; the number killed by hunters has decreased drastically during the past 40 years.