In the deep ocean, a sperm whale (Physeter macrocephalus) wrestles with its prey, a giant squid (Architeuthis dux). But this scene is only an artist's conception. No one had ever seen a giant squid alive in its natural habitat, the pitch-dark waters up to 1,000 meters (3,300 feet) beneath the ocean's surface, until September 2005, when a live, adult giant squid was caught on camera in the wild for the very first time by Japanese researchers. Still, most scientific knowledge of this huge invertebrate comes from dead specimens, washed ashore or mistakenly caught in fishing nets.

Scientists have good evidence, though, that this battle between giants actually occurs. On their skin, sperm whales often bear circular scars that match the suckers on a giant squid's tentacles—indicating that it isn't always easy for the whale to get a meal. Additionally, body parts and the hard, indigestible beaks of the giant squid often turn up in the stomachs of sperm whales, revealing that the whale sometimes wins.

Giant Squid: Fact and Fiction
Fictional accounts of sea monsters resembling the giant squid have fascinated readers since the time of Homer. Even today, little is known about this mysterious creature.

The giant squid is among the largest of all invertebrates; females can reach 20 meters (70 feet) in length. This animal has never been observed in its natural habitat, so scientists have few clues as to its geographical distribution, lifespan or behavior. Even its diet is a mystery. Scientists know that sperm whales prey upon the giant squid, but the squid's diet is unknown—the stomachs of most specimens are empty. Hints come from anatomy: the mouth has a beak consisting of an upper and lower jaw, useful perhaps for tearing the body of a fish or a crustacean. And the suckers that line the squid's arms and tentacles can latch on to other animals with tremendous suction, helping it capture prey and defend itself against attackers.

The giant squid reminds us of the remarkable diversity of life on our planet—and how much remains to be discovered about some of Earth's most spectacular animals.

Mythical Creature The giant squid may be the basis for tales of sea monsters since Homer's Odyssey to Jules Verne's 20,000 Leagues Under the Sea, fixed the squid as a monster in readers' minds. © The Mariners' Museum, Newport News, VA

Diving to the Depths
Made famous by Herman Melville's novel Moby Dick, the sperm whale—the largest of the toothed whales—is also one of the deepest diving marine mammals.

Feeding sperm whales routinely dive to about 500 meters (1,600 feet), and evidence indicates they often go much deeper. One whale was tracked by sonar at 2,500 meters (1.5 miles). Using their sharp, conical teeth, the whales snap up their prey, chiefly medium and large-sized squid, at these depths.

Between meals, sperm whales gather in social groups—females with young whales, and mature males in "bachelor pods." Only older bull males tend to be solitary. Evidence suggests that the groups of adult females are stable units, with breeding males roaming from group to group.

CONSERVATION: In Pursuit of Oil
Whale oil, burned in lamps, was the main source of home illumination in pre-Civil War America. After the whaling industry depleted coastal species, including bowhead and right whales, American whalers began their voyages in pursuit of sperm whales. From 1750 to 1850, whalers may have killed up to 5,000 a year. Teeth were valued for carving into scrimshaw; spermaceti from the head made smokeless candles; and ambergris, a substance sometimes found in the whale's gut, was used in perfume-making.

As recently as the 1960s, commercial whalers killed nearly 30,000 sperm whales in a single season. The oil was used not for home illumination but as an industrial lubricant and cosmetic ingredient. Then in 1986, the International Whaling Commission halted all commercial catches of large whales. Today's worldwide population size is difficult to determine; estimates suggest upwards of 350,000.