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Hammerhead Shark

Sphyrna

Photo: Hammerhead shark

Photo: Hammerhead shark (View larger version)

Photograph by Brian J. Skerry

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Hammerhead sharks are consummate predators that use their oddly shaped heads to improve their ability to find prey. Their wide-set eyes give them a better visual range than most other sharks. And by spreading their highly specialized sensory organs over their wide, mallet-shaped head, they can more thoroughly scan the ocean for food.

One group of sensory organs is the ampullae of Lorenzini, which allows sharks to detect, among other things, the electrical fields created by prey animals. The hammerhead's increased ampullae sensitivity allows it to find its favorite meal, stingrays, which usually bury themselves under the sand.

The great hammerhead is the largest of the nine identified species of this shark. It can grow up to 20 feet (6 meters) in length and weigh up to 1,000 pounds (450 kg), although smaller sizes are more common.

Found in temperate and tropical waters worldwide, far offshore and near shorelines, hammerheads are often seen in mass summer migrations seeking cooler water. They are gray-brown to olive-green on top with off-white undersides, and they have heavily serrated, triangular teeth. Their extra-tall, pointed dorsal fins are easily identifiable.

Most hammerhead species are fairly small and are considered harmless to humans. However, the great hammerhead's enormous size and fierceness make it potentially dangerous, though few attacks have been recorded.

The squat-headed hammerhead (Sphyrna mokarran) and the scalloped hammerhead (Sphyrna lewini) are listed as endangered and the smalleye hammerhead (Sphyrna tudes) and the smooth hammerhead (Sphyrna zygaena) are listed as vulnerable on the IUCN Red List of Threatened Species™.