Shark: Scalloped Hammerhead


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Scalloped Hammerhead Shark or Sphyrna lewini have a circumglobal distribution in tropical, subtropical and warm-temperate waters between latitudes 46°N and 36°S, They are coastal and semi-oceanic pelagic shark, found over continental and insular shelves and in nearby deeper water, ranging from the intertidal and surface to at least 275 m (1,600 ft) depth, but most often found above 25 m (82 ft).

Hammerhead sharks are distinguished from all other fishes by the shape of their heads. Their heads are flattened and laterally expanded into a hammer-shaped structure called the cephalofoi. The Scalloped Hammerhead is named for the notches found along the front edge of its cephalofoi.

Like all hammerhead sharks, Scalloped Hammerhead are aggressive predators and gain several advantages from the shape of their head. The unusual shape of their head give the sharks added lift and lets them make sharper turn than other sharks. The eyes and nostrils are located at the tips of their head extensions. The widely spaced eyes, nostrils, and sensing organs called the ampullae of Lorenzini that can detect the electric field given off by its prey buried in the sand, allow them to more successfully locate and hunt their prey. Their heads may also be used to pin stingray to the bottom, allowing them to successfully eat difficult to capture species.

Scalloped Hammerheads are usually solitary, but may form large schools of hundreds or more adults. They mate via internal fertilization and females will migrate to shallow inshore water to give birth. Juveniles will remain in the coastal zones, near the bottom for about two to three years before migrating to join the adults around deeper reefs, seamounts, and other open ecosystems.

The size at birth of Scalloped Hammerheads are about 42 to 55 cm. They can reach a maximum total length of about 370 to 420 cm. Males mature at about 140 to 165 cm and will reach at least 295 cm, while females mature at about 212 cm and will reach at least 309 cm.

These sharks have a very high metabolic rate and need a lot of food. Adult Scalloped Hammerheads primarily feed on fishes such as sardines, mackerel, herring, and stingray. Larger adults may also feed on smaller species of predatory shark such as the blacktip reef shark. Occasionally, they feed on cephalopods such as squid and octopus. Pups and juveniles feed mainly on smaller benthic reef fishes, demersal fishes and crustaceans.


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