Scalloped Hammerhead

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Scalloped hammerhead images (Sphyrna lewini) - stock photos, illustrations & facts of a shark with a distinctively shaped head

Conservation status | Threatened > Endangered
Scientific classification | Kingdom: Animalia > Phylum: Chordata > Class: Chondrichthyes > Order: Carcharhiniformes > Family: Sphyrnidae > Genus: Sphyrna > Species: S. lewini
Binomial name | Sphyrna lewini

Scalloped hammerheads, Sphyrna lewini, range worldwide in tropical, sup-tropical and warm temperate seas. They are also known as bronze hammerhead, kidney-headed, and southern hammerhead. Scalloped hammerhead sharks are a coastal pelagic species, and are found near shore, around seamounts or submerged reefs, and even in shallow waters like estuaries. At night, they hunt further offshore. They feed mostly on fish such as sardines, herring and mackerels, and also on cephalopods, crustaceans, and turtles. Large scalloped hammerhead sharks will eat other small shark species.

Like all hammerhead sharks, the scalloped hammerhead has a hammer shaped head with a central dent and an arched front edge. Sphyrna is the Greek word for hammer, which is how the scientific name was derived. The hammerhead shape is believed to increase their ability to maneuver, and because the shark's eyes and nostrils are at the tips of the extensions, this increases their ability to see, smell, and detect pressure differences in the ocean. Scalloped hammerhead sharks are a bronze or brownish grey fading to white on the underside. They can grow up 14 feet and 300 pounds, with the width of the hammer being 25-30% of the length. They can be observed being cleaned of parasites by other fish such as butterflyfish and angelfish.

Scalloped hammerhead sharks are not considered dangerous to people. Incidents with humans are rare. They can be solitary at times, but at other times will form huge schools of hundreds of individuals. Not all reasons for this are known but it is believed to be related to feeding patterns and reproduction. Females have been known to migrate, which is believed to be due to a stage in their sexual development. Groups will form huge schools in regions where there are seamounts and pinnacles, where the largest females will force the smaller ones out of the center. The males select a mate from the dominant females and the pairs leave the school to mate.

Scalloped hammerheads are viviparous, giving birth to live young that have an egg yolk placenta, after a nine month pregnancy. They produce between 15 to 30 pups, measuring 16 to 21 inches long, that have a soft hammer to make the birth process easier. The hammer cartilage grows harder as the pups grow.

Scalloped hammerheads were listed by the IUCN as Endangered. They are commonly taken in fisheries, fished using longlines, nets, and trawl nets. They are also fished as a “game” fish, and also caught as by-catch in longline fisheries targeting other species.
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