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Gregory R. Mann, Ph.D. {ret.}

Scalloped Hammerhead Shark

“Sphyrna lewini”

Scalloped Hammerhead Sharks are large sharks with moderately high first dorsal fins and low second dorsal and pelvic fins. They can be distinguished by the broadly arched front margin of their head that has a prominent median notch. The side “wings” of their heads are narrow with their rear margins swept backward. Scalloped Hammerheads are uniformly gray, gray-brown or olive on their dorsal (upper) surfaces, fading to white on their ventral (lower) surfaces and their pectoral fins are tipped with gray or black ventrally. Most of these sharks encountered by divers average 2-2.5 meters in length. Males mature at 1.5-1.75 meters and reach an average of 3 meters, females mature at about 2 meters. Maximum length of this species is known to be at least 3.7 meters and it is thought that a few individuals may reach a length of over 4 meters. Scalloped Hammerhead Sharks are coastal-pelagic, semi-oceanic sharks occurring over continental and insular (island) shelves and adjacent deep waters, often approaching close inshore and entering enclosed bays and estuaries. They are found in waters to about 275 meters in-depth. Huge schools of small migrating individuals move pole-ward in the summer in certain areas. Permanent resident populations also exist. Adults are solitary in pairs or schools; young are often found in large schools.

They feed mainly on fishes and squid, octopus and cuttlefishes, also lobsters, shrimps, crabs as well as other smaller sharks and rays. In the Indo-West Pacific, stomach contents have been found to include Sea SnakesScalloped Hammerheads are viviparous with a yolk-sac placenta. Pups are born following a 12 month gestation and a female produces 15-31 pups of 43-55 centimeters young in a litter. Pups occupy shallow coastal nursery grounds, often heavily exploited by inshore fisheries and then migrate offshore as they mature. Scalloped Hammerhead Sharks are considered potentially dangerous to people but usually non-aggressive and shy when approached by divers. Under baited conditions, Scalloped Hammerhead Sharks may make close approaches to divers but quickly lose interest and depart when they determine that the divers are not the source of the food odors.

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