SharkoFiles: Scalloped Hammerhead

The scalloped hammerhead sharks are sometimes referred to as the kidney-headed shark. The head of the shark is expanded laterally, resembling a hammer. These sharks are distinguished from other members of the hammerhead family by their scalloped-shape of the front edge of their cephalophoil. They have grayish copper coloration, with a characteristic shark shape, and a slightly longer first dorsal fin.

Scalloped hammerhead grow between 12 to 14 feet long. Scalloped hammerheads are generally considered as shy and are quite successful at avoiding people. This factor makes the shark species very difficult for scientists to study. They are rarely encountered by scuba divers compared to other shark species. The shark has a worldwide distribution and are found both in the on shore and off shore. The life span of scalloped hammerhead is thought to be above 30 years.

The scalloped hammerhead is unique to other hammerhead sharks such as the great hammerhead and the smooth hammerhead because of their indentation situated centrally on the front margin of the hammer-shaped head. The primary diet of scalloped hammerhead is teleost fishes and a variety of invertebrates such as other sharks and ray. Adult scalloped hammerheads have no known predators, while the juvenile or injured scalloped hammerheads are prone to being attacked or preyed upon by larger sharks. They are highly valued for their fins and are increasingly targeted in some areas.

The scalloped hammerhead shark belongs to the order carcharhiniformes, of the family Sphyrnidae sharks and genus Sphyrna. The scientific name of the shark is Sphyrna lewini.

Morphology

The Scalloped Hammerhead has an undulating margin to the front of the head with an indention medially. It has a low second dorsal fin, as well as a relatively straight posterior pelvic fin margin. The shark species have a brownish-gray or greyish copper to olive or bronze coloration. The adult scalloped hammerheads have cusky pectoral fin tips, without no other markings. Juvenile scalloped hammerheads have dark, lower caudal and second dorsal fin tips. Like most sharks, the scalloped hammerhead shark has special sensory cells that can be used to detect electric fields emitted by other fishes. They have small teeth with smooth or slightly serrated cusps on the wide base. The lower teeth are more erect and slender than the upper teeth. The males attain maturity when they grow to about six feet in total length, while for the females, reach maturity around eight feet.

Adaptation

The wide head of the scalloped hammerhead shark enables them to more precisely locate their prey buried in the sand. With the aid of their electrical sense organs called ampullae of Lorenzini, they can detect weak electrical fields. This enables them to detect the electrical cues that emanate from prey animals and even the weak electrical currents flowing through the earth’s magnetic fields. Certain species of scalloped hammerheads can detect voltages as low as one millionth of a volt.

Their diet consist mostly of teleost fishes and cephalopods. The invertebrates eaten by scalloped hammerhead include squid, octopus, shrimp, crabs, as well as lobsters.

Habitat

The scalloped hammerhead can be found mostly on the continental shelves and have a preference for deeper waters. The fish are often found at a depth of 1600 feet. When they come to the surface probably for mating, they are found at a depth of 80 feet. The scalloped hammerheads are sensitive to light. Due to their high social behavior, these sharks are found closer to shore lines during the day and at night they prefer to swim to the depth of the seas. The adults are known to swim in solitary or in small groups, and at times in pairs. Meanwhile, the juveniles can be found normally hanging out in larger groups. During hunting, the shark can either hunt individually or in groups based on the size of the prey, as well as the geographical position of the area.

Reproduction

The reproductive process of the shark is not really known. However, like other hammerheads, the scalloped hammerhead shark engages in a viviparous mode of reproduction. The scalloped hammerhead moves inshore to shallow water to give birth during the summer months. The gestation period is around 10 months. The size of the litter is flexible and can range between 15 and 30 pups. The pups approximately measure 15 to 18 inches in length when they are born. It is found that juvenile scalloped hammerhead sharks grow really slow in contrast to other sharks and are normally found in shallow waters.

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