Hammerhead sharks are the 9 extant species of sharks belonging to Sphyrnidae family, typically characterized by a flattened head resembling a hammer. These sharks are further classified into two genera - genus Sphyrna (with 8 species to its credit) and genus Eusphyra (with the winghead shark as the lone species).
- » Bonnethead shark or shovelhead (Sphyrna tiburo)
- » Great hammerhead (Sphyrna mokarran)
- » Scalloped bonnethead (Sphyrna corona)
- » Scalloped hammerhead (Sphyrna lewini)
- » Scoophead (Sphyrna media)
- » Smalleye hammerhead or golden hammerhead (Sphyrna tudes)
- » Smooth hammerhead (Sphyrna zygaena)
- » Whitefin hammerhead (Sphyrna couardi)
- » Winghead shark (Eusphyra blochii)
- » Depending on the species, gender and age, the length of this shark can vary from 3 feet to 20 feet. The great hammerhead shark is the largest among the hammerhead species, and can be as big as 20 feet or 6 meters in length and weigh 1,000 pounds (450 kg).
- » Their color can range from gray-brown to olive-green, with off-white belly. Other than their head, these sharks can be identified by their extended dorsal fin and mallet-shaped head.
- » The habitat of hammerhead sharks spans the warm waters of tropical and temperate seas. Generally, they keep to coastal and offshore waters. In summer, they are known to migrate in search of cool waters.
- » Unlike other sharks, hammerheads live in groups of 10-20 sharks - known as schools - during the day, and hunt alone at night. In rare cases, a school can have unusually large number of sharks. (A school of hammerheads with somewhere around 200 sharks was reported off the coast of Australia.)
- » It is believed that hammerhead sharks belong to the Carcharhinidae family. Of these, the wingedhead shark is considered to be the most basal member of the phylogenetic chart.
- » The cephalofoil, i.e. the flat, laterally extended head resembling a flattened hammer, acts as a wing or a flat surface, and puts the fish at advantage when it comes to close quarter maneuvers.
- » Some scientists say that the shape of the head evolved slowly over numerous generations, but there are others who believe that it is due to mutation that proved profitable to the hammerheads.
- » Hammerheads spend a lot of time well below the sea surface, at depths of more than 250 meters. They are creatures of the deep sea, and can reach a speed of 25 miles/hr (40 km/hr).
- » Eyes are located at the end of the lateral part of the head. These wide-set eyes improve their ability to see and locate their prey in the murky waters of the sea.
- » In addition to the eyes, they use a specialized sensory organs referred to as the ampullae of Lorenzini, to detect the electrical field generated around their prey's body. This organ is so sensitive that it even helps them locate small species like groupers, jacks, catfish, toadfish, boxfish, herring, etc.
- » Hammerheads also feed on cownose rays, guitarfish, eagle rays, butterfly rays, whiptail stingrays, octopuses, skates, squid, and crustaceans such as shrimp, mantis shrimp and crabs.
- » Stingrays, when they sense a predator, bury and hide themselves under the sand at the bottom of sea, but the field generated by the electrical activities in their bodies gives them away to hammerheads.
- » It is believed that hammerhead sharks can also receive and transmit low-frequency sonar waves to find a prey.
- » Their life span is recorded to be of 25 years, if they can successfully manage to evade their natural enemies such as the tiger sharks, killer whales or the great white shark.
- » These carnivore fish sport rows of extremely sharp and triangular teeth. Hammerheads, like other sharks, do not have mineralized bones in their body. Because of this reason, it is rare to find a fossilized shark, a fact which is in sharp contrast to dinosaurs. This has made it very difficult to determine the time of their appearance on Earth.
- » A female gives birth to 12-15 young ones at a time. The litter size in the Great Hammerhead sharks is 20-40 young ones. The female, though it is a fish, carries fertilized embryos which gets nutrients via umbilical cords, inside her. Gestation period is of 10-12 months. Young ones prefer shallow waters off coasts, wherein their enemies cannot penetrate.
- » Only the great hammerhead, the smooth hammerhead and the scalloped hammerhead are aggressive, and may attack a swimmer when provoked. Though relatively rare, unprovoked attacks cannot be ruled out. These sharks are likely to attack a swimmer or diver by mistaking him for a seal - their natural prey in the wild.