Hammerhead fish

Introduction:

The hammerhead sharks are a group of sharks in the family Sphyrnidae, so named for the unusual and distinctive structure of their heads, which are flattened and laterally extended into a "hammer" shape called a "cephalofoil". Most hammerhead species are placed in the genus Sphyrna while the winghead shark is placed in its own genus,Eusphyra. Many not necessarily mutually exclusive functions have been proposed for the cephalofoil, including sensory reception, maneuvering, and prey manipulation. Hammerheads are found worldwide in warmer waters along coastlines and continental shelves. Unlike most sharks, hammerheads usually swim in schools during the day, becoming solitary hunters at night. Some of these schools can be found near Malpelo Island in Colombia, Cocos Island off Costa Rica, and near Molokai Island in Hawaii. Large schools are also seen in southern and eastern Africa.The known species range from 0.9 to 6 m (3.0 to 20 ft) long and weigh from 3 to 580 kg (6.6 to 1,300 lb). They are usually light gray and have a greenish tint to them. Their bellies are white which allows them to be close to the bottom of the ocean and blend in to sneak up on their prey.Their heads have lateral projections which give them a hammer-like shape.


Reproduction:

Reproduction only occurs once a year for hammerhead sharks and usually occurs with the male shark biting the female shark violently until she agrees to mate with him.The hammerhead sharks exhibit a viviparous mode of reproduction with females giving birth to live young. Like other sharks, fertilization is internal with the male transferring sperm to the female through one of two intromittent organscalled claspers. The developing embryos are at first sustained by a yolk sac. When the supply of yolk is exhausted, the depleted yolk sac transforms into a structure analogous to a mammalian placenta (called a "yolk sac placenta" or "pseudoplacenta"), through which the mother delivers sustenance until birth. Once the baby sharks are born, they are not taken care of by the parents in any way. There is usually a litter of 12 to 15 pups; except for the Great Hammerhead which births litters of 20 to 40 pups. These baby sharks huddle together and swim toward warmer water and stay together until they are older and big enough to be on their own.

In 2007, the bonnethead shark was found to be capable of asexual reproduction via automictic parthenogenesis, in which a female'sovum fuses with a polar body to form a zygote without the need for a male. This was the first shark known to do this.

Diet:

Hammerhead sharks are known to eat a large range of items including fish, squid, octopus, crustaceans, and other sharks. Stingrays are a particular favorite. These sharks are often found swimming along the bottom of the ocean, stalking their prey. Their unique head is used as a weapon when hunting down prey. The hammerhead shark uses its head to pin down stingrays and eats the ray when the ray is weak and in shock. The Great Hammerhead, tending to be larger and more aggressive than most hammerheads, occasionally engages in cannibalism, being known to eat other hammerhead sharks, including their own young.