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Hammerhead Shark

(Sphyrna)

Short Description

The Hammerhead Sharks are a group of sharks ( there are 9 species) 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". All nine species have this projection on the sides of the face that ressemble a flattened hammer. Hammerheads are found worldwide in warmer waters along coastlines and continental shelves.

Long Description

Size
The 9 different species range in size from just under 1 metre long to over 3 metres long.

Identification
The shape of the head is the immediate identifier of a Hammerhead Shark. The eyes are positioned at the outer side of the hammer. They have small mouths out of proportion to their head size.

Diet
Hammerhead sharks are known to eat a large range of things, including fish, other sharks, squid, octopus, and crustaceans. Stingrays are a particular favourite. They are also known to eat their own young

Reproduction
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 organs called claspers.

Social Groups and Activity
Hammerheads seem to do a lot of bottom-hunting. They are also known to form schools during the day, sometimes in groups of over 100. In the evening, like other sharks, they become solitary hunters.
Hammerheads are notably one of the few animals that acquire a tan from prolonged exposure to sunlight, a feature shared by pigs and humans. Tanning occurs when a hammerhead is in shallow waters or close to the surface for long periods.

The hammer-like shape of the head was thought to help sharks find food, aiding in close-quarters maneuverability and allowing the shark to turn sharply without losing stability. The hammer would also shift and provide lift and it was recently found that the development of vision probably led to the hammer-like shape. The positioning of the eyes allow for 360 degree vision of the shark. Hammerheads are one of the most negatively buoyant of sharks, and as with all sharks, they have a sixth sense for detecting weak electromagnetic signals, and so by distributing the receptors over a wider area of the head, hammerheads can sweep for prey more effectively. These sharks have been able to detect an electrical signal of half a billionth of a volt. The hammer also allows the nostrils to be placed further apart, increasing its ability to detect chemical gradients and localize the source.

Of the nine known species of hammerhead, three can be dangerous to humans: the scalloped, great, and smooth hammerheads.

The great and the scalloped hammerhead are listed on the World Conservation Union's (IUCN) 2008 Red List as endangered, whereas the small-eye hammerhead is listed as vulnerable. The status given to these sharks is as a result of over-fishing and demand for their fins, an expensive delicacy.

Distribution Map

Hammerhead Shark  Distribution Map

Various

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