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Endangered Hammerhead Sharks

Updated on December 3, 2012

Plight of Hammerhead Sharks

The scalloped hammerhead's population has been reduced by 99% in the past 30 years in some parts of the world, due to overfishing and finning, and it is reckoned they will be extinct in our lifetime.

This has led to an increase in cownose rays,which were a popular choice of food for sharks, and this is turn has meant a sharp decrease in bay scallops (the food of choice of the cownose rays) around which an industry collapsed when there were none left to catch.

Studies have shown that ALL shark populations have been reduced by 50% in the north-west Atlantic in the past 30 years, and that ALL sharks could be eradicated forever in our lifetime, if steps are not taken to protect them.

Both the Great Hammerhead (Sphyrna mokarran) and the Scalloped Hammerhead (Sphyrna lewini) are on the International Union for the Conservation of Nature (IUCN)'s list of endangered species.

Hammerhead Sharks

Hammerheads are aggressive hunters, feeding on smaller fish, octopuses, squid, and crustaceans. They do not actively seek out human prey, but are very defensive and will attack when provoked. Photograph by Brian J. Skerry
Hammerheads are aggressive hunters, feeding on smaller fish, octopuses, squid, and crustaceans. They do not actively seek out human prey, but are very defensive and will attack when provoked. Photograph by Brian J. Skerry

Hammerhead sharks are found on continental shelves in the warmer and temperate oceans of the world. There are nine identified types in this species, the largest being the Great Hammerhead, which can reach 20' in length and weigh 1000lbs.

Of these nine, only 3 are considered to be potentially dangerous to humans - the great ,the smooth and the scalloped hammerheads.

They can often be seen in shoals heading for the cooler waters in the heat of summer. They are best identified from their tall pointed fin and their colouring which is grey/green on top and white underneath.

Their teeth are heavily serrated and triangular.

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The hammerhead shark's wide set eyes with 360 vision, gives it a much better vision than most other sharks, and it's reckoned that the hammer shaped head that gives it its name is used for its sensory organs to better help it detect food.

Hammerhead Sharks have all round vision.

Scientists have long argued over exactly why hammerhead sharks have such strangely shaped heads.

Now a team of scientists from Florida Atlantic University and the University of Hawaii in Manoa have conducted experiments that prove that hammerhead sharks have 360° vision.

By placing a variety of sharks with different head shapes into a large tank and shining lights from different angles, they were able to work out each animal’s reaction through special sensors placed on their skin to measure brain activity.

Through this method they were able to prove that hammerheads have anterior binocular vision.

This allows them to see directly ahead AND accurately judge the distance of any prey they spot. Basically this is a panoramic vision that allows them to see all round at the same time – up, down, in front and behind, simply by slightly moving their head from side to side as they swim.

This would be useful for them not only for catching prey, for avoiding becoming prey to larger sharks.

The hammerhead takes 16 years to mature enough to carry young and when she does, she often has litters of 20 - 40 at one time! However, they do not stay with the young, from birth they have to fend for themselves, and many do survive to adulthood.

A scalloped hammerhead shark. Photograph: Stephen Frink/Corbis
A scalloped hammerhead shark. Photograph: Stephen Frink/Corbis

Where are all the hammerhead sharks going?

It seems the vast majority of sharks are sold in Asian markets, mostly for their fins which have a terrifically high value now, which is then turned into shark's fin soup.

Once upon a time it was only the rich in China who could afford it, but now the middle classes are catching up due to the economic boom of the last 20 years.

What protective measures are being offered hammerhead sharks?

The hammerhead shark has not been seen in the Mediterranean Sea since 1995.

There have been moves by various authorities worlwide to protect the sharks, but the legislation is being totally ignored and unenforced. For example, at the world heritage site at the Galagapos Islands finning is banned but it goes on, and openly.

In Europe, only Croatia and Malta have extended protection towards sharks in their waters of the Mediterranean Sea.

Britain is one of the 5 European nations that continue to permit fins to be removed at sea, which of course kills the shark whose body is then dumped overboard.

There are no regulations in place in international waters to protect sharks, who are at the top of the oceanic food chain, but whose loss will result in an ecological imbalance which could have devastating consequences for all of us.



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