Sharks are the world’s most feared and impressive fish.
They belong to the super-order Selachimorpha and comprise 440 species, distributed all over the world. They are believed to have been in existence before the dinosaurs. In fact, scientists surmise that the earliest shark species swam earth’s waters some 420 million years ago.
The different shark species are diverse in terms of their physical appearance, distribution, diet and habits. The
 The magnificent Great White Shark - Carcharodon carcharias The Great White Shark
Averages an impressive 6.6 to 7 metres and the grizzly Ragged Tooth Shark comes in at about 3.6 metres. Different shark species prefer different waters but, generally, sharks are found all over the world. They may live anywhere between relatively shallow depths and about 2000 metres from the surface.
Some are even found on the ocean floor. There are a few rare species that have been designed to live in fresh water, while the vast majority are ocean dwellers. Generally, sharks prefer warmer waters. There are certain species that migrate, while others remain within a defined area for their entire life.
 Caribbean Reef Shark - Carcharhinus perezi - shot in the Northern Bahamas.
The shark’s body is streamlined to allow these effective hunters to glide through the water unhindered. Sharks that skate the ocean floor are usually flattened, allowing them to slide along the sand unnoticed. Unlike other fish, which have both bones and cartilage, sharks have only cartilage, increasing their flexibility and decreasing their weight to allow even faster movement. Their replaceable rows of teeth are used only for capturing their prey and tearing chunks of flesh off. They do not chew their food, but gulp it down.
All sharks are carnivores. However, their diet remains varied. Some species, including the mammoth Whale Shark, swim with their mouths open, allowing plankton and other small creatures to enter through huge filters. 
Scalloped Hammerhead Shark - Sphyrna lewini - photographed at Cocos Island. Sharks are believed to be relatively intelligent. They can learn to adopt patterns of behaviour and recognise certain people and objects. There have been several shark attacks on people, usually resulting in severe injuries and / or death. The Bull Shark is the most common predator for bathers as it frequents the same shallow waters in which the people are swimming. It also has high population numbers. Other common human attackers are the Great White, Tiger and Oceanic Whitetip sharks. To avoid attacks, it is essential that bathers remain within the swimming confines as set out by the lifeguards and that a bather exit the water immediately if they have a bleeding injury.
Sharks are gracious, magnificent in form and impressive in power. They continue to be threatened by hunting and pollution, yet remain one of the most fascinating and humbling creatures to encounter.
For more information, please view: http://www.sharkalliance.org/ and http://www.sharks.org/ and
 http://www.sharkfreemarinas.com/
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