The World of Sharks

There are about 510 species of sharks, but we still know precious little about these enigmatic and often elusive fish.

Scalloped hammerhead sharks (Sphyrna lewini) often swim alone, but large groups of the distinctively-shaped fish have been observed gathering at underwater mountains where they perform courtship “dances” with females taking up position in the centre of the circle.

Pre-historic in appearance, the bizarre Port Jackson shark (Heterodontus portjacksoni) is found around the southern, eastern and western coasts of Australia. Its teeth are small and pointy at the front and flat and wide at the back to crack and grind the shells of prey.

The most iconic of sharks, the great white (Carcharadon carcharias) is an inimitable predator but it has a less well-known social side as well. Groups of sharks gather and use body language to communicate with each other, sorting out disputes over kills and dominance. But when they do hunt for prey, it is with impressive speed – in excess of 20mph (32kph). They are possibly one of the most feared sharks but attacks on humans are very few.

Oceanic whitetip sharks (Carcharhinus longimanus) are distinguished by their very long and wide pectoral fins. These predators have extremely powerful jaws to grip their prey, and serrated teeth in its upper jaw to cut into flesh. Growing up to about 13ft (4m) in length, oceanic whitetip sharks are found in tropical and subtropical waters around the world, and can potentially be dangerous to humans.

The curious-looking tasselled wobbegong shark (Eurcrossorhinus dasypogon) is found around northern Australia, Indonesia and Papua New Guinea. Its unusual markings allow it to camouflage itself and quickly grab unsuspecting prey. Its frilly “beard” may act as bait, as it resembles tasty small sea creatures, luring the shark’s victims to its mouth.

Bigeye thresher sharks (Alopias superciliosus) are believed to be harmless to humans. The distinctive-looking fish’s huge eyes are positioned high in its head and may be adapted to help it find prey silhouetted near the water’s surface.

Ragged-tooth sharks (Carcharias taurus) are also known as grey nurse sharks or sand tiger sharks. They can reach over 10ft (3m) in length and their ragged-looking teeth, made up of larger teeth separated by smaller ones, give them a ferocious look. To stay buoyant, they gulp air from the surface and hold it in their stomachs. The sharks have been known to attack humans, but usually only when provoked.

The whale shark (Rhincodon typus) is a slow-moving filter feedingshark and the largest known extant fish species. The largest confirmed individual had a length of 12.65 m (41.50 ft) and a weight of more than 21.5 metric tons (47,000 lb), and unconfirmed reports of considerably larger whale sharks exist. The whale shark is found in tropical and warm oceans and lives in the open sea, with a lifespan of about 70 years.^[3] Whale sharks have very large mouths, and as filter feeders, they feed mainly on plankton.

Credit: BBC, Wikipedia.