Sharks, including rays and sandsharks, are known as cartilaginous fish since their "skeleton" is composed of cartilage rather than true bone. They are cold-blooded vertebrates that live in water, breathe by means of gills and use fins for locomotion.
Cartilaginous fish have five to seven gill openings on either side of the head and their rough skin is made up of tiny teeth-like structures called dermal denticles.
Most sharks have a number of rows of teeth in their jaw and as one tooth falls out it is replaced by another tooth from the row behind. Sharks have been around for 400-million years, even outliving dinosaurs.
There are more than 350 shark species, ranging in size from the enormous whale shark – which can grow to over 18m in length – to the tiny spined pygmy shark, which measures a mere 18cm. Sharks are found throughout the oceans of the world, from the icy polar regions to warm, tropical regions. Some, such as the Zambezi shark, can even be found in fresh water.
With their profusion of sharp teeth, sharks have earned a bad reputation due to isolated attacks which occur periodically along our coastline. In many cases, sharks mistake humans in wetsuits for their natural prey – seals or turtles.
It is important to remember that sharks play an important role in marine ecosystems, as they are often the top predators.
Of the 350 species of shark worldwide, only 20 are known to be potentially dangerous to man. There are fewer than 75 shark attacks per annum worldwide, so swimming in the sea is definitely safer than many other recreational pursuits.