Surprising Sharks at the Natural History Museum at Tring, 11 February – 6 July 2008
Sharks are fishes, but unlike most fish their skeletons are made of cartilage, which is lighter and more flexible than bone.
Although fishes are generally cold blooded, some fast-swimming sharks maintain a body temperature higher than the sea water around them.
Sharks cannot hover in the water like a goldfish, and must keep swimming forward to stop themselves sinking. Some sharks, however, habitually lie on the bottom of the sea.
Sharks were here when dinosaurs roamed the planet (over 450 million years ago).
There are more than 460 species of shark that live in all the world’s seas and oceans. Some sharks even live in rivers.
There are approximately 21 types of shark that can be seen around the coast of Britain, and they range in size from the small-spotted catshark at 40 centimetres to the 11-metre-long basking shark.
The largest shark is the whale shark, which has been spotted at over 12 metres long. That’s about the length of one and a half London buses.
The smallest shark is the spined pygmy shark that grows to around 15 centimetres long – the same size as a chocolate bar.
Sharks skins are covered in tiny teeth called denticles. This helps them swim more efficiently. Speedo worked with scientists at the Museum to develop a high performance swim-suit which copied this idea from sharks.
Tiger sharks have such a varied diet they have earned the nickname ‘garbage can sharks’. They will eat almost anything they encounter in the water: bony fish, sharks, seabirds, turtles, lobsters, cats, dogs, number plates and octopuses.
The biggest sharks in the sea, the whale shark and the basking shark, are completely harmless. They feed on small shrimps which they strain from the water using their gills while swimming along with their huge mouths open.
In many species of shark, the teeth are constantly replaced throughout the shark's life – some sharks can lose 30,000 teeth in a lifetime.
All sharks have many rows of teeth with new ones ready to replace old ones as they become worn. In some sharks, rows of teeth are replaced every eight to 10 days.
Sharks have very different types of teeth depending on their diet. The grinding pavement teeth of the Port Jackson shark are used to crush sea urchins, invertebrates and small fish and the pointed teeth of the kitefin shark help it to eat fish.
Some sharks produce live young while others lay special egg-cases on the sea bed.
The sand tiger shark pups developing inside the mother will eat each other until just one survives. This is called intra-uterine cannibalism.
Of the 460 different kinds of shark in the world, only three occasionally attack humans, most feed on shellfish and small fishes. Crocodiles, dogs and pigs kill more people each year than sharks do.