The sight of a shark with bits of human limb falling out of his or her mouth is more than enough to put anyone off their lunch.

However, like humans, they can get upset when their mating rituals are disturbed, and sometimes they attack human voyeurs. It is well known that you are more likely to get hit by lightning than be killed by a shark. However, not many people know just how much more likely this is.

Even if you exclude those states which are land-locked, you are still over one hundred times more likely to be killed by lightning than by a shark. A total of four people were killed by sharks last year, in the United States, Australia, Fiji and South Africa. Unfortunately, humans are less discriminating. For every human that is killed by a shark, about ten million sharks are killed by humans. Sharks are killed for their meat, their hides and their jaws. Their livers are used to make lubricant for aircraft and ointment for haemorrhoids, and their cartilage is used as a quack cure for cancer.

But the most disturbing assaults on them are for their fins. Shark-fin soup is considered a delicacy, costing up to $150 a bowl. Because there is more demand for the fins than for the rest of the animal, the animals are caught (often during tuna fishing), and their fins are cut off while they are still alive. The animal is then put back into the sea to die a slow, painful death, unable to swim properly.

As a result of this barbarity, some shark species are down by 80% since 1990. At the current rate, these animals will be extinct within another ten years. Unlike other fish, sharks bear only a small number of young, and take up to twenty years to reach sexual maturity.

Shark have been around for 400 million years. They are believed to have developed the first immune system, which, although very primitive, may contribute to their very low rates of cancer. Unlike more modern fishes, they have cartilage rather than bone. Their cartilage is believed (wrongly) to be a cure for cancer.

There are around 300 species of shark, from 30cm-long dwarf sharks to whale sharks and basking sharks which can grow up to 15m in length. Most of these species are shy and non-aggressive. In fact, the largest, the whale shark and the basking shark, feed on plankton. Only three types of shark are really dangerous to humans: the great white shark, the tiger shark and the bull shark. Some species are extremely rare: for example, only twelve megamouth sharks have ever been seen. Another interesting type is the hammerhead shark, whose head really does look like a hammer.

Hammerhead sharks have an unusual mating ritual, not unlike that found in some Australian pubs. The animals gather in schools, and dominant females fight their way to the middle. Males are attracted to the strongest females, which are the ones that manage to get closest to the centre of the group.

Sharks form an important part of ocean ecologies, since they are apex predators. Like land predators such as lions, sharks are needed to keep the entire ecological system in balance. Over-fishing of sharks off the Australian coast a few years ago led to a sharp increase in the number of octopi, and a decline in the number of spiny lobsters. In Florida, a reduction in the hammerhead shark population has led to a surge in the numbers of stingrays.

However, it is a testament to the maturity of the ecological movement that even animals such as these, which are not cute and cuddly, are attracting support and protection.

The US National Marine Fisheries Service has passed laws limiting the catch of 39 shark species in the Atlantic Ocean, Caribbean and Gulf of Mexico. Australia, New Zealand and Canada have also introduced controls on fishing. In Australia, questions have even been raised in the NSW parliament over the treatment of two black-tipped reef sharks who are being kept on public display in the Shark Hotel. Attitudes are changing.