The fascination is understandable – sharks have changed little in millions of years because they are almost perfectly designed to do what they do, which is eat. To a certain extent the fear is understandable too: they are one of the few natural predators that can feed on humans, and they sometimes do. However, that sometimes is actually almost never – we have more chances of being killed by bees or lightning than sharks. Nonetheless, attacks do happen, and whilst we still know little about them, there are some typical patterns of behaviour.

Sharks are generally found near the sea bed, where they feed on rubbish and fish. Humans are not normally part of their food chain. They do however have a very keen sense of smell. They can detect a drop of blood in millions of drops of water. Thus an injured person in the water in an area where sharks feed is in considerable danger. They are also attracted to splashing and erratic movement such as that of an injured fish, or a swimmer. They eat seals, and surfers on boards or people on small rafts have the same shape. They like to feed near the beach and around sandbars, where people gather. So, the potential danger is high when there is contact between sharks and people.

When a shark attacks

When a shark attacks, it is normally in one of two forms; both can be carried out at great speed and with no warning, and both can be fatal or result in serious injury:

Hit and run: the shark thinks something is food and bites it, then realises it is not and lets go. This kind of attack normally occurs near the surface and in poor visibility.

Bump and bite: the shark bumps against its prey to test it, then attacks. It will often circle and repeatedly bite at arms and legs. This is the most dangerous form of attack and often results in death, especially as it occurs in deeper water.

Avoiding shark attacks

There are measures that can be taken to avoid shark attacks:

- if a shark is seen, get out of the water. Do it calmly and without panic. Do not splash.

- If a shark actually gets close, a blow to the nose can be effective in deterring it. This needs to be done with great caution, as the shark’s mouth is close to the nose and even if it does not bite, teeth can cause serious injury.

- Stay in groups. Sharks prefer to attack individuals.

- Stay out of murky or polluted water and away from sandbars.

- Do not wear bright material – sharks see contrasts very well.

- Stay out of the water when the light is poor e.g. at dusk or at night. Sharks prefer these times and have a sensory advantage.

- Never enter the water with an open wound

Shark deterrents

Certain areas of military activity make contact with sharks highly probable - downed aircrews and navy personnel are obviously at risk, but also boarding parties on small craft. Military divers are particularly vulnerable as they often carry out work such as clearance, rescue and reconnaissance at night or at dusk, when sharks are most active.

Given this level of risk, much work has been done by both military and civilian organisations to find effective shark deterrents. Many types have been tested, the most common being chemical. These have generally not shown any significant success – a hungry and determined shark will not stop if there is food present. However, sharks detect prey using a range of very delicate electrical field and vibration sensors. Devices have now been developed which generate an electrical field which seems to cause discomfort to the shark – these weigh little and can be carried in webbing or life jackets. One advantage of these devices is that they have a limited range and cannot be detected beyond it, so revealing a diver’s location. Obviously these devices can be scaled up to protect an entire boat or even a complete operational area.

Use these exercises for further language practice:

Shark Chaser - "drag and drop exercise"

Facts about sharks - "word order exercise"