In sharks, as in many other animals, it is possible to get an idea of the animal’s behavioural state by paying attention to changes in behaviour and displays of the body and appendages. Such information can potentially be life saving for divers or surfers who regularly come into contact with the big sharks. The biologist R. Aidan Martin from the University of British Columbia has described various agonistic displays by sharks in order to learn more about these warning signals.

Displays include hunching of the back, fin flexing and rapid approach followed by sharp turns used as threat signals. The great white shark, furthermore, breaches the surface and splashes with the tail as a sign of a high aggression level.

Shark displays are mainly used as a form of conspecific communication usually employed in conflict situations. However, they are also employed in other situations where the shark feels threatened or unsure of the situation, such as proximity of human divers. Display intensity is dependent of factors such as the speed of approach of the diver and the escape routes available to the shark.

Although shark-diver interactions always contain an element of danger this can be minimised if the diver responds appropriately to the shark’s display. Dr. Martin gives the following advice to divers: Face the shark and maintain eye contact, back away from the displaying shark if possible toward a reef or wreck, surrender speared fish or capture marine animals immediately and last should the shark approach fend it off with any available object.

Source: R. Aidan Martin (2007). A review of shark agonistic displays: comparison of
display features and implications for shark–human interactions. Marine and Freshwater Behaviour and Physiology 40: 3-34.

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