Communication, defense, hygiene and predatory behavior are all reasons why a whale may breach the water. As of 2014, scientists are trying to find a single, definitive reason why whales exhibit breaching behavior.
Theories suggest that whales breach the water as a means of communication. When a whale leaps entirely out of the water and lands again, it creates a loud, intense sound. This sounds travels quickly through the water, leading scientists to believe that it is a way to communicate with other whales and animals that are within range. This signaling could be a way for the whale to attract a mate, warn off predators or share the location of a promising food source. Some observations of whales in the wild show that whales are more likely to breach when they are in pods and social groups. This behavior suggests that breaching is done for social reasons such as courting or competitiveness for dominance between males.
It is also possible that whales breach in order to catch and kill prey more efficiently. The loud noise and powerful force of the whale's body slapping back against the surface of the water may stun the prey long enough for the whale to catch it more easily. Furthermore, scientists theorize that breaching allows the whale to inhale more air in rough seas. Breaching may also help clear the whale's skin of parasites, barnacles and sea lice.