Brett Mullenger, of King's High School, asks :-
How do sharks communicate?
Peter Klimley, a marine animal behaviourist at the University of California at Davis's Bodega Marine Laboratory and author of the article 'The Predatory Behavior of the White Shark' in the American Scientist, vol 82, pl22-133, 1994, responded.
Unlike humans who communicate by speech, sharks usually pass information by performing conspicuous and exaggerated movements.
These may act as signals, indicating to a competitor an adversary's capacity to inflict harm. If the competitor heeds this signal, the signaler benefits by gaining access to a resource such as food without having to resort to fighting which might result in personal injury. For instance, after a white shark (Carcharodon carcharias) kills a seal, it often floats dead at the surface. Another shark is often attracted and attempts to feed upon the remainder of the seal. Both sharks may perform a threat behavior, Tail Slap. Each shark alternately rolls on its side, lifts its tail out of the water, and then brings it down against the water, propelling water toward the other. That shark which lifts more of its body out of the water and splashes water farther more times succeeds in feeding further on the prey. By deciding access to the prey with a show of strength involving the tail, both avoid the potentially dire consequence of using their huge jaws and large teeth. Thus, communication here is advantageous to both - an important decision is made without adversely affecting either's ability to capture prey in the future.
Communication between sharks is not only restricted to feeding. Female scalloped hammerhead sharks (Sphyrna lewini) perform a behavioral pattern, Cork-screw, while competing for a central position in the large schools that swim around underwater mountains, or seamounts. This behavioral pattern involves a rapid burst of swimming into a tight looping trajectory with the shark rotating its torso almost 360 degrees on its long axis before entering the circular trajectory. Light reflected from the belly of the shark may be a component of this signal. Large females force smaller females to the edges of the schools using Cork-screw. This behavior pattern is more frequent than the Hit, in which the head of a smaller female is contacted with the underside of the larger shark's snout. Again, this behavior fits the definition of a threat, an exaggerated behavior that demonstrates the individual's capacity to inflict harm. It is thought that males mate only with those females at the center of groups.