Of course your problem there is FINDING THE EARHOLE ON A SHARK!
Hearing and balance:
Whether sharks actually hear in the same sense that we do is unclear. The ears of sharks are completely internal. They are embedded within the chondrocranium (frontal skull). What looks like ear openings behind the eyes of sharks and rays are actually spiracles which primarily aid in respiration.
As in the inner ears of higher vertebrates the ears of sharks are responsible for balance and equilibrium. The inner ear of sharks consists of a series of ducts and sacs collectively known as the membranous labyrinth. These cavities are filled with endolymph which in sharks is mainly sea water that enters through the endolymphatic ducts. Around the membranous labyrinth is another series of fluid filled canals known as the cartilaginous labyrinth that are supplied through the perilymphatic ducts. The cartilaginous labyrinth protects and supports the more sensitive membranous labyrinth within. The sacculus is a large inner chamber into which the endolymphatic ducts lead. Within this is an area called the lagena that has been shown to receive sound waves in some fishes. Lining the walls of the sacculus are patches of sensory epithelium covered with sand grains and calcareous deposits known as otoliths. As the shark banks the endolymph fluid and otoliths lag behind slightly. Their swaying registers on nearby sensory hair cells that send signals to the brain resulting in sensations of imbalance that the shark then corrects. Imagine the importance of good balance in an environment where there are sometimes no visual cues at all to tell you which way is up.
At one time scientists thought that sharks may be able to hear with their entire bodies using their lateral line systems. This idea has since been discredited but the principle remains a reasonable one. Sound waves are after all little more than vibrations that fall within an animals auditory range. And, considering the importance of hearing it would make sense that such a successful group of animals as elasmobranchs would make use of it in one way or another.
