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Hearing and Balance
The most important stimulus to a shark is probably sound. The ears
of sharks are especially good in picking up low-frequency vibrations
from great distances. Work by A.N. Popper and R.R. Fay in the 70s
showed that the sharks ear did this by detecting the movement of
water particles, which carry vibrations, rather than from changes
in sound pressure. Sharks have two inner ears (one on each side
of the head) that are enclosed in the brain case, and are connected
to the outside via tiny ducts called endolymphatic ducts. Otherwise
the structure of a shark ear is similar to that of all vertebrate
ears - 3 semicircular canals, the utriculus, the sacculus and other
related structures all exist. Another important function of a shark's
ear (and indeed any fish's ears) is to provide information about
its position and speed.
(© J. Lokrantz/Azoteimages)
Sharks, like in other fishes have an acute vibration sense called
the lateralis system. This system consists of canals (found along
the whole body) which open at intervals to the surface. The canals
contain clusters of sensory cells that project hairlike projections,
which are enclosed in a gelatinous dome. The pores allow seawater
to flow freely in the canals, and vibrations cause the hairlike
projections to move slightly and trigger nerve impulses to the shark's
brain. In addition to sensing very minute vibrations, the lateralis
system helps give the shark additional information about balance
and movement.
(© J. Lokrantz/Azoteimages)
Ref: Springer VG and Gold JP (1989),
Sharks in quetion: the Smithsonian answear book, Smithsonian
Institution Press, Washington, D.C. London -- Taylor LR (editor) (1997),
Collins Sharks & Rays -The ultimate guide to underwater predators,
HarperCollins Publishers, London
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