Form and Function of Sharks 35
put a shark’s nose in contact with any floating, odor-releasing compound at
the water’s surface, especially oily or fatty particles that tend to float.
How well can sharks hear?
Sharks have good hearing, especially at the low frequencies that char-
acterize natural sounds and vibrations. Their hearing range is from 20
to 1100 Hertz (Hz), which is about the second to the sixth octave of the
musical scale. The lowest note on a tuba is 16 Hz, or close to the lowest
note a shark can hear. The normal range of human speech, between 85 and
255 Hz (maximally 1050 Hz for females), falls within the hearing range of
sharks.
Sharks are most sensitive to and attracted by sounds produced by their
prey, especially prey that might be injured or frightened. Such sounds tend
to be at the low end of the shark’s hearing range, and it is not surprising
that sharks respond strongest to sounds below 375 Hz. Juvenile Lemon
Sharks are attracted to sounds such as a quickly accelerating fish or a fish
swimming with a damaged tail, and to the drumming sound produced by
an injured marine catfish. A struggling grouper produces 10- to 150-Hz
sounds that can attract reef sharks from as far away as 200 m (656 ft). Prey
fish crunching on food can attract Lemon Sharks 10 to 15 m (33–50 ft)
away.
To hear these sounds, sharks use their inner ears and receptor cells scat-
tered around the body. Sharks have internal ears located inside their heads
on both sides rather than external ears like mammals. The inner ears are
linked to the outside by a very small canal that ends on the side of the head.
The body receptor cells occur between the scales, particularly under the
mouth and at the base of the pectoral fins. Other receptors are concen-
trated in the lateral line canals on the body and head, making a shark not
just a swimming nose but also a swimming ear.
The concentrations of receptor cells in shark species differ as a function
of ecology. Bottom-living sharks, skates, and rays have most of their recep-
tor cells on their backs (dorsal surfaces), whereas sharks that swim above
the bottom have the cells along their sides. Chimaeras, which also swim
above the bottom, have receptor cells in canals that run from their nose to
the tip of the tail.
Although we can detect sounds at higher frequencies than sharks can,
sharks do something we can’t, at least not when we’re underwater. They
can tell what direction a sound came from. You can demonstrate your in-
ability to do this by submerging yourself in a pool or pond, closing your
eyes, and having a friend bang on a bottle off to one side while underwater.
The noise appears to be coming from everywhere, something scuba div-