Page 16 - Shark

Amazing grace

Sharks are graceful swimmers
propelling themselves through the
water by beating their tails from side
to side. The pectoral fins are held out
from the body and as water flows over
them, lift is generated to keep the shark
from sinking. Further lift is produced by the
upper lobe of the tail, which tends to push the
head down, so that the shark can swim on the level.
“S” for Swimming Shark fins are not nearly as flexible as those of bony fish,
Sharks swim in a
series of S-shaped but adjustments to the angle at which the fins are held control
curves and use a
combination of fin whether the shark goes up, down, left, or right. Pectoral fins are
angles to “steer” to also used for braking. Some sharks that live on the seabed,
the left or right.
such as horn sharks (pp. 40–41) and epaulette sharks, can use
their pectoral fins to crawl along the bottom. Unlike bony fish, sharks cannot
move their pectoral fins like paddles so are unable to swim backward or
hover in the water. They also lack swim bladders, which act as buoyancy
aids in bony fish. However, they do have oil-rich livers (pp. 10–11)
that help reduce their weight in water.

Tail end
Undulations, or “S”-shaped, waves pass down
a shark’s body as it moves forward (above).
The tail bends more than the rest of the body,
producing a forward thrust.

STarry SmooTh-hound
The denticles on a shark’s skin line up CruiSing
with the direction of travel, helping to With pectoral fins held straight out
reduce drag (resistance to water). from its sides, the starry smooth-hound
These denticles may trap a film (right) keeps swimming at the same level.
of water, helping sharks move The two dorsal fins stop the shark from
through it more easily. rolling and its tail gives a forward thrust.

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