The tails (caudal fins) of sharks vary considerably between species
and are adapted to the lifestyle of the shark. The tail provides thrust
and so speed and acceleration is dependent on tail shape. Some typical
shark tail shapes are discussed below:
Tiger shark - The tiger sharks
tail is pronouncedly epicercal (the upper lobe is longer and heavier
than the lower lobe). Movement is controlled by swinging the body from
side to side. The large upper lobe delivers the maximum amount of power
for slow cruising or sudden bursts of speed. The tiger shark has a
varied diet, and because of this it must be able to twist and turn in
the water easily when hunting turtles, fish, stingrays, and other sharks.
Nurse shark - The nurse shark is common in shallow waters
around the tropical coasts of America and Africa, and is nocturnal. Its
prey consists mainly of invertebrates such as crabs, lobsters, sea urchins and octopuses.
This causes the sharks to spend most of their time on the seabed. As a
result high acceleration is not necessary and the lower lobe has almost
completely disappeared. They swim with an eel-like motion, using broad
sweeps of their elongated tails to cruise slowly.
Porbeagle - The porbeagle is a heavily built pelagic shark, closely related to the mako and great white, which hunts on schooling fishes such as mackerel and herring.
The tail is used for propulsion rather than having to swing their body
from side to side. The large lower lobe provides greater speed to help
them keep pace with their fast swimming prey, and their lateral keels
may reduce drag making for more efficient hunting.
Thresher shark - The thresher
is found in tropical and temperate waters around the world and feed on
fish and squid, which they are believed to herd, then stun with the
powerful and elongated upper lobe. The three species of thresher are
active and strong-swimming sharks - the evolution of the highly
elongated tail (which may be half of their total length) has not been
at the expense of speed or agility.
Great white shark - The great white
is primarily a coastal and offshore species, but can be found far from
land. Its body and tail have a shape similar to that of tuna. Its upper
and lower lobes are of almost equal size. This provides for both slow
cruising and fast chasing speeds.
Cookiecutter shark - The cookiecutter shark hunts squid and crustaceans,
but will attach itself to larger fish or dolphins with its strong
suction lips. Using its scoop-shaped lower jaw it will then cut out a
conical plug of flesh. Its tail has broad lower and upper lobes of
similar shape which are luminescent and may help to lure prey towards
In general, sharks swim ("cruise") at an average speed of 8 km/h
(5 mph), but when feeding or attacking, the average shark can reach
speeds upwards of 19 km/h (12 mph). The shortfin mako may range upwards of 50 km/h (31 mph). The shortfin mako shark is considered to be the fastest shark and one of the fastest fish. The great white shark is also capable of considerable bursts of speed. These exceptions may be due to the "warm-blooded", or homeothermic, nature of these sharks' physiology.