Page 18 - Shark

Continued from previous page

Tails and more tails

The shape of a shark’s tail suits its lifestyle. Many sharks have tail
fins where the upper lobe is larger than the lower, and as the tail
swings from side to side, this lobe produces lift that tends to
push the head down. This is compensated by lift from
the pectoral fins, which stops the shark from
sinking to the bottom. In fast sharks,
like the mako and great white, these
two lobes are almost equal in size.
Lift may also come from the base of the tail
which, in the mako, has small, horizontal keels.
The extra height of these more symmetrical-shaped
tails gives a more powerful thrust. Slow bottom-
dwellers, like the nurse, have less powerful tails
and their swimming motion is more
eel-like, with obvious waves
passing down to their tails.

Bonnethead’s tail
Bonnetheads are small
hammerheads (pp. 42–43) that grow to
about 5 ft (1.5 m) in length. Like all sharks,
the tail’s upper lobe contains an extension
of the vertebral column and is usually larger than
the lower lobe. The upper lobe is held at an angle so
it is raised above the shark’s midline (imagine a
line drawn through the shark from the tip of
its snout to the end of its body).

Tail of a
bonnethead thresher’s tail
shark The upper lobe of the tail
(left) of a thresher shark is
as long as its body. From 5–8 ft
(1.5–2.5 m) in length,
the tails of the three
different types of
thresher (pp. 58–59)
are by far the longest
of any shark. The tail
of a thresher is used
Tail of a to stun its prey and
thresher also can inflict nasty
shark injuries on anglers
when the sharks are
hauled on board.

Keel

Great white’s tail
The upper and lower lobes of a great
white’s tail fin are almost equal in size.
They lie high above, and low below,
the shark’s midline respectively. The
keel helps the big shark to turn. The
Tail view of a model first dorsal fin is rigid and prevents
of a great white shark the shark from rolling. Also a great
(pp. 28–29) white can jump out of the water.

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