Page 53 - Shark

chain waLL
This wall (left) of interlinked chains
surrounding an Australian beach
prevents any sharks from
getting in. Such walls are
too costly to protect more
than a few miles of beach.
Chemical repellants have
also been tried but they are
not effective, as any substance
released around a person in the
water disperses too quickly in
the waves.

invisibLe barrier
Sharks are very sensitive to
electric currents and here
an invisible electric barrier
is being tested. When the
current is off (top) the
lemon shark swims past,
but when the current is
switched on (left) the shark
protected beach turns back to avoid it. Cables
Experiments using screens made of bubbles released from air and even portable devices that
hoses on the seabed have been carried out, but shark nets, as on produce electrical pulses to deter
this Australian beach (above), still seem to offer the best protection. sharks have been tested in the sea.

death nets
Mesh nets, used to
protect beaches, kill
many sharks each year,
like the great white
(above) and hammer-
head (left). Sharks
entangled in nets are
not able to swim and
suffocate because they
cannot keep water
flowing over their
gills. Up to 1,400 sharK repeLLant
sharks, many of them The American scientist Dr. Eugenie Clark
harmless, as well as discovered that the Moses sole from the Red
dolphins, are caught Sea produces its own shark repellant. When
each year in South attacked, milky secretions ooze out of pores on
African nets. its skin, causing the shark to spit it out.

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