Sharks are not invulnerable.
While sharks were at one time the reigning royalty of
the undersea world, they do have several formidable enemies other than
man. The unfortunate shark that consumes a porcupine fish will suffer dire
consequences. This unique fish will inflate itself inside the shark’s
jaws, preventing the flow of water through the shark’s gills. This
defense mechanism will asphyxiate the larger creature. The great squid and
salt-water crocodile are both fierce shark hunters. The killer whale has
been seen to swallow a shark whole.
While dolphins and sharks have been known to coexist peacefully, a dolphin
can efficiently dispose of a shark. One technique of the dolphin is to
swim full-speed towards the abdomen of the shark, smacking into this
tender area and causing the shark’s delicate intestines to hemorrhage.
Dolphins also bump into the gills of the shark, which destroys the
shark’s ability to breathe. In one case, there was an aquarium where a
shark and several dolphins had been living together without difficulty for
some time when the dolphins, for unknown reasons, threw the shark out 20
feet away onto the floor.
For man, only approximately 10 percent of sharks are dangerous. However,
there are no known infallible shark repellents. In order to be effective,
a shark repellent must work before the shark attacks, as nothing short of
death will deter a shark once it has begun its run. The perfect shark
repellent must be effective against all species of sharks suspected of
being dangerous to man. As of yet, nothing has been devised that can
guarantee that a swimmer, diver or survivor of a sea disaster will be
given absolute protection against the possibility of a shark attack.