Behavior
Daily activity cycle
Recordings of the movements of tagged sharks suggest that most
sharks undergo daily activity rhythms. Their greatest activity
occurs during the twilight and dark hours.
Social behavior
Although sharks and batoids are basically asocial, many
species demonstrate various degrees of social behavior. For
instance, hammerhead sharks commonly school.
Symbiotic relationships
Pilotfish (usually Naucrates ductor, but there are
others) often travel with sharks. This may be due to the natural schooling behavior of
pilottish, or they may conserve energy by riding the
hydrodynamic bow wake of the shark. Pilotfish also eat small
amounts of food scraps released as the shark feeds.
Several species of small fishes, notably the cleaner wrasse
(Labroides dimidiatus), are "cleaners" that pick
debris and parasites from sharks.
Remora (several species in the family Echeneidae) commonly
attach themselves to sharks and batoids or ride their
hydrodynamic bow wakes. In addition, they may eat parasites of
sharks and batoids.
Parasites of sharks and batoids are mainly copepods (small
crustaceans) and flatworms.
Shark attack
Only 1/3 of the species of sharks have been associated with
attacks on humans or vessels. These species have three features in
common: they prey on fish or marine mammals, grow to a large
size, and visit warmer coastal waters where swimmers are apt
to be.
According to various researches (for example one of them was started in 1958 by the U.S. Office of Naval Research and the American
Institute of Biological Sciences) it was established that humans become prey by accident (through sight or sound, a shark may confuse swimmers or divers for its normal prey). Sharks may also attack from a territorial drive, with no intention to feed. A characteristic swimming pattern called agonistic display usually precedes attacks out of territoriality. The shark shakes its head and swims erratically with a hunched back, pectoral fins pointing down, and snout pointing up.
An analysis of 1,000 recent shark attacks world-wide showed
that well over 50% of the attacks were not feeding-related.
Up to 60% of shark attack injuries are slashes of the upper
jaw teeth. This behavior is typical of courtship advances by some
male sharks.
Sharks may also injure victims by bumping them vigorously,
but most sharks move in cautiously when attacking.
A Great White Shark (Carcharodon carcharias) rushes towards
its prey, attacking from beneath and behind. These sharks rely on
stealth and surprise to prey on seals, sea lions, and other
marine mammals.
After a great white shark bites its victim, it swims a
short distance away, waiting for its victim to bleed to
death. If rescuers are nearby, many human victims survive
the attack.
Great white shark populations may be
increasing along the coasts of California and Oregon due
to increasing populations of seals and sea lions. Marine
mammal populations are increasing as a result of federal
protection. Populations of predators naturally increase
as food becomes more readily available.
To reduce the chance of an attack by a great white
shark, swimmers and divers should stay clear of seal and
sea lion rookeries, or other known areas frequented by
the sharks.
Swimmers and skindivers at the surface are more
prone to attack than SCUBA divers beneath the water. At
the surface, a swimmer's or diver's silhouette resembles
that of a seal. Great white sharks may not be able to
make the distinction.
California has one of the highest great white shark
attack rates in the world. Yet fatalities average only
one every eight years.
There is no known effective shark deterrent.
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