great white shark - Friends of the Elephant Seal

GREAT WHITE SHARK
Great White Shark
Order - Lamniforme
Family - Lamnidae
Genus - Carcharodon
Species - Carcharias
Ha bit a t & D ist rib ut io n
The great white shark is found mostly in temperate seas throughout the
world's oceans. It makes infrequent visits to cold waters and has been
recorded off Alaska and Canada. Great whites can be found along the
temperate coastlines of the world, as the map below shows.
The white shark lives mainly in the upper part of the water column, near
the shore. However, it ranges from the surf line to well offshore and from
the surface to depths of over 775ft (250m). This shark commonly patrols
small coastal islands inhabited by pinnipeds, (seals, sea lions and walruses)
offshore reefs, banks and rocky headlands where there is deep -water close to
shore. The white shark usually cruises either just off the bottom or near the
surface.
World Distribution Map for the White Shark
Movement
Although information about the white shark's movements is limited, some
information has been gathered through tag-and-release programs in the
United States, South Africa and Australia. These studies reveal that the
white shark is capable of making movements on local, regional and
intercontinental scales.
Generally, it is the larger individuals that undertake long journeys across the
great oceans. The great white is also capable of short, high -speed pursuits
and even launching itself clear from the water (breaching). They are propelled
through the water by their powerful tails, and they use their fins for balance.
Sharks swim constantly, otherwise they will sink as they don't have a buoyant
swim bladder like other fish.
About halfway between Hawaii and the Baja
coast is an area researchers dubbed the “café,”
a gathering spot for the usually solitary animals. It is speculated the purpose is to forage
and mate. Peak time at the café is April to July,
when many males hang out there and females
drop by. Most of these sharks spend winters
nearer to the coasts of Hawaii or North America.
Distinctive Features
Unlike the true fishes,
sharks don’t have
internal bone, but
instead have a
cartilaginous skeleton.
The great white is one of the largest species of shark. The snout is short and
conical. The eye is circular and solid black. The five gill slits are long, and all in
front of the pectoral fin. The tail fin support area (caudal peduncle) has a wide
lateral keel that strengthens the fin’s movement. The caudal fin is crescentic
(both upper and lower lobes are about the same size). The upper part of the
body, roughly on a line through the eye to the pelvic fin, is dark to light grey.
Below this, the body is white. This coloration helps to camouflage the shark
when approaching prey.
Size
Males reach maturity at between 11 and 13 feet and females at 15 to 16 feet.
Most great white sharks encountered are 12-16 feet long. The largest reliable
measurements for white sharks are: length 21 feet, weight 4,140 pounds. On a
per-length basis, great whites from California waters seem more massive than
those from other regions.
Arrangement of Teeth
Male
Female
The teeth of the great white are large, arrowhead-shaped and serrated. They
have about 3,000 teeth at any one time. The teeth are in rows, which rotate
when needed. As teeth are lost, broken or worn down, teeth rotate in to
replace them.
Top tooth
Bottom tooth
So c ia l B ehavio r Of G reat W hit e S harks
White sharks are intelligent and have one of the largest brains for their body
size of any animal - more similar to mammals than other fish. Their sense
organs are outstanding. Great whites
primarily use their sense of smell and
their ability to sense the electrical
fields of other animals.
Great whites are usually solitary
animals but are occasionally seen in
pairs. Scientists are beginning to
understand more about the behavioral
interactions between great whites.
Sharks definitely interact with each
other and communicate using body
language. For instance stiff, arched bodies and gaping mouths (underwater)
seem to be threat displays warning off other sharks. Some of the great white's
swimming habits, such as a carefully timed turn away between two sharks on
approaching courses, is interpreted as maintenance of individual space. Parallel swimming with two sharks heading in the same direction also seems to be a
means for the shark to preserve its space from others.
When white sharks feed on the same prey, it doesn't make sense for one to
bite and wound the other as this may reduce either shark's future ability to
catch prey. For this reason white sharks use displays in order to discourage
other sharks. White sharks have been observed with their caudal fin out of
the water slapping the surface, usually in the direction of a second shark.
This "tail slap" is the most common avoidance display shown by white sharks.
Sometimes a white shark will
position itself between prey and
another shark, preventing the
second shark from feeding. White
sharks have also been known to
propel their body out of the
water and land flat against the
surface, causing a large splash.
This behavior is called a breach
and may represent a similar
message as the tail slap.
Breaching might also help
remove external parasites,
attract a mate or may be the
result of a vertical charge
approach toward its prey.
Reproduction
White sharks are ovoviviparous. Fertilization of the eggs occurs in the
female; later the eggs hatch inside her and she gives birth to live young.
Embryos are nourished through ingestion of unfertilized eggs, as there is no
placenta. Their size at birth ranges from 47 -59 inches in length. The newborn shark is not cared for by the mother, and swims away from her immediately after birth.
Scientists are uncertain of when the female becomes reproductive but their
estimates range between 10-14 years. White sharks are likely to produce
litters of 4 to 11 pups. Gestation time is unknown, but is thought to be quite
long, possibly up to 14 months. Scientists don't know how many litters a
female produces in her lifetime and aren't sure how long after the last litter a
female becomes receptive again. As in other species of sharks, the male
white shark most likely bites the female during mating.
Predators
The white shark is an apex predator (on top of the food chain) and as such, has very
few predators and a relatively small population. Killer whales and larger sharks pose
the only natural threat to an adult white shark. Humans are the greatest threat.
Despite being rare, the white shark's rate of capture by humans is alarmingly high.
This is due partly to the increasing value of its jaws and teeth. Their fins are also used
for shark fin soup. In the despicable practice of finning the fins are sliced off of the
shark and then the living animal is left to die. When fully utilized, the flesh is eaten,
the skin used for leather, the liver for oil and the carcass for fishmeal. As an apex
predator, its population is not large. The National Marine Fisheries Service estimates
there are 3,000 individuals (young of the year to adult) in the North East Pacific population.
Fo o d & Feeding
The white shark is a macro predator that is active during the daytime. Its
most important prey are marine mammals (including, seals, sea lions,
elephant seals, dolphins) and fish (including other sharks and rays). Marine
birds and sea otters are commonly found having suffered injuries from
encounters with white sharks, but are rarely eaten by them.
The white shark has multiple attack strategies available. With large pinnipeds such as
elephant seals, the attack is a fast upward vertical strike at the hindquarters of the
prey. The shark then backs off to allow the prey to bleed out and avoid a struggle.
An attack on smaller marine mammals may involve an initial strike from below or from
the surface. The prey may be dragged under and held there until it drowns. If the
first bite tells the shark that the prey is low in fat, or not even an animal, the prey will
be released. Their intelligence means they are able to adapt their hunting strategy
depending on the prey. In shallow waters they often use stealthy ambush techniques
to capture seals. Occasionally great whites swim with their ventral side up and
perform an inverted approach. White sharks sometimes scavenge from fishermen's
nets and long lines—often resulting in accidental injury to the shark.
The Elephant Seal and White Sharks
The behavior of elephant seals gives them some advantages against white sharks.
Because most pinnipeds live in coastal waters, and most of their hunting is done at
depths above 500 feet, that is where sharks hunt. Elephant seals are protected by the
fact that most of their time at sea is spent farther from the coast than other pinnipeds.
Elephant seals are solitary creatures at sea and spend most of their time below depths
normally hunted by white sharks making encounters between the two less likely.
The results of experiments reveal that when white sharks have a choice between a
square target and a seal-shaped target, they select the seal shape, as it is more
common in their natural environment. When only a single bait was presented, it was
regularly investigated. Some scientists believe diver and surfer silhouettes, when
viewed from below, resemble those of pinnipeds and that this misidentification by the
shark is the cause of most white shark attacks on
humans. Researchers suggest that white sharks
often strike unfamiliar objects to determine their
potential as food. Grasping an unfamiliar object
would be the shark's only reliable method of
determining whether it is suitable as prey. Great
white sharks prefer energy rich prey, such as
marine mammals, rather than less fatty, low
energy prey.