Tiger shark

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Tiger shark
Side view of a tiger shark.
Conservation status
Near Threatened
Scientific classification
Kingdom:	Animalia
Phylum:	Chordata
Class:	Chondrichthyes
Order:	Carcharhiniformes
Family:	Carcharhinidae
Genus:	Galeocerdo Müller & Henle 1837
Species:	G. cuvier
Binomial name
Galeocerdo cuvier Péron & Lesueur 1822
File:Tiger shark distribution.PNG
Tiger shark range (in blue)

The tiger shark (Galeocerdo cuvier) is one of nature's largest sharks. A mature shark can average 3.25-4.25 meters (10-14 feet) long and weigh 325-425 kilograms (850-1400 pounds). It is found in many tropical and temperate regions of the worlds oceans, and is especially common around islands in the central Pacific. The tiger shark hunts alone, usually at night. Its name is derived from the dark stripes down its body, which fade as the shark matures.

The tiger shark is a dangerous predator, known for eating a remarkably wide variety of things. Its usual diet consists of fish, seals, birds, smaller sharks, squid and turtles. It has sometimes been found with detritus such as license plates or pieces of old tires in its digestive tract. The Tiger shark is notorious for attacks on swimmers, divers and surfers in Hawaii; it is often referred to as the "bane of Hawaiian surfers" and "the wastebasket of the sea".

The tiger shark is second only to the great white in number of recorded human fatalities and is considered, along with the great white, bull shark and the oceanic whitetip shark to be one of the most dangerous to humans.

Taxonomy

The shark was first described by Peron and Lessueur in 1822 and was given the name Squalus cuvier. Johannes Peter Müller and Friedrich Gustav Jakob Henle, in 1837 renamed it Galeocerdo tigrinus. The genus, Galeocerdo, is derived from the Greek, galeos which means shark and Latin cerdus which means the hard hairs of pigs. It is often colloquially called the leopard shark and the man-eater shark.

The tiger shark is part of the order of Carcharhiniformes, members of this order are characterized by the presence of a nictitating membrane over the eye, two dorsal fins, an anal fin, and five gill slits. It is classified under the Carcharhinidae, commonly referred to as requiem sharks; the Carcharinidae family includes some of the most well known sharks such as the blue shark, lemon shark and bull shark. The tiger shark is the largest of the Carcharinidae family and is the only member of the sub-category Galeocerdo.

Distribution

The tiger shark is found in mainly tropical and sub-tropical waters, typically coastal. The shark's behaviour is primarily nomadic, but is guided by warmer currents, mainly in summer, as it flirts with the equator throughout the colder months. The shark tends to stay in deep waters that line reefs but does move into channels to pursue prey in lighter waters. In the western Pacific Ocean, the shark has been found as far north as Japan and as far south as New Zealand.

The shark has been known to move into shallow water - water that would normally be considered too shallow for a species of its size. It is also frequently found in river estuaries and harbors. At night it is usually found in shallow water.

Anatomy and appearance

Its skin can typically range from a blue or green hue to light with a white or light yellow underbelly. The distinguishing dark spots and stripes are most outstanding in young sharks and fade as the shark matures. A tiger shark may weigh up to one tonne (2,200 lb). It is usually three to five meters long (ten to sixteen feet), but some specimens have been up to seven meters long (twenty-three feet). Sexual maturity is reached at different stages for the sexes; males at 2.26 to 2.9 m (7 to 9 ft) whereas females become mature at 2.5 to 3.25 m (8 to 10 ft). It has been estimated that the tiger shark can swim at a maximum speed of around 32 km/h (20 mph), with short bursts of higher speeds that last only a few seconds.

The tiger shark's head is somewhat wedge-shaped, which makes it easy for the shark to turn quickly to one side. Tiger sharks have small pits on the side of their upper bodies which hold electrical sensors that enable them to pick up small muscle movements of other creatures, allowing them to hunt in darkness. A tiger shark generally has long fins and a long upper tail; the long fins act like wings and provide lift as the shark maneuvers through water, whereas the long tail provides bursts of speed. A tiger shark normally swims using lithe movements of its body. Its high back and dorsal fin act as a pivot, allowing it to spin quickly on its alliance.

Its teeth are flat, triangular, notched and serrated. Like most sharks, when a tiger shark loses or breaks one of its teeth, it grows a replacement tooth. The distinctive teeth seem to have evolved to be able to cut through turtle shells, and an adult tiger shark can easily bite through bone.

Diet

The tiger shark, which generally hunts at night, has a reputation for eating anything it has access to, ignoring what nutritional value the prey may or may not hold. Apart from its what is thought to be sparodic feeding, its most common foods include; common fish, squid,birds, seals, other sharks, and sea turtles. The shark has a number of features which make it a good hunter, such as excellent eyesight, which allows for access to murkier waters which can offer varieties of prey and its acute sense of smell which enable it to react to faint traces of blood in its waters and is able to follow them to the source. The tiger sharks ability to pick up on low-frequency pressure waves produced by the movements of swimming animals, for example the thrashing of an injured animal, enables the shark to be introduced to a variety of prey.

The shark is known to be aggressive. The ability to pick up low-frequency pressure waves enables the shark to advance towards an animal with confidence, even in the environment of murky water where it is often found. The shark is known to circle its prey and even study it by prodding it with its snout. The attack is a brutal confrontation, as the shark devours all of its prey. Because of its aggressive nature of feeding, it is common to find a variety of foreign objects inside the digestive track of a tiger shark. The most well known of these would be automobile number plates as well as petroleum cans and tires.

Recent information contradicts the notion that the tiger shark is a random and aggressive feeder, a description that has haunted the shark for the past 100 years. Although little has been documented on its behaviour, in particular its feeding patterns, suggestions have been made that the tiger shark represents a high type of specialization, meaning that when its common food supply is low, it has the ability to modify its regular diet to incorporate another form of prey.

Reproduction

File:Tiger shark caught in bay.jpg

A tiger shark caught in Kaneohe Bay, Oahu in 1966.

The tiger shark breeds by internal fertilization. Like mammals, they give birth to live young. The male tiger shark will insert one of its pelvic fins into the females genital opening, acting as a guide for the sperm to be introduced. The male has been known to use its teeth to hold the female still during the procedure, often causing the female considerable discomfort. Mating in the northern hemisphere will generally take place between the months of March and May, with the young being born around April or June the following year. In the southern hemisphere, mating takes place in November, December, or early January.

The young are nourished inside the female body. This developmental period can go on for 9 to 16 months, where the female can produce a litter ranging from 10 to 80 young. A newborn tiger shark is generally 51 to 76 cm long and usually leaves its mother upon birth, since it has a full set of teeth and can hunt. It is unknown how long tiger sharks live, but it has been speculated to be 20 years.

Dangers and conservation

Although shark attacks on humans are a relatively rare phenomenon, the tiger shark is responsible for a large percentage of the fatal attacks that do occur on humans, and is regarded as one of the most dangerous species of sharks. Tiger sharks reside in temperate waters as well as tropical waters. They are often found in river estuaries and harbors, as well as shallow water close to shore, where they are bound to come into contact with humans. Because of their curious nature of feeding it is expected that a tiger shark would normally attack a human if it came in contact with it. Tiger sharks are known to dwell in waters with runoff, such as where a river enters the ocean.

Tiger sharks have become a recurring problem in Hawaii and are considered the most dangerous sharks in Hawaiian waters. Tiger sharks are considered to be sacred 'aumakua' or ancestor spirits by the native Hawaiians, however during the years from 1959 to 1976, 4,668 tiger sharks were hunted down in an effort to control what was proving to be detrimental to the tourism industry. Even though over four and a half thousand were killed, little decrease was ever detected in the attacks on humans. It is illegal to feed sharks in Hawaii and any interaction with them is generally discouraged, such as cage diving.

The tiger shark is not directly under attack by commercial industries. There is however, a usual sequence of activities which sees the shark harvested for its fin and flesh. A tiger shark's liver is considered to be of high value as it contains a high vitamin A content, which is extracted to produce vitamin A oil. Similar to many other sharks, its skin is a valuable commodity for the handbag industry. A tiger shark's skin is sturdy and considered exotic for its tiger appearance.

See also

• List of sharks
• List of fatal, unprovoked shark attacks in the United States by decade

References

• Various (1995). WILDLIFE FACT FILE. Card 6, group 4; Tiger Shark. International Masters Publishers
• Daley, Audrey. (1994) Shark. Hodder & Stroughton ISBN 0340616547
• Knickle , Craig Biological Profile Florida Museum of Natural History. Retrieved January 22 2005.
• Tiger shark, Galeocerdo cuvier at marinebio.org
• Zoo-talk Zoo Talk. Retrieved January 22 2005.
• Gerneral nformation Enchanted Learning. Retrieved January 22 2005.
• Different diet information Shark Info. Retrieved January 22 2005.
• Tiger sharks in Hawaii Research program. Retrieved January 22 2005.
• Froese, Rainer; Pauly, Daniel (eds.). "Galeocerdo cuvier". FishBase. March 2005 version.
• "Galeocerdo cuvier". Integrated Taxonomic Information System. 07 April. {{cite web}}: Check date values in: |date= and |year= / |date= mismatch (help)

External links

• Platial Shark Attack Map
• Tiger Shark Pictures 20 pictures of tiger sharks
• Zoo-talk Tiger Shark Caught Eating Smaller Shark
• Tiger shark facts and pictures Facts about Tiger sharks