Tiger shark
The tiger shark is a species of ground shark, and the only extant member of the genus Galeocerdo and family Galeocerdonidae. It is a large predator, with females capable of attaining a length of over. Populations are found in many tropical and temperate waters, especially around central Pacific islands. Its name derives from the dark stripes down its body, which resemble a tiger's pattern, and fade as the shark matures.
The tiger shark is one of the most solitary, nocturnal hunters among sharks. It is notable for having the widest food spectrum of all sharks, with a range of prey that includes crustaceans, fish, seals, birds, squid, sea turtles, sea snakes, dolphins, even smaller sharks and other sources of food - actually it also has a reputation as a "garbage eater", consuming a variety of inedible, man-made objects that have been found to linger in its stomach. Tiger sharks have only one recorded natural predator, the orca and it is considered a near-threatened species because of the widespread custom of finning and fishing by humans.
The tiger shark is second only to the great white in recorded fatal attacks on humans, but these events are still exceedingly rare.
Taxonomy
The shark was first described by Peron and Lesueur in 1822, and was given the name Squalus cuvier. Müller and Henle in 1837 renamed it Galeocerdo tigrinus. The genus, Galeocerdo, is derived from the Greek galeos, which means shark, and kerdo, the word for fox. The species name honors naturalist Georges Cuvier. It is often colloquially called the man-eater shark.The tiger shark is a member of the order Carcharhiniformes, the most species-rich order of sharks, with more than 270 species also including the small catsharks and hammerhead sharks. Members of this order are characterized by the presence of a nictitating membrane over the eyes, two dorsal fins, an anal fin, and five gill slits. It is the largest member of the order, commonly referred to as ground sharks. It is the only extant member of Galeocerdo, the only member of the family Galeocerdonidae. The oldest remains of Galeocerdo extend back to the Eocene epoch, while the oldest fossils of the modern tiger shark Galeocerdo cuvier date to the Middle Miocene, around 13.8 million years ago.
Description
The tiger shark commonly attains an adult length of and weighs between. The International Game Fish Association's all-tackle record is. It is sexually dimorphic, with females being the larger sex. Mature females are often over while mature males rarely get that large. Exceptionally large females reportedly can measure over, and the largest males. Weights of particularly large female tiger sharks can exceed. One pregnant female caught off Australia reportedly measured long and weighed. Even larger unconfirmed catches have been claimed. Some papers have accepted a record of an exceptional, tiger shark, but since this is far larger than any scientifically observed specimen, verification would be needed. A 2019 study suggested that Pliocene tiger sharks could have reached in maximum length. There is variation in the speed of growth rates of juvenile tiger sharks depending on the region they inhabit, with some growing close to twice as fast as others.Among the largest extant sharks, the tiger shark ranks in average size only behind the whale shark, the basking shark, and the great white shark. This makes it the second-largest predatory shark, after the great white. Some other species such as megamouth sharks, Pacific sleeper sharks, Greenland sharks, and bluntnose sixgill sharks broadly overlap in size with the tiger shark, but as these species are comparatively poorly studied, whether their typical mature size matches that of the tiger shark is unclear. The great hammerhead, a member of the same taxonomic order as the tiger shark, has a similar or even greater average body length, but is lighter and less bulky, with a maximum known weight coming from a heavily pregnant long individual at.
Tiger shark teeth are unique with very sharp, pronounced serrations and an unmistakable sideways-pointing tip. Such dentition has developed to slice through flesh, bone, and other tough substances, such as turtle shells. Like most sharks, its teeth are continually replaced by rows of new teeth throughout the shark's life. Relative to the shark's size, tiger shark teeth are considerably shorter than those of a great white shark, but they are nearly as broad at the root as the great white's teeth and are arguably better suited to slicing through hard-surfaced prey.
A tiger shark generally has long fins to provide lift as the shark maneuvers through water, while the long upper tail provides bursts of speed. The tiger shark normally swims using small body movements.
Skin
The skin of a tiger shark can typically range from blue to light green with a white or light-yellow underbelly. The advantage of this is that when it is hunting for its prey, when prey looks at the shark from above, the shark will be camouflaged, since the water below is darker. When prey is below the shark and looks up the light underbelly will also camouflage the shark with the sunlight. This is known as countershading. Dark spots and stripes are most visible in young sharks and fade as the shark matures. Its head is somewhat wedge-shaped, which makes it easy to turn quickly to one side. They have small pits on the snout which hold electroreceptors called the ampullae of Lorenzini, which enable them to detect electric fields, including the weak electrical impulses generated by prey, which helps them to hunt. Tiger sharks also have a sensory organ called a lateral line which extends on their flanks down most of the length of their sides. The primary role of this structure is to detect minute vibrations in the water. These adaptations allow the tiger shark to hunt in darkness and detect hidden prey.Vision
Sharks do not have moveable upper or lower eyelids, but the tiger shark—among other sharks—has a nictitating membrane, which is a clear eyelid that can cover the eye. A reflective layer behind the tiger shark's retina, called the tapetum lucidum, allows light-sensing cells a second chance to capture photons of visible light. This enhances vision in low-light conditions.Distribution and habitat
The tiger shark is often found close to the coast, mainly in tropical and subtropical waters throughout the world. Its behavior is primarily nomadic, but is guided by warmer currents, and it stays closer to the equator throughout the colder months. It tends to stay in deep waters that line reefs, but it does move into channels to pursue prey in shallower waters. In the western Pacific Ocean, the shark has been found as far north as Japan and as far south as New Zealand. It has also been recorded in the Mediterranean Sea, but rarely, off Malaga, Sicily and Libya.Tiger sharks can be seen in the Gulf of Mexico, North American beaches, and parts of South America. It is also commonly observed in the Caribbean Sea. Other locations where tiger sharks are seen include off Africa, China, India, Australia, and Indonesia. Certain tiger sharks have been recorded at depths just shy of.
Feeding
The tiger shark is an apex predator and has a reputation for eating almost anything. These predators swim close inland to eat at night, and during the day swim out into deeper waters. Young tiger sharks are found to feed largely on small fish, as well as various small jellyfish, and mollusks including cephalopods. Around the time they attain, or near sexual maturity, their selection expands considerably, and much larger animals become regular prey. Numerous fish, mollusks, crustaceans, sea birds, sea snakes, marine mammals, common dolphins, spotted dolphins, dugongs, and sea turtles, the loggerhead and the green sea turtles ), are regularly eaten by adult tiger sharks. In fact, adult sea turtles have been found in up to 20.8% of studied tiger shark stomachs, indicating somewhat of a dietary preference for sea turtles where they are commonly encountered. They also eat other sharks, as well as rays, and sometimes even other tiger sharks.Due to high risk of predation, dolphins often avoid regions inhabited by tiger sharks. Injured or ailing whales may also be attacked and eaten. A group was documented killing an ailing humpback whale in 2006 near Hawaii. A scavenger, the tiger shark will feed on dead whales, and has been documented doing so alongside great white sharks. Tiger sharks have also been observed to feed on dead manta rays in the German Channel of Palau.
Evidence of dugong predation was identified in one study that found dugong tissue in 15 of 85 tiger sharks caught off the Australian coast. Additionally, examination of adult dugongs has shown scars from failed shark attacks. To minimize attacks, dugong microhabitats shift similarly to those of known tiger shark prey when the sharks are abundant.
The broad, heavily calcified jaws and nearly terminal mouth, combined with robust, serrated teeth, enable the tiger shark to take on these large prey. In addition, excellent eyesight and acute sense of smell enable it to react to faint traces of blood and follow them to the source. The ability to pick up low-frequency pressure waves enables the shark to advance towards an animal with confidence, even in murky water. The shark circles its prey and studies it by prodding it with its snout. When attacking, the shark often eats its prey whole, although larger prey are often eaten in gradual large bites and finished over time.
Notably, terrestrial mammals, including horses, goats, sheep, dogs, cats, and brown rats, are fairly common in the stomach contents of tiger sharks around the coasts of Hawaii. In one case, remains of two flying foxes were found in the stomach of this shark, and in another, an echidna was regurgitated by a tiger shark being tagged off Orpheus Island, Queensland. Because of its aggressive and indiscriminate feeding style, it often mistakenly eats inedible objects, such as automobile license plates, oil cans, tires, and baseballs. Due to their habits of eating essentially anything, Tiger sharks are often referred to as the "garbage can of the sea".