Tiger Shark

Tiger sharks are known to be potentially dangerous sharks that are scientifically termed Galeocerdo cuvier belongs to the family of Carcharhinidae. It is a species of the genus Galeocerdo that is only existing under this particular genus. The order of the tiger shark family is Carcharhiniformes and the class of it is denoted as Chondrichthyes. They are popularly known as man-eaters and are also scavengers of invertebrates and are known for their ferocious and voracity. They are macropredators that can attain a maximum length of over 5.5 meters that is an 18 feet long tiger shark.

They are mostly the dwellers of the tropical and temperate water found worldwide from the short-line of an open sea and are therefore often found in the Central Pacific Ocean in general. As some dark stripes are commonly seen on the lower body area down from the head and neck in almost all sharks. Therefore its name is tiger shark derived from the stripe resembling that of a tiger. The tiger-like stripe pattern is very prominent in the juvenile tiger shark fish but slowly fades away as it ages.

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The tiger shark fish is nocturnal by nature as they are mostly active at night and are solidarity in nature as they prefer to hunt the prey individually and not in a clad or group. They are also cannibals as they prey on smaller sharks of their families. They have the widest range of preying that includes turtles, squids, dolphins, sea snakes, birds that comes near to the water level, seals, fishes and crustaceans. They are also profoundly known as garbage eaters as their stomach contains a lot of man-made dumps that are found on the sea beds. Though tiger sharks are known to be the apex-predator in the Reagan they dwell in but they are also sometimes prayed by killer whales. 

Because of decades-old practice of human of phishing and finning of the whales, they are now almost endangered and is declared as the species on the verge of extinction. After white sharks, the tiger shark is the second species that has a record of attacking humans though such events are very rare.

Description of Tiger Shark

The tiger shark fish belongs to the order Carcharhiniformes that is one of the species-rich orders that includes near about 270 species that includes both the members of small sharks and the hammerhead sharks. The species of this order have unique characteristics as they possess a nictitating membrane over the eye area, five-gill slits, two dorsal fins and an anal fin. The tiger shark is also referred to as a requiem shark as they are the biggest member of the family Carcharhinidae. This family also includes some of the slender but very powerful and deadly sharks such as blue sharks, lemon sharks and bull sharks.

Usually, the average length of a tiger shark fish ranges from 3.25 to 4.25meters (10.8 to 13.11 feet). The average weight of tiger sharks ranges from 385 to 635 kgs. They are sexually dimorphic and thus the females are exceptionally larger than the males of the family and can attain a height of 5 meters (16.5 ft) whereas the maximum height that a male tiger shark can attain is 4 meters (13.1 ft). Few of the tiger shark females can exceed a weight of 900 kgs (2000lbs). On the coast of Australia, one of the pregnant mother sharks was caught that weighed around 1545 kgs and was the biggest 18-foot tigerfish known back then. After that many larger caught tiger sharks are reported though they are still unconfirmed. In some of the papers the tiger shark as long as 7.4 meters have been recorded.

Among the similar shark species, the tiger sharks fall for an average height and ranked after the whale sharks, basking sharks and the great white shark. Though they are considered as the second largest predator shark after the great white shark. 

Teeth 

The teeth orientation and the shape of the tiger shark are very unique with noticeable pointed edged teeth called serration teeth and distinctive and well defined sideways-pointed tips. Such development of the teeth orientation and shape is to support the shark to tear and slice through flesh, bones and even the hardest surfaces such as the covering shell of the turtle. The dentation of the shark is such that the row of teeth is replaced by the new ones at some regular intervals throughout its lifespan, the same as other sharks. Though the size of the tiger shark teeth is smaller than that of the white shark, the roots of the teeth are equally broader in respect to the latter and are more defined to slice through the hard surfaces more efficiently

The longer fins of the tiger shark help them in manoeuvring through the water as they provide a lift to the shark. The upper tiger shark tail provides them with a great burst of speed. But the tiger shark tends to swim with small body movements where the dorsal fins act as a pivot that helps them to spin on the axis of the body and the fins are distinctively very close to the tail of the shark. The structure of the upper and lower teeth of the tiger shark is given below

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Skin 

The skin colour of an adult shark ranges from blue to light green with a white or yellowish-white belly. The main advantage of the shark is that when the prey is over the shark due to the darker blue and green shades of the body, it camouflages with the darker watercolour at the depth of the ocean. Whereas, when the prey is underneath the shark due to the sunlight falling on the surface of the water it appears more white and thus the whitish underbelly of the shark again camouflages with the water. This entire process is known as countershading. The bold and dark spots and stripes are visible on the median or juvenile sharks and fade as the shark attains maturity. Because of the wedged- shape of the head of the shark, it can turn quickly to one side. 

The projected part of its mouth holds electroreceptors that are scientifically denoted as ampullae of Lorenzini. They help them to detect any kind of electric impulses around including the very weak electric impulse radiate from the preys that help them to locate and hunt them down. Their main function is to detect any kind of minor vibrations in the water and thus greatly supports them in hunting in the dark and find out the hidden prey. 

Vision

Unlike other sharks that cannot move the upper and lower eyelids, tiger sharks because of the presence of the nictitating membrane over the eyes, have eyelids that are properly covering the eye. The light-sensing cell in its eyes allows them to capture the photons of the visible light due to the presence of tapetum lucidum also known as the retina of the shark. Thus their low-light vision is also enhanced. 

Feeding Habit

These sharks usually swim near the inland of the ocean to feed on the prey and in the morning move deep into the ocean water. Young sharks do not go for larger prey and are often seen feeding on small fishes, jellyfish and molluscs that also includes cephalopods. But as they attend sexual maturity and grows about 3 meters in length, their feeding range also expands from small prey to relatively larger marine species. They mostly like to feed on sea turtles as a study suggested that almost 20.8% of the sea turtles are found in the stomach of an adult tiger whale. But they regularly feed on fishes, sea birds, sea snakes and other big mammals like bottlenose dolphins, common dolphins, dugongs, seals and sea lions. They are also apex predators of some of the largest species such as loggerheads, leatherbacks and the large green turtles that they almost feen on regularly. They often attack the injured or ailing whales, other sharks including the juvenile sharks of their own species as well rays. Because of the nondiscriminatory and aggressive nature of feeding tiger sharks, the dolphins avoid dwelling in the regions they exist.

Since the shark has the ability to sense the low-frequency pressure of the waves in the water, it enables them to hunt confidently even in murky water. They usually hunt down prey by encircling it and then study the prey by poking with its snout. As the shark attacks, it often eats the whole prey at once, while the larger prays are eaten in big chunks and pieces and is finished over some time. 

On the coast of Hawaii, as the stomach of a large tiger shark was studied, goats, sheep, dogs, cats as well as brown rats were identified as being preyed on. In one of the cases, the stomach of the tiger shark has the remains of the two flying foxes. Due to the nondiscriminatory predatory behaviour of the shark, they often end up eating a lot of toxic as well as harmful man-made dumps in the ocean.

Predating on Tiger Whales

Even being the apex predator of the ocean water, they are often preyed on and hunt down by pods of killer whales. The method of killing the tiger shark by killer whales is to lure them to the surface of the water and then grab its mid-body in an upside-down position. This induces tonic immobility and the shark eventually drowns. They usually bite down the fins of the shark first and then draw them and endeavour them to the mid of the water level.

Distribution and Habitat

They have majorly distributed in the topical as well as the subtropical water throughout the world and often dwell near the sea costs. They are the habitats of the warmer water and they prefer to be near the equator during the entire winter season. They are nomadic by nature as they prefer to stay in the deep water during the morning hours and tends to stay near the reef in the small depth during the night for the prey. They also move into the line of narrow channels that has very shallow water for the search of prey. In the western Pacific ocean, their habitat stretched farther north to Japan and further south to New Zealand. They are also once recorded in the Mediterranean, once at the coast of Spain and once at Sicily.

They can go up to a depth of 900 meters into the ocean on average. But they also swim into the stream of shallow channels that are considered to be too shallow of the water depth in accordance to their size. But a recent study claims that a tiger shark dwells at a depth of 350 meters and not less on average. Thus it makes the tiger shark uncommon in various shallow channels of the sea. 

Reproduction in Tiger Shark

The male tiger shark matures at an average length ranging from 2.3 to 2.9 meters whereas the female shark attains sexual maturity at an average length of 2.5 to 3.5. The average weight of the sexual weight specimen varies from 80 to 130 kgs. The females usually mate once every three years. As they mate by internal breeding they are considered a mammal family. During the breeding, the male tiger shark inserts either one of his claspers into the female’s genital opening referred to as cloaca. During this process, the male tiger shark holds the female firmly with its teeth so that the female stay still and this causes a lot of discomfort to the female tiger shark. They usually mate from the month of March to May in the Northern Hemisphere. The birth of the baby tiger sharks takes place in the month of April and June of the following year. Thus it has an almost a year gestation period. However, in the southern hemisphere, mating takes place in the month of December or early January.

It takes almost 16 months for the young ones to develop completely inside the mother’s womb. A litter can range from 10 to 80 pups at one time. The newborns are of a length that ranges from 51 to 76 cms. The average lifespan of a tiger shark is almost 12 years.    

Threats to a Tiger Shark 

The tiger sharks were massively hunted in targeted or non-targeted fisheries primarily for their liver, flesh and fins. They were under a fishing spree every year and the population of the tiger shark reduced sharply where they were abundantly fished at one point in time. As the demand for the fins and the livers increases the killing of the sharks rapidly increased to a state where their population worldwide declined to a point that they are declared as near-threatened species by the International Union of Conservation of nature. And the major cause of the decline was recorded as excessive finning and fishing by humans.

In 2018, the Department of Conservation of New-Zealand have declared the species as a migrant but qualifies under the class of “Secure Overseas”. Though the flesh of the tiger shark is of no high nutrition value the liver oil is very rich in Vitamin A and is therefore used to produce artificial Vitamin oils. They are mostly killed in the big-game fishers but they are also used for their distinctive skin colour.