Tiger Sharks

It 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 (Spain), Sicily (Italy) and Libya.

It 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 900 m.

Description

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.

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.

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 2.3 m, or near sexual maturity, their selection expands considerably, and much larger animals become regular prey. Numerous fish, mollusks (including gastropods and cephalopods), crustaceans, sea birds, sea snakes, marine mammals (e.g. bottlenose dolphins (Tursiops), common dolphins (Delphinus), spotted dolphins (Stenella), dugongs (Dugong dugon), seals and sea lions), and sea turtles (including the three largest species: the leatherback (Dermochelys coriacea), the loggerhead (Caretta caretta) and the green sea turtles (Chelonia mydas)), 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 (including adult sandbar sharks (Carcharhinus plumbeus)), 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 (Megaptera novaeangliae) 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 (Tachyglossus aculeatus) 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”.

Predation by orcas

Tiger sharks are preyed on by orcas. Orcas have been recorded hunting and killing tiger sharks by holding them upside down to induce tonic immobility in order to drown the shark. The orcas bite off the shark’s fins before disemboweling and devouring it.

Swimming efficiency and stealth

All tiger sharks generally swim slowly, which, combined with cryptic coloration, may make them difficult for prey to detect in some habitats. They are especially well camouflaged against dark backgrounds. Despite their sluggish appearance, tiger sharks are one of the strongest swimmers of the sharks. Once the shark has come close, a speed burst allows it to reach the intended prey before it can escape.

Reproduction

Males reach sexual maturity at 2.3 to 2.9 m and females at 2.5 to 3.5 m. Typical weight of relatively young sexually mature specimens, which often locally comprise the majority of tiger sharks encountered per game-fishing and scientific studies, is around 80 to 130 kg. Females mate once every three years.

The tiger shark is ovoviviparous; its eggs hatch internally and the young are born live when fully developed. Tiger sharks are unique among all sharks in the fact that they employ embrytrophy to nourish their young inside the womb. The young gestate in sacks filled with a nourishing fluid. This allows the young to dramatically increase in size, even without a placental connection to the mother.

The young develop inside the mother’s body up to 16 months. Litters range from 10 to 80 pups. A newborn is generally 51 to 76 cm long. How long tiger sharks live is unknown, but they can live longer than 12 years.

They breed by internal fertilization. The male inserts one of his claspers into the female’s genital opening (cloaca), acting as a guide for the sperm. The male uses his teeth to hold the female still during the procedure, often causing the female considerable discomfort. Mating in the Northern Hemisphere generally takes place between March and May, with birth between April and June the following year. In the Southern Hemisphere, mating takes place in November, December, or early January.

Relationship with humans

Although sharks rarely bite humans, the tiger shark is reported to be responsible for a large share of fatal shark-bite incidents, and is regarded as one of the most dangerous shark species. They often visit shallow reefs, harbors, and canals, creating the potential for encounter with humans.