TIGER SHARKS

Galeocerdo cuvier


THREATS

· Fishing: tiger shark fishing is carried out in different parts of the world. They are caught for sport, to get their liver oil (source of vitamin A), for their meat, for their skin to make leather, and especially for their fins, very sought after in Asian cooking to prepare “shark fin soup”. They are also caught in drifting nets and as bycatch.

· Marine pollution: Due to their indiscriminate eating habits, they often eat by mistake inedible objects derived from human pollution such as plastics, car number plates, oil cans, tires and balls.

· Tourism: between 1959 and 2000, 4,668 sharks were killed to protect the tourism industry.


CONSERVATION

· Red List (IUCN): classified as near threatened(NT).

· Organizations: No specific conservation measures for the tiger sharks are in place. But several organizations like “Save Our Seas Foundation”, “Shark Research Institute”, “The Shark Trust” and “Bite-back” are working to conserve sharks worldwide. They are campaigning to reduce catches and stop practices such as finning, in order to ensure the survival of these animals.

SCIENTIFIC NAME: Galeocerdo cuvier

Common Name: Tiger shark.

Kingdom: Animalia.

Phylum: Chordata.

Class: Chondrichthyes.

Order: Carcharhiniformes

Family: Carcharhinidae

Genus: Galeocerdo

DESCRIPTION

It is one of the biggest sharks in the world. Its main feature is a series of transverse dark stripes on the back and sides. These bands tend to fade with age, being very pronounced in youth and generally absent when they reach more than three meters long.

The overall colour of their skin is dark bluish green to grey on top, which is a great camouflage. They will often attack their prey from below and their colour makes them go unnoticed since it mimics the bottom. The ventral area and the face have a white or yellowish white colouring.

The nose is flat and the head is wide and flat, being almost rectangular, with a large mouth surrounded by well developed labial folds. The eyes are large and round. The nostrils are elongated, developed and located almost at the front. The jaws are huge and have large, sharp teeth with serrated edges and curved cusps.

This so distinctive body shape, with a large head and upper body, becomes increasingly thinner towards the tail.

Size:

Length: 3-5.5m            Weight: 350-650Kg


HABITAT

This species is found mainly in tropical and subtropical waters worldwide. It has a mainly nomadic behaviour, but is guided by warm currents, and remains close to the Equator during the colder months. It usually remains in the deep waters surrounding the reefs, but can also move into channels to pursue its prey in shallow waters.

In the Western Pacific, it is found from southern New Zealand to northern Japan. It also lives in coastal waters around the Indian Ocean, Persian Gulf and Red Sea. In America it inhabits the Pacific coast from southern California to northern Chile, including several islands like the Galapagos. In the Atlantic, it is found from River Plate to New England, being very abundant in the Caribbean Sea and the Gulf of Mexico. In Africa it is present from the Gulf of Guinea up to Morocco and the Canary Islands. Occasionally it ventures into the Strait of Gibraltar. It is also present in Australia and Hawaii.

Usually they move in coastal waters of a depth of 6 to 12m, although they have been observed at depths of 3m. The maximum depth for them to swim in is about 900m.

                                                                                                            


FEEDING

Tiger sharks are predominantly nocturnal and solitary predators. They have a voracious appetite and attack a wide variety of prey: jellyfish, cephalopods (squid), fish, seabirds, sea snakes, sea turtles (leatherback, loggerhead and green turtles), marine mammals (bottlenose dolphin, common dolphin, spotted dolphins and even humpback whales), dugongs, seals, sea lions, rays, other sharks and can sometimes eat other tiger sharks.

They will swim in circles around their prey and when they attack, they often eat their prey whole, although larger preys will be eaten in several big bites.


BIOLOGY

The tiger shark is a solitary, nocturnal animal. They swim about 16km/day, approaching the shore at night to feed and swimming away into deeper waters to spend the day.

Life expectancy for this species is still unknown, but is estimated to be around 12 years.


Reproduction:

Males reach sexual maturity between 2.3-2.9m and females between 2.5-3.5m. Females mate once every three years, occurring in the northern hemisphere between March and May and in the southern hemisphere between November and January.

They are ovoviviparous, i.e. they reproduce by internal fertilization. The male inserts sperm into the female genital opening, using his teeth to hold the female still during the process. After fertilization, the eggs hatch inside the female’s uterus and continue their development there, receiving food through the yolk sac. They are born once fully developed, after a gestation period of 14 to 16 months, and there can be anywhere between 30 to 80 pups.