Galeocerdo cuvier
Leopard shark
(Also: Maneater shark; Spotted shark; Tiger Shark; Tiger shark; Tiger-shark)

Tiger sharks are found in many subtropical and tropical waters, primarily from 45°N to 32°S. Tiger sharks have been sighted from the eastern coast of North America to the eastern coast of Brazil. This includes the coasts of southern North America, Mexico, and Latin America along the Gulf of Mexico. Tiger sharks also populate the coasts of China, India, Africa, Japan, and many islands of the Pacific Ocean. (Driggers III, et al., 2008; Kneebone, et al., 2008; Simpfendorfer, 2005; Wirsing, et al., 2007)

Tiger sharks are a saltwater species. Although they prefer the sea grass ecosystems of the costal areas, they occasionally inhabit other areas due to prey availability. Tiger sharks spend approximately 36 % of their time in shallow coastlne habitats (Heithaus et al., 2002), generally at depths of 2.5 to 145 m. This species, however, has been documented several kilometers from the shallow areas and at depths up to 350 m. Females are observed in shallow areas more often than males. Tiger sharks have also been documented in river estuaries and harbors ("Tiger Shark (Galeocerdo cuvier)", 2010; Heithaus, et al., 2002; Heithaus, et al., 2006; Simpfendorfer, 2005)

Tiger sharks are one of the largest carnivores in the ocean. Juveniles have tiger-like stripes, which fade as they grow older. Tiger sharks are blue or green in color with a light yellow or white under-belly. This speices has a large blunt nose on the end of a wedge-shaped head. Tiger sharks have serrated teeth, making it easy to tear flesh and crack the bones and shells of their prey. They have a heterocercal tail, meaning the dorsal lobe of the caudal fin is longer than the ventral lobe. Adults range from 3.25 to 4.25 m in length, although tiger sharks of 6 to 7.5 m in length have been documented. Female tiger sharks are on average 2.92 m in length and are smaller than males, which are on average 3.20 m in length. Adult tiger sharks typically weigh 385 to 635 kg, with largest sharks reaching 862 kg. ("Tiger Shark: Galeocerdo Cuvier", 2010; Heithaus, et al., 2007; Pratt, Jr., 1988; Read, 2010)

Embryos of tiger sharks are fertilized internally. A yolk sac forms around the embryos to provide necessary nutrients during the 13 to 16 month gestation period. As the yolk begins to run out near the end of the gestation period, the embryo draws nutrients directly from the mother. At birth, tiger sharks are fully developed and independent. They are born with tiger-like stripes on their back and a lightly colored yellow or white belly which allows them to blend in with the environment. These stripes fade as the juveniles reach adulthood, which is around 6 to 8 years. Males reach maturity earlier than females. ("Tiger Shark (Galeocerdo cuvier)", 2010)

Tiger sharks are polygynandrous, meaning males and females have multiple mates; they do not pair-bond at any time. Not much is known regarding the the behaviors of finding, attracting, and defending mates of tiger sharks. (Gruber and Myrberg, Jr., 1977; Pratt, Jr., 1988; Whitney and Crow, 2007)

Male tiger sharks reach sexual maturity when they reach an average length of 292 cm, whereas females reach sexual maturity when 330 to 345 cm in length. Females mate once every three years. Breeding seasons differ in the northern and southern hemispheres. In the northern hemisphere, females delay fertilization until March or May in order to give birth between May and June of the following year. In the southern hemisphere, females delay mating until November or January in order to give birth between February and March of the following year. Tiger sharks are one of the few species that are ovoviviparous. Females give birth to 10 to 80 pups per litter after a gestation period of 16 months. Many of these pups will not survive to adulthood. Pups weigh 3 to 6 kg at birth. (Pratt, Jr., 1988; Whitney and Crow, 2007)

Male tiger sharks have diametric testes, which are capable of synthesizing a larger amount of sperm than radial or compound testes. The females have external ovaries that appear on the epigonal organ, which is a primary lymphoid tissue in elasmobranchs. (Pratt, Jr., 1988; Whitney and Crow, 2007)

Female tiger sharks typically gives birth in a nursery, which provides protection during birth and to the young directly after birth. Tiger sharks are born independent, and mothers do not help their pups to find food, shelter or to survive. Males play no role in the lives of their offspring. Pups, however, are born with traits that help them survive without parents, including camouflage patterning, teeth to help capture prey, and speed to avoid predators. (Driggers III, et al., 2008)

The average lifespan of tiger sharks in the wild is 27 years, though some may live to 50 years of age. Tiger sharks in captivity do not live as long, a maximum of 17 to 20 years. In captivity, this species tends to die of starvation rather than old age, as food that is already dead is less appealing to tiger sharks. (Branstetter, et al., 1987; Garcia, et al., 2008; Kneebone, et al., 2008)

Tiger sharks are a nocturnal predators and are solitary except during the mating seasons or while communally feeding on large carcasses. During these group feedings, tiger sharks have a loose social hierarchy where larger sharks feed first. Smaller sharks circle around the carcass until the larger sharks are full, then move in to feed. Violence is minimal during these scavenging feasts. In tiger sharks, the heterocercal tail, or caudal fin, is the primary source of propulsion. The caudal fin produces a downward thrust of water behind the center of balance in a shark, which should cause its head to turn upwards. However, because the tail also moves side to side, it keeps the head from turning upwards. Because of this, tiger sharks move in an S-shaped fashion. (Essapian, 1962; Gruber and Myrberg, Jr., 1977; Heithaus, 2001; Tang and Newbound, 2004; Thomson and Simanek, 1977)

Tiger sharks have very large home ranges. Individuals attached with transmitters swam up to 16 km in a single day and did not return to that area for close to a year. Tiger sharks have large territories of about 23 square kilometers. (Gruber and Myrberg, Jr., 1977; Holland, et al., 1999; Thomson and Simanek, 1977)

Tiger sharks rely on electromagnetic receptors to perceive their environment and to hunt prey. Sensing organs called Ampullae of Lorenzini, located on the end of their nose, are filled with a jelly-like substance that reads electromagnetic signals. These signals are sent from the pores to the sensory nerve, and then to the brain. While hunting, tiger sharks uses this ability to detect electromagnetic signals given off by fish. Tiger sharks also use these organs to sense changes in water pressure and temperature (Plessis, 2010). Members of this species also have a lateral line on both sides of the body that runs from the gill line to the base of the tail. The lateral line reads the vibrations in the water from the movement of other animals nearby. Ampullae of Lorenzini and lateral lines also help detect electromagnetic signals from other sharks. While communally feeding on carcasses, sharks give off signals signifying dominance and thus the order in which they feed. (Kalmijn, 2000; Kneebone, et al., 2008; Plessis, 2010; Tang and Newbound, 2004)

The diet of tiger sharks includes mollusks, birds, snakes, crustaceans, sea turtles, and dugongs. Serrated teeth give this species the ability to penetrate the shells of sea turtles. Tiger sharks often scavenge dead or injured whales, and large tiger sharks can survive several weeks without feeding. This species most likely relies on stealth rather than strength and speed to catch prey. They are well camouflaged, allowing them to get within striking range of prey. If prey flee, tiger sharks may back off, not taking part in high-speed pursuits. However, tiger sharks are capable of short bursts of speed once their prey are within range. (Heithaus, et al., 2002; Heithaus, 2001)

Tiger sharks are some of the largest predators in the ocean and have few species feed on them. Some juvenile tiger sharks, however, fall prey to other sharks. Female tiger sharks gives birth in a nursery, which provides protection during the birthing process and to pups in the absence of parents. The coloration of tiger sharks provides camouflage against predators as well. Humans also fish for tiger sharks. (Cressey and Lachner, 1970; Driggers III, et al., 2008; Tang and Newbound, 2004)

As top predators in their ecosystem, it is possible that tiger sharks control populations of prey species, although this has not been verified. Tiger sharks also serve as a host for remoras, which are small suckerfish. Tiger sharks and remoras share a commensal relationship: remoras attach to tiger sharks near the underbelly, and use the shark for transportation and protection. Remoras also feed on materials dropped by tiger sharks. Recently, copepods, specifically sea louse, have been discovered around the eyes of tiger sharks in Australia. (Dill, et al., 2003; Heithaus, et al., 2002; Heithaus, et al., 2006; Wirsing, et al., 2007)

Tiger sharks are a popular gamefish, which are typically captured and released for sport. They are very strong, fast and perform aerial acts when hooked. Fishing for these sharks is tiring, as tiger sharks are not quickly or easily exhausted. In some states, permits such as a saltwater fishing license allow fishermen to collect the shark as a trophy. ("Fishing for shark in the Florida Keys", 2010; "Recreational fishing regulations for Virginia's marine waters", 2010)

Although very unlikely, tiger sharks enter shallow, populated areas of coast and attack humans on rare occasions. (Gruber and Myrberg, Jr., 1977; Heithaus, et al., 2006)

Currently, the total number of tiger sharks worldwide is unknown. However, they are listed as near threatened on the IUCN Red List. One major initiative to protect this species has been the limitation of the number of sharks taken by fisherman (i.e., one per vessel with a specific license). ("Recreational fishing regulations for Virginia's marine waters", 2010)