Bull shark

Bull shark, Zambezi River shark, or colloquially Zambi, are common in warm, shallow waters along coasts throughout the world. They are known for their particularly unpredictable behavior, as they often travel up rivers and can pose a threat to those who venture into the water there. Due to their habits, they are probably responsible for the majority of attacks on humans that take place near shore, including many attacks attributed to other species ^*. Bull sharks can travel inland by swimming up rivers, and have a unique tolerance for fresh water. Those found far from the ocean are the same species as the marine bull shark, and are not true freshwater sharks (unlike the river sharks of the genus Glyphis).

Naming

The name, "bull shark", comes from its stocky shape and broad, flat snout and behavior. In India, the bull shark is often called the Sunderbans or Ganges shark and is considered a delicacy for Bengali fish curries. In Africa it is often called Zambezi River shark or just Zambi. Its wide range and diverse habitats result in many other local names, such as Nicaragua shark, cub shark, shovelnose shark, freshwater whaler, among others.(Allen, 101)

Distribution and habitat

The bull shark is common in coastal areas of warm oceans, in rivers and lakes, both in salt and fresh water. In the Atlantic it is found from Massachusetts to South Brazil and from Morocco to Angola, in the Indian Ocean it is found from South Africa to Kenya, India, Vietnam to Australia, and in the Pacific from Baja California to Ecuador. They are also found in the central Amazon River, and have been recorded as far up the Mississippi River as Illinois. They are also found in the fresh water Lake Nicaragua and the Ganges and Brahmaputra rivers of West Bengal and Assam in eastern India and adjoining Bangladesh. It is found from the surface to a depth of 150 m, but most commonly it does not swim deeper than 30 m. ^*

Anatomy and appearance

Bull sharks are large and stout. The males of this species can reach 2.1 m (6.9 ft) long and weigh 90 kg (198.4 lb). The females can be much larger, 3.5 m (11.5 ft) long and 230 kg (507 lb). It is wider in comparison to its length than most sharks. It is grey on top and white below. The second dorsal fin is smaller than the first.

Diet

The bull shark has a carnivorous diet, and will eat almost anything that comes its way, like fishes, including other sharks, rays, dolphins, turtles, birds, molluscs, echinoderms, crustaceans and even terrestrial mammals.

Behavior

Bull sharks are mostly sluggish, solitary animals who cruise through shallow waters. They do not view humans as prey under normal conditions, but may bite when threatened, out of curiosity, or in water where visibility is poor and a human could be mistaken for a prey animal. Despite their apparent docility at times, they are capable of surprising bursts of speed, and can be highly aggressive. Often, they will charge their prey in an attempt to knock out the victim, hence the name "bull". Their aggression is fueled by testosterone, the bull shark having one of the highest testosterone levels of all animals.

Attack Patterns

Bull sharks have the ability to navigate shallow and dirty waters and can attack almost anything that is moving or living. A bull shark will generally brush its nose against the prey item before biting. Attacks are usually by ambushing their prey, with the shark approaching at a fast speed and colliding with its victim.

Reproduction

Breeding takes place in the summer, often in brackish water of river mouths. After a gestation of about a year, bull sharks give birth to as many as 13 live young (they are viviparous). The young are about 70 cm long at birth and take as long as 10 years to reach maturity.

References

Database entry includes justification for why this species is near threatened
Allen, Thomas B. The Shark Almanac. New York: The Lyons Press, 1999. ISBN 1558215824

Sharks | Viviparous fish

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