Shark of the month: Bull shark

The Bull Shark (Carcharhinus leucas) also known as the Zambezi shark, is a large predator that can be found in warm shallow waters throughout the world. Unlike most shark species, bull sharks have the ability to swim and survive in fresh water and can be found thousands of miles up rivers. Bull sharks owe their name to the sturdy form of their body and their unpredictable behavior.

 

Anatomy and appearance

Bull Sharks are not very long sharks, but they tend to be very thick and stocky. The average size of an adult bull shark is about 2.3 meters in length and 130 kg in weight, but specimens have been found up to 3.5 meters long and weighing about 300 kg. Like most sharks, they have counter shading meaning that they are grey on top and white on the bottom. Bull sharks have a broad, flat snout which is not very long. They have two triangular shaped dorsal fins, but no interdorsal ridge.

A key feature that separates bull sharks from most shark species is their rectal gland. The rectal gland is used for storing and excreting salt from the body, which allows them to control their salinity levels even when they are in freshwater environments.

Habitat

Bull sharks are generally found in warm, shallow waters with temperatures around 32 degrees Celsius. They are found along the coasts of southern North America, Central America, South America, Africa, the Indian Ocean, as well as the Indo-Pacific near Southeast Asia. Specimens have been reported being seen nearly 2,000 miles up the Amazon and Mississippi rivers as well as being in golf course lakes after floods.

By www.iucn.org – CC BY-SA 3.0

Diet

Due to their ability to feed in both freshwater and salt-water environments, bull sharks feed on a vast array of prey species. They feed on numerous bony fish, stingrays, other sharks, birds, turtles, crustaceans, and some mammals. They tend to hunt in murky waters because it allows them to sneak up on their prey. They’ve developed an unique hunting method; bull sharks first bump into their prey and then they bite. Pound for pound, bull sharks have the strongest bite force compared to all shark species.

Population

Bull sharks are viviparous, meaning that they give birth to free-swimming young. They have a gestation period of about one year and can give birth to one to twelve young per birthing. When they are born, adolescent bull sharks are around 65 to 75 centimeters long. They reach sexual maturity after around fifteen years and are about 270 centimeters long at this age.

Conservation

Bull sharks are listed as Near Threatened by the International Union for Conservation of Nature (IUCN). Bull sharks have long gestation periods, reach sexual maturity at a late age, and give birth to few young making them vulnerable to intense fishing and hunting pressures. They are harvested for their fins and meat, which are used to make the prized Chinese dish shark fin soup. Due to their role as apex predators, bull sharks are very important to the environments they inhabit and are a necessity for a healthy reef and ecosystem.

Relationship to humans

Bull sharks are often found in shallow waters along coastal areas and rivers therefore it’s likely that there will be an encounter between these sharks and humans. There are many registered attacks on humans by this shark – according to the international Shark Attack file the bull shark is the third species with most attacks on humans. Only great white sharks and tiger sharks have more registered attacks on humans.

Originally written by Elizabeth Ward-Sing and edited by Isabelle Walter

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