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bull shark
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What is a bull shark?
The bull shark (Carcharhinus leucas) is a large shark found globally in shallow coastal waters. It is one of the few shark species that can live in fresh water, and has been found in rivers and lakes. Bull sharks are heavy predators that consume fish, seabirds, marine turtles, and marine mammals. They are gray with a white underbelly, have a blunt snout, and a large dorsal fin. Female bull sharks can grow up to 4 meters (about 13 feet) in length and weigh as much as 316.5 kg (about 700 pounds).
Bull sharks are aggressive, and attacks on humans have been recorded. The IUCN classifies the bull shark as a vulnerable species due to commercial and recreational fishing, beach-protection programs, water pollution, and habitat loss.
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Where do bull sharks usually live?
Bull sharks (Carcharhinus leucas) are commonly found in shallow coastal lagoons, estuaries, and harbors within tropical and subtropical oceans and seas worldwide. They are unique among shark species because they can live and breed in freshwater environments.
Bull sharks have been observed in various freshwater habitats, such as Lake Nicaragua, the Zambezi River in Africa (hundreds of kilometers upstream), and the Amazon River in Peru (nearly 3,700 km upstream). They are aggressive and have been known to attack humans.
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What do bull sharks eat?
The bull shark (Carcharhinus leucas) is a large, aggressive shark found in tropical and subtropical coastal waters, and it is one of the few shark species that can live in freshwater environments.
Bull sharks are active predators that hunt in coral reef areas and nearshore waters less than 30 metres (98 feet) deep. They prey on other fishes, seabirds, marine turtles, and marine mammals. They also consume crustaceans and scavenge garbage and waste.
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How are bull sharks able to live in both freshwater and saltwater?
The bull shark is unique because it can live in both freshwater and saltwater environments. Most fish can only survive in one or the other. Bull sharks achieve this through osmoregulation, which allows them to maintain a balance between water and dissolved materials, regardless of environmental conditions.
When a bull shark moves into fresh water, its urine flow increases, decreasing the urea concentration in its blood. In saltwater, marine fish, including bull sharks, drink large quantities of seawater, retain most of the water, and excrete salt through special cells in their gills. This process allows them to adjust to the reversal of osmotic gradients when moving between fresh and saltwater.
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Why are bull sharks considered dangerous to humans?
Bull sharks are considered dangerous to humans because they are aggressive and have been known to attack people. They are one of the largest shark species, along with tiger sharks and white sharks, known to attack humans. Bull sharks often inhabit the same areas as humans, increasing the chance of encounters. They also have poor vision and may mistake humans for prey. Though most bull shark attacks are nonfatal and unprovoked, they can still inflict serious injuries due to the shark's size and bite force.
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How do bull sharks contribute to the health of aquatic ecosystems?
Bull sharks, as apex predators in shallow coastal waters, coral reefs, and estuaries, play a crucial role in maintaining the balance of their ecosystems. By preying on other fishes, seabirds, marine turtles, and marine mammals, they help control the populations of these species. This prevents any single species from dominating the ecosystem and helps maintain biodiversity. As a result, bull sharks contribute to the overall health and stability of their aquatic environments.
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bull shark, (Carcharhinus leucas), species of large predatory shark found in shallow coastal lagoons, estuaries, and harbours in tropical and subtropical oceans and seas worldwide. The bull shark is one of only a few shark species also capable of living and breeding in freshwater environments. Bull sharks have been found in Lake Nicaragua, several hundred kilometres up Africa’s Zambezi River, and nearly 3,700 km (about 2,300 miles) up the Amazon River in Peru. The bull shark is recognized by its blunt snout, large dorsal fin, pale to dark gray dorsal coloration, and white underside. The species is aggressive, and bull shark attacks on people have been recorded.
The bull shark is a large active predator. The biggest females can reach 4 metres (about 13 feet) in length and weigh as much as 316.5 kg (about 700 pounds). Males are slightly smaller, growing to a length of 3.6 metres (11.8 feet). The species hunts in coral reef areas and nearshore waters less than 30 metres (98 feet) deep to prey upon other fishes as well as seabirds, marine turtles, and marine mammals. However, it can also consume crustaceans and scavenge garbage and waste disposed of in rivers or at sea. Adult bull sharks are harvested in fishing operations, but they have few natural predators. Young bull sharks may be eaten by other sharks and by crocodiles.
Male bull sharks become sexually mature by age 14 or 15, whereas females become sexually mature at age 18. Bull sharks are viviparous; that is, females retain the fertilized eggs within their body until the young are capable of independent existence. Fertilization takes place internally after a courtship in which the male may bite the female’s fins and body during copulation. After a gestation period lasting about 10–11 months, between 1 and 13 young are born tail first. Females tend to reproduce every other year. Bull sharks usually live for 23 to 28 years, but some have lived as long as 32 years.
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Bull sharks, along with white sharks and tiger sharks, are the largest and most dangerous species known to attack humans. The habitats of bull sharks and humans overlap, increasing the chances of an encounter. In addition, bull sharks have poor vision. Since they rely on electroreception (in which sharks can detect weak electrostatic fields given off by their prey) and their sense of smell to hunt, they can mistake humans in the water for other prey. Studies have implicated bull sharks in more than 120 recorded attacks worldwide throughout history. However, the majority of these (nearly 100) have been nonfatal and unprovoked, which suggests that the bull sharks may simply have been investigating with a probing bite what they considered to be foreign objects in the water, and, because of the shark’s size and bite force, the result was serious injuries.
Bull sharks are classified as a vulnerable species by the International Union for Conservation of Nature and Natural Resources (IUCN). The IUCN notes that the commercial fishing industry, as well as the recreational fishing industry, targets bull sharks for their meat, fins, liver oil, and skin. Bull sharks are also killed by members of beach-protection programs (who often single out large sharks as threats to bathers) and by water pollution and habitat loss in rivers, estuaries, and along shorelines, as people transform natural areas for agricultural and urban uses.