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The bull shark (Carcharhinus leucas), often referred to as the Zambezi shark (or zambi) in Africa and the Lake Nicaragua shark in Nicaragua, is a type of requiem shark that is typically found around the world in warm, shallow waters along rivers and coasts. It is infamous for its aggressive behavior and is generally found in social, external brackish, and freshwater systems, especially the lower portions of rivers.
See the fact file below for more information on Bull Shark or alternatively, you can download our 28-page Bull Sharks worksheet pack to utilize within the classroom or home environment.
Key Facts & Information
Overview
- Bull sharks can stay in salt and fresh water since they are euryhaline. Although they have been known to travel up rivers for long distances, even as far as Alton, Illinois, on the Mississippi River, which is around 1,100 kilometers (700 miles) from the coast, there have been very few freshwater contacts with humans documented.
- The bulk of nearshore shark attacks, including many cases of shark bites mistakenly attributed to other species, are likely the result of more giant bull sharks. Despite being able to thrive in freshwater habitats, bull sharks, unlike river sharks of the genus Glyphis, are not actual freshwater sharks.
Etymology
- Bull sharks are known for their aggressive, erratic behavior, significant, flat snouts, and stocky shapes. The Sundarbans or Ganges shark and the bull shark can be mistaken for each other in India.
- It is also known as the Zambezi River shark or “zambi” in Africa. Due to its extensive range and varied habitats, this species is known locally as the Ganges River shark, Lake Nicaragua shark, river shark, freshwater, River whaler, cub shark, and shovelnose shark, among many others.
Characteristics
- The moniker “bull shark” refers to the animal’s short, blunt snout, bold personality, and propensity to headbutt prey before striking.
- They are medium-sized sharks with long pectoral fins and thick, sturdy bodies. Particularly on adolescent bull sharks, the fins have dark tips and are gray on top and white underneath.
- The female bull shark is larger than the male, and both are significant stout sharks. At birth, the bull shark can reach a maximum length of 81 cm (2 ft 8 in). The average adult female bull shark measures 2.4 meters (8 feet) long and weighs 130 kilograms (290 pounds), whereas the average adult male measures 2.25 meters (7 feet) and weighs 95 kilograms (209 lb).
- While 3.5 m (11 ft) is the typical maximum size reported, there is just one record of a female specimen measuring exactly 4.0 m. (13 ft). Bull sharks are white below and grey on top, making them broader and heavier than other requiem sharks of equivalent length.
- More compact than the first dorsal fin is the second. The bull shark lacks an inner dorsal ridge, a tiny snout, and a caudal fin that is longer and lower than the more giant sharks. Bull sharks have the most vital biting force of any studied cartilaginous fish, with a maximum power of 5,914 newtons (1,330 lbs) per bite.
Distribution and Habitat
- You can occasionally find the bull shark in salt and freshwater streamlets if they are deep adequately, as well as in rivers, lakes, and coastal regions of warm waters. Although you can find it down to 150 meters (490 feet), it rarely swims more than 30 meters (98 ft).
- It can be found in the Atlantic from Massachusetts to southern Brazil and Morocco to Angola. Bull shark populations can also be found in several significant rivers, with the Brisbane River considered home to more than 500 bull sharks. During the Queensland floods of 2010–2011, one was reportedly observed swimming across Brisbane, Queensland, Australia’s flooded streets.
- Several were spotted in one of Goodna, Queensland’s main streets, not long after the floods. Just north of Brisbane, Moreton Bay caught a bull shark in the canals of Scarborough. There are even more of the Gold Coast and Queensland canals.
- To get to Iquitos in Peru and Bolivia, the bull shark had to travel 4,000 km (2,500 mi) up the Amazon River. Additionally, you can find it in Lake Nicaragua, West Bengal’s Ganges and Brahmaputra Rivers, Assam in Eastern India, and neighboring Bangladesh.
- It can survive in salty water, such as in South Africa’s St. Lucia Estuary. Since at least 1924, reports of bull sharks in the Tigris River upstream in Baghdad have been made.
- The species prefer warm currents. Bull shark sightings in Lake Pontchartrain increased significantly during Hurricane Katrina. Bull sharks have occasionally made it as far upstream as Alton, Illinois, on the Mississippi River and Manchester, Ohio, on the Ohio River.
- Additionally, bull sharks have been spotted in Maryland‘s Potomac River. Many bull sharks live in a lake on a golf course in Car book, Logan City, Queensland, Australia, and they became trapped after the Logan and Albert Rivers flooded in 1996. The golf course has tapped into the novelty by hosting the “Shark Lake Challenge,” a monthly competition.
Behavior
Freshwater Tolerance
- The bull shark is the most well-known among the 43 elasmobranch species in 10 genera and four families recorded in freshwater. Sawfish and stingrays (Dasyatidae, Potamotrygonidae, and others) are other species that enter rivers (Pristidae). Sandbar sharks (Carcharhinus plumbeus), smooth dogfishes (Triakidae), and some skates (Rajidae) frequently enter estuaries.
- Because the bull shark is diadromous, it can easily transition between fresh and salt water. Additionally, these fish are euryhaline species that can adapt to various salinities. The bull shark is a rare cartilaginous fish species that inhabit freshwater ecosystems. Most euryhaline fish are bony species like salmon and tilapia and are not closely interconnected to bull sharks. Evolutionary hypotheses explain why the bull shark had a population bottleneck during the last ice age.
- This bottleneck may have favored the genes for the osmoregulatory system, which may have split the bull shark from other members of the Elasmobranchii subclass. Because of the buildup of urea and trimethylamine oxide in their blood, elasmobranchs’ ability to access fresh water is restricted. However, bull sharks living in new water exhibit a substantially lower urea concentration in their blood than elasmobranchs.
- Despite this, a bull shark in freshwater has a substantially greater solute content (i.e., osmolarity) than the surrounding environment. Osmosis and the loss of salt and chloride from the shark’s body cause a significant influx of water to cross the gills. The rectal gland, kidneys, liver, and gills are just a few of the organs that bull sharks in freshwater have to keep the right mix of salt and water.
- Every elasmobranch has a rectal gland that helps it expel extra salt that it has collected while living in seawater. Bull sharks conserve sodium and chloride in freshwater habitats by reducing the rectal gland’s salt-excretory activity. The kidneys produce large amounts of diluted urine, but they also significantly impact the active reabsorption of solutes into circulation.
- While urea is formed in the liver as needed with variations in environmental salinity, the gills of bull sharks are likely involved in the uptake of sodium and chloride from the nearby fresh water. Recent research also demonstrates that sharks living in freshwater have considerably bigger negative buoyancies than those residing in marine areas, raising the cost of living in freshwater.
- It has since been established that bull sharks collected in freshwater had lower liver densities than sharks caught in marine areas. It might lower the additional expense of increased negative buoyancy. Bull sharks can control their body temperature to survive in either fresh or salt water. It can live its entire life in freshwater, but it does not occur, primarily because the shark needs to reproduce.
- Bull shark pups migrate out into the sea to procreate after leaving the brackish water where they are born. Bull sharks may only live in freshwater. However, tests on these animals revealed that they perished after four years. When opened the stomach, only two tiny, unrecognizable fish were visible. Since bull sharks’ primary food source is marine life, malnutrition may have been the cause of death.
- A study discovered that bull sharks spent most of their time in estuary mouths, and regardless of how salty the water was, they remained at the river’s mouth. However, a bull shark’s preference for fresh or salt water depends on its age since, as it gets older, it becomes more tolerant to salinity extremes.
- Most newly born or discovered very young bull sharks are in freshwater habitats, but the older bull sharks were found in saltwater habitats because they had improved tolerance to salinity.
- One of the reasons adult bull sharks enter rivers is to reproduce; this behavior is assumed to be a physiological tactic to promote juvenile survival rates and bull shark fitness in general. The young are born in fresh water and remain there until they can leave since they do not strongly tolerate excessive salinity.
- At first, researchers believed the sharks in Lake Nicaragua belonged to a unique species called the Lake Nicaragua shark (Carcharhinus nicaraguensis). After comparing specimens, taxonomists synonymized them in 1961. Bull sharks marked inside a lake have later been caught in the open ocean (and vice versa), some making the trek in as little as seven to eleven days.
Diet
- Bony fish, tiny sharks, including other bull sharks, and stingrays make up most of the bull shark’s diet. Turtles, birds, dolphins, terrestrial animals, crustaceans, and echinoderms can also be found in their diet. They hunt in murky waters where victims find it more difficult to spot approaching sharks. Bull sharks assault their prey by bumping them before biting them.
- They continue to bite and assault prey after the initial contact until the target cannot escape. Although the bull shark hunts alone, it occasionally pairs up with another bull shark to make snatching and deceiving victims easier. The bull shark, a member of the Carcharhinus family, is no exception to the rule that sharks are opportunistic feeders.
- Sharks typically eat in short spurts, but in times of food scarcity, they digest for extended periods to prevent hunger. Bull sharks will restate the food in their stomachs to escape a predator as part of their survival strategy. It is a diversionary approach, and if the predator advances to eat the regurgitated food, the bull shark can take advantage of the opening to flee.
Reproduction
- Bull sharks typically mate in late summer and early fall. One to thirteen live young can be born to a bull shark after a 12-month gestation. They are free-swimming, viviparous, and delivered live.
- Juvenile bull sharks are born in flat, safe places; the bull shark does not nurture its offspring. Standard nursery settings include river mouths, coastal lagoons, and other low-salinity estuaries. While the female bull shark cannot start reproducing until 18, the male bull shark can begin at 15.
- Bull shark females must be between 175 cm and 235 cm in length to generate viable eggs that can fertilize. Bull shark courtship behavior has yet to be extensively studied. The male may bite the female on the rear until she can roll over, at which point the male can mate. Adult females frequently have scratches from mating.
Human Encounters
- Many experts regard bull sharks as the world’s most dangerous sharks. They have historically been joined as the three species most likely to attack humans by their more well-known cousins, great whites and tiger sharks.
- The 1916 Jersey Shore shark attacks, which served as the basis for Peter Benchley’s novel Jaws, may have been caused by one or more bull sharks. Two fatal bites in fresh and brackish waters have led to speculation that bull sharks may have been to blame.
- Bull sharks have attacked swimmers near Sydney Harbour’s inlets. Bull sharks have bitten swimmers in India’s Ganges, Brahmaputra, Mahanadi, and other rivers.
- Although the sand tiger shark was also held responsible during the 1960s and 1970s, the Ganges shark, Glyphis gangeticus, is a critically endangered river shark species. Off the coast of Florida, bull shark attacks on people have also occurred.
Hunting
- The world’s oceans have shallow, warm waters where they can be seen cruising. They are swift, agile hunters who will consume nearly anything they sight, including fish, dolphins, and even other sharks.
- They do not, in and of themselves, eat people. However, they frequently attack people unintentionally or out of curiosity in the murky waters of estuaries and bays.
Threats to Survival
- Bull sharks are heavily hunted for their meat, hides, and oils, and their population is likely declining. According to one study, their average lengths dramatically decreased during the previous three decades. The bull shark is classified as nearly endangered by the IUCN.
Bull Shark Worksheets
This is a fantastic bundle which includes everything you need to know about Bull Sharks across 28 in-depth pages. These are ready-to-use Bull Sharks worksheets that are perfect for teaching students about the Bull Shark, scientifically known as Carcharhinus Leucas, which is one of the shark species that can live in both seawater and freshwater and is commonly found in tropical and subtropical areas. This species is known by several different names depending on its whereabouts: Zambezi shark, Nicaragua shark, Fitzroy Creek whaler, Swan River whaler or Ganges River shark.
Complete List Of Included Worksheets
- Bull Sharks Facts
- Sharky Profile
- Let’s Get Physical
- It’s Feeding Time!
- Oceanic Crossword
- Into the Blue
- Word Attack
- Cruising
- Shark Tale
- Truth Under the Sea
- Conserve and Protect
Frequently Asked Questions
What is a bull shark?
The bull shark (Carcharhinus leucas), often referred to as the Zambezi shark (or zambi) in Africa and the Lake Nicaragua shark in Nicaragua, is a type of requiem shark that is typically found around the world in warm, shallow waters along rivers and coasts. It is infamous for its aggressive behavior and is generally found in social, external brackish, and freshwater systems, especially the lower portions of rivers.
What are the characteristics of a bull shark?
They are medium-sized sharks with long pectoral fins and thick, sturdy bodies. Particularly on adolescent bull sharks, the fins have dark tips and are gray on top and white underneath.
Can bull sharks live in freshwater?
Because the bull shark is diadromous, it can easily transition between fresh and salt water. Additionally, these fish are euryhaline species that can adapt to various salinities. The bull shark is a rare cartilaginous fish species that inhabit freshwater ecosystems.
Do bull sharks attack humans?
Many experts regard bull sharks as the world’s most dangerous sharks. They have historically been joined as the three species most likely to attack humans by their more well-known cousins, great whites and tiger sharks.
Are bull sharks endangered?
Bull sharks are heavily hunted for their meat, hides, and oils, and their population is likely declining. According to one study, their average lengths dramatically decreased during the previous three decades. The bull shark is classified as nearly endangered by the IUCN.
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