The bull shark (''Carcharhinus leucas''), also known as the Zambezi shark (informally zambi) in

Africa Africa is the world's second-largest and second-most populous continent after Asia. At about 30.3 million km2 (11.7 million square miles) including adjacent islands, it covers 20% of Earth's land area and 6% of its total surfac ...

and

Lake Nicaragua Lake Nicaragua or Cocibolca or Granada (, , or ) is a freshwater lake in Nicaragua. Of tectonic origin and with an area of , it is the largest fresh water lake in Central America, the List of lakes by area, 19th largest lake in the world (by are ...

shark in

Nicaragua Nicaragua, officially the Republic of Nicaragua, is the geographically largest Sovereign state, country in Central America, comprising . With a population of 7,142,529 as of 2024, it is the third-most populous country in Central America aft ...

, is a species of

requiem shark Requiem sharks are sharks of the family Carcharhinidae in the order Carcharhiniformes. They are migratory, live-bearing sharks of warm seas (sometimes of brackish or fresh water) and include such species as the bull shark, lemon shark, blac ...

commonly found worldwide in warm, shallow waters along coasts and in rivers. It is known for its aggressive nature, and presence mainly in warm, shallow

brackish Brackish water, sometimes termed brack water, is water occurring in a natural environment that has more salinity than freshwater, but not as much as seawater. It may result from mixing seawater (salt water) and fresh water together, as in estuari ...

and

freshwater Fresh water or freshwater is any naturally occurring liquid or frozen water containing low concentrations of dissolved salts and other total dissolved solids. The term excludes seawater and brackish water, but it does include non-salty mi ...

systems including

estuaries An estuary is a partially enclosed coastal body of brackish water with one or more rivers or streams flowing into it, and with a free connection to the open sea. Estuaries form a transition zone between river environments and maritime environm ...

and (usually) lower reaches of

river A river is a natural stream of fresh water that flows on land or inside Subterranean river, caves towards another body of water at a lower elevation, such as an ocean, lake, or another river. A river may run dry before reaching the end of ...

s. Their aggressive nature has led to ongoing shark-culling efforts near beaches to protect beachgoers, which is one of the causes of bull shark populations continuing to decrease. Bull sharks are listed as vulnerable on the

IUCN Red List The International Union for Conservation of Nature (IUCN) Red List of Threatened Species, also known as the IUCN Red List or Red Data Book, founded in 1964, is an inventory of the global conservation status and extinction risk of biological ...

. Bull sharks are

euryhaline Euryhaline organisms are able to adapt to a wide range of salinities. An example of a euryhaline fish is the short-finned molly, '' Poecilia sphenops'', which can live in fresh water, brackish water, or salt water. The green crab ('' Carcinus m ...

and can thrive in both

salt In common usage, salt is a mineral composed primarily of sodium chloride (NaCl). When used in food, especially in granulated form, it is more formally called table salt. In the form of a natural crystalline mineral, salt is also known as r ...

and fresh water. They are known to travel far up rivers, and have been known to travel up the

Mississippi River The Mississippi River is the main stem, primary river of the largest drainage basin in the United States. It is the second-longest river in the United States, behind only the Missouri River, Missouri. From its traditional source of Lake Ita ...

as far as

Alton, Illinois Alton ( ) is a city on the Mississippi River in Madison County, Illinois, United States, about north of St. Louis, Missouri. The population was 25,676 at the 2020 United States census, 2020 census. It is a part of the River Bend (Illinois), Riv ...

, about from the ocean, but few freshwater interactions with humans have been recorded. Larger-sized bull sharks are probably responsible for the majority of nearshore

shark attack A shark attack is an attack on a human by a shark. Every year, around 80 unprovoked attacks are reported worldwide. Despite their rarity, many people fear shark attacks after occasional serial attacks, such as the Jersey Shore shark attacks of ...

s, including many incidents of shark bites attributed to other species. Unlike the

river shark ''Glyphis'' is a genus in the family Carcharhinidae, commonly known as the river sharks. They live in rivers or coastal regions in and around south-east Asia, Africa and parts of Australia. Taxonomy This genus contains only three extant specie ...

s of the genus '' Glyphis'', bull sharks are not true

freshwater shark Freshwater sharks are sharks that live in freshwater environments. While the majority of sharks are solely marine, a small number of shark species have adapted to live in freshwater. The river sharks (of the genus ''Glyphis'') live in freshwater a ...

s, despite their ability to survive in freshwater habitats. This shark appears in the image of the 2000 colones bill from

Costa Rica Costa Rica, officially the Republic of Costa Rica, is a country in Central America. It borders Nicaragua to the north, the Caribbean Sea to the northeast, Panama to the southeast, and the Pacific Ocean to the southwest, as well as Maritime bo ...

Etymology

The name "bull shark" comes from the shark's stocky shape, broad, flat snout, and aggressive, unpredictable behavior. In India, the bull shark may be confused with the Sundarbans or

Ganges shark The Ganges shark (''Glyphis gangeticus'') is a critically endangered species of requiem shark found in the Ganges River (Padma River) and the Brahmaputra River of India and Bangladesh. It is often confused with the more common bull shark (''Car ...

. In Africa, it is also commonly called the

Zambezi River The Zambezi (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. Its drainage basin covers , slightly less than half of t ...

shark, or just "zambi". Its wide range and diverse habitats result in many other local names, including

Ganges River The Ganges ( ; in India: Ganga, ; in Bangladesh: Padma, ). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international which goes through India, Bangladesh, Nepal and China." is a trans-boundary rive ...

shark, Fitzroy Creek whaler, van Rooyen's shark,

shark, river shark, freshwater whaler, estuary whaler, Swan River whaler, cub shark, and shovelnose shark.

Evolution

Some of the bull shark's closest living relatives do not have the capabilities of

osmoregulation Osmoregulation is the active regulation of the osmotic pressure of an organism's body fluids, detected by osmoreceptors, to maintain the homeostasis of the organism's water content; that is, it maintains the fluid balance and the concentration ...

. Its genus, ''

Carcharhinus ''Carcharhinus'' is the type genus of the family (biology), family Carcharhinidae, the requiem sharks. One of 12 genera in its family, it contains over half of the species therein. It contains 35 extant and eight extinct species to date, with lik ...

'', also includes the

sandbar shark The sandbar shark (''Carcharhinus plumbeus''), also known as the brown shark or thickskin shark, is a species of requiem shark, and part of the family Carcharhinidae, native to the Atlantic Ocean and the Indo-Pacific. It is distinguishable by i ...

, which is not capable of osmoregulation. The bull shark shares numerous similarities with river sharks of the genus ''Glyphis'', and other species in the genus ''Carcharhinus'', but its

phylogeny A phylogenetic tree or phylogeny is a graphical representation which shows the evolutionary history between a set of species or Taxon, taxa during a specific time.Felsenstein J. (2004). ''Inferring Phylogenies'' Sinauer Associates: Sunderland, M ...

has not been cleared yet.

Anatomy and appearance

Bull sharks are large and stout, with females being larger than males. The bull shark can be up to in length at birth. Adult female bull sharks average long and typically weigh , whereas the slightly smaller adult male averages and . While a maximum size of is commonly reported, a single record exists of a female specimen of exactly . A long pregnant individual reached . The maximum weight of the long pregnant female can be over , ranking it among the largest of the

s. Bull sharks are wider and heavier than other

s of comparable length, and are grey on top and white below. The second

dorsal fin A dorsal fin is a fin on the back of most marine and freshwater vertebrates. Dorsal fins have evolved independently several times through convergent evolution adapting to marine environments, so the fins are not all homologous. They are found ...

is smaller than the first. The bull shark's

caudal fin Fins are moving appendages protruding from the body of fish that interact with water to generate thrust and help the fish swim. Apart from the tail or caudal fin, fish fins have no direct connection with the back bone and are supported only ...

is longer and lower than that of the larger sharks, and it has a small

snout A snout is the protruding portion of an animal's face, consisting of its nose, mouth, and jaw. In many animals, the structure is called a muzzle, Rostrum (anatomy), rostrum, beak or proboscis. The wet furless surface around the nostrils of the n ...

, and lacks an interdorsal ridge. Bull sharks have a bite force up to , weight for weight the highest among all investigated cartilaginous fishes. A female Carcharhinus leucas at the Shark Reef Marine Reserve, Fiji - pone.0016597.s006.ogv, A female Bull Shark in Fiji Carcharhinus leucas upper teeth.jpg, Upper teeth Carcharhinus leucas lower teeth.jpg, Lower teeth SEM Carcharhinus leucas, 9x (3261812961).jpg,

Electron micrograph A micrograph is an image, captured photographically or digitally, taken through a microscope or similar device to show a magnify, magnified image of an object. This is opposed to a macrograph or photomacrograph, an image which is also taken ...

of an upper tooth

Exceptional specimens

In early June 2012, off the coast of the

Florida Keys The Florida Keys are a coral island, coral cay archipelago off the southern coast of Florida, forming the southernmost part of the continental United States. They begin at the southeastern coast of the Florida peninsula, about south of Miami a ...

near the western part of the

Atlantic Ocean The Atlantic Ocean is the second largest of the world's five borders of the oceans, oceanic divisions, with an area of about . It covers approximately 17% of Earth#Surface, Earth's surface and about 24% of its water surface area. During the ...

, a female believed to measure at least and was caught by members of the R.J. Dunlap Marine Conservation Program. In the

Arabian Sea The Arabian Sea () is a region of sea in the northern Indian Ocean, bounded on the west by the Arabian Peninsula, Gulf of Aden and Guardafui Channel, on the northwest by Gulf of Oman and Iran, on the north by Pakistan, on the east by India, and ...

, off the coast of

Fujairah Fujairah City () is the capital of the emirate of Fujairah in the United Arab Emirates. It is the List of cities in the United Arab Emirates, seventh-largest city in UAE, located on the Gulf of Oman (part of the Indian Ocean). It is the only Em ...

in the

United Arab Emirates The United Arab Emirates (UAE), or simply the Emirates, is a country in West Asia, in the Middle East, at the eastern end of the Arabian Peninsula. It is a Federal monarchy, federal elective monarchy made up of Emirates of the United Arab E ...

, a pregnant shark weighing and measuring long was caught in February 2019, followed by another specimen weighing about and measuring about the same in length, in January 2020. Unconfirmed reports suggest that the very largest, exceptional specimens can possibly weigh up to .

Distribution and habitat

The bull shark is commonly found worldwide in coastal areas of warm oceans, in rivers and

lake A lake is often a naturally occurring, relatively large and fixed body of water on or near the Earth's surface. It is localized in a basin or interconnected basins surrounded by dry land. Lakes lie completely on land and are separate from ...

s, and occasionally salt and freshwater streams if they are deep enough. It is found to a depth of , but does not usually swim deeper than . In the

Atlantic The Atlantic Ocean is the second largest of the world's five oceanic divisions, with an area of about . It covers approximately 17% of Earth's surface and about 24% of its water surface area. During the Age of Discovery, it was known for se ...

, it is found from

Massachusetts Massachusetts ( ; ), officially the Commonwealth of Massachusetts, is a U.S. state, state in the New England region of the Northeastern United States. It borders the Atlantic Ocean and the Gulf of Maine to its east, Connecticut and Rhode ...

to southern

Brazil Brazil, officially the Federative Republic of Brazil, is the largest country in South America. It is the world's List of countries and dependencies by area, fifth-largest country by area and the List of countries and dependencies by population ...

, and from

Morocco Morocco, officially the Kingdom of Morocco, is a country in the Maghreb region of North Africa. It has coastlines on the Mediterranean Sea to the north and the Atlantic Ocean to the west, and has land borders with Algeria to Algeria–Morocc ...

Angola Angola, officially the Republic of Angola, is a country on the west-Central Africa, central coast of Southern Africa. It is the second-largest Portuguese-speaking world, Portuguese-speaking (Lusophone) country in both total area and List of c ...

. Populations of bull sharks are also found in several major rivers, with more than 500 bull sharks thought to be living in the

Brisbane River The Brisbane River (Turrbal language, Turrbal: ) is the longest river in South East Queensland, Australia. It flows through the city of Brisbane, before emptying into Moreton Bay on the Coral Sea. John Oxley, the first European to explore the ...

. One was reportedly seen swimming the flooded streets of

Brisbane Brisbane ( ; ) is the List of Australian capital cities, capital and largest city of the States and territories of Australia, state of Queensland and the list of cities in Australia by population, third-most populous city in Australia, with a ...

Queensland, Australia Queensland ( , commonly abbreviated as Qld) is a state in northeastern Australia, and is the second-largest and third-most populous state in Australia. It is bordered by the Northern Territory, South Australia and New South Wales to the west, ...

, during the

2010–11 Queensland floods 1 (one, unit, unity) is a number, numeral, and glyph. It is the first and smallest positive integer of the infinite sequence of natural numbers. This fundamental property has led to its unique uses in other fields, ranging from science to sp ...

. Several were sighted in one of the main streets of

Goodna Goodna is a Suburbs and localities (Australia), suburb on the eastern edge of the City of Ipswich in Queensland, Australia. In the , Goodna had a population of 10,391 people. Geography Goodna is from the Brisbane central business district, ...

, Queensland, shortly after the peak of the January 2011, floods. A large bull shark was caught in the canals of

Scarborough Scarborough or Scarboro may refer to: People * Scarborough (surname) * Earl of Scarbrough Places Australia * Scarborough, Western Australia, suburb of Perth * Scarborough, New South Wales, suburb of Wollongong * Scarborough, Queensland, sub ...

, just north of Brisbane within Moreton Bay. Still greater numbers are in the canals of the

Gold Coast, Queensland The Gold Coast, also known by its initials, GC, is a coastal city and region in the state of Queensland, Australia, located approximately south-southeast of the centre of the list of Australian capital cities, state capital, Brisbane. It is ...

. In the warmer months of the year, bull sharks frequent

Sydney Harbour Port Jackson, commonly known as Sydney Harbour, is a ria, natural harbour on the east coast of Australia, around which Sydney was built. It consists of the waters of Sydney Harbour, Middle Harbour, North Harbour and the Lane Cove River, Lane ...

. In the

Pacific Ocean The Pacific Ocean is the largest and deepest of Earth's five Borders of the oceans, oceanic divisions. It extends from the Arctic Ocean in the north to the Southern Ocean, or, depending on the definition, to Antarctica in the south, and is ...

, it can be found from

Baja California Baja California, officially the Free and Sovereign State of Baja California, is a state in Mexico. It is the northwesternmost of the 32 federal entities of Mexico. Before becoming a state in 1952, the area was known as the North Territory of B ...

Ecuador Ecuador, officially the Republic of Ecuador, is a country in northwestern South America, bordered by Colombia on the north, Peru on the east and south, and the Pacific Ocean on the west. It also includes the Galápagos Province which contain ...

. The bull shark has traveled up the Amazon River to

Iquitos Iquitos (; ) is the capital city of Peru's Maynas Province, Peru, Maynas Province and Loreto Region. It is the largest metropolis in the Peruvian Amazon, east of the Andes, as well as the List of cities in Peru, ninth-most populous city in Peru ...

Peru Peru, officially the Republic of Peru, is a country in western South America. It is bordered in the north by Ecuador and Colombia, in the east by Brazil, in the southeast by Bolivia, in the south by Chile, and in the south and west by the Pac ...

and north

Bolivia Bolivia, officially the Plurinational State of Bolivia, is a landlocked country located in central South America. The country features diverse geography, including vast Amazonian plains, tropical lowlands, mountains, the Gran Chaco Province, w ...

. It also lives in freshwater

, in the Ganges and

Brahmaputra The Brahmaputra is a trans-boundary river which flows through Southwestern China, Northeastern India, and Bangladesh. It is known as Brahmaputra or Luit in Assamese, Yarlung Tsangpo in Tibetan, the Siang/Dihang River in Arunachali, and ...

Rivers of

West Bengal West Bengal (; Bengali language, Bengali: , , abbr. WB) is a States and union territories of India, state in the East India, eastern portion of India. It is situated along the Bay of Bengal, along with a population of over 91 million inhabi ...

, and

Assam Assam (, , ) is a state in Northeast India, northeastern India, south of the eastern Himalayas along the Brahmaputra Valley, Brahmaputra and Barak River valleys. Assam covers an area of . It is the second largest state in Northeast India, nor ...

in Eastern

India India, officially the Republic of India, is a country in South Asia. It is the List of countries and dependencies by area, seventh-largest country by area; the List of countries by population (United Nations), most populous country since ...

and adjoining

Bangladesh Bangladesh, officially the People's Republic of Bangladesh, is a country in South Asia. It is the List of countries and dependencies by population, eighth-most populous country in the world and among the List of countries and dependencies by ...

. It can live in water with a high salt content as in St. Lucia Estuary in

South Africa South Africa, officially the Republic of South Africa (RSA), is the Southern Africa, southernmost country in Africa. Its Provinces of South Africa, nine provinces are bounded to the south by of coastline that stretches along the Atlantic O ...

. Bull sharks have been recorded in the

Tigris River The Tigris ( ; see below) is the eastern of the two great rivers that define Mesopotamia, the other being the Euphrates. The river flows south from the mountains of the Armenian Highlands through the Syrian and Arabian Deserts, before merging ...

since at least 1924 as far upriver as Baghdad, and has been rumored to also inhabit the

Cahora Bassa The Cahora Bassa lake—in the Portuguese colonial era (until 1974) known as Cabora Bassa, from Nyungwe ''Kahoura-Bassa'', meaning "finish the job"—is Africa's fourth-largest artificial lake, situated in the Tete Province in Mozambique. In Afri ...

lake upstream of the

Zambezi The Zambezi (also spelled Zambeze and Zambesi) is the fourth-longest river in Africa, the longest east-flowing river in Africa and the largest flowing into the Indian Ocean from Africa. Its drainage basin covers , slightly less than half of t ...

. The species has a distinct preference for warm currents. After

Hurricane Katrina Hurricane Katrina was a powerful, devastating and historic tropical cyclone that caused 1,392 fatalities and damages estimated at $125 billion in late August 2005, particularly in the city of New Orleans and its surrounding area. ...

, many bull sharks were sighted in

Lake Pontchartrain Lake Pontchartrain ( ; ) is an estuary located in southeastern Louisiana in the United States. It covers an area of with an average depth of . Some shipping channels are kept deeper through dredging. It is roughly oval in shape, about from w ...

. In July 2023 some local fishermen in the

Atchafalaya River The Atchafalaya River () is a distributary of the Mississippi River and Red River of the South, Red River in south central Louisiana in the United States. It flows south, just west of the Mississippi River, and is the fifth largest river in N ...

have reported increasing numbers. Bull sharks have occasionally gone as far upstream in the

. Bull sharks have also been found in the

Potomac River The Potomac River () is in the Mid-Atlantic (United States), Mid-Atlantic region of the United States and flows from the Potomac Highlands in West Virginia to Chesapeake Bay in Maryland. It is long,U.S. Geological Survey. National Hydrography D ...

in St. Mary's County,

Maryland Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It borders the states of Virginia to its south, West Virginia to its west, Pennsylvania to its north, and Delaware to its east ...

. From 1996 to 2013, a golf course lake at Carbrook,

Logan City The City of Logan is a local government area (LGA) located in the south of Greater Brisbane in South East Queensland (SEQ), Australia. Situated between the City of Brisbane to the north and the City of Gold Coast to the south, the City of Lo ...

, Queensland, Australia was the home to several bull sharks. They were trapped following a flood of the

Logan Logan may refer to: Places * Mount Logan (disambiguation) Australia * Logan (Queensland electoral district), an electoral district in the Queensland Legislative Assembly * Logan, Victoria, small locality near St. Arnaud * Logan City, local gove ...

and

Albert Albert may refer to: Companies * Albert Computers, Inc., a computer manufacturer in the 1980s * Albert Czech Republic, a supermarket chain in the Czech Republic * Albert Heijn, a supermarket chain in the Netherlands * Albert Market, a street mar ...

Rivers in 1996, and resided in the lake until 2013, when they disappeared after another series of floods. The golf course capitalized on the novelty, changing their logo to feature the sharks and hosting a monthly tournament called the "Shark Lake Challenge".

Behavior

Freshwater tolerance

The bull shark is the best known of 43 species of

elasmobranch Elasmobranchii () is a subclass of Chondrichthyes or cartilaginous fish, including modern sharks ( division Selachii), and batomorphs (division Batomorphi, including rays, skates, and sawfish). Members of this subclass are characterised by h ...

, across 10 genera and four families, to have been reported in fresh and/or

water. Other species that enter rivers include the

stingrays Stingrays are a group of sea rays, a type of cartilaginous fish. They are classified in the suborder Myliobatoidei of the order Myliobatiformes and consist of eight families: Hexatrygonidae (sixgill stingray), Plesiobatidae (deepwater stin ...

( Dasyatidae,

Potamotrygonidae River stingrays or freshwater stingrays are Neotropical freshwater fishes of the family (biology), family Potamotrygonidae in the Order (biology), order Myliobatiformes, one of the four orders of Batoidea, batoids, cartilaginous fishes related to ...

and others) and

sawfish Sawfish, also known as carpenter sharks, are a family of very large rays characterized by a long, narrow, flattened rostrum, or nose extension, lined with sharp transverse teeth, arranged in a way that resembles a saw. They are among the lar ...

(

Pristidae Sawfish, also known as carpenter sharks, are a Family (biology), family of very large batoidea, rays characterized by a long, narrow, flattened rostrum (anatomy), rostrum, or nose extension, lined with sharp transverse plane, transverse teeth, ...

). Some

skate Skate or Skates may refer to: Fish *Skate (fish), several genera of fish belonging to the family Rajidae * Pygmy skates, several genera of fish belonging to the family Gurgesiellidae * Smooth skates or leg skates, several genera of fish belongin ...

s ( Rajidae), smooth dogfishes ( Triakidae), and

s ('' Carcharhinus plumbeus'') regularly enter estuaries. The bull shark is

diadromous Fish migration is mass relocation by fish from one area or body of water to another. Many types of fish migrate on a regular basis, on time scales ranging from daily to annually or longer, and over distances ranging from a few metres to thousa ...

, meaning they can swim between salt and fresh water with ease, as they are

fish—able to quickly adapt to a wide range of salinities. Thus, the bull shark is one of the few cartilaginous fishes that have been reported in freshwater systems. Many of the euryhaline fish are bony fishes, such as

salmon Salmon (; : salmon) are any of several list of commercially important fish species, commercially important species of euryhaline ray-finned fish from the genera ''Salmo'' and ''Oncorhynchus'' of the family (biology), family Salmonidae, native ...

tilapia Tilapia ( ) is the common name for nearly a hundred species of cichlid fish from the coelotilapine, coptodonine, heterotilapine, oreochromine, pelmatolapiine, and tilapiine tribes (formerly all were "Tilapiini"), with the economically mos ...

, and are not closely related to bull sharks. Evolutionary assumptions can be made to help explain this sort of evolutionary disconnect, with one being that the bull shark experienced a

population bottleneck A population bottleneck or genetic bottleneck is a sharp reduction in the size of a population due to environmental events such as famines, earthquakes, floods, fires, disease, and droughts; or human activities such as genocide, speciocide, wid ...

during the last ice age. This bottleneck may have separated the bull shark from the rest of the Elasmobranchii subclass and favored the genes for an osmoregulatory system. Elasmobranchs' ability to enter fresh water is limited because their blood is normally at least as salty (in terms of

osmotic strength Osmotic concentration, formerly known as osmolarity, is the measure of solute concentration, defined as the number of wiktionary:osmole, osmoles (Osm) of solute per litre (L) of Solution (chemistry), solution (osmol/L or Osm/L). The osmolarity of ...

) as seawater through the accumulation of

urea Urea, also called carbamide (because it is a diamide of carbonic acid), is an organic compound with chemical formula . This amide has two Amine, amino groups (–) joined by a carbonyl functional group (–C(=O)–). It is thus the simplest am ...

and

trimethylamine oxide Trimethylamine ''N''-oxide (TMAO) is an organic compound with the formula . It is in the class of amine oxides. Although the anhydrous compound is known, trimethylamine ''N''-oxide is usually encountered as the dihydrate. Both the anhydrous an ...

, but bull sharks living in fresh water show a significantly reduced concentration of urea within their blood. Despite this, the solute composition (i.e. osmolarity) of a bull shark in fresh water is still much higher than that of the external environment. This results in a large influx of water across the gills due to osmosis and loss of sodium and chloride from the shark's body. However, bull sharks in fresh water possess several organs with which to maintain appropriate salt and water balance; these are the rectal gland, kidneys, liver, and gills. All elasmobranchs have a rectal gland which functions in the excretion of excess salts accumulated as a consequence of living in seawater. Bull sharks in freshwater environments decrease the salt-excretory activity of the rectal gland, thereby conserving sodium and chloride. The kidneys produce large amounts of dilute urine, but also play an important role in the active reabsorption of solutes into the blood. The gills of bull sharks are likely to be involved in the uptake of sodium and chloride from the surrounding fresh water, whereas urea is produced in the liver as required with changes in environmental salinity. Recent work also shows that the differences in density of fresh water to that of marine waters result in significantly greater negative buoyancies in sharks occupying fresh water, resulting in increasing costs of living in fresh water. Bull sharks caught in freshwater have subsequently been shown to have lower liver densities than sharks living in marine waters. This may reduce the added cost of greater negative buoyancy. Bull sharks are able to regulate themselves to live in either fresh or salt water. It can live in fresh water for its entire life, but this does not happen, mostly due to the reproductive needs of the shark. Young bull sharks leave the brackish water in which they are born and move out into the sea to breed. While is theoretically possible for bull sharks to live purely in fresh water, experiments conducted on bull sharks found that they died within four years. The stomach was opened and all that was found were two small, unidentifiable fishes. The cause of death could have been starvation since the primary food source for bull sharks resides in salt water. In a research experiment, the bull sharks were found to be at the mouth of an estuary for the majority of the time. They stayed at the mouth of the river independent of the salinity of the water. The driving factor for a bull shark to be in fresh or salt water, however, is its age; as the bull shark ages, its tolerance for very low or high salinity increases. The majority of the newborn or very young bull sharks were found in the freshwater area, whereas the much older bull sharks were found to be in the saltwater areas, as they had developed a much better tolerance for the salinity. Reproduction is one of the reasons why adult bull sharks travel into the river—it is thought to be a physiological strategy to improve juvenile survival and a way to increase overall fitness of bull sharks. The young are not born with a high tolerance for high salinity, so they are born in fresh water and stay there until they are able to travel out. Initially, scientists thought the sharks in

belonged to an

endemic Endemism is the state of a species being found only in a single defined geographic location, such as an island, state, nation, country or other defined zone; organisms that are indigenous to a place are not endemic to it if they are also foun ...

species, the Lake Nicaragua shark (''Carcharhinus nicaraguensis''). In 1961, following

specimen Specimen may refer to: Science and technology * Sample (material), a limited quantity of something which is intended to be similar to and represent a larger amount * Biological specimen or biospecimen, an organic specimen held by a biorepository f ...

comparisons, taxonomists synonymized them.Fresh Waters: Unexpected Haunts.
elasmo-research.org. Accessed 6 April 2008. Bull sharks tagged inside the lake have later been caught in the

open ocean The pelagic zone consists of the water column of the open ocean and can be further divided into regions by depth. The word ''pelagic'' is derived . The pelagic zone can be thought of as an imaginary cylinder or water column between the surfa ...

(and vice versa), with some taking as few as seven to 11 days to complete the journey. A study of six bull sharks confined to a stagnant golf course lake in

Brisbane, Australia Brisbane ( ; ) is the List of Australian capital cities, capital and largest city of the States and territories of Australia, state of Queensland and the list of cities in Australia by population, third-most populous city in Australia, with a ...

, from 1996 to 2013 uncovered their adaptability to low-salinity environments, marking the longest recorded residency for the species under such conditions, and demonstrating their ability to live indefinitely in low-salinity aquatic environments.

Diet

The bull shark is a marine

apex predator An apex predator, also known as a top predator or superpredator, is a predator at the top of a food chain, without natural predators of its own. Apex predators are usually defined in terms of trophic dynamics, meaning that they occupy the hig ...

, capable of taking a variety of prey. The bull shark's diet consists mainly of

bony fish Osteichthyes ( ; ), also known as osteichthyans or commonly referred to as the bony fish, is a Biodiversity, diverse clade of vertebrate animals that have endoskeletons primarily composed of bone tissue. They can be contrasted with the Chondricht ...

and small sharks, including other bull sharks, and stingrays. Their diet can also include turtles, birds, dolphins, terrestrial mammals,

crustacean Crustaceans (from Latin meaning: "those with shells" or "crusted ones") are invertebrate animals that constitute one group of arthropods that are traditionally a part of the subphylum Crustacea (), a large, diverse group of mainly aquatic arthrop ...

s, and

echinoderm An echinoderm () is any animal of the phylum Echinodermata (), which includes starfish, brittle stars, sea urchins, sand dollars and sea cucumbers, as well as the sessile sea lilies or "stone lilies". While bilaterally symmetrical as ...

s. They hunt in murky waters where it is harder for the prey to see the shark coming. Bull sharks have been known to use the bump-and-bite technique to attack their prey. After the first initial contact, they continue to bite and tackle prey until the prey is unable to flee. The bull shark is a solitary hunter, though may briefly pair with another bull shark to make hunting and tricking prey easier.

Shark Sharks are a group of elasmobranch cartilaginous fish characterized by a ribless endoskeleton, dermal denticles, five to seven gill slits on each side, and pectoral fins that are not fused to the head. Modern sharks are classified within the ...

s are

opportunistic 300px, ''Opportunity Seized, Opportunity Missed'', engraving by Theodoor Galle, 1605 Opportunism is the practice of taking advantage of circumstances — with little regard for principles or with what the consequences are for others. Opport ...

feeders, and the bull shark is no exception to this, as it is part of the ''Carcharhinus'' family of sharks. Normally, sharks eat in short bursts, and when food is scarce, sharks digest for a much longer period of time in order to avoid starvation. As part of their survival mechanism, bull sharks will regurgitate the food in their stomachs in order to escape from a predator. This is a distraction tactic; if the predator moves to eat the regurgitated food the bull shark can use the opportunity to escape.

Reproduction

Bull sharks mate during late summer and early autumn, often in bays and estuaries. After

gestating Gestation is the period of development during the carrying of an embryo, and later fetus, inside viviparous animals (the embryo develops within the parent). It is typical for mammals, but also occurs for some non-mammals. Mammals during pregnanc ...

for 12 months, a bull shark may give birth to 1 to 13 live young.Fact Sheet: Bull Sharks
Sharkinfo.ch (15 October 1999). Retrieved on 30 November 2013. They are

viviparous In animals, viviparity is development of the embryo inside the body of the mother, with the maternal circulation providing for the metabolic needs of the embryo's development, until the mother gives birth to a fully or partially developed juve ...

, born live and free-swimming. The young are about at birth. The bull shark does not rear its young; the young bull sharks are born into flat, protected areas. Coastal lagoons, river mouths, and other low-salinity estuaries are common nursery habitats. The male bull shark is able to begin reproducing around the age of 15 years while the female cannot begin reproducing until the age of 18 years. The size of a fully matured female bull shark to produce viable eggs for fertilization seems to be 175 cm to 235 cm. The courting routine between bull sharks has not been observed in detail as of yet. The male likely bites the female on the tail until she can turn upside down and the male can copulate at that point. Mature females commonly have scratches from the mating process.

Interactions with humans

Since bull sharks often dwell in very shallow waters, are found in many types of habitats, are territorial by nature, and have no tolerance for provocation, they may be more dangerous to humans than any other species of shark. Bull sharks are one of the three shark species (along with the

tiger shark The tiger shark (''Galeocerdo cuvier'') is a species of ground shark, and the only extant member of the genus '' Galeocerdo'' and family Galeocerdonidae. It is a large apex predator, with females capable of attaining a length of over . Popula ...

and

great white shark The great white shark (''Carcharodon carcharias''), also known as the white shark, white pointer, or simply great white, is a species of large Lamniformes, mackerel shark which can be found in the coastal surface waters of all the major ocea ...

) most likely to bite humans. One or several bull sharks may have been responsible for the

Jersey Shore shark attacks of 1916 The Jersey Shore shark attacks of 1916 were a series of shark attacks along the coast of New Jersey, in the United States, between July 1 and 12, 1916, in which four people were killed and one critically injured. The incidents occurred during a ...

. While it is a common misconception that these attacks were the inspiration for the novel '' Jaws'', its author

Peter Benchley Peter Bradford Benchley (May 8, 1940 – February 11, 2006) was an American author. He is best known for his bestselling novel '' Jaws'' and co-wrote its movie adaptation with Carl Gottlieb. Several more of his works were also adapted for both ...

has stated this is not the case. The speculation that bull sharks may have been responsible is based on two fatal bites occurring in brackish and fresh water. Bull sharks have attacked swimmers around the

inlets. In India, bull sharks swim up the

Ganges The Ganges ( ; in India: Ganga, ; in Bangladesh: Padma, ). "The Ganges Basin, known in India as the Ganga and in Bangladesh as the Padma, is an international which goes through India, Bangladesh, Nepal and China." is a trans-boundary rive ...

, Bramaputra, Mahanadi, and other Indian rivers and have bitten bathers. Many of these bite incidents were attributed to the

, ''Glyphis gangeticus'', a critically endangered river shark species, although the

sand tiger shark The sand tiger shark (''Carcharias taurus''), grey/gray nurse shark (in Australia), spotted ragged-tooth shark (in South Africa), or blue-nurse sand tiger, is a species of shark that inhabits subtropical and temperate waters worldwide. It inhabit ...

was also blamed during the 1960s and 1970s. Bull sharks have also attacked humans off the coast of Florida.

Visual cues

Behavioral studies have confirmed that sharks can take visual cues to discriminate between different objects. The bull shark is able to discriminate between colors of mesh netting that is present underwater. It was found that bull sharks tended to avoid mesh netting of bright colors rather than colors that blended in with the water. Bright yellow mesh netting was found to be easily avoided when it was placed in the path of the bull shark. This was found to be the reason that sharks are attracted to bright yellow survival gear rather than ones that were painted black.

Energy conservation

In 2008, researchers tagged and recorded the movements of young bull sharks in the

Caloosahatchee River The Caloosahatchee River is a river on the southwest Gulf Coast of the United States, Gulf Coast of Florida in the United States, approximately long.U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National ...

estuary. They were testing to find out what determined the movement of the young bull sharks. It was found that the young bull sharks synchronously moved downriver when the environmental conditions changed. This large movement of young bull sharks were found to be moving as a response rather than other external factors such as predators. The movement was found to be directly related to the bull shark conserving energy for itself. One way the bull shark is able to conserve energy is that when the tidal flow changes, the bull shark uses the tidal flow in order to conserve energy as it moves downriver. Another way for the bull shark to conserve energy is to decrease the amount of energy needed to osmoregulate the surrounding environment.

Ecology

Humans are the biggest threat to bull sharks. Larger sharks, such as the

and

, may attack them, but typically only target juveniles. Crocodiles may be a threat to bull sharks in rivers.

Saltwater crocodile The saltwater crocodile (''Crocodylus porosus'') is a crocodilian native to saltwater habitats, brackish wetlands and freshwater rivers from India's east coast across Southeast Asia and the Sundaland to northern Australia and Micronesia. It ha ...

s have been observed preying on bull sharks in the rivers and estuaries of

Northern Australia The unofficial geographic term Northern Australia includes those parts of Queensland and Western Australia north of latitude 26th parallel south, 26° and all of the Northern Territory. Those local government areas of Western Australia and Q ...

, and a

Nile crocodile The Nile crocodile (''Crocodylus niloticus'') is a large crocodilian native to freshwater habitats in Africa, where it is present in 26 countries. It is widely distributed in sub-Saharan Africa, occurring mostly in the eastern, southern, and ce ...

was reportedly sighted consuming a bull shark in South Africa.

Conservation

The bull shark is listed as a vulnerable species on the IUCN Red List and its population is decreasing. Despite its status, the species isn't named as a protected species. Threats to the bull shark are numerous, such as getting caught in fishing nets, overfishing for their oil, skin, and meat, pollution to their habitat, and more. In many areas of the world, including Australia and South Africa, there are shark-culling measures around beaches to prevent attacks on beach-goers. Researchers tried to fix the problem of sharks getting too close to land by testing out a device called the SharkSafe Barrier™. This barrier used magnetic and visual stimuli, which utilized rows of piping to create a continuous magnetic field to deter the sharks. However, researchers concluded that the technology needs to be improved and tested further before it can be implemented as a reliable safety measure.O'Connell, Craig Patrick; Gressle, Juliet; Crews, Julia; King, Andre A.; He, Pingguo (2022-01). "Evaluating the effects of a SharkSafe Barrier™ shoreline deployment on bull shark ( Carcharhinus leucas ) behaviour". ''Aquatic Conservation: Marine and Freshwater Ecosystems''. 32 (1): 55–65. doi:10.1002/aqc.3732.

ISSN An International Standard Serial Number (ISSN) is an eight-digit to uniquely identify a periodical publication (periodical), such as a magazine. The ISSN is especially helpful in distinguishing between serials with the same title. ISSNs a ...

1052-7613 Other research is being conducted to come up with conservation solutions for the bull sharks. One example is The Nature Conservancy satellite tagging sharks to track their migration and find their habitats in order to guide what areas require further protection projects.

References

Sources

* * * *

Sunday Herald Sun The ''Herald Sun'' is a conservative daily tabloid newspaper based in Melbourne, Australia, published by The Herald and Weekly Times, a subsidiary of News Corp Australia, itself a subsidiary of the American Murdoch owned News Corp. The ''Her ...

, Sunday, 23 April 2005

External links

* (5 min 23 second video with audio) * {{Taxonbar, from=Q190469

bull shark The bull shark (''Carcharhinus leucas''), also known as the Zambezi shark (informally zambi) in Africa and Lake Nicaragua shark in Nicaragua, is a species of requiem shark commonly found worldwide in warm, shallow waters along coasts and in riv ...

Viviparous fish Pantropical fish Euryhaline fish of Nicaragua Fish of Lake Nicaragua

Articles containing video clips Apex predators