Bull Shark (Carcharhinus leucas): Facts, Habitat and Diet

What does a bull shark look like?

The bull shark is built like a heavyweight. It is wider and heavier than other gray requiem sharks of the same length, with a short, broad, bluntly rounded snout that is shorter than the width of its mouth. The eyes are small, a hint that sight may matter less to a shark that often hunts in cloudy water.

The back is pale to dark gray and the belly white, a pattern called countershading that makes the shark harder to see from above and below. The first dorsal fin is large and triangular, the second dorsal fin is much smaller, and there is no ridge of skin between the two dorsal fins. The pectoral fins are broad and angular. Young bull sharks have dusky or dark-tipped fins that fade with age.

The upper teeth are broad, triangular and heavily serrated, ideal for cutting, while the lower teeth are narrower and pointed for gripping. Bull sharks look very similar to several other gray coastal sharks, such as sandbar, dusky and blacktip sharks, and even experts can find them hard to tell apart in murky water.

How big do bull sharks get?

Females are larger than males. Adult females average about 2.4 m (8 ft) long and 130 kg (290 lb), while adult males average about 2.25 m (7.4 ft) and 95 kg (210 lb). Size also varies by region: bull sharks off North America tend to grow larger than those in Central America.

A single female of 4 m (13 ft) has been reported, but this is exceptional. Because bull sharks are so thickset, a large one is much heavier than a slimmer shark of the same length.

Where do bull sharks live?

Bull sharks live along tropical and subtropical coasts around the world. In the western Atlantic they range from Massachusetts to southern Brazil, with many moving north along the US East Coast in summer and returning south as the water cools. In the eastern Atlantic they occur from Morocco to Angola, and in the Pacific from Baja California to Ecuador. They are also widespread in the Indian Ocean and western Pacific, from South Africa and Mozambique to India, Southeast Asia, Fiji and Australia.

Most bull sharks stay in shallow water, usually less than 30 m (100 ft) deep, although they have been recorded down to about 150 m (490 ft). They favor bays, lagoons, harbors, mangrove creeks and river mouths, and they often swim in water that is only waist-deep.

What sets them apart is their use of rivers and lakes. Bull sharks have been reported as far up the Mississippi River as Alton, Illinois, near St. Louis, roughly 1,800 km (1,100 mi) of river from the Gulf of Mexico, about 3,700–4,000 km (2,300–2,500 mi) up the Amazon in Peru, in Lake Nicaragua in Central America, and in the Ganges, Zambezi and Tigris river systems. In Australia they live in the Brisbane River and the canals of the Gold Coast, and they visit Sydney Harbour in the warmer months. Many local names reflect this, including Zambezi shark, Lake Nicaragua shark and Swan River whaler.

How can bull sharks survive in fresh water?

Most sharks die quickly in fresh water. Their blood is kept about as salty as seawater by high levels of urea, so in a river water would flood into their bodies through the gills. The bull shark is a euryhaline fish, meaning it can cope with a wide range of salinities.

When a bull shark moves into fresh water, it lowers the amount of urea and salt in its blood, its kidneys produce large amounts of very dilute urine, and the salt-excreting rectal gland slows down so that the shark keeps the salts it needs. The gills help by taking up sodium and chloride from the surrounding water. Living in fresh water still has costs: fresh water is less dense than seawater, so the sharks sink more easily and use more energy to stay up. The full story is explained in Can bull sharks live in freshwater?

The bull shark is not a true river shark, though. Adults spend most of their lives in coastal seas and estuaries and return to brackish water to give birth. The genuine river sharks belong to the genus Glyphis, a group of rare species found in parts of Asia and northern Australia.

What do bull sharks eat?

Bull sharks are opportunistic predators that eat almost anything they can catch. Bony fish make up most of their diet, along with smaller sharks (including young bull sharks), stingrays and other rays. They also take sea turtles, seabirds, dolphins, crabs, shrimp and sea urchins, and occasionally land mammals that fall or wade into rivers.

They usually hunt alone in murky water, where prey has little chance of seeing them coming. A bull shark may bump a target before biting, then bite repeatedly until the prey cannot escape. Their jaws are powerful: one study estimated a bite force of up to 5,914 newtons (about 1,330 pounds-force) in a large bull shark, which for its body size is among the strongest bites measured in any shark.

Reproduction and life cycle

Bull sharks are viviparous, meaning they give birth to live young that are nourished through a placenta-like connection to the mother, as in mammals. Mating has rarely been seen, but females often carry bite scars from males, mostly on their pectoral and pelvic fins. Pregnancy lasts about 10–12 months, and females usually breed every other year.

Litters range from 1 to 13 pups, each about 56–81 cm (22–32 in) long. Females give birth in shallow, low-salinity nurseries such as coastal lagoons, estuaries and river mouths. In Florida, young bull sharks grow up in places like the Indian River Lagoon and the Caloosahatchee River. These nurseries offer plenty of food and few large predators, since most bigger sharks avoid low-salinity water. There is no parental care: the pups are on their own from birth.

Young bull sharks grow quickly at first, about 16–18 cm (6–7 in) a year, then more slowly. They mature late. Estimates vary by region, but studies in the Gulf of Mexico suggest that males mature at about 14–15 years and females at about 18 years, at lengths of roughly 1.6–2.3 m (5.2–7.5 ft).

Lifespan, predators and threats

Bull sharks are long-lived. Age studies based on growth rings in the vertebrae have found sharks of 21–28 years in the Gulf of Mexico and a female of about 32 years off South Africa. Individuals have also lived around 30 years in public aquariums.

Adult bull sharks have few natural predators. Young ones are eaten by tiger sharks, great white sharks and larger bull sharks, and saltwater crocodiles have been seen catching bull sharks in rivers in northern Australia.

People are the main threat. Bull sharks are caught on longlines, in gillnets and by recreational anglers, and their meat, fins, skin and liver oil are used. Because they live so close to shore, they also suffer from pollution and the loss of estuaries and mangroves, which are their nurseries. In parts of Australia and South Africa, nets and baited drumlines set to protect beaches also catch and kill bull sharks.

Conservation status

The IUCN Red List lists the bull shark as Vulnerable, with a decreasing population, in an assessment published in 2021. The main cause is fishing pressure across much of its range. Slow growth, late maturity and small litters every second year mean that bull shark populations recover slowly once they are reduced.

The species has little specific protection in most countries, although it is covered by fisheries rules in some regions. Researchers tag bull sharks with acoustic and satellite tags to map their nurseries and migrations, information that helps managers decide which estuaries and coastal waters most need protection.

Are bull sharks dangerous to people?

The bull shark is one of the “big three” sharks most often linked to serious unprovoked bites, along with the white shark and the tiger shark. The International Shark Attack File lists 119 confirmed unprovoked bites by bull sharks since records began, 26 of them fatal. The true number is probably higher, because bull sharks are hard to identify and are likely behind many bites recorded only as “unidentified shark”.

Bull sharks are not hunting people. Their risk comes from where they live: warm, shallow, murky water near beaches, harbors and river mouths, exactly where people swim and wade. The full picture, with comparisons, is in Are bull sharks the most dangerous shark?, and local species and risk are covered in sharks in Florida.

Even so, bites are very rare compared with the millions of people who swim in bull shark waters every year. Avoiding murky water, river mouths after heavy rain, and swimming at dawn, dusk or night lowers the risk further. Anyone bitten needs emergency medical help immediately: call 911 (US), 112 (EU) or 999 (UK).

Myths and facts

Myth: bull sharks are freshwater sharks. They are coastal sea sharks that can tolerate fresh water. Most bull sharks spend most of their lives in salt or brackish water.

Myth: Lake Nicaragua has its own landlocked shark. Scientists once described the lake’s sharks as a separate species, Carcharhinus nicaraguensis, but in 1961 they were shown to be bull sharks. Later tagging proved that the sharks travel between the lake and the Caribbean Sea along the San Juan River, some in as little as 7–11 days.

Myth: the 1916 New Jersey shark attacks were definitely bull sharks. Three of those bites happened in Matawan Creek, a narrow tidal creek where a bull shark seems likely, but a white shark caught nearby was also blamed at the time. The case has never been settled.

Fact: bull sharks can live in a golf course lake. After a flood in 1996, several bull sharks were trapped in a lake at a golf course in Logan, Queensland, and lived there for about 17 years until further flooding around 2013. Compared with relatives such as the tiger shark and the great white shark, the bull shark is by far the most at home in rivers and lakes.