Bull Shark Guide (Carcharhinus leucas): Characteristics, size, habitats

The bull shark (Carcharhinus leucas) is known for its aggressive behavior and preference for living near densely populated areas, such as tropical coasts. It is a very common species. It can tolerate both brackish and fresh water, often venturing into rivers and tributaries within the continent.

For these reasons, many specialists consider the bull shark the most dangerous of all sharks. Historically, among the three species most likely to attack humans, they are alongside their more famous relatives, the great white shark and the tiger shark. They are medium-sized sharks, though with considerable size and weight compared to other cartilaginous fish, with robust bodies and long pectoral fins. Their upper part is gray, while their lower part is white. The fins have dark spots, especially in young specimens.

They can be found in shallow, warm waters of all the world's oceans. These fast and agile predators eat anything they find, from fish and dolphins to other sharks. Humans are not part of their typical diet. However, they frequent the murky waters of estuaries and bays, where they sometimes attack people by accident or curiosity.

Currently, the bull shark is not classified as a threatened or endangered species. However, in many places, they are fished for their meat, skin, and oil, which is likely reducing their population. A study has revealed that their average length has significantly decreased in recent decades.

Characteristics of the Bull Shark (Carcharhinus leucas)

The bull shark (Carcharhinus leucas) has a robust body with two large dorsal fins and a long tail with a long upper lobe and a precaudal pit. Its upper part is gray and the lower part is white. In August 2007, an albino specimen was photographed in South West Rocks, Australia. Additionally, it lacks an interdorsal ridge and has a small snout.

Size and weight

Bull sharks can reach up to 3.2 meters in length. Males have an average size of 2.1 meters, while females reach about 2.2 meters. Newborns can measure up to 81 cm in length, and there are records of adult females up to 4.0 meters in length. The difference between males and females is notable, with females being generally larger.

Bull sharks are large and robust, with females being larger than males. Newborn bull sharks can measure up to 81 cm in length. Adult females average 2.4 meters in length and weigh around 130 kg, while adult males are slightly smaller, averaging 2.25 meters and 95 kg. Although a maximum size of 3.5 meters is commonly reported, there are records of a female specimen measuring 4.0 meters. A pregnant specimen measuring 3.25 meters in length weighed 450 kg. The maximum weight can exceed 600 kg, placing it among the largest requiem sharks. Bull sharks are wider and heavier than other requiem sharks of similar length, and they are gray on the upper part and white on the lower part. The second dorsal fin is smaller than the first, and the caudal fin is longer and lower compared to other sharks. It has a small snout and lacks an interdorsal ridge.

Bull sharks have a bite force of up to 5,914 newtons, the highest among all cartilaginous fish investigated relative to their weight.

Habitat

The bull shark is commonly found in coastal areas of warm oceans, in rivers and lakes, and occasionally in freshwater and saltwater streams if they are deep enough. It inhabits depths of up to 150 meters but generally does not swim more than 30 meters deep. In the Atlantic, it can be found from Massachusetts to southern Brazil and from Morocco to Angola.

Carcharhinus leucas lives alone or in small groups. It inhabits the sandy bottoms of the continental shelf, up to 200 meters deep, although it can also be found swimming slowly between two waters, especially at dusk, when it is more active.

Bull sharks are euryhaline, meaning they can live in both freshwater and saltwater. They are known to swim upstream and have been sighted in the Mississippi River up to Alton, Illinois, about 1,100 kilometers from the ocean. However, freshwater interactions with humans are rare. Larger bull sharks are likely responsible for most shark attacks near the coast, including many incidents attributed to other species.

Unlike river sharks of the genus Glyphis, bull sharks are not true freshwater sharks, although they can survive in freshwater habitats. Their aggressive behavior and ability to live in various conditions make them considered dangerous to humans.

Freshwater Habitat (Rivers and Lakes)

There are populations of bull sharks in several major rivers. It is estimated that over 500 bull sharks live in the Brisbane River. During the Queensland floods of 2010-2011, a bull shark was reported swimming in the flooded streets of Brisbane. Several bull sharks were seen on one of the main streets of Goodna, Queensland, after the peak of the January 2011 floods. A large bull shark was caught in the canals of Scarborough, north of Brisbane, within Moreton Bay. An even greater number are found in the canals of the Gold Coast, Queensland. During the warmer months of the year, bull sharks frequent Sydney Harbor. In the Pacific, they are found from Baja California to Ecuador.

Migrations and Unusual Sightings

The bull shark has traveled 4,000 km upstream in the Amazon River to Iquitos, Peru, and northern Bolivia. It also lives in the freshwater lake of Nicaragua, in the Ganges and Brahmaputra rivers of West Bengal, in Assam in eastern India, and in Bangladesh. It can survive in water with high salinity, such as in the St. Lucia estuary in South Africa. Bull sharks have been recorded in the Tigris River since at least 1924, upstream to Baghdad, and are rumored to inhabit Cahora Bassa Lake, upstream of the Zambezi. The species shows a clear preference for warm currents.

Sightings After Natural Disasters

After Hurricane Katrina, many bull sharks were sighted in Lake Pontchartrain. In July 2023, local fishermen in the Atchafalaya River reported an increase in their number. Occasionally, bull sharks have traveled upstream in the Mississippi River to Alton, Illinois. They have also been found in the Potomac River in Maryland.

Unusual Habitats

A lake on a golf course in Carbrook, Logan City, Queensland, Australia, is home to several bull sharks that were trapped after flooding from the Logan and Albert rivers in 1996. The golf course has capitalized on this uniqueness and organizes a monthly tournament called the "Shark Lake Challenge".

Global Distribution of the Bull Shark

This shark is found in the Atlantic, Pacific, and Indian Oceans, as well as in the Mediterranean and Adriatic Seas. In the western Atlantic, it inhabits coastal waters from the Gulf of Maine to Florida, the northern Gulf of Mexico, around the Bahamas and Bermuda, and from Brazil to Argentina. In the eastern Atlantic, it is found from the Mediterranean Sea to the Canary Islands, Spain, also in Cape Verde, along the coasts of Senegal and Ghana, and from southern Nigeria to Cameroon. In the western Indian Ocean, it ranges from South Africa to southern Mozambique, excluding Madagascar. It has also been sighted in the Red Sea and off the coasts of India. In the western Pacific, it is found in the waters around Japan, China, and Australia.

In Playa del Carmen, Cabo Pulmo, and Cancun, Mexico, bull sharks can be seen during guided boat and swimming activities, although sightings are not always guaranteed.

Migrations

In South Africa and Australia, bull sharks undertake an annual migration that can cover more than 1,000 kilometers. They are born during the summer in relatively cold waters (approximately 16°C). After birth, they swim north to sites with suitable rocks or caves, often at a depth of 20 meters, where they mate in winter. They then swim to warmer waters for gestation. In the fall, they return south to give birth in colder waters. This cycle can cover up to 3,000 kilometers.

Behavior with Humans and Other Sharks

In bull shark specimens, the sharp teeth protruding from their jaws are noticeable. Although the bull shark is often associated with being a dangerous animal due to its considerable size and prominent teeth that point outward, they are actually quite docile. They often swim with the waves, sometimes very close to humans, but only a few cases of bull shark attacks on people have been recorded, generally related to spearfishing, rod fishing, or shark feeding. When these sharks show aggression, they tend to steal fish or bait rather than directly attack humans.

Due to their large size and calm temperament, this shark species is commonly exhibited in aquariums worldwide.

Visual Cues

Behavioral studies have shown that sharks can follow visual cues to differentiate between different objects. The bull shark can discriminate between the colors of mesh nets underwater. It was found that they tend to avoid brightly colored nets compared to those that blend in with the water. For example, bright yellow mesh nets are more easily avoided by bull sharks, which explains why they are attracted to bright yellow survival gear instead of black gear.

Diet

The bull shark is a marine predator capable of capturing a wide variety of prey. Its diet consists mainly of bony fish and small sharks, including other bull sharks, as well as stingrays. They can also consume turtles, birds, dolphins, terrestrial mammals, crustaceans, and echinoderms. They hunt in murky waters where the prey has more difficulty seeing the shark. Bull sharks use a technique of bumping and biting to capture their prey; after the first contact, they continue to bite and attack until the prey cannot escape.

These sharks are solitary hunters, although they sometimes briefly pair with other specimens of their species to facilitate hunting and deceive their prey. They feed opportunistically, eating in short bursts, and when food is scarce, they digest over a longer period to avoid starvation. As a survival mechanism, bull sharks can regurgitate the food in their stomachs to distract a predator and escape.

Reproduction

Bull sharks mate in late summer and early autumn, often in bays and estuaries. After a 12-month gestation period, a female can give birth to 1 to 13 live young. They are viviparous, meaning the young are born alive and swim freely. At birth, the young measure about 70 cm. The bull shark does not care for its young; they are born in flat, protected areas such as coastal lagoons and river mouths.

Males can begin to reproduce around 15 years old, while females cannot do so until they are 18 years old. The size of a mature female to produce viable eggs seems to be between 175 cm and 235 cm. Although the courtship routine between bull sharks has not been observed in detail, it is believed that the male bites the female on the tail until she can turn upside down and the male can copulate. Mature females often have scratches due to the mating process.

Energy Conservation

In 2008, researchers tagged and recorded the movements of young bull sharks in the Caloosahatchee River estuary. They discovered that young bull sharks moved synchronously downstream when environmental conditions changed, a direct response to conserve energy. When tidal flow changes, bull sharks use this flow to save energy by moving downstream. Additionally, they can reduce the energy needed to osmoregulate the surrounding environment.

Ecology

Humans are the greatest threat to bull sharks. Although larger sharks, such as the tiger shark and the great white shark, can attack juveniles, they typically do not pose a significant threat to adults. In rivers, crocodiles can also be a threat. Saltwater crocodiles in northern Australia and Nile crocodiles in South Africa have been observed preying on bull sharks.

Conservation of the Species Carcharhinus leucas

The bull shark is listed as a vulnerable species on the IUCN Red List, with a declining population. Despite this status, the species is not formally protected. Threats include accidental capture in fishing nets, overfishing for oil, skin, and meat, and habitat pollution. In some parts of the world, such as Australia and South Africa, measures exist to cull sharks near beaches to prevent attacks on swimmers. Devices such as the SharkSafe Barrier™ that use magnetic and visual stimuli to deter sharks have been tested, although more research and development are needed for their effective implementation.

Additionally, research is ongoing to find conservation solutions. An example is the satellite tagging of sharks by The Nature Conservancy to track their migration and determine which areas need more protection projects.

Common Names for the Bull Shark

Although the official name of the bull shark is Carcharhinus leucas, it is also known by other names depending on the region or country, such as:

• Zambezi shark or zambi (in Africa)
• Lake Nicaragua shark (in Nicaragua)
• Sarda shark (in some Spanish-speaking regions like Spain)

The bull shark (Carcharhinus leucas), known in Spanish as tiburón sarda, belongs to the family Carcharhinidae and the order Carcharhiniformes, should not be confused with Carcharias taurus, known as the sand tiger shark, grey nurse (FAO name), spotted ragged-tooth shark, or sand shark, which is a species of lamniform shark belonging to the family Odontaspididae that inhabits the Atlantic, Indian, and Pacific Oceans as they are not closely related.

Etymology

The name "bull shark" derives from the shark's robust shape, broad and flat snout, and aggressive and unpredictable behavior. In India, the bull shark may be confused with the Sundarbans shark or the Ganges shark. In Africa, it is commonly known as the Zambezi river shark or simply "zambi."

Due to its wide distribution and diverse habitats, it has many other local names, including Ganges river shark, Fitzroy Creek whaler, Van Rooyen's shark, Lake Nicaragua shark, river shark, freshwater whaler, estuary whaler, Swan river whaler, shovel-nosed shark, and sharp-toothed shark.

Classification of the Bull Shark: Carcharhinus leucas

• Kingdom: Animalia
• Phylum: Chordata
• Class: Chondrichthyes (cartilaginous fishes)
• Order: Carcharhiniformes
• Family: Carcharhinidae
• Genus: Carcharhinus
• Species: Carcharhinus leucas

The bull shark (Carcharhinus leucas) belongs to the family Carcharhinidae, while the great white shark (Carcharodon carcharias) is classified within the family Lamnidae. They share the class Chondrichthyes for being cartilaginous fishes, although both species are not directly related beyond the order level, which is Lamniformes for the great white shark and Carcharhiniformes for the bull shark.

Evolution

Some of the bull shark's closest relatives do not have the ability to osmoregulate, that is, the ability to regulate the concentration of salts and other solutes in the body, thus maintaining osmotic balance with the environment. Its genus, Carcharhinus, includes the sandbar shark, which also cannot osmoregulate. The bull shark shares many similarities with river sharks of the genus Glyphis and other species of the genus Carcharhinus, although its phylogeny is not yet fully clarified.

The Largest Bull Sharks Sighted in the World

In June 2012, near the coast of the Florida Keys, large bull sharks were documented by the RJ Dunlap Marine Conservation Program. In February 2019, in the Arabian Sea off the coast of Fujairah in the United Arab Emirates, a pregnant female weighing 347.8 kg and measuring 3 meters long was captured, followed by another specimen of approximately the same size in January 2020. Unconfirmed reports suggest that the largest specimens can weigh up to 900 kg.