Everything You Need to Know About the Bull Shark

The Bull Shark is a highly aggressive marine creature that usually roams shallow tropical waters. It can live in both brackish and fresh waters, since it can adapt its organism to venture upstream by ascending against the current. It is counted as one of the three shark species that can attack humans. Find out much more below.

The Bull Shark

Also known as sardinian, lamia or Zambezi shark, the Carcharhinus leucas is a variety of carcarriniforme elasmobranch that is part of the Carcharhinidae family. The bull shark is one of the few specimens of this species that ascends upstream to occupy fresh waters. Its body length is up to 3,4 meters.

Physical characteristics

The bull shark only has a 50% concentration of salt in its bloodstream, which is why it can change salt water very easily. As an interesting tidbit, your urine output increases 20-fold when swimming in fresh water.
They are considered mature between 15 and 20 years old, and their known life expectancy is 25 years. Adults are approximately 3,5 meters long and weigh close to 300 kilograms. This shark can be seen in various parts of the world, including areas of high biodiversity such as the Caribbean Sea and Florida.
Usually, the females have greater size and longevity, and in most cases they live up to 17 years. Males, in contrast, live an average of 13 years.
The first dorsal fin is huge and triangular, it arises a little after the pectoral insertion and they do not have an intercostal crest.
The snout is much smaller than the width of the mouth and rounded in shape.
Its eyes are extremely small, which suggests that vision is not very important, since it usually maneuvers through murky waters.
Like all varieties of sharks, the bull shark is extremely agile in the water, reaching speeds of up to 20 kilometers per hour.
Its body presents colorations that go from dark gray to pale gray, which descends to an almost white tone on its lower side. Young specimens exhibit dark spots on their fins, but these spots fade as they develop.
Their jaws can reach a length of up to 245 centimeters, their teeth are wide, triangular and jagged.

Common name

With the scientific name Carcharhinus leucas, the bull shark is known in English-speaking nations as "Bull Shark", and should not be confused for this reason with Carcharias taurus, which in Spanish is known as tiger shark (also silky tiger or damsel fish) and which is not even part of the same taxonomic order.

Using in this case a textual translation of their common denomination between these languages is a common mistake that tends to confuse very different species. With this clarification we get rid of the ambiguity between these species that are not even phylogenetically close (the last related ancestor of these two species lived about 140 million years ago).

Feeding Habits

The bull shark's diet consists primarily of bony fish and small sharks. In the western Atlantic, they commonly eat mullet, tarpon, catfish, sea bass, horse mackerel, and snapper. They also feed on rays and young sharks, including small specimens of their own species, when they venture into shallow areas used as nursery grounds. They are considered to have a very varied diet, which may include other marine animals such as dolphins and turtles.

They often eat sea turtles, dolphins, crabs and some sea birds. They are considered somewhat lazy, but they have the ability to make fast bursts of about 19 kilometers per hour to catch tiny and agile prey.

Distribution

The bull shark can be found in the shallow, warm waters of all the world's oceans, especially along tropical coasts. They also travel vast distances in fresh water, crossing rivers and reaching lakes. It can be found inland in the Amazon in South America reaching as far north as Peru.

It is also found in the Zambezi (which is why it is also called the Zambezi shark) and the Limpopo in Africa, in Lake Cocibolca in Nicaragua, Tortuguero canals in Costa Rica and the Ganges in India. In the Pacific Ocean it is found from Baja California to Peru and from Taiwan to Australia and New Zealand. In the Atlantic Ocean from the Antilles, Colombia and Venezuela to Brazil.

Reproduction

Why is bull shark reproduction a key issue? Bull sharks have been characterized as vulnerable given their low reproductive potential. What does this mean? Sharks have numerous reproductive limitations that have placed them in danger:

They generate very few offspring, this is also called low fertility.
They reach their sexual maturity late.
Their gestation periods are very long.

Reproduction in sharks is a key issue in determining the size and health of their population. It is very important to understand the reproductive cycle of bull sharks, since this defines the minimum time for their population to double. Here are some significant traits about bull shark reproduction to keep in mind:

The bull shark's reproductive system is placental viviparous, fertilization is internal and the embryos evolve in a pair of uteruses exchanging nutrients and waste through a placenta.
Bull sharks reach sexual maturity late. Males reach maturity by reaching a length of 157 to 226 centimeters while females reach 180 to 230 centimeters in length.
Bull sharks can give birth to between 1 and 13 pups, of which the number that manages to exceed their first years is very scarce, since one of their mothers' traits is not to care for them at birth. For this reason, these sharks tend to have their young in coastal waters, in order to protect them from predators.
The gestation periods of sharks are very long. For the bull shark it is about ten to eleven months, since the shark gives birth to its pups, they have very slow development rates and face many dangers when growing up. A young bull shark has a length of 60 centimeters at birth.

All these circumstances of the reproductive cycle of bull sharks are particular. The analysis of the poor reproductive potential is essential for the scientists who work in Playa del Carmen in order to determine the effect that illegal fishing is having on the population of bull sharks in this locality.

Natural History

Their diet consists of all kinds of animals, including other sharks. It can be dangerous to humans, as it hunts where people usually swim. The ability of this shark to enter fresh water is thanks to a special gland in its kidney that allows it to retain salt water in its body and expel fresh water, which would be lethal to other varieties of sharks.

So incredible is the evolution of this creature that its kidneys, liver and rectal gland can gradually adapt to the salinity of the aquatic environment in which they find themselves. By changing their environment, their kidneys displace less salt and more urea from the bloodstream through urine, allowing them to move through places where no other species of shark could.

Fresh water causes the cells of other sharks to burst and subsequently kill them. Bull sharks can remain in rivers, lagoons and estuaries for almost a year or more, which allows them to get closer to humans. A 2012 investigation found that the bull shark is the shark with the most powerful bite, with about 612 kilograms of force for an adult individual.

Even today, the scientific community ignores the reasons why this species moves to fresh waters. Several theories are considered, such as that these animals travel to fresh water to get rid of parasites that live only in salt water or that they do so as a way of ingesting other nutrients that do not exist in the sea; however, this has not yet been fully confirmed.

It is also known that this shark in mating season is one of the animals with the highest levels of testosterone, even higher than those of a male African elephant and even more so when in heat, which makes it a highly territorial creature.

The bull shark's upper body is colored greenish and light brown, appropriate for the habitats it inhabits. Female bull sharks conceive in estuaries, where the young grow and develop to reach a larger size and then go out to sea.

Relationship with Humans

Since it is a species that regularly moves in shallow waters, it is very possible to encounter humans, who usually frequent these spaces for swimming or other activities such as diving.

Attacks on Humans

The Zambezi shark doesn't have as exaggerated a reputation for man-eating as its relative, the great white shark (Carcharodon carcharias), but its ability to enter rivers and shallow waters, where it hunts, suggests that this shark is responsible for most attacks on humans. It frequently comes too close to divers. Statistics show that, although attacks are relatively rare, worrying cases have been documented over the years, highlighting the importance of water safety.

Attacks are very rare, but in some seas, nets have been set up to mark the limits of where people can swim. The International Shark Attack File (ISAF) has recorded a total of 1580 verified bull shark attacks on humans from 100 to the present.

Bull Shark Diving

Diving with bull sharks is a growing attraction in Playa del Carmen, Mexico, with enthusiasts coming from all over the world to observe them in their natural environment. It's important to know that, to fully appreciate them and safely, it's recommended to know something about their characteristics. Below, we'll answer the most common questions about this misunderstood marine giant and also share some interesting facts that set them apart from any other shark species.

Did you know that there is more than one Bull Shark?

First of all, it is necessary to clarify that the animal that many of us know as the bull shark (Carcharhinus Leucas) is actually called sarda shark, Zambezi shark or lamia shark, and should not be confused with the Carcharias Taurus, which is also known as calls like bull shark, sand tiger shark or damsel shark.

Such confusion is due to the fact that the Carcharhinus Leucas is called in English "bull shark", which translates literally as "bull shark". The use of this name to refer to the Sardinian shark is already so frequent that it has been regularized, but it is good to keep in mind that there are two sharks with this name, which are not related.

The Bull Shark, Capable of Living in Fresh and Salt Waters

When a group of researchers studied the existence of a shark in the sweet and calm waters of the Great Lake Nicaragua, also known as Cocibolca, they thought that it was a strange species that only lived in that place. Then the year of 1877 passed and the discovery was so amazing that the government of the Central American country ordered to issue a special edition of stamps with the figure of the shark as an emblem of national identity.

Such conjecture remained alive for a century, until in 1976 other specialists determined that a species frequent in tropical and subtropical waters, called Carcharhinus leucas or bull shark, certainly lived there. The scholars reported how the fish settled in the lake after having crossed the San Juan River, which serves as a connection to the Caribbean Sea. An event that continues to occur today although its population has been reduced due to fishing, according to experts from this nation.

“There is no more information about how many remain in the lake, but the migration from the sea ascending the river to reach the lake has attracted scientists for years,” said Mundo Elda Brizuela, a documentary filmmaker from Costa Rica who is carrying out a project to the preservation of this fish in the region. Bull sharks, whose bite is considered to be the most powerful of any kind of shark, usually live in marine waters although they also have an unusual ability to adapt their organism to fresh waters.

Only a few other species of the Glyphis family, commonly known as river sharks, possess this ability. These sharks can be found north of Australia. However, the bull shark is the only species with this marvelous ability that roams the waters of the Americas, although specimens also exist in the Zambezi River, the fourth longest river in Africa, and in the Pacific and Indian Oceans.

The Carcharhinus Leucas

It is a frequent animal in tropical and subtropical waters that inhabits marine waters, as well as in mouths and fresh waters, such as rivers and lakes.

340 centimeters is the longest known length for one of these specimens.
From 90 to 230 kilograms is the weight of this fish, according to its age.
The bull shark is one of the most important predators in the waters of the state of Florida (USA) and the coast of the Caribbean Sea.

On this continent, it has been observed both in Lake Nicaragua and in Lake Maracaibo, Venezuela, as well as in the Amazon and Mississippi rivers (USA) and on the coast of Florida. The fish, additionally, draws the attention of researchers for its impressive presence.

“When a small shark ascends the Mekong River (in Southeast Asia), few people notice it. But when huge, toothy bull sharks patrol the lofty slopes of some of the world's largest rivers, that's a thing," says Leslie Kaufman, a biology scholar at Boston University in the United States.

remarkable tolerance

Most sharks could not survive in fresh water because they do not have the ability to adapt their body to a less brackish environment. But certain organs of this creature such as the kidneys, liver and rectal gland gradually adjust to the salinity of the water in which they are found. When moving towards fresh water, their kidneys discard less salt and more urea from the bloodstream through urine, which is estimated as the opposite process to the osmoregulation that these animals frequently suffer.

"Being notoriously tolerant of fresh water enables them to ascend the river for thousands of kilometers, sometimes entering lakes quite far from the sea," says José Castro, a fisheries biologist at the United States National Oceanic and Atmospheric Administration (NOAA). .

In general, sharks cannot modify their osmoregulation process. If they enter a freshwater environment, they will take in too much water in proportion to their density of body solvents and this will cause them to lose too much salt, making it impossible for them to survive. Castro points out that newborn and young sharks opt for estuaries and rivers throughout their lives, and as they grow they enter more saline waters of coastal bays.

A Question That Remains

The reasons why this species settles in fresh waters are still unknown to the scientific community. However, Castro indicates, there are several hypotheses: that these animals move to these waters to shed parasites that only survive in salty waters or if they do so as a way of ingesting other nutrients that they do not obtain in the sea. "Until now we only understand that they are fully capable of moving in and out of fresh and marine waters, but their reasons are still a mystery," he says.

Dangerous ?

The bull shark is one of the most important predators in the coastal waters of the state of Florida and the Caribbean. As it usually lives in shallow waters (below 30 meters) that are frequently visited by human beings, it is usual that the shark attacks that could occur there are blamed on this species.

The fish shows a combination of sharp and large teeth, powerful jaws and a varied diet, which includes other sea animals such as dolphins and turtles. Due to its features, specialists classify it as one of the three species most likely to attack humans, the others being the tiger shark and the white shark. However, experts indicate that man is one of the greatest threats to this species.

Despite the fact that its population is not in danger of disappearing according to the International Union for the Conservation of Nature (IUCN), exhibiting itself in waters that can be accessed by human beings places it in a condition of vulnerability to fishing and alterations. environmental factors linked to the modification of their habitat.

Traditionally, bull sharks are commercially fished for their skin, meat and liver oil, despite the fact that today, according to the IUCN, their fins are the product whose significance drives demand for this and numerous other species. .

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