The Bull shark (Carcharhinus leucas) is a requiem shark commonly found worldwide in warm, shallow waters along coasts and in rivers. The Bull shark is known for its aggressive nature, and presence in warm, shallow brackish and freshwater systems including estuaries and rivers. The Bull shark is not a true exclusive freshwater shark but tolerate freshwater quite well for extended periods of time because the Bull shark is capable of osmoregulation. The Bull shark is considered one of the more dangerous sharks to humans when invading its territory. Humans can also become a case of mistaken identity as the Bull shark check out its prey with the bump and bite technique. The Bull shark is one species of shark we frequently dive with here in Jupiter Fl, click here to watch our videos and watch Bull sharks in action!
Photo: © 2018, Harry Stone, Planet Shark Divers, all rights reserved.
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List NEAR THREATENED
Average Size and Length: Adult female Bull sharks average 7.9 feet long, and males average 7.4 feet. A maximum size of 11 feet is commonly reported, a single record exists of a female 13.1 feet long.
Average Weight: Adult female Bull sharks weigh an average of 290 pounds, and 209 pounds in males. The maximum recorded weight of a Bull shark is 694 pounds, and still possibilities of larger sharks. One count records a fisherman caught a 771.9-pound Bull shark on shore with a rod and reel.
Current Rare Mythical Sightings: One very interesting known home of the Bull shark is at a golf course lake at Carbook, Logan City, Queensland, Australia. It is the home to actually several Bull sharks. They were trapped following a flood of the Logan and Albert Rivers in 1996. The golf course has capitalized on the novelty and now hosts a monthly tournament called the “Shark Lake Challenge”. Alligators aren’t the only gold course predators anymore!
Another interesting tidbit is that Bull sharks were blamed for a series of attacks in 1916, which served inspiration for Peter Benchley’s book Jaws, which Steven Spielberg turned into a blockbuster movie in 1975.
Teeth and Jaw: Bull sharks have a bite force up to 5,914 newtons or 1,330 lbf. This is the highest among all investigated cartilaginous fishes yet. The Bull shark has around 50 rows of teeth in its jaws, and each row has about 7 teeth, for a grand total of around 350 teeth in its mouth at any given time. Upper jaw teeth of the bull shark are broad, triangular, and heavily serrated. Lower jaw teeth have a broad base, and are narrow and triangular with fine serrations. Anterior teeth are erect and nearly symmetrical, while posterior teeth become more oblique in shape.
Head: The Bull shark has a blunt, rounded shout, with small eyes. The Bull shark does not have the best eyesight.
Tail: The Bull shark’s caudal fin is longer and lower than that of the larger sharks.
Demographic, Distribution, Habitat, Environment and Range: The Bull shark is commonly found worldwide in coastal areas of warm oceans and currents, in rivers and lakes, and occasionally salt and freshwater streams if they are deep enough. It is found to a depth of 490 feet, but does not usually swim deeper than 98 feet). In the Atlantic, it is found from Massachusetts to southern Brazil, and from Morocco to Angola. We frequently share the ocean with our Bull sharks of Jupiter, Florida. Check out our YouTube channel to watch them in action! (add the link).
The Bull shark commonly enters estuaries, bays, harbors, lagoons, and river mouths. It is one of very few species that readily move into freshwater, and apparently can spend long periods of time in such environments. Research has proven that they can tolerate hypersaline water as high as 53 parts per thousand (Simpfendorfer and Burgess 2009).
We now know that 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. One was reportedly seen swimming the flooded streets of Brisbane, Queensland, Australia, during the 2010-11 Queensland floods. Several were sighted in one of the main streets of Goodna, Queensland. Locally, they enter the Indian River lagoon and the South Fork River often. Jeremy Wade visited Stuart a few years back, and caught one (as well as a Goliath Grouper) in the river on camera.
In the Pacific Ocean, it can be found from Baja California to Ecuador. The Bull shark has traveled a great distance, 2,500 miles, up the Amazon River to Iquitos in Peru, and north Bolivia. Others suggest that the Bull shark even lives in freshwater Lake Nicaragua, in the Ganges and Brahmaputra Rivers of West Bengal, and Assam in Eastern India and adjoining Bangladesh. It can live in water with a high salt content as in St. Lucia Estuary in South Africa. Bull sharks have been recorded in the Tigris River since at least 1924 as far upriver as Baghdad.
The Bull shark is resilient and resourceful, and after Hurricane Katrina, it was recorded that many bull sharks were sighted in Lake Pontchartrain. Bull sharks have occasionally gone as far upstream in the Mississippi River as Alton, Illinois, and up the Ohio River as far as Manchester, Ohio. Bull sharks have also been found in the Potomac River in Maryland.
Bull sharks have an unusual migratory pattern in comparison to other sharks. They are found in rivers all over the world. They give birth in the fresh water of rivers. The young bull sharks are free from predators while they grow up in the river before they go out to the sea to find mates.
Diet: The Bull shark’s diet consists mainly of bony schooling fish like tarpon mullet, catfishes, menhaden, snook, jacks, mackerel, snappers, and gar, and small sharks, including sting rays and even other Bull sharks. They are known to also eat crustaceans, turtles, birds, dolphins, terrestrial mammals (like small dogs), and echinoderms. 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 they are unable to flee. Quite often from South Carolina down to South Florida, surfers and ocean bathers have been exploratorily bitten by Bull sharks when these humans invade their waters in murky conditions or at dawn and dusk. As noted above, they have much smaller eyes than other sharks of its family, and are though that its eyesight isn’t the best, one reason why mistaken identity happens often with the aggressive Bull shark.
The Bull shark is known to be a solitary hunter, although brief moments exist in which the Bull shark teams up with another bull shark to make hunting and to tricking prey easier.
As part of their survival, 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.
Young bull sharks can fall prey to Tiger sharks, Sandbar sharks, and other Bull sharks. A crocodile in South Africa was also reported to have consumed a Bull shark.
Aesthetic Identification: Bull sharks are pale to dark gray above, fading to a counter-shaded pale cream color on their underside. In younger sharks, the fins have dark tips which fade to a more diffuse dusky color as they grow. They have stout bodies and are bigger for requiem sharks.
Bull sharks lack an interdorsal ridge. The first dorsal fin is large and broadly triangular with a pointed apex. The second dorsal fin is significantly smaller and originates over or slightly behind the pectoral insertion. The pectoral fins are also large, broad and angular.
Biology and Reproduction: Parasites of the Bull shark include the copepods Pandarus sinuatus and Perissopus dentatus. They can be found attached to the body surface, often in the axil region of the pectoral and pelvic fins.
Bull sharks have the capabilities of osmoregulation, and they are diadromous and considered euryhaline fish. The ability to be able to survive in both fresh and salt water also gives another benefit that has been driven by evolution. Because the majority of sharks are only able to survive in salt water, the Bull shark has evolved to have their offspring in the fresh water where other sharks cannot enter.
Bull sharks are viviparous. Bull sharks’ mate during late summer and early autumn, often in freshwater or in the brackish water of river mouths. After gestating for 12 months, a Bull shark may give birth to 1 to 13 live pups. Young Bull sharks are about 27.6 inches at birth. The Bull shark does not rear its young; the young Bull sharks are born into flat, protected areas such as coastal lagoons, river mouths, and other low-salinity estuaries are common nursery habitats, like the many here in Florida and in South Carolina.
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 worthwhile eggs for fertilization seems to be 175 cm to 235 cm. More than likely, research suggests that the male likely bites the female on the tail until she can turn upside down and the male can copulate. This can be aggressive and violent. Seeing scratches and other marks on a mature female which may be from the mating ritual is quite common. Age of maturity is between 15-20 years and the known lifespan is over 25 years.
Behavioral Traits, Sensing and Intelligence: As discussed above, Bull sharks are diadromous and considered euryhaline, capable of osmoregulation and have a high tolerance of fresh water. 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 reproduction. Young Bull sharks leave the brackish water in which they are born and move out into the sea to breed.
Bull sharks are known to be territorial, aggressive and unpredictable. They do not have tolerance when being provoked.
Bull sharks have smaller eyes and may not have the best eyesight. Research suggests that is because they do not need the best eyesight in brackish/murky water during the poorly sunlit parts of the day, and therefore since they do not see their prey first, there are many cases of mistaken identity. Despite not having the best eyesight, Bull sharks are known to take visual cues. Studies show that 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. This is very important because it gives an insight into how Bull sharks are able to pick up certain visual keys underwater that might give them an advantage when seeking out certain prey. When we dive with Bull sharks, and other sharks as well, we do not wear contrasting colors; we wear all black gear.
In 2008, researchers tagged and recorded the movements of young Bull sharks here in Florida in the Caloosahatchee River estuary. These were efforts 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. This movement was 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. (Ortega, Lori A.; Heupel, Michelle R.; van Beynen, Philip & Motta, Philip J. (2009). “Movement patterns and water quality preferences of juvenile bull sharks (Carcharhinus lecuas) in a Florida estuary“. Environmental Biology of Fishes. 84 (4): 361–373).
Speed: Bull sharks appear sluggish as they cruise slowly along the bottom, but are capable of quick bursts that allow them to capture smaller, agile prey. They have been recorded to move at over 11 mph over short distances.
Bull Shark Future and Conservation: The Bull shark is not a targeted species in most commercial fisheries, it is regularly captured on bottom longline gear. It is more often targeted in small artisanal fisheries because of its abundance in nearshore environments. The meat is either used for fish meal or sold in local markets for human consumption. The fins are used in Asia for shark fin soup while the skin is frequently used for leather.
However, The Bull shark is considered a game fish in the southeastern U.S. and South Africa, and is fished by rod and reel from shore, piers, and bridges. Here in Florida, we are fighting to put an end to land-based shark fishing. It is a danger to bathers on shore, and a danger to the animals themselves. Often when we dive observing Bull sharks, most of them have mouths full of fish hooks that we try and remove.
Often here in Florida and other parts of the Caribbean Bull sharks are frequently observed on recreational feeding dives.
The Bull shark isn’t protected in any of its range as of yet, there is a lot of room for conservation and awareness.
Bull Shark Recorded Attacks on Humans: According to ISAF, Bull sharks are historically responsible for at least 100 unprovoked attacks on humans around the world, 27 of which have been fatal. However, it is likely that this species may responsible for many more. In addition, it is also known that they are responsible on mistaken identity. In short, Bull sharks are potentially dangerous and a threat to humans especially when provoked. It is important to always exercise care and respect for the Bull shark when in its space.