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Biological Profiles




BULL SHARK
Order - Carcharhiniformes
Family - Carcharhinidae
Genus - Carcharhinus
Species - leucas
Carcharhinus leucas
Taxonomy

The bull shark was first described by Valenciennes in Muller & Henle (1839) as Carcharias (Prionodon) leucas, and later changed to the currently valid name Carcharhinus leucas. The genus name Carcharhinus is derived from the Greek "karcharos" = sharpen and "rhinos" = nose. It has also appeared in the literature as Carcharias (Prionodon) zambezensis, Carcharhinus zambezensis, Prionodon platyodon, Squalus platyodon, Squalus obtusus, Eulamia nicaraguensis, Carcharias azureus, Carcharias spenceri, Galeolamna (Bogimba) bogimba, Galeolamna greyi mckaili, and Carcharhinus vanrooyeni.


Common Names

The bull shark gets its name from its stout appearance and pugnacious reputation. The French know the shark as requin bouledogue, and the Spanish as tiburon sarda. It is known by many different common names throughout its range including Zambezi shark, Van Rooyen's shark (Africa); Ganges shark (India); Nicaragua shark (Central America); freshwater whaler, estuary whaler, and Swan River whaler (Australia); shovelnose shark, square-nose shark, river shark, slipway grey shark, ground shark, and cub shark.


Geographical Distribution

Bull sharks occur in tropical to subtropical coastal waters worldwide as well as in numerous river systems and some freshwater lakes. They have been reported 3700 km (2220 mi) up the Amazon River in Peru, and over 3000 km (1800 mi) up the Mississippi River in Illinois. A population in Lake Nicaragua (Central America) was once thought to be landlocked, but they gain access to the ocean through rivers and estuaries. In the western Atlantic bull sharks migrate north along the coast of the U.S. during summer, swimming as far north as Massachusetts, and then return to tropical climates when the coastal waters cool.


Distribution Map of the Bull Shark
World distribution map for the bull shark.

Habitat
bull shark
A young bull shark cruises the Caribbean shallows.
©Jeremy Stafford-Deitsch


The bull shark prefers to live in shallow coastal waters less than 100 feet deep (30 m), but ranges from 3-450 feet deep (1-150 m). It commonly enters estuaries, bays, harbors, lagoons, and river mouths. It is the only shark species that readily occurs in freshwater, and apparently can spend long periods of time in such environs. It is not likely that the bull shark's entire life cycle occurs within a freshwater system, however. There is evidence that they can breed in freshwater, but not as regularly as they do in estuarine and marine habitats. Juvenile bull sharks enter low salinity estuaries and lagoons as readily as adults do, and use these shallow areas as nursery grounds. They can also tolerate hypersaline water as high as 53 parts per thousand.




Biology

bull shark
Carcharhinus leucas
ex Garrick (1982) NOAA Tech. Rep. NMFS Circ. 445
bull shark
The bluntly rounded snout of an adult bull shark.
Source unknown


Distinctive Features
Bull sharks are very robust-bodied and have a blunt, rounded snout. They lack an interdorsal ridge. The first dorsal fin is large and broadly triangular with a pointed apex. The second dorsal fin is significantly smaller. The pectoral fins are also large and angular. Bull sharks have relatively small eyes as compared to other carcharhinid sharks, which suggests that vision may not be as important a hunting tool for this species which often occurs in turbid waters.

bull shark
Up-close view of the bull shark's eye
©Tobey Curtis

bull shark
Bull shark
© George Burgess
Coloration
Bull sharks are pale to dark gray above, fading to white on their underside. In younger individuals the fins have black tips which fade to a dusky color as they grow.


Dentition
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.
bull shark
Ex Garrick (1982) NOAA Tech. Rep. NMFS Circ. 445
bull shark
The jaws of an 8-foot (245 cm) bull shark captured in the Gulf of Mexico
©Tobey Curtis
Size, Age & Growth
The maximum reported length of the bull shark is 11.5 feet (350 cm), weighing over 500 pounds (230 kg). Size at birth is around 29 inches (75 cm). Females grow larger than males, averaging 7.8 feet (240 cm) as adults, weighing around 285 pounds (130 kg). This is the result of a longer lifespan of about 16 years, compared to 12 years for males. Males average 7.3 feet (225 cm) and weigh 209 pounds (95 kg). Growth rates calculated from captive bull sharks were estimated to be about 11 inches (28 cm) per year in the first years of life, slowing to half that rate after about 4 years of age.


Food Habits
Bony fishes and small sharks make up the vast majority of the bull shark's diet. In the western Atlantic they commonly feed on mullet, tarpon, catfishes, menhaden, gar, snook, jacks, mackerel, snappers, and other schooling fish. They also regularly consume stingrays and juvenile sharks including small individuals of their own species in their inshore nursery habitats. Other food items occasionally reported in bull sharks include sea turtles, dolphins, crabs, shrimp, sea birds, squid, and dogs. Bull sharks often appear sluggish as they slowly cruise along the bottom, but are quite quick and effective at capturing smaller, agile prey, and are capable of burst speeds of over 11 mph (19 km/h).
bull shark
A bull shark feeding in the shallows
© Brooke Flammang


Reproduction
Age of maturation of bull sharks varies according to geographic location. One study in the southern Gulf of Mexico found that the age of maturity was 10 years (6.85 feet (204 cm) total length, TL) for females and 9-10 years (6.23-6.56 feet (190-200 cm) TL) for males. Another study in the northern Gulf of Mexico determined the age of maturity to be 6.89 feet (210cm) TL /14-15 years for males and ~7.38 feet (~225 cm) TL/18years for females.

One to 13 pups are nourished internally by the mother for 10-11 months, and they then give birth to live, free-swimming young. In the Gulf of Mexico mating occurs during summer months, and the pups are born the following April-June. Mating and birthing occurs year-round in the warmest parts of the bull shark's range. Females often bear mating scars on their dorsum. Coastal lagoons, river mouths, and other low-salinity estuaries are common nursery habitats.

bull shark
A large, possibly pregnant female bull shark
© Jeremy Stafford-Deitsch
bull shark
A tagged bull shark pup being released in its nursery ground
© FLMNH

Predators
Adult bull sharks are unlikely to have any natural predators. Young bull sharks, however, can fall prey to large tiger sharks (Galeocerdo cuvier), sandbar sharks (Carcharhinus plumbeus), and other bull sharks. A crocodile in South Africa was also reported to have consumed a bull shark.


Parasites
Parasites of the bull shark include Pandarus sinuatus and Perissopus dentatus. These copepods parasitize the body surface of this shark.


Importance to Humans


bull shark
A 5-foot bull shark caught on a bottom longline off the southeast coast of the U.S.
© FLMNH
Though the bull shark is not a targeted species in most commercial fisheries, it is regularly captured on bottom longline gear. In the southeastern U.S. commercial shark fishery the bull shark comprises less than 1% of the catch. 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 sold to Asia for shark fin soup. The hide is good quality for leather.

Recreationally, the bull shark is considered a popular game fish in the southeastern U.S. and South Africa, and is often fished for by rod and reel from shore, piers, and bridges. According to the International Game Fish Association (IGFA), the largest bull shark caught on rod and reel weighed 771 lb. 9 oz. (347 kg) and was caught near Cairns, Australia. On some occasions bull sharks are observed at recreational shark feeding dives in the Caribbean. They are not usually kept in captivity, but have survived in some aquaria for over 15 years.



Danger to Humans

According to the International Shark Attack File (ISAF) bull sharks are historically responsible for at least 69 unprovoked attacks on humans around the world, 17 of which resulted in fatality. In reality this species is likely responsible for many more, and has been considered by many experts to be the most dangerous shark in the world. It's large size, occurrence in freshwater bodies, and greater abundance in close proximity to numerous human populations in the tropics makes it more of a potential threat than either the white shark or tiger shark. Since the bull shark occurs in numerous Third World regions including Central America, Mexico, India, east and west Africa, the Middle East, Southeast Asia, and South Pacific Islands, attacks are often not reported. The bull shark is also not as easily identifiable as the white or tiger shark, so is likely responsible for a large percentage of attacks with unidentified culprits.

bull shark
Photographers interacting with large bull sharks in the Bahamas
© Jeremy Stafford-Deitsch

The bull shark has been considered to be a potential culprit in the infamous series of five attacks in New Jersey in 1916 which resulted in four tragic fatalities over a 12 day period. Three of these attacks occurred in Matawan Creek, a shallow tidal river, only 40 feet (12 m) across, 1.5 miles (2.4 km) from bay waters, and over 15 miles (24 km) from the open ocean; not a location where any other large shark species would likely occur. A 7.5 foot (2.25 m) white shark was captured two days after the last attack, however, just 4 miles (6.4 km) from the mouth of Matawan Creek, and allegedly contained human remains in its stomach. A 9 foot (2.7 m) bull shark was also captured a day later only 10 miles (16 km) from Matawan. This has been a topic of controversy for many years, and there is evidence that points at both the bull shark and the white shark as culprits.

These are some things that can be done to avoid the chance of an unwanted encounter with a bull shark:
  1. Avoid swimming near river mouths or other estuaries with turbid waters where bull sharks are known to occur.
  2. Do not swim near schools of fish in inshore areas. These schools are often pursued by large predators.
  3. Be cautious if spearfishing. Bull sharks are known to approach spearfishermen carrying their catch.
  4. Do not duplicate the practices of some television "adventurers" who flagrantly disregard common sense for showboating around sharks while underwater.



Conservation

bull shark
©Brooke Flammang
Though the bull shark is not a targeted species, it is captured in fisheries around the world. Due to this shark's life history and environmental requirements, which bring it in close proximity to human populations, it could potentially be heavily impacted by human activities in these inshore regions. The inshore nursery grounds of this species could be particularly threatened. The Natal Sharks Board report that the average size of bull sharks caught in their beach nets have significantly declined in recent years, which does not bode well for South African populations of the species. The bull shark is not legally protected in any part of its range. Further research is necessary on this unique species of shark so more can be understood of its biological, ecological, and fisheries significance.

The bull shark is currently listed by the World Conservation Union (IUCN) as "Near Threatened", but does not meet criteria to be considered endangered or vulnerable at this time. The IUCN is a global union of states, governmental agencies, and non-governmental organizations in a partnership that assesses the conservation status of species.

Prepared by:
Tobey Curtis