Interesting Bull Shark Facts (Carcharhinus leucas)

Sharks That Live in Fresh and Salt Water

The bull shark is also known as the Zambezi shark or Nicaragua shark.
The bull shark is also known as the Zambezi shark or Nicaragua shark. Luis Javier Sandoval / Getty Images

The bull shark (Carcharhinus leucas) is an aggressive shark found throughout the world in warm, shallow waters along coasts, in estuaries, in lakes, and in rivers. Although bull sharks have been found inland as far as the Mississippi River in Illinois, they aren't a true freshwater species. The bull shark is listed as "near threatened" by the International Union for Conservation of Nature (IUCN).

Essential Bull Shark Facts

  • Bull sharks get their common name both from their appearance and their behavior. The shark is large and stocky, with a broad, flat snout and an unpredictable, aggressive nature. Females are larger than males. A typical female bull shark is 2.4 m (7.9 ft) long and weighs 130 kg (290 lb), while a male averages 2.25 m (7.4 ft) and 95 kg (209 lb). The largest recorded bull shark was a 4.0 m (13.1 ft) female. The bite force of a bull shark is 5914 Newtons, which is the highest for any fish, weight for weight.
  • There are 43 elasmobranch species found in freshwater. Sand sharks, sawfish, skates, and stingrays are other species that can enter rivers. Bull sharks are capable of osmoregulation, which means they can control their internal osmotic pressure when external salinity changes. This also makes then euryhaline (able to adapt to different salinities) and diadromous (readily able to swim between fresh and salt water). Bulls sharks give birth to four to ten live young in fresh water. Over time, the sharks gain a tolerance for salinity. Newborn or young sharks are usually found in fresh water, while older sharks tend to live in salt water. Young bull sharks flow with the tides to conserve energy needed for movement and osmoregulation. However, bull sharks can live their entire lives in fresh water. Adult life in fresh water is not ideal, as most of the shark's food lives in the sea.
  • Bull sharks mainly eat bony fish and smaller sharks, including bull sharks. As opportunistic predators, they also eat terrestrial mammals, birds, turtles, crustaceans, echinoderms, and dolphins. They use the bump-and-bite strategy to attack prey, typically hunting in murky water. Usually bull sharks are solitary hunters, although they may hunt in pairs to trick prey. Although bull sharks hunt in murky water, they can see color and use it to seek prey. They can be attracted to bright yellow gear, for example. The sharks hunt both during the day and at night.
  • Adult sharks mate in late summer or early autumn. It takes 10 years for a shark to reach maturity. In the mating ritual, the male bites the female's tail until she turns upside down, allowing him to copulate. Mature females often have bite marks and scratches.
  • Bull sharks are apex predators, so their main threat is mankind. However, they may be attacked by great white sharks, tiger sharks, and crocodiles. The average life span of a bull shark is 16 years.

    How Dangerous Is the Bull Shark?

    The bull shark is believed to be responsible for most shark attacks in shallow water, even though the International Shark Attack File (ISAF) cites the great white shark (Carcharodon carcharias) as responsible for the largest number of bites to humans. The ISAF notes great white bites are often correctly identified, but it's difficult to tell bull sharks apart from other members of the family Carcharhinidae (the requiem sharks, which include the blacktip, whitetip, and grey reef shark). In any case, the great white, bull shark, and tiger shark are the "big three" where shark bites are concerned. All three are found in areas frequented by humans, have teeth designed to shear, and are large and aggressive enough to pose a threat.

    How to Recognize a Bull Shark

    If you see a shark in fresh water, chances are good it's a bull shark. While the genus Glyphis includes three species of river sharks, they are rare and have only been documented in parts of Southeast Asia, Australia, and New Guinea.

    Bull sharks are gray on top and white underneath. They have a small, bullish snout. This helps camouflage them so they are harder to see viewed from below and blend in with the riverbed or sea floor when viewed from above.

    The first dorsal fin is larger than the second one and is angled rearward. The caudal fin is lower and longer than that of other sharks.

    Tips for Telling Sharks Apart

    If you're swimming in the surf, it's not a smart idea to get close enough to identify a shark, but if you see one from a boat or land, you may want to know what type it is:

    • Sandbar sharks also have rounded snouts, but their dorsal fins are larger and more triangular than those of bull sharks.
    • Blacktip sharks are shaped much like bull sharks, but they have pointed snouts and white anal fins. Note juvenile bull sharks may have black-tipped fins, so coloration is not a good way to distinguish these species.
    • Lemon sharks have blunt snouts, but they are yellow-green to olive-gray in color and both their dorsal fins are about the same size. Lemon shark dorsal fins angle back like those of a bull shark.
    • Spinner sharks have pointed shouts, black tipping on their anal fins, and a band of Z-shaped lines on their sides.
    • Tiger sharks have a dark stripe on their sides.
    • Great white sharks are very large (10-15 ft long), have black eyes, and pointed snouts. Their coloration is similar to the bull shark (gray on top, white underneath).