8 Incredible Facts About Bull Sharks

These formidable fish are not nearly as simple as they might seem.

bull shark off the coast of Mozambique
A bull shark swims at the Pinnacles dive site off the coast of Mozambique.

Fiona Ayerst / Getty Images

Bull sharks are large, stout predators found in tropical and subtropical waters around the world, typically close to coastlines. Their name is reportedly inspired by their stocky appearance and blunt, rounded snout, as well as their relatively aggressive behavior.

They may lack the widespread name recognition of great whites, but bull sharks are also considered a potential threat to humans who venture into the ocean, with more than 100 historical attacks linked to their species. At the same time, however, a beach-goer is more likely to be killed by rip currents or lightning than by a bull shark (or by any other shark), and these ancient fish face far more danger from us than we do from them.

From their biological quirks to their relationship with our species, here are a few interesting facts you may not know about bull sharks.

1. Bull Sharks Out-Bite Great Whites

A bull shark bites into a tuna off the coast of Fiji.
A bull shark bites into a tuna off the coast of Fiji. Terry Moore / Stocktrek Images / Getty Images

Bull sharks mainly eat bony fish and smaller sharks, but they're opportunistic feeders, also taking prey like birds, crustaceans, dolphins, terrestrial mammals, and turtles.

The bite force of bull sharks is among the highest of any fish, according to a 2012 study published in the journal Zoology. The species can bite with a force of 5,914 Newtons, the study found, which is more powerful than the bite of 12 other sharks and shark-like fish the researchers used for comparison — including the great white shark and the great hammerhead.

2. They Can Thrive in Freshwater or Saltwater

bull shark in shallow water
Bull sharks often gravitate toward shallow water. Rainervon Brandis / Getty Images

While most sharks are limited to marine habitats, bull sharks can live for long periods and even reproduce in either freshwater or saltwater. That's because they're capable of osmoregulation, a process in which the sharks can adjust the salt-to-water ratio in their bodies based on the water around them. Thanks to special adaptations from their excretory systems, they retain salt and produce more diluted urine while they're in freshwater, then begin to produce saltier urine again when they're back in the ocean.

3. They Can Swim Surprisingly Far Up Rivers

A bull shark swims through a river at Costa Rica's Corcovado National Park.
A bull shark swims through a river at Costa Rica's Corcovado National Park. pefcon / Getty Images

Bull sharks may generally hang out in the ocean, or at least nearby, but the species has also proven perfectly willing to venture far inland via rivers. In 1937, for example, two fishermen caught a bull shark near Alton, Illinois, some 1,750 miles (2,800 km) upriver from New Orleans. The species is also known to travel even farther up the Amazon River, with reports of bull sharks as far upstream as Iquitos, Peru, nearly 2,200 miles (3,500 km) from the ocean.

Bull sharks often reproduce in freshwater habitats and can even establish a long-term presence there. Waterways with known bull shark populations include the Brisbane River in Queensland, Australia; the Brahmaputra and Ganges rivers of eastern India; Lake Nicaragua; Lake Pontchartrain; and the Potomac River.

4. They Give Birth to Live Young

A pregnant bull shark swims off the coast of Playa del Carmen, Quintana Roo, Mexico.
A pregnant bull shark swims off the coast of Playa del Carmen, Quintana Roo, Mexico. Ken Kiefer 2 / Getty Images

Bull sharks are viviparous, which means that unlike most sharks, they give birth to live young rather than laying eggs. Their mating season often occurs in late summer or early fall, and the developing pups are nourished in their mother's body by a yolk-sac placenta. After a roughly 11-month gestation period, the mother gives birth to a litter of one to 13 pups, often opting for a freshwater or low-salinity part of her range, such as coastal lagoons, river mouths, or estuaries.

The parents do not rear their young, but they can help protect them by giving birth in these coastal or inland habitats. While adult bull sharks have no natural predators (aside from humans), their pups can fall victim to other sharks. Since most sharks stick to saltwater, however, the pups may face better odds of survival if they spend some time growing up in a river or lake before venturing out to sea.

5. They Have More Than a Dozen Common Names

Bull sharks are also known by at least 15 other common names in various parts of the world, according to the Florida Museum of Natural History.

These include: requin bouledogue in French-speaking countries; Tiburon sarda in Spain; Zambezi shark or Van Rooyen’s shark in South Africa; the Ganges shark in India (but this name is also given to the freshwater river shark Glyphis gangeticus); the Nicaragua shark in Central America; the freshwater whaler, estuary whaler, and Swan River whaler in Australia; the shovelnose shark, square-nose shark, river shark, slipway grey shark, ground shark, and cub shark in various English-speaking parts of the world.

6. They May Have Been the Inspiration for 'Jaws'

Philadelphia Inquirer front page from July 15, 1916
The Philadelphia Inquirer front page from July 15, 1916. Library of Congress

The 1974 novel "Jaws," which inspired the 1975 blockbuster film of the same title, was itself at least loosely based on some real-life events. Those include a string of shark attacks off the New Jersey coast in July 1916, in which four people died and one was injured.

The novel and movie both feature a great white shark as the culprit, and that species also has been widely blamed for the 1916 attacks. According to some experts, however, details of the 1916 attacks suggest a bull shark may have been likelier. Great whites are relatively rare in New Jersey, especially in inland waterways, and two of the attacks took place in a creek in Matawan, located about 10 miles (16 km) from the ocean. Bull sharks are much more commonly found in habitats like this, and although great whites have more of a reputation for attacking people, bull sharks are also considered one of the most dangerous shark species for humans.

7. They Are Much Less Dangerous to Us Than We Are to Them

Bull sharks are often cited as one of the three most frequent attackers of humans. According to the International Shark Attack File (ISAF), they rank No. 3 in terms of overall attacks, with 116 total attacks in the historical record, of which 25 were fatal and unprovoked. That follows only great whites (326 total attacks, 52 fatal and unprovoked) and tiger sharks (129 total, 34 fatal and unprovoked). The ISAF warns all these statistics should be taken with a grain of salt, however, given the difficulty of positively identifying the species behind most attacks.

However, sharks pose a minimal risk to humans overall, and there are easy ways to minimize the risk even further. The odds of an attack are roughly one in 11 million, which pales in comparison to deadlier beach hazards such as boats, rip currents, and lightning. Research suggests sharks do not see humans as enticing prey, and most "attacks" are actually exploratory bites, after which the shark typically moves on. That said, for large predators with powerful bites like bull sharks, even a test bite like this can fatally wound a person, so they should be treated with caution and respect.

While sharks kill fewer than 10 people globally per year, people kill an estimated 100 million sharks every year, largely due to fishing, finning, and accidental bycatch. Along with other hazards like climate change and the decline of prey species, this has raised widespread concern about the future of sharks, keystone predators that play vital ecological and economic roles.

8. They Aren't Protected in Any Part of Their Range

bull shark swimming off the coast of Playa del Carmen, Mexico
Bull sharks are listed as near threatened by the International Union for Conservation of Nature. Rodrigo Friscione / Getty Images 

Bull sharks are still a common species, found in many warm waters around the world, but even these formidable and flexible predators are at risk from humans. They are listed as near threatened by the International Union for Conservation of Nature (IUCN), which means they do not currently qualify as endangered or threatened, but are either "close to qualifying or likely to qualify for a threatened category in the near future."

While bull sharks' ability to frequent freshwater habitats may protect their pups from predators, it also puts them in closer proximity to people, which endangers them far more than us. According to the IUCN:

"The frequent use of estuarine and freshwater areas by the bull shark makes it more susceptible to deleterious human impacts than species of sharks occurring in other coastal or offshore areas. Bull sharks more frequently encounter humans while in waters of low salinity, and are thereby subjected to increased fishing pressure and environmental changes associated with habitat modification."

Bull sharks are commonly caught in both recreational and commercial fisheries, and although they are not a common target species, they still often taken either as bycatch or as part of a multi-species fishery, the IUCN explains. Bull sharks currently lack specific legal protections throughout their range, according to the Florida Museum, and the IUCN cites "no specific management or conservation" programs. On the bright side, however, there is still time to protect the species before it suffers a steeper decline, and it may have already benefitted from restrictions on the dangerous use of gill nets in many fisheries.