Bull sharks, scientifically known as Carcharhinus leucas, inhabit warm coastal waters globally, from tropical to subtropical regions. They are often found in shallow areas like coastlines, bays, estuaries, and lagoons. This species is known as one of the most encountered and potentially threatening sharks in human-frequented environments.
Unique Freshwater Adaptations
Bull sharks are unique for their ability to tolerate both saltwater and freshwater environments, a trait called euryhalinity. Unlike most shark species that are exclusively marine, they possess specialized physiological mechanisms. These include kidneys and rectal glands that regulate internal salt balance. This allows them to move freely between oceans, rivers, and lakes, surviving in varying salinity levels, including brackish waters.
This capability allows bull sharks to travel thousands of kilometers upstream into major river systems. They have been documented far up the Mississippi River (Alton, Illinois, 1,100 km from the ocean) and deep within the Amazon River (near Iquitos, Peru, 4,000 km from the Atlantic). They are also found in Lake Nicaragua. Their presence in such diverse environments increases the likelihood of interactions with human populations, as these waterways are often used for recreation.
Physical Prowess and Predatory Nature
Bull sharks are effective predators due to their physical characteristics. They have a robust, stocky build, providing power and agility. Females are larger than males, typically averaging 2.4 meters (8 feet) and 130 kilograms (290 pounds), though some reach 4 meters (13 feet) and over 315 kilograms (694 pounds). They also have a broad, flat snout and wide head.
Bull sharks have powerful jaws and teeth. Their upper jaw has broad, triangular teeth with prominent serrations, while the lower jaw has narrower, pointed teeth with finer serrations. This dentition, combined with a bite force up to 5,914 newtons (1,330 pounds-force), allows them to take down diverse prey. As opportunistic feeders, their diet includes bony fish, other sharks, rays, turtles, birds, and terrestrial mammals. Their hunting strategy often involves ambush tactics, using poor visibility in murky waters to approach prey undetected before striking.
Aggressive Behavior and Territoriality
Bull sharks are known for their aggressive and unpredictable nature. They show little fear or hesitation when encountering humans. This temperament is partly attributed to high testosterone levels in males, which contribute to their territoriality and readiness to confront perceived threats. Unlike some sharks that might retreat after an exploratory bite, bull sharks are more likely to commit to an attack and deliver multiple bites.
Their territorial tendencies are pronounced in shallow, turbid waters, common near river mouths and coastal areas with human activity. In these low-visibility conditions, bull sharks use sensitive electroreceptors to detect electrical fields, making them effective hunters. The “bump-and-bite” behavior involves a shark head-butting an object or potential prey before a full attack, especially if it perceives an intrusion or is assessing a meal.