Bull Shark

The bull shark is a large, robust requiem shark renowned for its remarkable ability to survive in freshwater as well as saltwater, thanks to specialized kidney and gland function that regulates salt balance. This adaptability allows bull sharks to travel far up major rivers and inhabit freshwater lakes, sometimes hundreds of kilometers from the sea. Found in warm coastal waters worldwide, bull sharks have a stocky build, blunt snout, and small eyes relative to their body size. They are apex predators in the ecosystems they occupy and are considered one of the more adaptable large shark species. The IUCN currently lists the bull shark as Vulnerable, with populations affected by coastal habitat degradation, river damming, and fishing pressure throughout its range.

Field marks for the bull shark:

• Short, broad, rounded snout and small eyes
• Stocky, heavy-set body compared to other requiem sharks of similar length
• Plain grey to grey-brown back fading to a white or pale belly
• Large, tall first dorsal fin positioned well forward
• No interdorsal ridge, distinguishing it from similarly sized dusky or tiger sharks

Adults reach roughly 2.1-3.4 m. Its blunt snout and thickset body, combined with its presence far up rivers or in freshwater lakes, are strong identification clues distinguishing it from other coastal sharks.

Bull sharks occupy an unusually wide range of environments, from shallow coastal marine waters and estuaries to brackish lagoons and entirely freshwater rivers and lakes. They are found worldwide in tropical and subtropical regions and are known to travel far inland, having been recorded thousands of kilometers up rivers such as the Amazon and Mississippi, and residing permanently in freshwater bodies like Lake Nicaragua. They typically inhabit water less than 30 m deep, favoring turbid, warm conditions near river mouths, mangroves, and shorelines. Juveniles often use low-salinity estuaries and river systems as nursery habitat, offering protection from larger marine predators.

Bull sharks are solitary, opportunistic predators that feed mainly on fish, but also take crustaceans, mollusks, sea turtles, birds, and occasionally other sharks and rays. They are most active at dusk and during turbid conditions, using ambush tactics in low-visibility water. Bull sharks are viviparous, with females giving birth to live litters of roughly 1-13 pups after a gestation period of around 10-11 months, often using river mouths and estuaries as pupping and nursery grounds. Their euryhaline physiology, allowing movement freely between salt and fresh water, is a key ecological adaptation that lets them exploit a broader range of habitats and prey than most other shark species.