The biology of the bull shark is still little known but it shows extraordinary physiological adaptations that allow it to persist in both freshwater and saltwater. Bull sharks have been captured in places you would never imagine a shark to be found; in the foothills of the Peruvian Andes, 3,700 kilometres up the Amazon River; and in Lake Nicaragua, the largest lake in Central America. However, the bull shark may not be able to complete its entire life cycle in freshwater, and all sharks in freshwater require access to saltwater through rivers and estuaries (2) (3). Its swims slowly and heavily, usually near the bottom, concealing its surprising agility and speed employed when attacking prey (2), and deceiving one into believing this may not be one of the most dangerous species of tropical shark, as it is frequently cited (2) (5) (6). Along with the great white and tiger shark the bull shark is responsible for the most accidents involving people (2); a result of its tendency to take large prey and the proximity of its habitat to the activities of humans (2). The bull shark's broad and varied diet includes bony fishes, other shark species (even occasionally young bull sharks), sea turtles, birds, dolphins, and terrestrial mammals (2). The bull shark is viviparous, giving birth to 1 to 13 young in each litter after a pregnancy of 10 to 11 months (2). The female gives birth in late spring and early summer in both hemispheres, in estuaries, river mouths, and very occasionally in freshwater lakes (2). Mating takes place at the same time of the year but it is unknown where exactly as it has never been directly observed (4).
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