The bull shark (Carcharhinus leucas) is also known as the bull whaler, and is found across the world in warm shallow waters along the coasts in tropical and subtropical seas and oceans, and also in freshwater rivers and lakes. Their ability to exist in both saltwater and freshwater has confused scientists for a long time. It has now been accepted that they are not true freshwater sharks. These sharks are famous for their unpredictable and aggressive behavior. Further, unlike other sharks, bull sharks can tolerate freshwater and can travel far up into the rivers. This fact, combined with the fact that they lurk in shallow water has made them responsible for a majority of shark attacks on humans. Appearance and Behavior Bull sharks have been so named because of their stock shape, a snout that is broad and flat, and their aggressive behavior which is usually unpredictable. Like all sharks, their skeleton is not made of bones. The body is made of cartilage which is tough and fibrous, but not as hard as a bone. These sharks are wider when compared to other sharks of similar length, and are gray on top with a white bottom. Males can reach 7 feet in length and weigh about 200 pounds, while females are larger, and can be 12 feet long and weigh up to 750 pounds. Their teeth are very sharp and saw-like, which leaves a crescent shaped bite mark. Further, they are located in rows which rotate into use as and when they are required. The first two rows of teeth are used to obtain the prey while the other rotates to place when needed. If a tooth is lost or broken, then it is replaced by a new one that rotates into its place. Regarding their fins, they have the unique distinction of their second dorsal fin being smaller than the first one fin. Bull sharks are solitary hunters, are extremely territorial, and attack other animals and humans that enter their territory. They are among the four species of sharks that are considered to be most dangerous to humans. It is interesting to note here, that the Jersey Shore shark attack in 1916 is attributed to the bull sharks. This incident inspired the famous movie series, 'Jaws'. These are apex predators, and are generally not attacked by other animals. Although humans are their biggest threat, as their meat is considered to be a delicacy in many parts of the world, they are also on occasions attacked by larger sharks like the tiger shark and the great white shark. Incidents where saltwater crocodiles have attacked and eaten them have also been reported. Diet The diet includes fish, sharks, dolphins, turtles, birds, crustaceans and terrestrial mammals. As a matter of fact, they can eat almost anything. They use the bump and bite technique to attack their prey. Reproduction They reach sexual maturity at the age of ten years, and breed during the summer usually in the brackish water of river mouths. These sharks reproduce sexually, wherein, the male uses claspers, which is an extension of the pelvic fins to transfer the sperm to the females. Blue sharks are viviparous in nature. Here, the eggs hatch inside the body of the female, and the baby sharks are fed with the help of a placenta through which the nourishment is transferred from the mother to the baby. The gestation period lasts for a year, after which, the shark gives birth to as many as 13 young pups. The young sharks are about 30 inches in length. They are born with a full set of teeth, and are fully ready to take care of themselves. Their fins are covered with black tips, but the black marks disappear as they grow older. They usually swim away from the mother, as sometimes the mothers too can eat them.