CARCHARHINUS LEUCAS (VALENCIENNES, IN MÜLLER AND HENLE, 1839)
FAMILY CARCHARINIDAE (REQUIEM SHARKS)
Identification: A large, heavy set-bodied shark with a broad snout, relatively small eyes, a large, pointed first dorsal fin, and without an interdorsal ridge.The teeth are broadly triangular and serrated. The dorsal body coloration is a dusky gray that fades to white ventrally.
Size: The maximum reported size is 3.5 m and over 230 kg. Females reach a maximum length of 3.5 m and males 3.0 m. Females grow larger than males and average a length of 240 cm weighing 130 kg. Males have an average length of 225 cm weighing 95 kg. Size at birth ranges from 59-81 cm.
Distribution: The bull shark is found in many different parts of the world and can travel long distances. This shark is most common in subtropical coastal waters but can also be found in numerous river systems and in some lakes. They have been reported 3,700 km up the Amazon River and over 3,000 km up the Mississippi River. A bull shark population was thought at one time to be land locked in Lake Nicaragua, but after extensive research it was determined that they were able to reach the ocean through rivers and estuaries.
Habitat: The bull shark prefers shallow coastal waters less than 30 m deep. However, individuals have been located down to 150 m. This shark is commonly found in rivers, estuaries, and bays. This is the only shark species that is known to readily occur in freshwater systems. Young bull sharks live their early years in bays and estuaries until large enough to venture into the ocean. These sharks can also tolerate hypersaline waters up to 53 parts per thousand.
Biology: Bull sharks are viviparous with litter sizes ranging from 1-13 pups. The pups are nourished inside the mother for 10-11 months. Bays and estuaries are common nursery grounds. In warm water habitats, mating and birthing is year-round, but in cooler water areas birthing usually occurs during the summer months. Males reach maturity at about 192 cm and females about 205 cm at an age between 5 and 6 years, respectively. They prey on bony fishes, other sharks, rays, dolphins, turtles, birds, molluscs, echinoderms and crustaceans. Bull sharks have also been known to eat rats, hippos, dogs and even horses! This shark is primarily a solitary hunter that cruises the shallow water for any prey of suitable size. Bull sharks use the “bump and bite” technique of prey capture. The bump is an investigative technique that assists the shark in identifying prey.
General interest: The Bull shark is an aggressive shark as well as intensely territorial. It is considered to be one of the four most dangerous sharks, along with the white shark (Carcharodon carcharias), tiger shark (Galeocerdo cuvier), and oceanic whitetip (Carcharhinus longimanus), to humans. Numerous attacks by these sharks on humans have been reported from tropical regions. Its close proximity to populated shore lines and its aggressive behavior makes this shark extremely dangerous. In many countries the rivers that this animal frequents coincides with popular bathing and recreational areas. This creates more human interaction and thus more attacks. The greatest threat to this shark is from over-fishing. The meat is used for food and the hide is tanned for leather.
By Clinton Moran
Pacific Shark Research Center
Moss Landing Marine Laboratories
8272 Moss Landing Road, Moss Landing, CA 95039