Bull Shark (Carcharhinus leucas): The Most Aggressive Shark

Bull sharks, Carcharhinus leucas (Müller and Henle, 1839), aka zambezi, ganges (often confused with the Ganges river shark, Glyphis gangeticus), ground sharks, river sharks, freshwater whalers, estuary whalers, shovelnoses, slipway greys, and swan river whalers, are massive and fearsome sharks with a short, broad, blunt snouts, small eyes, and triangular saw-edged upper teeth. Their characteristic barrel-shaped body lacks an interdorsal ridge. The first dorsal fin is broad and triangular and less than 3.2 times height of second dorsal fin. They are gray in color on the dorsal side and white on the ventral side, and have fins often seen with dark tips, particularly in juveniles. Females tend to be larger than males, reaching up to 3.5 external link m maximum length and a maximum weight of 317 external link kg. They are reported to live up to 25 years.

Bull sharks are aggressive, common, and usually live near high-population areas like tropical shorelines. They are not bothered by brackish and freshwater, and even venture far inland via rivers and tributaries.

Because of these characteristics, many experts consider bull sharks to be the most dangerous sharks in the world. Historically, they are joined by their more famous cousins, great whites and tiger sharks, as the three species most likely to attack humans.

Bull sharks get their name from their short, blunt snout, as well as their pugnacious disposition and a tendency to head-butt their prey before attacking. They are medium-size sharks, with thick, stout bodies and long pectoral fins. They are gray on top and white below, and the fins have dark tips, particularly on young bull sharks.
They are found cruising the shallow, warm waters of all the world’s oceans. Fast, agile predators, they will eat almost anything they see, including fish, dolphins, and even other sharks. Humans are not, per se, on their menus. However, they frequent the turbid waters of estuaries and bays, and often attack people inadvertently or out of curiosity.

Bull sharks currently are not threatened or endangered. However, they are fished widely for their meat, hides, and oils, and their numbers are likely shrinking. One study has found that their average lengths have declined significantly over the past few decades.

World Range & Habitat
The bull shark is a widespread coastal and freshwater shark inhabiting shallow waters in bays, estuaries, rivers, and lakes. They have a unique ability to penetrate far up rivers and  hypersaline external link bays, particularly when they're young. They have often been found hundreds of km from the sea. Adults can also be found near estuaries and freshwater inflows to the sea. Found typically between 3-30 external link m in depth.

They range from the western Atlantic: Massachusetts, USA to southern Brazil; eastern Atlantic: Morocco, Senegal to Angola; Indo-West Pacific: Kenya and South Africa to India, and Vietnam to Australia; eastern Pacific: southern Baja California, Mexico to Ecuador and possibly Peru. They are a sympatric species (occupying the same range without loss of identity from interbreeding) with C. amboinensis external link and the Ganges shark, G. gangeticus external link. Off KwaZulu-Natal, South Africa, it has been suggested that bull sharks and the very similar C. amboinensis avoid competing with one another by occupying separate habitats in the region.

Bull sharks are the most common of about 6 species of shark in their genus: the Ganges shark (Glyphis gangeticus), speartooth shark (Glyphis glyphis), Irrawaddy rivers shark (Glyphis siamensis), Borneo river shark (Glyphis sp. B), and New Guinea river shark (Glyphis sp. C), that can travel between salt and fresh water or live in fresh water for prolonged periods.

Feeding Behavior (Ecology)
A solitary hunter, bull sharks feed on bony fishes, other sharks such as young sandbar sharks, rays, mantis shrimps, crabs, squid, sea snails, sea urchins, mammalian carrion, sea turtles, and, occasionally, garbage. Definitely an opportunistic species!
Life History

Bull sharks are viviparous external link (live bearers), with a yolk-sac placenta, and give birth to 1-13 young per litter. Their size at birth is about 60-80 external link cm in length. In the western north Atlantic off Florida and the Gulf of Mexico, and off South Africa, the young are born in late spring or early summer. Off Nicaragua, females may have young throughout the year, with a peak in spring and early summer. The estimated gestation period is 10-11 months. Males reach sexual maturity between 1.6 and 2.3 external link m in length, females at 1.8 to 2.3 external link m, both between 15-20 years. Mating features distinct pairing with embrace; the male nips at the female's back and grasps one of her pectoral fins in his mouth. Females often have courtship scars.

Conservation Status/Additional Comments
Bull sharks, Carcharhinus leucas, are considered one of the most dangerous species of tropical shark; they've been implicated in a number of attacks on humans. They are fished commercially and sold fresh, fresh-frozen, or smoked for human consumption. They are also finned for shark fin soup. Their hides are sold for leather, their liver for oil, and their carcass for fishmeal.

According to the  International Shark Attack File (ISAF) at the Florida Museum of Natural History Ichthyology Department, here are some things you should do to avoid bull sharks:
- Avoid swimming near river mouths or other estuaries with turbid waters where bull sharks are known to occur.
- Do not swim near schools of fish in inshore areas. These schools are often pursued by large predators.
- Be cautious if spearfishing. Bull sharks are known to approach spearfishermen carrying their catch.
- Do not duplicate the practices of some television "adventurers" who flagrantly disregard common sense while showboating around sharks.

Source: http://marinebio.org/species.asp?id=83

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