Bull Sharks (River Whaler)

(Carcharhinus leucas)

 

Bull Sharks occur in parts of the Swan Canning Riverpark and the public should be aware of this when wading or swimming in the river. These sharks can be dangerous and aggressive. Unlike most sharks, Bull Sharks tolerate fresh-brackish water and thus can travel far up rivers.

Description
The Bull Shark can be recognised by its stout body, short blunt snout, triangular serrated teeth in the upper jaw and no fin markings as an adult. The species has a rather large second dorsal fin and small eyes, and no skin ridge between two dorsal fins. It is grey above and pale below, sometimes with a pale stripe on the flank. The species grows to a length of 3.4m(1).

Distribution
This species has a widespread distribution in tropical and warm temperate waters worldwide. In Australia, the Bull Shark occurs from Perth, around the northern coastline and down the east coast to Sydney(2). In the Swan Canning Riverpark they have been caught as far upstream as the Maylands Yacht Club.

Habitat
The Bull Shark can live in a wide range of habitats from coastal marine and estuarine to freshwater. It has been recorded from the surf zone down to a depth of at least 150metres(2). It is the only species of shark that is known to stay for extended periods in freshwater. It has been reported nearly 4000km from the sea in the Amazon River system, and is known to breed in Lake Nicaragua, Central America(2).

Biology
Relatively little is known about the biology of the Bull Shark but it shows extraordinary adaptations that allow it to persist in both freshwater and saltwater. The Bull Shark cannot complete its entire life cycle in freshwater and requires access to saltwater through rivers and estuaries(1).

The Bull Shark is viviparous, giving birth to 1-13 young in each litter after a gestation of 10 to 11 months. The female gives birth in late spring and early summer in estuaries, river mouths and the young are born 55-85cm long(2). Mating takes places at the same time of the year.

Bull Sharks are mature at 9-10 years and can live 20-30 years(3).

Bull Sharks swim slowly and heavily, usually close to the bottom and are known to be an ambush predator. Their diet is broad and varied and includes fish, other sharks, sea turtles, birds, dolphins, crustaceans, echinoderms, molluscs and terrestrial mammals.

Along with the Great White and Tiger sharks, the Bull Shark has a reputation for being dangerous. This is a result of its tendency to take large prey and the proximity of its habitat to the activities of humans. There has been one fatality in the Swan Canning Riverpark when a young boy was attacked in the lower estuary during the 1920’s(4). In recent years there have been several other fatal Bull Shark attacks on Australia’s East Coast.

Threats
In some parts of the world the Bull Shark is a popular game fish. Its habitat is vulnerable to modification and pollution caused by human activities.

Conservation
The IUCN consider there to be insufficient information to determine the extent to which the Bull Shark may be threatened and further research is required to determine the conservation status of this shark.

Management messages
Shark sightings should be reported to the Water Police - 24hr hotline: (08) 9442 8600.

References:
1. Stephens, J.D. (1987). Sharks. Golden Press Pty Ltd. NSW.
2. Last, P.R. & Stephens, J.D. (2009). Sharks and Rays of Australia. CSIRO Publishing.
3. Cruz-Martinez, A, Chiappa-Carrara, X. and Arenas-Fuentes, V. (2005). Age and Growth of the Bull Shark, Carcharhinus leucas from Southern Gulf of Mexico. Journal of the Northwest Atlantic Fisheries Sciences 35: 367-374.
4. Edwards, H.(2009). In “Historical Encyclopaedia of WA”. (eds: Gregory, J & Gothard, J).UWA Press

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