In the week we celebrate the World Fish Migration Day we take a look at the impressive Bull Shark.
Common name: Bull shark
Scientific name: Carcharhinus leucas (named by Müller & Henle in 1839)
Conservation status: Near threatened
Diet: usually bony fishes, other sharks and rays (althought, the larger individuals can also eat shrimps, crabs, squids, sea snails, sea urchins, mammals or sea turtles)
Size: 2,1- 3,4 m
Weight: 90-230 kg
Average life span in the wild: 16 years
This agressive species is the only shark that can alternate between sea and fresh waters for long periods, thanks to its adaptive osmoregulation capabilities. It can cover great distances up to 180 kilometers in 24 hours. Adults are often found near estuaries and freshwater inflows to the sea.
The Bull shark has a worldwide distribution in tropical and warm temperate areas, with seasonal appearances in cool, temperate waters. Primarily the Bull shark is an inhabitant of continental shelf waters to a depth of about 150 m (but mostly less than 30 m), but it commonly moves into estuarine and fresh waters. It has been documented travelling large distances up rivers, including the Zambezi. This has resulted in multiple descriptions and numerous common names for the species, including Zambezi Shark.
Reproduction is by viviparity. Most litter sizes range between 6-8. The gestation period is 10-11 months, with birth normally occurring in late spring and summer.
Pregnant females migrate to estuarine areas to give birth. The juveniles remain in these areas until temperatures drop below optimum levels and then migrate to warmer offshore waters.
Its frequent use of estuarine and freshwater areas makes it more susceptible to deleterious human impacts than species of sharks occurring in other coastal or offshore areas.
Bull Sharks are commonly caught in both commercial and recreational fisheries. However, in most situations, this sharks are not normally a fishery target species but are caught as bycatch or as part of a multi-species fishery.
While, in some places, the Bull shark has been exploited commercially for its skin, liver oil and flesh, currently its fins are the major product driving demand.
This shark is also exploited by large aquariums for display.
In Nicaragua, Bull sharks have been seen leaping up river rapids, salmon-like, to reach inland Lake Nicaragua.
Map – Compagno, L.; Dando, M. and Fowler, S. (2005). Sharks of the World. Collins Field Guides. ISBN 0-00-713610-2.