The blacktip shark (Carcharhinus limbatus) is a species of requiem shark, and part of the family Carcharhinidae. It is common to coastal tropical and subtropical waters around the world, including brackish habitats. Genetic analyses have revealed substantial variation within this species, with populations from the western Atlantic Ocean isolated and distinct from those in the rest of its range.
Swift, energetic piscivores, blacktip sharks are known to make spinning leaps out of the water while attacking schools of small fish. Both juveniles and adults form groups of varying size. Like other members of its family, the blacktip shark is viviparous; females bear one to 10 pups every other year. Young blacktip sharks spend the first months of their lives in shallow nurseries, and grown females return to the nurseries where they were born to give birth themselves. In the absence of males, females are also capable of asexual reproduction. Common names used for the blacktip shark include blackfin shark, blacktip whaler, common or small blacktip shark, grey shark, and spotfin ground shark.
Blacktip sharks are commonly encountered by divers and coastal fishermen in South Africa. During the sardine run they are frequently encountered feeding on shoals of sardines, anchovy and other bait fish. Whist they do not appear to generate or maintain baitballs, the blacktip sharks are one of the primary opportunistic predators once a baitball forms.
The coloration is gray to brown above and white below, with a conspicuous white stripe running along the sides. The pectoral fins, second dorsal fin, and the lower lobe of the caudal fin usually have black tips. The pelvic fins and rarely the anal fin may also be black-tipped. The first dorsal fin and the upper lobe of the caudal fin typically have black edges. Some larger individuals have unmarked or nearly unmarked fins. Blacktip sharks can temporarily lose almost all their colors during blooms, or “whitings”, of coccolithophores. This species attains a maximum known length of 2.8 m (9.2 ft), though 1.5 m (4.9 ft) is more typical, and a maximum known weight of 123 kg (271 lb).
Distribution and habitat
Most blacktip sharks are found in water less than 30 m (98 ft) deep over continental and insular shelves, though they may dive to 64 m (210 ft). Favored habitats are muddy bays, island lagoons, and the drop-offs near coral reefs; they are also tolerant of low salinity and enter estuaries and mangrove swamps. Although an individual may be found some distance offshore, blacktip sharks do not inhabit oceanic waters.
Biology and ecology
The blacktip shark is an extremely fast, energetic predator that is usually found in groups of varying size. Segregation by sex and age does not occur; adult males and nonpregnant females are found apart from pregnant females, and both are separated from juveniles. Predator avoidance may also be the reason why juvenile blacktips do not congregate in the areas of highest prey density in the bay. Adults have no known predators.
Blacktip sharks are social and usually found in groups. Like the spinner shark, the blacktip shark is known to leap out of the water and spin three or four times about its axis before landing. Some of these jumps are the end product of feeding runs, in which the shark corkscrews vertically through schools of small fish and its momentum launches it into the air. Observations in the Bahamas suggest that blacktip sharks may also jump out of the water to dislodge attached sharksuckers (Echeneis naucrates), which irritate the shark’s skin and compromise its hydrodynamic shape. The speed attained by the shark during these jumps has been estimated to average 6.3 m/s (21 ft/s).
As one of the most common large sharks in coastal waters, the blacktip shark is caught in large numbers by commercial fisheries throughout the world, using longlines, fixed-bottom nets, bottom trawls, and hook-and-line. The meat is of high quality and marketed fresh, frozen, or dried and salted. In addition, the fins are used for shark fin soup, the skin for leather, the liver oil for vitamins, and the carcasses for fishmeal. Blacktip sharks are one of the most important species to the northwestern Atlantic shark fishery, second only to the sandbar shark (C. plumbeus). The flesh is considered superior to that of the sandbar shark, resulting in the sandbar and other requiem shark species being sold under the name “blacktip shark” in the United States. The blacktip shark is also very significant to Indian and Mexican fisheries, and is caught in varying numbers by fisheries in the Mediterranean and South China Seas, and off northern Australia.