Blacktip Reef Shark

With a length up to 6 feet (1.8 m) and weight up to 100 pounds (45 kg) blacktip reef sharks are considered a small to medium-sized shark. The blacktip reef shark is a common reef shark that can easily be identified by its black-tipped fins. Below the black tip on the large first dorsal fin or back fin, there are black splotches followed by a white band. Most of the dorsal part of the body is a light grey-brown which fades to white near the ventral or stomach area. Like most sharks, the blacktip exhibits countershading. This means the shark has a dark-colored back and a light-colored belly. When viewed from below, the blacktip blends in with the brightness of the sunny waters above. Viewed from above, the shark blends in with the dark ocean bottom. Countershading camouflages the animal, allowing it to sneak up on unsuspecting prey. The blacktip has a short round snout or nose. The teeth are long, thin, and serrated or saw-toothed, which are suited for its diet of reef fish.

Blacktip reef sharks live in shallow lagoons and on coral reefs near reef drop-offs. In general, these sharks do not swim deeper than 33 feet (10 m), but can be found as far as 250 feet (75 m) down. These fish also live in mangrove areas, moving in and out with the tide. Blacktip reef sharks even venture into fresh water but don’t swim too far in from the ocean. These sharks are active swimmers that can most often be found cruising along the bottom. Sometimes blacktip reef sharks can be found swimming at the surface in very shallow waters. They will travel alone or in small groups. As often the most abundant apex predator within its ecosystem, the blacktip reef shark plays a major role in structuring inshore ecological communities. Its diet is composed primarily of small teleost fishes, including mullet, groupers, grunters, jacks, mojarras, wrasses, surgeonfish, and smelt-whitings. Groups of blacktip reef sharks in the Indian Ocean have been observed herding schools of mullet against the shore for easier feeding.

When receptive to mating, a female blacktip reef shark swims slowly in a sinusoidal pattern near the bottom with her head pointed down; observations in the wild suggest female sharks release chemical signals that allow males to track them. Blacktip reef shark are live-bearing or viviparous fish. The gestation period has been reported as 10–11 months long in the Indian Ocean and Pacific islands, and 7–9 months long off northern Australia. Parturition occurs from September to November, with females making use of shallow nursery areas interior of the reef. Newborn pups measure 40–50 cm (16–20 in) long in the Indian Ocean and off northern Australia, while free-swimming pups as small as 33 cm (13 in) long have been observed in the Pacific islands. The litter size is 2–5 (typically 4), and is not correlated with female size. Young blacktip reef sharks commonly form large groups in water barely deep enough to cover their bodies, over sand flats or in mangrove swamps close to shore. During high tide, they also move onto flooded coral platforms or seaweed beds. Growth is initially rapid; one documented captive shark grew an average of 23 cm (9.1 in) per year in its first two years of life. The growth rate slows to around 5 cm (2.0 in) per year in juveniles and adults. Males and females mature sexually at lengths of 95 cm (37 in) and 97 cm (38 in) respectively off northern Australia, and 105 cm (41 in) and 110 cm (43 in), respectively, off Aldabra. Males mature at 97 cm (38 in) long off Palmyra Atoll.

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Biology

Reproduction