Blacktip Reef Shark

A robustly built species with a streamlined "typical shark" form, the blacktip reef shark has a short, wide, rounded snout and moderately large, oval eyes. Each nostril has a flap of skin in front that is expanded into a nipple-shaped lobe. Not counting small symphysial (central) teeth, the tooth rows number 11–13 (usually 12) on either side of the upper jaw and 10–12 (usually 11) on either side of the lower jaw. The upper teeth are upright to angled and narrowly triangular in shape, bearing serrations that are more coarse on the bases; the lower teeth are similar, but more finely serrated. The teeth of adult males are more abruptly curved than those of females. The pectoral fins are large and narrowly falcate (sickle-shaped), tapering to points. The sizable first dorsal fin is high with a curving S-shaped rear margin, and originates over the free rear tips of the pectoral fins. The second dorsal fin is relatively large with a short rear margin, and is placed opposite the anal fin. There is no ridge between the dorsal fins. This shark is a pale grayish-brown above and white below, with an obvious white band on the sides extending forward from above the anal fin. All the fins have black tips highlighted by lighter-colored borders, which are especially striking on the first dorsal fin and lower caudal fin lobe. …

The blacktip reef shark is found throughout nearshore waters of the tropical and subtropical Indo-Pacific. In the Indian Ocean, it occurs from South Africa to the Red Sea, including Madagascar, Mauritius, and the Seychelles, and from there eastward along the coast of the Indian subcontinent to Southeast Asia, including Sri Lanka, the Andaman Islands, and the Maldives. In the Pacific Ocean, it is found from southern China and the Philippines to Indonesia, northern Australia and New Caledonia, and also inhabits numerous oceanic islands, including the Marshall, Gilbert, Society, and Hawaiian Islands and Tuamotu. Contrary to what most sources state, there is a report suggesting that the specimens of this species from Japanese waters might be from Taiwan, however a number of sightings and captures of this species have been reported from the inshore waters of Ishigaki Island of Okinawa Prefecture in southern Japan. A Lessepsian migrant, this shark has colonized the eastern Mediterranean Sea by way of the Suez Canal. Although it has been reported from a depth of 75 m (246 ft), the blacktip reef shark is usually found in water only a few meters deep, and can often be seen swimming close to shore with its dorsal fin exposed. Younger sharks prefer shallow, sandy flats, while older sharks are most common around reef ledges and can also be found near reef drop-offs. …

Along with the grey reef shark (C. amblyrhinchos) and the whitetip reef shark (Triaenodon obesus), the blacktip reef shark is one of the three most common sharks inhabiting coral reefs in the Indo-Pacific. This species predominates in shallow habitats, while the other two are mostly found deeper. Fast-swimming and active, the blacktip reef shark may be encountered alone or in small groups; large "social" aggregations have also been observed. For the most part, juvenile and adult sharks are not segregated by sex, save for the movements of pregnant females to give birth. Individuals exhibit strong fidelity to particular areas, where they may remain for several years. A tracking study off Palmyra Atoll in the central Pacific has found the blacktip reef shark has a home range of around 0.55 km2 (0.21 mi2), among the smallest of any shark species. The size and location of the range does not change with time of day. Within this range, 3–17% of the area constitute favored hunting patches that are disproportionately occupied by the resident shark. The sharks spend most of their time swimming back and forth along reef ledges, making occasional short forays onto sandy flats. Their average swimming speed decreases when the tide rises at night, possibly because the influx of cooler water reduces their metabolism, or the accompanying movement of prey fishes makes foraging easier. …

Like the other members of its family, the blacktip reef shark is viviparous, though the details of its life history vary across its range. Its reproductive cycle is annual off northern Australia, with mating taking place from January to February, as well as off Moorea in French Polynesia, where mating occurs from November to March. The cycle is biennial off Aldabra, where intense competition within and between species for food may constrain females to only bearing young every other year. Earlier accounts from the Indian Ocean by Johnson (1978), Madagascar by Fourmanoir (1961), and the Red Sea by Gohar and Mazhar (1964), indicated a biannual cycle in these regions with two breeding seasons per year from June to July and December to January. If accurate, the shorter reproductive cycles of these subpopulations may be a consequence of warmer water. 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. Once the male finds her, he closes to around 15 cm (5.9 in) and follows her with his snout oriented towards her vent. A courting male may also bite the female behind her gills or on her pectoral fins; these mating wounds heal completely after 4–6 weeks. …