Blacktip Reef shark
A wide-ranging species with notable fin markings
Family: Carcharhinidae – Requiem sharks
Common Name– Ground Sharks
Common Name– Requiem Sharks
Status: IUCN Red List NEAR THREATENED
Average Size and Length: The average length of Blacktip Reef sharks is around 5.2 feet long. Very rarely sharks may reach 5.9 feet to 6.6 feet.
Average Weight: The maximum recorded weight is 30 pounds.
Teeth and Jaw: Excluding the small symphysial teeth, the tooth rows number 11–13 (but typically 12) on either side of the upper jaw and 10–12 (but typically 11) on either side of the lower jaw. The upper teeth are upright to angled and narrowly triangular, with serrations that are coarser on the bases. The lower teeth are similar, but more finely serrated. The teeth of adult males are more abruptly curved than the teeth of female Blacktip Reef sharks.
Head: The Blacktip Reef shark has a rounded shout that is short and wide. Its eyes are oval and large. The nostrils have skin flaps on them.
Demographic, Distribution, Habitat, Environment and Range: The Blacktip Reef shark is found throughout nearshore waters of the tropical and subtropical Indo-Pacific. In the Indian Ocean, it can be found 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 the Andaman Islands, Sri Lanka, 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, Tuamotu, and Hawaiian Islands and. The Blacktip Reef shark is a Lessepsian migrant and has colonized the eastern Mediterranean Sea traveling the Suez Canal.
Although it has been reported from a depth of 246 feet, the Blacktip Reef shark is usually found in water only a few feet deep and can often be seen swimming close to shore with its dorsal fin exposed, just like the movie cliché. The younger Blacktip Reef sharks prefer clear, shallow, sandy flats, while older sharks are most common around reef ledges and can also be found near reef drop-offs. On occasion, they have also been reported from brackish estuaries and lakes in Madagascar, and freshwater environments in Malaysia, though it is not able to tolerate low salinity to the same degree as the Bull shark. At Aldabra in the Indian Ocean, Blacktip Reef sharks congregate in the channels between reef flats during low tide and travel to the mangroves when the water rises. There is some evidence that the Blacktip Reef sharks from the northern and southern areas of its distribution are migratory.
Diet: The Blacktip Reef shark primarily eats small teleost fishes, including groupers, mullet, grunters, jacks, mojarras, wrasses, smelt-whitings, and surgeonfish.
Groups of Blacktip Reef sharks in the Indian Ocean have been observed herding schools of mullet against the shore. This makes catching prey much easier.
Blacktip Reef sharks will also eat octopus, squid, cuttlefish, shrimp, and mantis shrimp. Sometimes even carrion and smaller sharks, sea snakes (several species in northern Australia) and rays. Blacktip Reef sharks off Palmyra Atoll have been documented preying on seabird chicks that have fallen out of the nests into the water. Some odd items have been found in the stomachs of Blacktip Reef sharks, like stones, turtle grass, algae, coral, hydrozoa, bryozoan and even rats!
Blacktip reef sharks, particularly the small sharks can fall prey to larger fishes, including groupers, grey reef sharks, Tiger sharks and even bigger Blacktip Reef sharks.
Aesthetic Identification: The Blacktip Reef shark has a robust shape and is quite streamlined. It is a pale grayish-brown above and white counter-shaded below. It has a 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 a beautiful shark.
The pectoral fins are large and narrowly falcate tapering to points. The 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 large with a short rear margin and is placed opposite the anal fin. There is no ridge between the dorsal fins.
Biology and Reproduction: Known parasites of the Blacktip Reef shark include the tapeworms: Anthobothrium lesteri, Nybelinia queenslandensis, Otobothrium alexanderi, and Platybothrium jondoeorum, myxosporidian in the genus Unicapsula, and the monogenean Dermophthirius melanopteri. There has been one case of a Blacktip Reef shark that died from an infectious disease that was caused by the bacterium Aeromonas salmonicida subsp. salmonicida.
The Blacktip Reef shark is viviparous. Its reproductive cycle is different depending on its location. It is annual off northern Australia, with mating taking place from January to February. It is annual 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 result 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. Some research suggests this could be due to warmer waters.
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 5.9 inches 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. After a period of synchronous swimming, the male pushes the female on her side and positions her so her head is against the bottom and her tail is raised. Once the female is in position, the male inserts one of his claspers into her cloaca. Copulation lasts for several minutes, after which the sharks separate and resume their regular behavior Porcher, I.F. (April 2005). “On the gestation period of the blackfin reef shark, Carcharhinus melanopterus, in waters off Moorea, French Polynesia“. Marine Biology. 146 (6): 1207–1211).
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 16–20 inches long in the Indian Ocean and off northern Australia, while free-swimming pups as small as 13 inches long have been observed in the Pacific islands.
The litter size is 2–5 (but usually 4). Young Blacktip Reef sharks may 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. They grow extremely fast during the first two years, then slows down.
Males and females mature sexually at about 37 inches and 38 inches off northern Australia. Off Aldabra, 41 inches and 43 inches, and off Palmyra Atoll, 38 inches.
Behavioral Traits, Sensing and Intelligence: Like many sharks, the Blacktip Reef shark does not have any cone cells in its retina, limiting its ability to discriminate colors and fine details. Instead, its vision is adapted for sensitivity to movement or contrast under low light conditions, which is further enhanced by the presence of a reflective tapetum lucidum. Experiments have shown that this shark is capable of detecting small objects up to 1.5–3 m (5–10 ft) away but is unable to clearly discern the shape of the object. Electroreception is another means by which the Blacktip Reef shark can locate prey; its ampullae of Lorenzini have a sensitivity of approximately 4 nV/cm and an effective range of 25 cm (10 in). Tester, A.L. & S. Kato (1966). “Visual target discrimination in blacktip sharks (Carcharhinus melanopterus) and grey sharks (C. menisorrah)“. Pacific Science. 20 (4): 461–471)
The Blacktip Reef shark can become more excited and less timid in the presence of other Blacktip Reef sharks. Power by numbers, they have also been known to engage in feeding frenzies on occasion. Feeding activity may be greater at night than during the day.
Researchers working at Enewetak Atoll in the Marshall Islands have found the blacktip reef shark can be readily attracted by splashing or striking metal tools against hard objects underwater, as well as by the scent of both healthy and injured fish (Hobson, E.S. (1963). “Feeding behavior in three species of sharks“. Pacific Science. 17: 171–193).
The Blacktip Reef shark can be found alone or can be found in schooling groups. It is typically timid and skittish and often very difficult to approach. Blacktip reef sharks are cooperative pack hunters.
Speed: The Blacktip Reef shark is extremely active and is a fast simmer. Their average swimming speed decreases when the tide rises at night. This could be because the invasion of cooler water reduces their metabolism, or the accompanying movement of prey fishes makes foraging easier. Blacktip Reef sharks at Aldabra tend to be more mobile than those at Palmyra, with recorded individual movements of up to 1.6 miles over 7 hours.
Blacktip Reef Shark Future and Conservation: The blacktip reef shark is a regular catch of coastal fisheries, such as those operating off Thailand and India, but is not targeted or considered commercially important. The meat (sold fresh, frozen, dried and salted, or smoked for human consumption), liver oil, and fins are used by humans. They have a low reproductive rate, and thus need conservation. They can reproduce in captivity as well. The Blacktip Reef shark can be centered around ecotourism.
Blacktip Reef Shark Recorded Attacks on Humans: The Blacktip Reef shark seldom poses a danger to humans unless roused by food. People wading through shallow water are at risk of having their legs mistakenly bitten. In 2009, ISAF reported 11 unprovoked attacks, and 21 total attacks with no fatalities. Spear fisherman can be at a higher risk.