Grey reef sharks are active at all times of the day, with activity levels peaking at night.[4] At Rangiroa, groups of around 30 sharks spend the day together in a small part of their collective home range, dispersing at night into shallower water to forage for food. Their home range is about 0.8 km2 (0.31 sq mi).[25] At Enewetak in the Marshall Islands, grey reef sharks from different parts of the reef exhibit different social and ranging behaviors. Sharks on the outer ocean reefs tend to be nomadic, swimming long distances along the reef, while those around lagoon reefs and underwater pinnacles stay within defined daytime and night-time home ranges.[26] Where there are strong tidal currents, grey reef sharks move against the water: towards the shore with the ebbing tide and back out to sea with the rising tide. This may allow them to better detect the scent of their prey, or afford them the cover of turbid water in which to hunt.[25]


On the infrequent occasions when they swim in oceanic waters, grey reef sharks often associate with marine mammals or large pelagic fishes, such as sailfish (Istiophorus platypterus). There is an account of around 25 grey reef sharks following a large pod of bottlenose dolphins (Tursiops sp.), along with 25 silky sharks (C. falciformis) and a single silvertip shark.[13] Rainbow runners (Elagatis bipinnulata) have been observed rubbing against grey reef sharks, using the sharks' rough skin to scrape off parasites.[14]
Grey reef sharks are prey for larger sharks, such as the silvertip shark.[9] At Rangiroa Atoll in French Polynesia, great hammerheads (Sphyrna mokarran) feed opportunistically on grey reef sharks that are exhausted from pursuing mates.[15] Known parasites of this species include the nematode Huffmanela lata and several copepod species that attach to the sharks' skin,[16][17] and juvenile stages of the isopods Gnathia trimaculata and G. grandilaris that attach to the gill filaments and septa (the dividers between each gill).[18][19]
Although still abundant at Cocos Island and other relatively pristine sites, grey reef sharks are susceptible to localized depletion due to their slow reproductive rate, specific habitat requirements, and tendency to stay within a certain area. The IUCN has assessed the grey reef shark as Near Threatened; this shark is taken by multispecies fisheries in many parts of its range and used for various products such as shark fin soup and fishmeal.[2] Another threat is the continuing degradation of coral reefs from human development. There is evidence of substantial declines in some populations. Anderson et al. (1998) reported, in the Chagos Archipelago, grey reef shark numbers in 1996 had fallen to 14% of 1970s levels.[30] Robbins et al. (2006) found grey reef shark populations in Great Barrier Reef fishing zones had declined by 97% compared to no-entry zones (boats are not allowed). In addition, no-take zones (boats are allowed but fishing is prohibited) had the same levels of depletion as fishing zones, illustrating the severe effect of poaching. Projections suggested the shark population would fall to 0.1% of pre-exploitation levels within 20 years without additional conservation measures.[31] One possible avenue for conservation is ecotourism, as grey reef sharks are suitable for shark-watching ventures, and profitable diving sites now enjoy protection in many countries, such as the Maldives.[6]
The small shark is named for its distinct black-tipped fins. Not to be confused with the blacktip shark, a larger species with similar fin coloration, the blacktip reef shark can be found in shallow inshore waters throughout the Indo-Pacific, including coral reefs, reef flats and near drop offs. It may be seen in mangrove areas and even freshwater environments near to shore, moving in and out with the tide. The blacktip reef shark feeds primarily on fish, including many common reef fishes, but will also consume crustaceans, mollusks, and even snakes!

The snout is rather short, broad, and rounded, without prominent flaps of skin beside the nostrils. The eyes are large and circular, with nictitating membranes (protective third eyelids). There are 11–13 tooth rows in either half of both jaws. The teeth have broad bases, serrated edges, and narrow cusps; the front 2–4 teeth on each side are erect and the others increasingly oblique. The five pairs of gill slits are moderately long, with the third gill slit over the origin of the pectoral fins.[4] The first dorsal fin is high and falcate (sickle-shaped). There is a low interdorsal ridge running behind it to the second dorsal fin, which is relatively large with a short free rear tip. The origin of the first dorsal fin lies over or slightly forward of the free rear tips of the pectoral fins, and that of the second dorsal fin lies over or slightly forward of the anal fin. The pectoral fins are long and narrow, tapering to a point.[2] The dermal denticles are closely spaced and overlapping, each with five (sometimes seven in large individuals) horizontal low ridges leading to marginal teeth.[4]

WWF works to preserve the coral habitats where reef sharks live through the creation and improved management of marine protected areas, elaboration of fisheries management plans, and the introduction of fishing bans to protect vulnerable species including reef sharks. WWF also promoted the understanding that communities can derive more economic value from reef sharks through tourism than through their capture. We support local communities to set up appropriate ecotourism systems and infrastructure to ensure well-managed and sustainable shark tourism operations.
Along with the blacktip reef shark (C. melanopterus) and the whitetip reef shark (Triaenodon obesus), the grey reef shark is one of the three most common sharks inhabiting Indo-Pacific reefs. They actively expel most other shark species from favored habitats, even species larger in size.[3] In areas where this species co-exists with the blacktip reef shark, the latter species occupies the shallow flats, while the former stays in deeper water.[4] Areas with a high abundance of grey reef sharks tend to contain few sandbar sharks (C. plumbeus), and vice versa; this may be due to their similar diets causing competitive exclusion.[11]
The Caribbean reef shark infrequently attacks humans. In general, a shark attack on a human is behaviorally similar to an attack upon natural prey. A human is more susceptible to being attacked if the shark is cornered and feels that there is no escape route. In situations like these, the shark may rake the victim during the attack resulting in lacerations.
The grey reef shark (Carcharhinus amblyrhynchos, sometimes misspelled amblyrhynchus or amblyrhinchos)[2] is a species of requiem shark, in the family Carcharhinidae. One of the most common reef sharks in the Indo-Pacific, it is found as far east as Easter Island and as far west as South Africa. This species is most often seen in shallow water near the drop-offs of coral reefs. The grey reef shark has the typical "reef shark" shape, with a broad, round snout and large eyes. This species can be distinguished from similar species by the plain or white-tipped first dorsal fin, the dark tips on the other fins, the broad, black rear margin on the tail fin, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.9 m (6.2 ft) long.
Reproduction is viviparous; once the developing embryos exhaust their supply of yolk, the yolk sac develops into a placental connection through which they receive nourishment from their mother. Mating is apparently an aggressive affair, as females are often found with biting scars and wounds on their sides.[4] At the Fernando de Noronha Archipelago and Atol das Rocas off Brazil, parturition takes place at the end of the dry season from February to April, while at other locations in the Southern Hemisphere, females give birth during the Amazon summer in November and December.[4][12] The average litter size is four to six, with a gestation period of one year. Females become pregnant every other year.[8] The newborns measure no more than 74 cm (29 in) long; males mature sexually at 1.5–1.7 m (59–67 in) long and females at 2–3 m (79–118 in).[4]

Off Enewetak, grey reef sharks exhibit different social behaviors on different parts of the reef. Sharks tend to be solitary on shallower reefs and pinnacles. Near reef drop-offs, loose aggregations of five to 20 sharks form in the morning and grow in number throughout the day before dispersing at night. In level areas, sharks form polarized schools (all swimming in the same direction) of around 30 individuals near the sea bottom, arranging themselves parallel to each other or slowly swimming in circles. Most individuals within polarized schools are females, and the formation of these schools has been theorized to relate to mating or pupping.[25][26]

The grey reef shark has a streamlined, moderately stout body with a long, blunt snout and large, round eyes. The upper and lower jaws each have 13 or 14 teeth (usually 14 in the upper and 13 in the lower). The upper teeth are triangular with slanted cusps, while the bottom teeth have narrower, erect cusps. The tooth serrations are larger in the upper jaw than in the lower. The first dorsal fin is medium-sized, and there is no ridge running between it and the second dorsal fin. The pectoral fins are narrow and falcate (sickle-shaped).[4]
The Caribbean reef shark has an interdorsal ridge from the rear of the first dorsal fin to the front of the second dorsal fin. The second dorsal fin has a very short free rear tip. The snout of C. perezi is moderately short and broadly rounded. It has poorly developed, low anterior nasal flaps and relatively large circular eyes. Caribbean reef sharks also have moderately long gill slits with the third gill slit lying above the origin of the pectoral fin. Comparison to similar sharks:

Blacktip reef sharks, Carcharhinus melanopterus (Quoy and Gaimard, 1824), are small sharks measuring up to 1.8 m with short, bluntly-rounded snouts, oval eyes, and narrow-cusped teeth. They have 2 dorsal fins and no interdorsal ridges. Juveniles (< 70 cm) are yellow-brown on their dorsal (upper) sides, white on their ventral (under) sides; adults are brownish-gray and white, respectively. All their fins have conspicuous black or dark brown tips, and posterior (rear) dark edges on their pectoral fins and their upper lobe of their caudal (tail) fins. The prominent black tips of their first dorsal fin contrasts with a light band below it; a conspicuous dark band on their flanks which extends to their pelvic fins. Maximum weight: 24 kg; frequents depth ranges from the surface to 75 m.
Grey reef sharks are fast-swimming, agile predators that feed primarily on free-swimming bony fishes and cephalopods. Their aggressive demeanor enables them to dominate many other shark species on the reef, despite their moderate size. Many grey reef sharks have a home range on a specific area of the reef, to which they continually return. However, they are social rather than territorial. During the day, these sharks often form groups of five to 20 individuals near coral reef drop-offs, splitting up in the evening as the sharks begin to hunt. Adult females also form groups in very shallow water, where the higher water temperature may accelerate their growth or that of their unborn young. Like other members of its family, the grey reef shark is viviparous, meaning the mother nourishes her embryos through a placental connection. Litters of one to six pups are born every other year.

The Caribbean reef shark infrequently attacks humans. In general, a shark attack on a human is behaviorally similar to an attack upon natural prey. A human is more susceptible to being attacked if the shark is cornered and feels that there is no escape route. In situations like these, the shark may rake the victim during the attack resulting in lacerations.
The Caribbean reef shark has an interdorsal ridge from the rear of the first dorsal fin to the front of the second dorsal fin. The second dorsal fin has a very short free rear tip. The snout of C. perezi is moderately short and broadly rounded. It has poorly developed, low anterior nasal flaps and relatively large circular eyes. Caribbean reef sharks also have moderately long gill slits with the third gill slit lying above the origin of the pectoral fin. Comparison to similar sharks:
During mating, the male grey reef shark will bite at the female's body or fins to hold onto her for copulation.[13] Like other requiem sharks, it is viviparous: once the developing embryos exhaust their supply of yolk, the yolk sac develops into a placental connection that sustains them to term. Each female has a single functional ovary (on the right side) and two functional uteruses. One to four pups (six in Hawaii) are born every other year; the number of young increases with female size. Estimates of the gestation period range from 9 to 14 months. Parturition is thought to take place from July to August in the Southern Hemisphere and from March to July in the Northern Hemisphere. However, females with "full-term embryos" have also been reported in the fall off Enewetak. The newborns measure 45–60 cm (18–24 in) long. Sexual maturation occurs at around seven years of age, when the males are 1.3–1.5 m (4.3–4.9 ft) long and females are 1.2–1.4 m (3.9–4.6 ft) long. Females on the Great Barrier Reef mature at 11 years of age, later than at other locations, and at a slightly larger size. The lifespan is at least 25 years.[4][20][24]
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