Grey Reef Shark

Grey Reef Shark's description

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). The coloration is grey above, sometimes with a bronze sheen, and white below. The entire rear margin of the caudal fin has a distinctive, broad, black band. There are dusky to black tips on the pectoral, pelvic, second dorsal, and anal fins. Individuals from the western Indian Ocean have a narrow, white margin at the tip of the first dorsal fin; this trait is usually absent from Pacific populations. Grey reef sharks that spend time in shallow water eventually darken in color, due to tanning. Most grey reef sharks are less than 1.9 m (6.2 ft) long. The maximum reported length is 2.6 m (8.5 ft) and the maximum reported weight is 33.7 kg (74 lb).

Grey Reef Shark's facts

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Grey reef shark can reach 5 to 6.6 feet in length and 29 to 33 kg in weight.
Grey reef sharks are usually grey in color. Those that live in shallow water have darker skin due to tanning.
Grey reef shark has elongated body, rounded snout and large eyes.
Grey reef sharks have triangular, serrated and very sharp teeth. They usually have 14 teeth in the upper jaw and 13 in the lower jaw.
Grey reef shark swims slowly most of the time, but it can achieve the speed of 25 miles per hour when chasing the prey.
Grey reef sharks are active throughout the whole day. They reach the peak of activity at night.
Grey reef sharks are active predators and true carnivores (meat-eaters). They hunt and eat different types of fish, crabs and squids.
Grey reef sharks have excellent sense of smell. They can smell tuna fish in 10 billionth part of the water.
Main predators of grey reef sharks are humans and large sharks.
Grey reef sharks occasionally attack people. Most attacks happened during the feeding time, when sharks become overexcited.
Grey reef shark shows specific behavior when it is threatened. It swims side to side with arched back, raised head and dropped pectoral fins. This unusual tactic serves to intimidate the opponent and it is often displayed in front of the divers.
Grey reef sharks gather in groups of 10 to 20 animals during the day, but they generally prefer solitary life. They hunt on their own during the night.
Males attain sexual maturity when they reach the length of 4.3 to 4.9 feet. Females become sexually mature at the length of 3.9 to 4.6 feet. This happens usually at the age of 5 to 7 years.
Males are very aggressive during the mating. They bite females and hold them tight with their sharp teeth during insemination. Pregnancy lasts from 9 to 14 months (usually 12) and ends with 1 to 4 pups. Females are viviparous (they give birth to live babies).
Grey reef shark can survive up to 25 years in the wild.

Grey Reef Shark's Behavior & Ecology

This is a very social species, often seen building “schools” of more than 100. They are active both during the day as well as at night. Social hierarchies and dominance varies depending on the habitat of various shark populations, but a social structure is almost always apparent. Because they are larger than most other species of Reef Shark, they are considered the most dominant species in the sensitive reef ecosystem.

Threat display

The "hunch" threat display of the grey reef shark is the most pronounced and well-known agonistic display (a display directed towards competitors or threats) of any shark. Investigations of this behavior have been focused on the reaction of sharks to approaching divers, some of which have culminated in attacks. The display consists of the shark raising its snout, dropping its pectoral fins, arching its back, and curving its body laterally. While holding this posture, the shark swims with a stiff, exaggerated side-to-side motion, sometimes combined with rolls or figure-8 loops. The intensity of the display increases if the shark is more closely approached or if obstacles are blocking its escape routes, such as landmarks or other sharks. If the diver persists, the shark will either retreat or launch a rapid open-mouthed attack, slashing with its upper teeth. Most observed displays by grey reef sharks have been in response to a diver (or submersible) approaching and following it from a few meters behind and above. They also perform the display towards moray eels, and in one instance towards a much larger great hammerhead (which subsequently withdrew). However, they have never been seen performing threat displays towards each other. This suggests the display is primarily a response to potential threats (i.e. predators) rather than competitors. As grey reef sharks are not territorial, they are speculated to be defending a critical volume of "personal space" around themselves. Compared to sharks from French Polynesia or Micronesia, grey reef sharks from the Indian Ocean and western Pacific are not as aggressive and less given to displaying.

Grey Reef Shark's Feeding

Grey reef sharks feed mainly on bony fishes, with cephalopods such as squid and octopus being the second-most important food group, and crustaceans such as crabs and lobsters making up the remainder. The larger sharks take a greater proportion of cephalopods. These sharks hunt individually or in groups, and have been known to pin schools of fish against the outer walls of coral reefs for feeding. They excel at capturing fish swimming in the open, and they complement hunting whitetip reef sharks, which are more adept at capturing fish inside caves and crevices. Their sense of smell is extremely acute, being capable of detecting one part tuna extract in 10 billion parts of sea water. In the presence of a large quantity of food, grey reef sharks may be roused into a feeding frenzy; in one documented frenzy caused by an underwater explosion that killed several snappers, one of the sharks involved was attacked and consumed by the others.

Grey Reef Shark's Reproduction

During mating, the male grey reef shark will bite at the female's body or fins to hold onto her for copulation. 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.

Grey Reef Shark's Conservation

Grey reef shark is protected species in maldives.

Grey Reef Shark's Relationship with Humans

The grey reef shark and human beings have an interesting relationship. The sharks are valued for their fins, which are used for food items such as shark fin soup. However, this shark species is usually out of the range of commercial shark fisheries. Grey reef sharks are often curious about divers when they first enter the water and may approach quite closely, though they lose interest on repeat dives. They can become dangerous in the presence of food, and tend to be more aggressive if encountered in open water rather than on the reef. There have been several known attacks on spearfishers, possibly by mistake, when the shark struck at the speared fish close to the diver. This species will also attack if pursued or cornered, and divers should immediately retreat (slowly and always facing the shark) if it begins to perform a threat display. Photographing the display should not be attempted, as the flash from a camera is known to have incited at least one attack. Although of modest size, they are capable of inflicting significant damage: during one study of the threat display, a grey reef shark attacked the researchers' submersible multiple times, leaving tooth marks in the plastic windows and biting off one of the propellers. The shark consistently launched its attacks from a distance of 6 m (20 ft), which it was able to cover in a third of a second. As of 2008, the International Shark Attack File listed seven unprovoked and six provoked attacks (none of them fatal) attributable to this species. 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. 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. 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. 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.

Grey Reef Shark habitat

The species is found in clear tropical waters often from 10 m to more than 50 m around coral reefs, particularly near drop-offs and passes of fringing reefs. It is more common at ancient atolls, and less common at high profile islands with extensive human habitation, or in turbid continental waters (Randall 1986, Wetherbee et al. 1997). At unexploited sites Grey Reef Sharks are one of the most common tropical reef sharks that may be found in groups or individually. Potentially dangerous when harassed, they have been shown to display stereotypical threats (Johnson and Nelson 1973, Nelson 1981, Randall 1986). Divers are advised to keep their distance and not take strobe photographs when sharks display erratic swimming.

Males mature at 120-140 cm total length (TL) and attain a size of 185 cm; females mature at about 125 cm TL and attain 190 cm (Wetherbee et al. 1997) at about seven years. Litters are small, up to six embryos (Compagno 1984b, Last and Stevens 1994, Wetherbee et al. 1997). Seasonality is uncertain because of limited data. Parturition may be in August with a nine month gestation possible in the southern hemisphere (Stevens and McLoughlin 1991). Mating and fertilisation take place in March-May (or July). Pupping appears to occur from March to July off Hawaii, suggesting a 12 month gestation, but females reproduce every other year (Wetherbee et al. 1997). Fishes form the bulk of the prey while squids, octopuses and crustaceans are less important food items (Salini et al. 1992, Wetherbee et al. 1997).

Grey Reef Shark threats

This shark shows high site fidelity and some local populations have been severely depleted by modest fishing pressure, as has been shown off Hawaii (Wetherbee et al. 1997). Very marked declines of sharks, including Grey Reef Sharks, have been reported in the Chagos Archipelago (Indian Ocean) between the 1970s and 1996. Shark numbers here were reduced to only 14% of the numbers found in the 1970s (Anderson et al. 1998). The quality of its coral reef habitat is threatened in many parts of the world.

Species Details

Details of Grey Reef Shark will be displayed below