Gray reef shark
Encyclopedia
The grey reef shark is a species of requiem shark
, 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 reef
s. 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.
Grey reef sharks are fast-swimming, agile predators that feed primarily on free-swimming bony fishes and cephalopod
s. 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 5–20 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 that the mother nourishes her embryo
s through a placenta
l connection. Litters of 1–6 pups are born every other year.
Grey reef sharks were the first shark species known to perform a threat display
, a stereotyped behavior warning that it is prepared to attack. The display involves a "hunched" posture with characteristically dropped pectoral fins, and an exaggerated, side-to-side swimming motion. Grey reef sharks often do so if they are followed or cornered by divers to indicate that they perceive a threat. This species has been responsible for a number of attacks
on humans and should be treated with caution, especially if they begin to display. Grey reef sharks are caught in many fisheries and are susceptible to local population depletion due to their low reproduction rate and limited dispersal
. As a result, the International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
.
Dutch ichthyologist Pieter Bleeker
first described the grey reef shark in 1856 as Carcharias (Prionodon) amblyrhynchos, in the scientific journal
Natuurkundig Tijdschrift voor Nederlandsch-Indië. Later authors moved this species to the genus Carcharhinus. The type specimen was a 1.5 m (4.9 ft) long female from the Java Sea
. Other common name
s used for this shark around the world include black-vee whaler, bronze whaler, Fowler's whaler shark, graceful shark, graceful whaler shark, grey shark, grey whaler shark, longnose blacktail shark, school shark, and shortnose blacktail shark. Some of these names are also applied to other species.
In older literature, the scientific name of this species was often given as C. menisorrah. The blacktail reef shark (C. wheeleri), native to the western Indian Ocean, is now regarded as the same species as the grey reef shark by most authors. It was originally distinguished from the grey reef shark by a white tip on the first dorsal fin, a shorter snout, and one fewer upper tooth row on each side. Based on morphological
characters, vertebral counts, and tooth shapes, Garrick (1982) concluded that the grey reef shark is most closely related to the silvertip shark
(C. albimarginatus). This interpretation was supported by a 1992 allozyme
phylogenetic analysis by Lavery.
The grey reef shark is native to the Indian
and Pacific Ocean
s. In the Indian Ocean, it occurs from South Africa
to India
, including Madagascar
and nearby islands, the Red Sea
, and the Maldives
. In the Pacific Ocean
, it is found from southern China
to northern Australia
and New Zealand
, including the Gulf of Thailand
, the Philippines
, and Indonesia
. This species has also been reported from numerous Pacific islands, including American Samoa
, the Chagos Archipelago
, Easter Island
, Christmas Island
, the Cook Islands
, the Marquesas Islands
, the Tuamotu Archipelago, Guam
, Kiribati
, the Marshall Islands
, Micronesia
, Nauru
, New Caledonia
, the Marianas Islands, Palau
, the Pitcairn Islands
, Samoa
, the Solomon Islands
, Tuvalu
, the Hawaiian Islands
, and Vanuatu
.
Generally a coastal, shallow-water species, grey reef sharks are mostly found in depths of less than 60 m (196.9 ft). However, they have been known to dive to 1000 m (3,280.8 ft). They are found over continental and insular shelves, preferring the leeward (away from the direction of the current) sides of coral reefs with clear water and rugged topography. They are frequently found near the drop-offs at the outer edges of the reef, and less commonly within lagoon
s. On occasion, this shark may venture several kilometers out into the open ocean
.
The grey reef shark has a streamlined, moderately stout body with a long, blunt snout and large, round eyes. There are 13–14 tooth rows on each side of both jaws (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 (8.4 ft) and the maximum reported weight is 33.7 kg (74.3 lb).
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. Grey reef sharks actively expel most other shark species from favored habitats, even species that are larger in size. In areas where this species co-exists with the blacktip reef shark, the latter species occupy the shallow flats while the grey reef sharks stay in deeper water. Areas with a high abundance of grey reef sharks tend to contain few sandbar shark
s (C. plumbeus), and vice-versa; this may be due to their similar diets causing competitive exclusion.
On the infrequent occasions when they swim in oceanic waters, grey reef sharks often associate with marine mammal
s or large pelagic fish
es such as sailfish
(Istiophorus platypterus). There is an account of around 25 grey reef sharks following a large pod of bottlenose dolphin
s (Tursiops sp.), along with 25 silky shark
s (C. falciformis) and a single silvertip shark. Rainbow runner
s (Elagatis bipinnulata) have been observed rubbing against grey reef sharks, using the sharks' rough skin to scrape off parasites.
Grey reef sharks are prey for larger sharks such as the silvertip shark
. At Rangiroa Atoll in French Polynesia
, great hammerhead
s (Sphyrna mokarran) feed opportunistically on grey reef sharks that are exhausted from pursuing mates. Known parasites of this species include the nematode
Huffmanela lata and several copepod
species that attach to the sharks' skin, and juvenile stages of the isopods Gnathia trimaculata and G. grandilaris that attach to the gill
filaments and septa
(the dividers between each gill).
s such as squid
and octopus
being the second-most important food group, and crustaceans such as crab
s and lobster
s making up the remainder. The larger sharks take a greater proportion of cephalopods. Grey reef sharks hunt individually or in groups. They have been known to pin schools of fish against the outer walls of coral reefs for feeding. These sharks 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.
develops into a placenta
l connection that sustains them to term. Each female has a single functional ovary
(on the right side) and two functional uterus
es. 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 (16–24 in) long. Sexual maturation occurs at around 7 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.
Grey reef sharks are active at all times of the day, with activity levels peaking at night. 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. The home range of a grey reef shark is about 0.8 square kilometre. 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 nighttime home ranges. 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.
There is little evidence of territoriality in the grey reef shark; individuals will tolerate others of their species entering and feeding within their home ranges. Off Hawaii, individual grey reef sharks may stay around the same part of the reef for up to three years, while at Rangiroa they regularly shift their location by up to 15 km (9.3 mi). Individual grey reef sharks at Enewetak become highly aggressive at specific locations, suggesting that they may exhibit dominant behavior over other sharks in their home areas.
, female grey reef sharks form aggregations in shallow water from March to June. The number of sharks per group differs from year to year. Each day, the sharks begin arriving at the aggregation area at 9:00 A.M., reaching a peak in numbers during the hottest part of the day in the afternoon, and dispersing by 7:00 P.M. Individual sharks return to the aggregation site every one to six days. It is speculated that these female sharks are taking advantage of the warmer water to speed their growth or that of their embryos. The shallow waters may also enable them to avoid unwanted attention by males.
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 5–20 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.
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 there are obstacles 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 eel
s, and in one instance towards a much larger great hammerhead (which subsequently withdrew). However, grey reef sharks have never been seen performing threat displays towards each other. This suggests that 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.
, 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, grey reef sharks 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
lists 7 unprovoked and 6 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 International Union for Conservation of Nature (IUCN) has assessed the grey reef shark as Near Threatened
; this shark is taken by multi-species 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 that, in the Chagos Archipelago, grey reef shark numbers in 1996 had fallen to 14% of 1970s levels. Robbins et al.. (2006) found that 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 that 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.
Requiem shark
Requiem sharks are a family, Carcharhinidae, of sharks in the order Carcharhiniformes, containing migratory, live-bearing sharks of warm seas such as the tiger shark, the blue shark, the bull shark, and the milk shark.The name may be related to the French word for shark, "requin", itself of...
, family
Family (biology)
In biological classification, family is* a taxonomic rank. Other well-known ranks are life, domain, kingdom, phylum, class, order, genus, and species, with family fitting between order and genus. As for the other well-known ranks, there is the option of an immediately lower rank, indicated by the...
Carcharhinidae. One of the most common reef sharks in the Indo-Pacific
Indo-Pacific
The Indo-Pacific is a biogeographic region of the Earth's seas, comprising the tropical waters of the Indian Ocean, the western and central Pacific Ocean, and the seas connecting the two in the general area of Indonesia...
, it is found as far east as Easter Island
Easter Island
Easter Island is a Polynesian island in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian triangle. A special territory of Chile that was annexed in 1888, Easter Island is famous for its 887 extant monumental statues, called moai, created by the early Rapanui people...
and as far west as South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
. This species is most often seen in shallow water near the drop-offs of coral reef
Coral reef
Coral reefs are underwater structures made from calcium carbonate secreted by corals. Coral reefs are colonies of tiny living animals found in marine waters that contain few nutrients. Most coral reefs are built from stony corals, which in turn consist of polyps that cluster in groups. The polyps...
s. 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
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
, 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.
Grey reef sharks are fast-swimming, agile predators that feed primarily on free-swimming bony fishes and cephalopod
Cephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s. 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 5–20 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 that the mother nourishes her embryo
Embryo
An embryo is a multicellular diploid eukaryote in its earliest stage of development, from the time of first cell division until birth, hatching, or germination...
s through a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection. Litters of 1–6 pups are born every other year.
Grey reef sharks were the first shark species known to perform a threat display
Shark threat display
Shark threat display, a type of agonistic display, is a behaviour observed in some sharks when they feel threatened or protective. It consists of a contorting of the body into a series of "ritualized" postures coupled with an exaggerated swimming style...
, a stereotyped behavior warning that it is prepared to attack. The display involves a "hunched" posture with characteristically dropped pectoral fins, and an exaggerated, side-to-side swimming motion. Grey reef sharks often do so if they are followed or cornered by divers to indicate that they perceive a threat. This species has been responsible for a number of attacks
Shark attack
A shark attack is an attack on a human by a shark. Every year around 60 shark attacks are reported worldwide, although death is quite unusual. Despite the relative rarity of shark attacks, the fear of sharks is a common phenomenon, having been fueled by the occasional instances of serial attacks,...
on humans and should be treated with caution, especially if they begin to display. Grey reef sharks are caught in many fisheries and are susceptible to local population depletion due to their low reproduction rate and limited dispersal
Biological dispersal
Biological dispersal refers to species movement away from an existing population or away from the parent organism. Through simply moving from one habitat patch to another, the dispersal of an individual has consequences not only for individual fitness, but also for population dynamics, population...
. As a result, the International Union for Conservation of Nature (IUCN) has assessed this species as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
.
Taxonomy and phylogeny
Pieter Bleeker
Pieter Bleeker was a Dutch medical doctor and ichthyologist, famous for his work on the fishes of East Asia – Atlas Ichthyologique des Orientales Neerlandaises – which was published 1862–1877....
first described the grey reef shark in 1856 as Carcharias (Prionodon) amblyrhynchos, in the scientific journal
Scientific journal
In academic publishing, a scientific journal is a periodical publication intended to further the progress of science, usually by reporting new research. There are thousands of scientific journals in publication, and many more have been published at various points in the past...
Natuurkundig Tijdschrift voor Nederlandsch-Indië. Later authors moved this species to the genus Carcharhinus. The type specimen was a 1.5 m (4.9 ft) long female from the Java Sea
Java Sea
The Java Sea is a large shallow sea on the Sunda Shelf. It was formed as sea levels rose at the end of the last ice age. The Java Sea lies between the Indonesian islands of Borneo to the north, Java to the south; Sumatra to the west, and Sulawesi to the east...
. Other common name
Common name
A common name of a taxon or organism is a name in general use within a community; it is often contrasted with the scientific name for the same organism...
s used for this shark around the world include black-vee whaler, bronze whaler, Fowler's whaler shark, graceful shark, graceful whaler shark, grey shark, grey whaler shark, longnose blacktail shark, school shark, and shortnose blacktail shark. Some of these names are also applied to other species.
In older literature, the scientific name of this species was often given as C. menisorrah. The blacktail reef shark (C. wheeleri), native to the western Indian Ocean, is now regarded as the same species as the grey reef shark by most authors. It was originally distinguished from the grey reef shark by a white tip on the first dorsal fin, a shorter snout, and one fewer upper tooth row on each side. Based on morphological
Morphology (biology)
In biology, morphology is a branch of bioscience dealing with the study of the form and structure of organisms and their specific structural features....
characters, vertebral counts, and tooth shapes, Garrick (1982) concluded that the grey reef shark is most closely related to the silvertip shark
Silvertip shark
The silvertip shark is a large species of requiem shark, family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. This species is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m...
(C. albimarginatus). This interpretation was supported by a 1992 allozyme
Allozyme
Variant forms of an enzyme that are coded by different alleles at the same locus are called allozymes. These are opposed to isozymes, which are enzymes that perform the same function, but which are coded by genes located at different loci....
phylogenetic analysis by Lavery.
Distribution and habitat
Indian Ocean
The Indian Ocean is the third largest of the world's oceanic divisions, covering approximately 20% of the water on the Earth's surface. It is bounded on the north by the Indian Subcontinent and Arabian Peninsula ; on the west by eastern Africa; on the east by Indochina, the Sunda Islands, and...
and Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
s. In the Indian Ocean, it occurs from South Africa
South Africa
The Republic of South Africa is a country in southern Africa. Located at the southern tip of Africa, it is divided into nine provinces, with of coastline on the Atlantic and Indian oceans...
to India
India
India , officially the Republic of India , is a country in South Asia. It is the seventh-largest country by geographical area, the second-most populous country with over 1.2 billion people, and the most populous democracy in the world...
, including Madagascar
Madagascar
The Republic of Madagascar is an island country located in the Indian Ocean off the southeastern coast of Africa...
and nearby islands, the Red Sea
Red Sea
The Red Sea is a seawater inlet of the Indian Ocean, lying between Africa and Asia. The connection to the ocean is in the south through the Bab el Mandeb strait and the Gulf of Aden. In the north, there is the Sinai Peninsula, the Gulf of Aqaba, and the Gulf of Suez...
, and the Maldives
Maldives
The Maldives , , officially Republic of Maldives , also referred to as the Maldive Islands, is an island nation in the Indian Ocean formed by a double chain of twenty-six atolls oriented north-south off India's Lakshadweep islands, between Minicoy Island and...
. In the Pacific Ocean
Pacific Ocean
The Pacific Ocean is the largest of the Earth's oceanic divisions. It extends from the Arctic in the north to the Southern Ocean in the south, bounded by Asia and Australia in the west, and the Americas in the east.At 165.2 million square kilometres in area, this largest division of the World...
, it is found from southern China
China
Chinese civilization may refer to:* China for more general discussion of the country.* Chinese culture* Greater China, the transnational community of ethnic Chinese.* History of China* Sinosphere, the area historically affected by Chinese culture...
to northern Australia
Australia
Australia , officially the Commonwealth of Australia, is a country in the Southern Hemisphere comprising the mainland of the Australian continent, the island of Tasmania, and numerous smaller islands in the Indian and Pacific Oceans. It is the world's sixth-largest country by total area...
and New Zealand
New Zealand
New Zealand is an island country in the south-western Pacific Ocean comprising two main landmasses and numerous smaller islands. The country is situated some east of Australia across the Tasman Sea, and roughly south of the Pacific island nations of New Caledonia, Fiji, and Tonga...
, including the Gulf of Thailand
Gulf of Thailand
The Gulf of Thailand , also known in to Malays as Teluk Siam literally meant Gulf of Siam, is a shallow arm of the South China Sea.-Geography:...
, the Philippines
Philippines
The Philippines , officially known as the Republic of the Philippines , is a country in Southeast Asia in the western Pacific Ocean. To its north across the Luzon Strait lies Taiwan. West across the South China Sea sits Vietnam...
, and Indonesia
Indonesia
Indonesia , officially the Republic of Indonesia , is a country in Southeast Asia and Oceania. Indonesia is an archipelago comprising approximately 13,000 islands. It has 33 provinces with over 238 million people, and is the world's fourth most populous country. Indonesia is a republic, with an...
. This species has also been reported from numerous Pacific islands, including American Samoa
American Samoa
American Samoa is an unincorporated territory of the United States located in the South Pacific Ocean, southeast of the sovereign state of Samoa...
, the Chagos Archipelago
Chagos Archipelago
The Chagos Archipelago , is a group of seven atolls comprising more than 60 individual tropical islands in the Indian Ocean; situated some due south of the Maldives archipelago. This chain of islands are the southernmost archipelago of the Chagos-Laccadive Ridge a long submarine mountain range...
, Easter Island
Easter Island
Easter Island is a Polynesian island in the southeastern Pacific Ocean, at the southeasternmost point of the Polynesian triangle. A special territory of Chile that was annexed in 1888, Easter Island is famous for its 887 extant monumental statues, called moai, created by the early Rapanui people...
, Christmas Island
Christmas Island
The Territory of Christmas Island is a territory of Australia in the Indian Ocean. It is located northwest of the Western Australian city of Perth, south of the Indonesian capital, Jakarta, and ENE of the Cocos Islands....
, the Cook Islands
Cook Islands
The Cook Islands is a self-governing parliamentary democracy in the South Pacific Ocean in free association with New Zealand...
, the Marquesas Islands
Marquesas Islands
The Marquesas Islands enana and Te Fenua `Enata , both meaning "The Land of Men") are a group of volcanic islands in French Polynesia, an overseas collectivity of France in the southern Pacific Ocean. The Marquesas are located at 9° 00S, 139° 30W...
, the Tuamotu Archipelago, Guam
Guam
Guam is an organized, unincorporated territory of the United States located in the western Pacific Ocean. It is one of five U.S. territories with an established civilian government. Guam is listed as one of 16 Non-Self-Governing Territories by the Special Committee on Decolonization of the United...
, Kiribati
Kiribati
Kiribati , officially the Republic of Kiribati, is an island nation located in the central tropical Pacific Ocean. The permanent population exceeds just over 100,000 , and is composed of 32 atolls and one raised coral island, dispersed over 3.5 million square kilometres, straddling the...
, the Marshall Islands
Marshall Islands
The Republic of the Marshall Islands , , is a Micronesian nation of atolls and islands in the middle of the Pacific Ocean, just west of the International Date Line and just north of the Equator. As of July 2011 the population was 67,182...
, Micronesia
Micronesia
Micronesia is a subregion of Oceania, comprising thousands of small islands in the western Pacific Ocean. It is distinct from Melanesia to the south, and Polynesia to the east. The Philippines lie to the west, and Indonesia to the southwest....
, Nauru
Nauru
Nauru , officially the Republic of Nauru and formerly known as Pleasant Island, is an island country in Micronesia in the South Pacific. Its nearest neighbour is Banaba Island in Kiribati, to the east. Nauru is the world's smallest republic, covering just...
, New Caledonia
New Caledonia
New Caledonia is a special collectivity of France located in the southwest Pacific Ocean, east of Australia and about from Metropolitan France. The archipelago, part of the Melanesia subregion, includes the main island of Grande Terre, the Loyalty Islands, the Belep archipelago, the Isle of...
, the Marianas Islands, Palau
Palau
Palau , officially the Republic of Palau , is an island nation in the Pacific Ocean, east of the Philippines and south of Tokyo. In 1978, after three decades as being part of the United Nations trusteeship, Palau chose independence instead of becoming part of the Federated States of Micronesia, a...
, the Pitcairn Islands
Pitcairn Islands
The Pitcairn Islands , officially named the Pitcairn, Henderson, Ducie and Oeno Islands, form a group of four volcanic islands in the southern Pacific Ocean. The islands are a British Overseas Territory and overseas territory of the European Union in the Pacific...
, Samoa
Samoa
Samoa , officially the Independent State of Samoa, formerly known as Western Samoa is a country encompassing the western part of the Samoan Islands in the South Pacific Ocean. It became independent from New Zealand in 1962. The two main islands of Samoa are Upolu and one of the biggest islands in...
, the Solomon Islands
Solomon Islands
Solomon Islands is a sovereign state in Oceania, east of Papua New Guinea, consisting of nearly one thousand islands. It covers a land mass of . The capital, Honiara, is located on the island of Guadalcanal...
, Tuvalu
Tuvalu
Tuvalu , formerly known as the Ellice Islands, is a Polynesian island nation located in the Pacific Ocean, midway between Hawaii and Australia. Its nearest neighbours are Kiribati, Nauru, Samoa and Fiji. It comprises four reef islands and five true atolls...
, the Hawaiian Islands
Hawaiian Islands
The Hawaiian Islands are an archipelago of eight major islands, several atolls, numerous smaller islets, and undersea seamounts in the North Pacific Ocean, extending some 1,500 miles from the island of Hawaii in the south to northernmost Kure Atoll...
, and Vanuatu
Vanuatu
Vanuatu , officially the Republic of Vanuatu , is an island nation located in the South Pacific Ocean. The archipelago, which is of volcanic origin, is some east of northern Australia, northeast of New Caledonia, west of Fiji, and southeast of the Solomon Islands, near New Guinea.Vanuatu was...
.
Generally a coastal, shallow-water species, grey reef sharks are mostly found in depths of less than 60 m (196.9 ft). However, they have been known to dive to 1000 m (3,280.8 ft). They are found over continental and insular shelves, preferring the leeward (away from the direction of the current) sides of coral reefs with clear water and rugged topography. They are frequently found near the drop-offs at the outer edges of the reef, and less commonly within lagoon
Lagoon
A lagoon is a body of shallow sea water or brackish water separated from the sea by some form of barrier. The EU's habitat directive defines lagoons as "expanses of shallow coastal salt water, of varying salinity or water volume, wholly or partially separated from the sea by sand banks or shingle,...
s. On occasion, this shark may venture several kilometers out into the open ocean
Pelagic zone
Any water in a sea or lake that is not close to the bottom or near to the shore can be said to be in the pelagic zone. The word pelagic comes from the Greek πέλαγος or pélagos, which means "open sea". The pelagic zone can be thought of in terms of an imaginary cylinder or water column that goes...
.
Description
Dorsal fin
A dorsal fin is a fin located on the backs of various unrelated marine and freshwater vertebrates, including most fishes, marine mammals , and the ichthyosaurs...
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
Sun tanning
Sun tanning or simply tanning is the process whereby skin color is darkened or tanned. The process is most often a result of exposure to ultraviolet radiation from the sun or from artificial sources, such as a tanning bed, but can also be a result of windburn or reflected light...
. Most grey reef sharks are less than 1.9 m (6.2 ft) long. The maximum reported length is 2.6 m (8.4 ft) and the maximum reported weight is 33.7 kg (74.3 lb).
Biology and ecology
Blacktip reef shark
The blacktip reef shark is a species of requiem shark, family Carcharhinidae, easily identified by the prominent black tips on its fins...
(C. melanopterus) and the whitetip reef shark
Whitetip reef shark
The whitetip reef shark is a species of requiem shark, family Carcharhinidae, and the only member of its genus. A small shark usually not exceeding in length, this species is easily recognizable by its slender body and short but broad head, as well as tubular skin flaps beside the nostrils, oval...
(Triaenodon obesus), the grey reef shark is one of the three most common sharks inhabiting Indo-Pacific reefs. Grey reef sharks actively expel most other shark species from favored habitats, even species that are larger in size. In areas where this species co-exists with the blacktip reef shark, the latter species occupy the shallow flats while the grey reef sharks stay in deeper water. Areas with a high abundance of grey reef sharks tend to contain few sandbar shark
Sandbar shark
The sandbar shark, Carcharhinus plumbeus, is a species of requiem shark, family Carcharhinidae, native to the Atlantic Ocean and the Indo-Pacific. It is distinguishable by its very high first dorsal fin and inter-dorsal ridge....
s (C. plumbeus), and vice-versa; this may be due to their similar diets causing competitive exclusion.
On the infrequent occasions when they swim in oceanic waters, grey reef sharks often associate with marine mammal
Marine mammal
Marine mammals, which include seals, whales, dolphins, and walruses, form a diverse group of 128 species that rely on the ocean for their existence. They do not represent a distinct biological grouping, but rather are unified by their reliance on the marine environment for feeding. The level of...
s or large pelagic fish
Pelagic fish
Pelagic fish live near the surface or in the water column of coastal, ocean and lake waters, but not on the bottom of the sea or the lake. They can be contrasted with demersal fish, which do live on or near the bottom, and reef fish which are associated with coral reefs.The marine pelagic...
es such as sailfish
Sailfish
'Sailfish' are two species of fish in the genus Istiophorus, living in warmer sections of all the oceans of the world. They are predominately blue to gray in color and have a characteristic erectile dorsal fin known as a sail, which often stretches the entire length of the back...
(Istiophorus platypterus). There is an account of around 25 grey reef sharks following a large pod of bottlenose dolphin
Bottlenose Dolphin
Bottlenose dolphins, the genus Tursiops, are the most common and well-known members of the family Delphinidae, the family of oceanic dolphins. Recent molecular studies show the genus contains two species, the common bottlenose dolphin and the Indo-Pacific bottlenose dolphin , instead of one...
s (Tursiops sp.), along with 25 silky shark
Silky shark
The silky shark is a species of requiem shark, family Carcharhinidae, named for the smooth texture of its skin. It is one of the most abundant sharks in the pelagic zone, and can be found around the world in tropical waters. Highly mobile and migratory, this shark is most often found over the edge...
s (C. falciformis) and a single silvertip shark. Rainbow runner
Rainbow runner
The rainbow runner , also known as the rainbow yellowtail, Spanish jack and Hawaiian salmon, is a common species of pelagic marine fish of the jack family, Carangidae. The species is widespread throughout the tropical and subtropical waters of the world, inhabiting both coastal as well as far...
s (Elagatis bipinnulata) have been observed rubbing against grey reef sharks, using the sharks' rough skin to scrape off parasites.
Grey reef sharks are prey for larger sharks such as the silvertip shark
Silvertip shark
The silvertip shark is a large species of requiem shark, family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. This species is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of 800 m...
. At Rangiroa Atoll in French Polynesia
French Polynesia
French Polynesia is an overseas country of the French Republic . It is made up of several groups of Polynesian islands, the most famous island being Tahiti in the Society Islands group, which is also the most populous island and the seat of the capital of the territory...
, great hammerhead
Great hammerhead
The great hammerhead is the largest species of hammerhead shark, family Sphyrnidae, attaining a maximum length of 6.1 m . It is found in tropical and warm temperate waters worldwide, inhabiting coastal areas and the continental shelf...
s (Sphyrna mokarran) feed opportunistically on grey reef sharks that are exhausted from pursuing mates. Known parasites of this species include the nematode
Nematode
The nematodes or roundworms are the most diverse phylum of pseudocoelomates, and one of the most diverse of all animals. Nematode species are very difficult to distinguish; over 28,000 have been described, of which over 16,000 are parasitic. It has been estimated that the total number of nematode...
Huffmanela lata and several copepod
Copepod
Copepods are a group of small crustaceans found in the sea and nearly every freshwater habitat. Some species are planktonic , some are benthic , and some continental species may live in limno-terrestrial habitats and other wet terrestrial places, such as swamps, under leaf fall in wet forests,...
species that attach to the sharks' skin, and juvenile stages of the isopods Gnathia trimaculata and G. grandilaris that attach to the gill
Gill
A gill is a respiratory organ found in many aquatic organisms that extracts dissolved oxygen from water, afterward excreting carbon dioxide. The gills of some species such as hermit crabs have adapted to allow respiration on land provided they are kept moist...
filaments and septa
Septum
In anatomy, a septum is a wall, dividing a cavity or structure into smaller ones.-In human anatomy:...
(the dividers between each gill).
Feeding
Grey reef sharks feed mainly on bony fishes, with cephalopodCephalopod
A cephalopod is any member of the molluscan class Cephalopoda . These exclusively marine animals are characterized by bilateral body symmetry, a prominent head, and a set of arms or tentacles modified from the primitive molluscan foot...
s such as squid
Squid
Squid are cephalopods of the order Teuthida, which comprises around 300 species. Like all other cephalopods, squid have a distinct head, bilateral symmetry, a mantle, and arms. Squid, like cuttlefish, have eight arms arranged in pairs and two, usually longer, tentacles...
and octopus
Octopus
The octopus is a cephalopod mollusc of the order Octopoda. Octopuses have two eyes and four pairs of arms, and like other cephalopods they are bilaterally symmetric. An octopus has a hard beak, with its mouth at the center point of the arms...
being the second-most important food group, and crustaceans such as crab
Crab
True crabs are decapod crustaceans of the infraorder Brachyura, which typically have a very short projecting "tail" , or where the reduced abdomen is entirely hidden under the thorax...
s and lobster
Lobster
Clawed lobsters comprise a family of large marine crustaceans. Highly prized as seafood, lobsters are economically important, and are often one of the most profitable commodities in coastal areas they populate.Though several groups of crustaceans are known as lobsters, the clawed lobsters are most...
s making up the remainder. The larger sharks take a greater proportion of cephalopods. Grey reef sharks hunt individually or in groups. They have been known to pin schools of fish against the outer walls of coral reefs for feeding. These sharks 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
Olfaction
Olfaction is the sense of smell. This sense is mediated by specialized sensory cells of the nasal cavity of vertebrates, and, by analogy, sensory cells of the antennae of invertebrates...
is extremely acute, being capable of detecting one part tuna
Tuna
Tuna is a salt water fish from the family Scombridae, mostly in the genus Thunnus. Tuna are fast swimmers, and some species are capable of speeds of . Unlike most fish, which have white flesh, the muscle tissue of tuna ranges from pink to dark red. The red coloration derives from myoglobin, an...
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
Feeding frenzy
In ecology, a feeding frenzy is a situation where oversaturation of a supply of food leads to rapid feeding by predatory animals. For example, a large school of fish can cause nearby sharks to enter a feeding frenzy. This can cause the sharks to go wild, biting anything that moves, including each...
; in one documented frenzy caused by an underwater explosion that killed several snappers
Lutjanidae
Snappers are a family of perciform fish, mainly marine but with some members inhabiting estuaries, feeding in freshwater. Some are important food fish. One of the best known is the red snapper....
, one of the sharks involved was attacked and consumed by the others.
Life history
During mating, male grey reef sharks will bite at the female's body or fins to hold onto her for copulation. Like other requiem sharks, the grey reef shark is viviparous: once the developing embryos exhaust their supply of yolk, the yolk sacYolk sac
The yolk sac is a membranous sac attached to an embryo, providing early nourishment in the form of yolk in bony fishes, sharks, reptiles, birds, and primitive mammals...
develops into a placenta
Placenta
The placenta is an organ that connects the developing fetus to the uterine wall to allow nutrient uptake, waste elimination, and gas exchange via the mother's blood supply. "True" placentas are a defining characteristic of eutherian or "placental" mammals, but are also found in some snakes and...
l connection that sustains them to term. Each female has a single functional ovary
Ovary
The ovary is an ovum-producing reproductive organ, often found in pairs as part of the vertebrate female reproductive system. Ovaries in anatomically female individuals are analogous to testes in anatomically male individuals, in that they are both gonads and endocrine glands.-Human anatomy:Ovaries...
(on the right side) and two functional uterus
Uterus
The uterus or womb is a major female hormone-responsive reproductive sex organ of most mammals including humans. One end, the cervix, opens into the vagina, while the other is connected to one or both fallopian tubes, depending on the species...
es. 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
Gestation period
For mammals the gestation period is the time in which a fetus develops, beginning with fertilization and ending at birth. The duration of this period varies between species.-Duration:...
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
Enewetak
Enewetak Atoll is a large coral atoll of 40 islands in the Pacific Ocean, and forms a legislative district of the Ralik Chain of the Marshall Islands. Its land area totals less than , surrounding a deep central lagoon, in circumference...
. The newborns measure 45–60 cm (16–24 in) long. Sexual maturation occurs at around 7 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
Great Barrier Reef
The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
mature at 11 years of age, later than at other locations, and at a slightly larger size. The lifespan is at least 25 years.
Behavior
Enewetak
Enewetak Atoll is a large coral atoll of 40 islands in the Pacific Ocean, and forms a legislative district of the Ralik Chain of the Marshall Islands. Its land area totals less than , surrounding a deep central lagoon, in circumference...
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 nighttime home ranges. 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.
There is little evidence of territoriality in the grey reef shark; individuals will tolerate others of their species entering and feeding within their home ranges. Off Hawaii, individual grey reef sharks may stay around the same part of the reef for up to three years, while at Rangiroa they regularly shift their location by up to 15 km (9.3 mi). Individual grey reef sharks at Enewetak become highly aggressive at specific locations, suggesting that they may exhibit dominant behavior over other sharks in their home areas.
Sociality
Social aggregation is well documented in grey reef sharks. In the northwestern Hawaiian Islands, large numbers of pregnant adult females have been observed slowly swimming in circles in shallow water, occasionally exposing their dorsal fins or backs. These groups last from 11:00 A.M. to 3:00 P.M., corresponding to peak daylight hours. Similarly, at Sand Island off Johnston AtollJohnston Atoll
Johnston Atoll is a atoll in the North Pacific Ocean about west of Hawaii. There are four islands located on the coral reef platform, two natural islands, Johnston Island and Sand Island, which have been expanded by coral dredging, as well as North Island and East Island , an additional two...
, female grey reef sharks form aggregations in shallow water from March to June. The number of sharks per group differs from year to year. Each day, the sharks begin arriving at the aggregation area at 9:00 A.M., reaching a peak in numbers during the hottest part of the day in the afternoon, and dispersing by 7:00 P.M. Individual sharks return to the aggregation site every one to six days. It is speculated that these female sharks are taking advantage of the warmer water to speed their growth or that of their embryos. The shallow waters may also enable them to avoid unwanted attention by males.
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 5–20 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.
Threat display
Shark threat display
Shark threat display, a type of agonistic display, is a behaviour observed in some sharks when they feel threatened or protective. It consists of a contorting of the body into a series of "ritualized" postures coupled with an exaggerated swimming style...
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 there are obstacles 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
Submersible
A submersible is a small vehicle designed to operate underwater. The term submersible is often used to differentiate from other underwater vehicles known as submarines, in that a submarine is a fully autonomous craft, capable of renewing its own power and breathing air, whereas a submersible is...
) approaching and following it from a few meters behind and above. They also perform the display towards moray eel
Moray eel
Moray eels are cosmopolitan eels of the family Muraenidae. The approximately 200 species in 15 genera are almost exclusively marine, but several species are regularly seen in brackish water and a few, for example the freshwater moray can sometimes be found in freshwater...
s, and in one instance towards a much larger great hammerhead (which subsequently withdrew). However, grey reef sharks have never been seen performing threat displays towards each other. This suggests that 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.
Human interactions
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 spearfishersSpearfishing
Spearfishing is an ancient method of fishing that has been used throughout the world for millennia. Early civilizations were familiar with the custom of spearing fish from rivers and streams using sharpened sticks....
, 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, grey reef sharks 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
International Shark Attack File
The International Shark Attack File is a global database of shark attacks. It began as an attempt to catalogue shark attacks on servicemen during World War II. The Office of Naval Research funded it from 1958 until 1968. During that time a panel of shark experts developed a standard system for...
lists 7 unprovoked and 6 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 International Union for Conservation of Nature (IUCN) has assessed the grey reef shark as Near Threatened
Near Threatened
Near Threatened is a conservation status assigned to species or lower taxa that may be considered threatened with extinction in the near future, although it does not currently qualify for the threatened status...
; this shark is taken by multi-species fisheries in many parts of its range and used for various products such as shark fin soup
Shark fin soup
Shark fin soup is a popular soup item of Chinese cuisine usually served at special occasions such as weddings and banquets, or as a luxury item in Chinese culture. The shark fins provide texture while the taste comes from the other soup ingredients.There is controversy over the practice of shark...
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 that, in the Chagos Archipelago, grey reef shark numbers in 1996 had fallen to 14% of 1970s levels. Robbins et al.. (2006) found that grey reef shark populations in Great Barrier Reef
Great Barrier Reef
The Great Barrier Reef is the world'slargest reef system composed of over 2,900 individual reefs and 900 islands stretching for over 2,600 kilometres over an area of approximately...
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
Poaching
Poaching is the illegal taking of wild plants or animals contrary to local and international conservation and wildlife management laws. Violations of hunting laws and regulations are normally punishable by law and, collectively, such violations are known as poaching.It may be illegal and in...
. Projections suggested that 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
Ecotourism
Ecotourism is a form of tourism visiting fragile, pristine, and usually protected areas, intended as a low impact and often small scale alternative to standard commercial tourism...
, as grey reef sharks are suitable for shark-watching ventures and profitable diving sites now enjoy protection in many countries, such as the Maldives.