Grey reef shark

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Grey reef shark
Scientific classification Edit this classification
Domain: Eukaryota
Kingdom: Animalia
Phylum: Chordata
Class: Chondrichthyes
Subclass: Elasmobranchii
Subdivision: Selachimorpha
Order: Carcharhiniformes
Family: Carcharhinidae
Genus: Carcharhinus
Species:
C. amblyrhynchos
Binomial name
Carcharhinus amblyrhynchos
(Bleeker, 1856)
Range of the grey reef shark
Synonyms

Carcharias amblyrhynchos Bleeker, 1856
Carcharias menisorrah* Müller & Henle, 1839
Carcharias nesiotes Snyder, 1904
Carcharhinus wheeleri Garrick, 1982
Galeolamna coongoola Whitley, 1964
*ambiguous synonym

The grey reef shark or gray reef shark (Carcharhinus amblyrhynchos, sometimes misspelled amblyrhynchus or amblyrhinchos)

tail fin
, and the lack of a ridge between the dorsal fins. Most individuals are less than 1.88 m (6.2 ft) long.

The grey reef shark is a fast-swimming, agile

viviparous, meaning the mother nourishes her embryos through a placental
connection. Litters of one to six pups are born every other year.

The grey reef shark was the first shark species known to perform a

fisheries and is susceptible to local population depletion due to its low reproduction rate and limited dispersal. As a result, the International Union for Conservation of Nature
has assessed this species as endangered.

Taxonomy and phylogeny

Dutch

type specimen was a 1.5 metres (4.9 ft)-long female from the Java Sea.[4] Other common names 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.[2]

In older literature, the scientific name of this species was often given as C. menisorrah.

phylogenetic analysis by Lavery.[8]

Description

Identifying features of the grey reef shark include dark edges on all fins except for the first dorsal fin.

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

pectoral fins are narrow and falcate (sickle-shaped).[4]

The coloration is grey above, sometimes with a bronze sheen, and white below. The entire rear margin of the

anal fins.[9] 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.[5] Grey reef sharks that spend time in shallow water eventually darken in color, due to tanning.[10] Most grey reef sharks are less than 1.9 m (6.2 ft) long.[4] The maximum reported length is 2.6 m (8.5 ft) and the maximum reported weight is 33.7 kg (74 lb).[9]

Distribution and habitat

Photo of shark swimming next to large, brightly colored coral head
Coral reef drop-offs are favored habitat for grey reef sharks.

The grey reef shark is native to the

Marianas Islands, Palau, the Pitcairn Islands, Samoa, the Solomon Islands, Tuvalu, the Hawaiian Islands, and Vanuatu.[1]

Generally a coastal, shallow-water species, grey reef sharks are mostly found in depths less than 60 m (200 ft).[11] However, they have been known to dive to 1,000 m (3,300 ft).[2] 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, particularly near reef channels with strong currents,[12] and less commonly within lagoons. On occasion, this shark may venture several kilometers out into the open ocean.[4][11]

Biology and ecology

Photo of long-finned shark, swimming
A female grey reef shark off Wake Island - this species is one of the most common sharks on Indo-Pacific reefs.

Along with the

competitive exclusion.[11] The consumptive influence of grey reef sharks on reef fish communities is likely to vary depending on whether sharks forage within the reef environment, or on pelagic resources (like they have been observed to do at Palmyra Atoll).[13]

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). One account has 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.[14] Rainbow runners (Elagatis bipinnulata) have been observed rubbing against grey reef sharks, using the sharks' rough skin to scrape off parasites.[15]

Grey reef sharks are themselves prey for larger sharks, such as the

isopods Gnathia trimaculata and G. grandilaris that attach to the gill filaments and septa (the dividers between each gill).[19][20]

Feeding

The lower teeth of the grey reef shark are narrower than upper teeth.

Grey reef sharks feed mainly on bony fishes, with

smell is extremely acute, being capable of detecting one part tuna extract in 10 billion parts of sea water.[14] 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.[24]

Life history

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

Sexual maturation occurs 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][21][25]

Behavior

Photo of shark in twilit waters with coral head in background
Grey reef sharks become more active as night approaches.

Grey reef sharks are active at all times of the day, with activity levels peaking at night.

tidal currents occur, grey reef sharks move against the water, toward 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.[26]

Little evidence of

territoriality is seen in the grey reef shark; individuals tolerate others of their species entering and feeding within their home ranges.[28] Off Hawaii, individuals may stay around the same part of the reef up to three years,[29] while at Rangiroa, they regularly shift their locations up to 15 km (9.3 mi).[28] Individual grey reef sharks at Enewetak become highly aggressive at specific locations, suggesting they may exhibit dominant behavior over other sharks in their home areas.[3]

Sociality

Photo of dozens of sharks swimming in shallow water over pink coral
Grey reef sharks often group together during the day, such as this aggregation at Kure Atoll in the Hawaiian Islands.

Social aggregation is well documented in grey reef sharks. In the northwestern Hawaiian Islands, large numbers of pregnant females have been observed slowly swimming in circles in shallow water, occasionally exposing their dorsal fins or backs. These groups last from 11:00 to 15:00, corresponding to peak daylight hours.[29] Similarly, at Sand Island off Johnston Atoll, females 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 09:00, reaching a peak in numbers during the hottest part of the day in the afternoon, and dispersing by 19:00. Individual sharks return to the aggregation site every one to six days. These female sharks are speculated to be 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.[10]

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.[26][27]

Threat display

Drawings showing threatening and nonthreatening postures from front and side underlain with a line that is jagged and red on the left and gently curving and blue on the right
The posture of a grey reef shark during normal swimming (right) and a threat display (left) - the bottom line shows the shark's swimming pattern.

The "hunch"

agonistic display (a display directed toward 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 may either retreat or launch a rapid, open-mouthed attack, slashing with its upper teeth.[3]

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 toward moray eels, and in one instance toward a much larger great hammerhead (which subsequently withdrew). However, they have never been seen performing threat displays toward 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 thought 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.[3]

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.[4] 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.[14] 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.[4] Photographing the display should not be attempted, as the flash from a camera is known to have incited at least one attack.[3] 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.[15] As of 2008, the International Shark Attack File listed seven unprovoked and six provoked attacks (none of them fatal) attributable to this species.[30]

Although still abundant in 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

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.[31] 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.[32] 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]

References

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    doi:10.2305/IUCN.UK.2020-3.RLTS.T39365A173433550.en. Retrieved 19 November 2021.{{cite journal}}: CS1 maint: multiple names: authors list (link
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  7. ^ Garrick, J.A.F. (1982). Sharks of the genus Carcharhinus. NOAA Technical Report, NMFS Circ. 445.
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  9. ^ a b c d Bester, C. Biological Profiles: Grey Reef Shark Archived 2008-06-04 at the Wayback Machine. Florida Museum of Natural History Ichthyology Department. Retrieved on April 29, 2009.
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  12. ^ Dianne J. Bray, 2011, Grey Reef Shark, Carcharhinus amblyrhynchos, in Fishes of Australia, accessed 25 August 2014, http://www.fishesofaustralia.net.au/Home/species/2881 Archived 2014-12-15 at the Wayback Machine
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  22. ^ "Gombessa IV expedition". Archived from the original on 2020-06-11. Retrieved 2018-10-12.
  23. ^ Gombessa IV on arte.tv (archive.org)
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  25. ^ Robbins, W.D. (2006). Abundance, demography and population structure of the grey reef shark (Carcharhinus amblyrhynchos) and the white tip reef shark (Triaenodon obesus) (Fam. Charcharhinidae). PhD thesis, James Cook University.
  26. ^ a b c Martin, R.A. Coral Reefs: Grey Reef Shark. ReefQuest Centre for Shark Research. Retrieved on April 30, 2009.
  27. ^ a b McKibben J.N.; Nelson, D.R. (1986). "Pattern of movement and grouping of gray reef sharks, Carcharhinus amblyrhyncos, at Enewetak, Marshall Islands". Bulletin of Marine Science. 38: 89–110.
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  30. ^ ISAF Statistics on Attacking Species of Shark. International Shark Attack File, Florida Museum of Natural History, University of Florida. Retrieved on May 1, 2009.
  31. ^ Anderson, R.C.; Sheppard, C.; Spalding, M. & Crosby, R. (1998). "Shortage of sharks at Chagos". Shark News. 10: 1–3.
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External links

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