Are there so few reef sharks because of human activities such as fishing and finning, or were there never very many to start with? To answer this question, a team of marine biologists (which did not include Friedlander) decided to count reef sharks at coral reefs close and far to human settlements to better understand how humans impact their populations.
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.
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, individuals may stay around the same part of the reef for up to three years, while at Rangiroa, they regularly shift their locations by up to 15 km (9.3 mi). 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.
Blowhole Cliffed coast Coastal biogeomorphology Coastal erosion Concordant coastline Current Cuspate foreland Discordant coastline Emergent coastline Feeder bluff Fetch Flat coast Graded shoreline Headlands and bays Ingression coast Large-scale coastal behaviour Longshore drift Marine regression Marine transgression Raised shoreline Rip current Rocky shore Sea cave Sea foam Shoal Steep coast Submergent coastline Surf break Surf zone Surge channel Swash Undertow Volcanic arc Wave-cut platform Wave shoaling Wind wave Wrack zone
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.
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. 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. The dermal denticles are closely spaced and overlapping, each with five (sometimes seven in large individuals) horizontal low ridges leading to marginal teeth.
The Caribbean reef shark was originally described from off the coast of Cuba as Platypodon perezi by Poey in 1876. Bigelow and Schroeder later described the same species as Carcharhinus springeri in 1944 and the reef shark appears in much literature under this scientific name. The genus name Carcharhinus is derived from the Greek “karcharos” = sharpen and “rhinos” = nose. The currently accepted valid name is C. perezi (Poey 1876).
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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 metres (4.9 ft)-long female from the Java Sea. 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.
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.
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The grey reef shark is native to the Indian and Pacific Oceans. 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.
A reef is a bar of rock, sand, coral or similar material, lying beneath the surface of water. Many reefs result from abiotic processes (i.e. deposition of sand, wave erosion planing down rock outcrops, and other natural processes), but the best known reefs are the coral reefs of tropical waters developed through biotic processes dominated by corals and coralline algae.