The Caribbean Reef Shark is known to become aggressive in the presence of food, but they are mostly only considered dangerous to humans because of its size. This shark was fished in Belize for almost the entire 20th century. They were used to make local delicacies in addition to liver oil (mostly used in cosmetics). Their low reproduction rate combined with a high level of hunting and fishing have caused the numbers to dwindle. The shark is now considered to be near threatened. Many countries and organizations have banned the commercial fishing of this species.
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Grey reef sharks were the first shark species known to perform a threat display, a stereotypical behavior warning that it is prepared to attack.[3] 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 they perceive a threat. This species has been responsible for a number of attacks on humans, so should be treated with caution, especially if they begin to display. They 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 has assessed this species as Near Threatened.
This species is commonly found in shallow waters on and near coral reefs and occasionally in brackish waters. Juveniles are typically found in extremely shallow water (±15 to 100 cm) inside lagoons, often swimming along the shoreline; adults typically occur on shallow parts of the forereef, often moving over the reef crest and onto the reef flat at flood tide. Individual adults inhabit a relatively small home range of ±2.5 km2 and appear to reside close to their home reef but occasionally cross deepwater channels between adjacent reefs.
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.

Grey reef sharks were the first shark species known to perform a threat display, a stereotypical behavior warning that it is prepared to attack.[3] 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 they perceive a threat. This species has been responsible for a number of attacks on humans, so should be treated with caution, especially if they begin to display. They 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 has assessed this species as Near Threatened.
Although still abundant at Cocos Island and other relatively pristine sites, grey reef sharks are susceptible to localized depletion due to their slow reproductive rate, specific habitat requirements, and tendency to stay within a certain area. The IUCN has assessed the grey reef shark as Near Threatened; this shark is taken by multispecies fisheries in many parts of its range and used for various products such as shark fin soup and fishmeal.[2] Another threat is the continuing degradation of coral reefs from human development. There is evidence of substantial declines in some populations. Anderson et al. (1998) reported, in the Chagos Archipelago, grey reef shark numbers in 1996 had fallen to 14% of 1970s levels.[30] Robbins et al. (2006) found grey reef shark populations in Great Barrier Reef fishing zones had declined by 97% compared to no-entry zones (boats are not allowed). In addition, no-take zones (boats are allowed but fishing is prohibited) had the same levels of depletion as fishing zones, illustrating the severe effect of poaching. Projections suggested the shark population would fall to 0.1% of pre-exploitation levels within 20 years without additional conservation measures.[31] One possible avenue for conservation is ecotourism, as grey reef sharks are suitable for shark-watching ventures, and profitable diving sites now enjoy protection in many countries, such as the Maldives.[6]
Grey reef sharks are prey for larger sharks, such as the silvertip shark.[9] At Rangiroa Atoll in French Polynesia, great hammerheads (Sphyrna mokarran) feed opportunistically on grey reef sharks that are exhausted from pursuing mates.[15] Known parasites of this species include the nematode Huffmanela lata and several copepod species that attach to the sharks' skin,[16][17] and juvenile stages of the isopods Gnathia trimaculata and G. grandilaris that attach to the gill filaments and septa (the dividers between each gill).[18][19]

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.[3]

Despite its abundance in certain areas, the Caribbean reef shark is one of the least-studied large requiem sharks. They are believed to play a major role in shaping Caribbean reef communities. These sharks are more active at night, with no evidence of seasonal changes in activity or migration. Juveniles tend to remain in a localized area throughout the year, while adults range over a wider area.[7]
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One useful definition distinguishes reefs from mounds as follows: Both are considered to be varieties of organosedimentary buildups – sedimentary features, built by the interaction of organisms and their environment, that have synoptic relief and whose biotic composition differs from that found on and beneath the surrounding sea floor. Reefs are held up by a macroscopic skeletal framework. Coral reefs are an excellent example of this kind. Corals and calcareous algae grow on top of one another and form a three-dimensional framework that is modified in various ways by other organisms and inorganic processes. By contrast, mounds lack a macroscopic skeletal framework (see stromatolite). Mounds are built by microorganisms or by organisms that don't grow a skeletal framework. A microbial mound might be built exclusively or primarily by cyanobacteria. Excellent examples of biostromes formed by cyanobacteria occur in the Great Salt Lake in Utah, and in Shark Bay on the coast of Western Australia.
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