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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 to 15:00, corresponding to peak daylight hours. 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.
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).
Blacktip reef sharks are fast, pursuit predators that prefer reef fishes, but also feeds on stingrays, crabs, mantis shrimps and other crustaceans, cephalopods, and other mollusks. In the Maldives, this species has been documented feeding cooperatively on small schooling fishes, herding them against the shore and feeding en masse. Feeds heavily on sea snakes in northern Australia. A large individual (1.6 m) was observed attacking a green sea turtle, Chelonia mydas, in North Male’ Atoll, Maldives.
This sturdy shark is abundant in the Caribbean, and because of its average features, is often confused with other requiem sharks. Usually growing 6.5 to 10 feet long, these are the apex predator of their food web. They have been found ‘sleeping’ in caves and on the ocean floor, behavior that is still unexplained. There has been concern over eating these sharks because of the build-up of toxins in their flesh, but now they are valued for tourism more than food, which brings its own safety issues.
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The Caribbean reef shark infrequently attacks humans. In general, a shark attack on a human is behaviorally similar to an attack upon natural prey. A human is more susceptible to being attacked if the shark is cornered and feels that there is no escape route. In situations like these, the shark may rake the victim during the attack resulting in lacerations.
Despite sharks being portrayed as notorious aggressive animals, very few incidents have involved blacktip reef sharks, none being fatal. Still the importance of an apex predator is vital to a balanced and healthy ecosystem. Unfortunately, this species is very susceptible to reef gill netting. And sharks all around continue to be threatened by fishing pressure resulting in a decrease in many shark populations.
Based on morphological similarities, Jack Garrick in 1982 grouped this species with the bignose shark (C. altimus) and the sandbar shark (C. plumbeus), while Leonard Compagno in 1988 placed it as the sister species of the grey reef shark (C. amblyrhynchos). A phylogenetic analysis based on allozyme data, published by Gavin Naylor in 1992, indicated that the Caribbean reef shark is the sister taxon to a clade formed by the Galapagos shark (C. galapagensis), dusky shark (C. obscurus), oceanic whitetip shark (C. longimanus), and the blue shark (Prionace glauca). However, more work is required to fully resolve the interrelationships within Carcharhinus.
This species is taken by commercial and artisanal longline and gillnet fisheries throughout its range. It is valued for meat, leather, liver oil and fishmeal. The Caribbean reef shark is the most common shark landed in Colombia (accounting for 39% of the longline catch by occurrence), where it is utilized for its fins, oil and jaws (sold for ornamental purposes). In Belize, this species is mainly caught as bycatch on hook-and-line intended for groupers and snappers; the fins are sold to the lucrative Asian market and the meat sold in Belize, Mexico, and Guatemala to make "panades", a tortilla-like confection. A dedicated shark fishery operated in Belize from the mid-1900s to the early 1990s, until catches of all species saw dramatic declines. The flesh of this species may contain high levels of methylmercury and other heavy metals.
Grey reef sharks were the first shark species known to perform a threat display, a stereotypical 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 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.
Ancient reefs buried within stratigraphic sections are of considerable interest to geologists because they provide paleo-environmental information about the location in Earth's history. In addition, reef structures within a sequence of sedimentary rocks provide a discontinuity which may serve as a trap or conduit for fossil fuels or mineralizing fluids to form petroleum or ore deposits.