The Black-tip Shark (Carcharhinus melanopterus) is a species of shark of the family Carcharhinidae, easily identified by the black tips of its fins, especially on the first dorsal fin and the caudal fin. It is one of the most abundant sharks in the tropical coral reefs of the Indian Ocean and Pacific Ocean. This species prefers shallow coastal waters and frequently exposes its first dorsal fin in these areas. Most Black-tipped Sharks live on reef margins and sandy bottoms, but they are also known to support brackish or freshwater environments. This species generally reaches a length of 1.6 m. Black-tip Sharks are sedentary and live in very small areas and may remain in the same area for several years. They are active predators of small bone fish, cephalopods and crustaceans, and are also known to feed on marine snakes and seabirds. The data collected concerning the life cycle of the Black-tip Shark are sometimes contradictory and there appear to be significant differences depending on the geographical location within the range of the species. Like other members of its family, this shark is viviparous and females give birth to between two and five young babies every two years, every year or sometimes twice a year. Indeed, according to its habitat the gestation period of this shark can be 7-9 months, 10-11 months or 16 months. Newborns live in coastal waters and in shallower waters than adults, often forming large groups in areas flooded by high tides. Shy and capricious, the Black-tip Shark is difficult to approach and rarely represents a danger to humans, unless it is excited by food. However, bathers in shallow waters can sometimes have their legs bitten by mistake. This shark is fished for its meat, fins and liver oil, but is not considered to be a commercially important species. The International Union for Conservation of Nature assessed the near threatened species. Although the species as a whole remains widespread and relatively common, overfishing of this shark and its slow rate of reproduction has led to its decline in a number of localities.
The Caribbean reef shark is a viviparous species, meaning its developing embryos are nourished via a placental connection. The litters average four to six pups. Although this shark’s reproduction has not been studied in the northern hemisphere, but to the south, parturition occurs during the Amazon summer of November to December. Pregnant females are often found to have biting scars from males on the sides of their bodies, due to the aggressive behaviors of males during mating. Gestation is believed to take approximately one year. A pregnant female with biting scars and wounds on the sides of her body, taken off the coast of north-northeastern Brazil, carried four near-term embryos. One was a 27.5 in. (700 mm) long male and three were females measuring 27.0 in. (685 mm), 27.4 in. (697 mm), and 27.7 in. (704 mm) in length. Because she was carrying near-term embryos, it is postulated that this area may be a pupping ground. Although such captures have shed light on the topic, relatively little is known about the reproduction of the Caribbean reef shark. Much information has been obtained from a pregnant female carrying four near-term embryos off the coast of northeastern Brazil. This female had scars and wounds on her side. Because the shark carried near-term embryos, it is postulated that this area may be a pupping ground.
The Caribbean reef shark has an interdorsal ridge from the rear of the first dorsal fin to the front of the second dorsal fin. The second dorsal fin has a very short free rear tip. The snout of C. perezi is moderately short and broadly rounded. It has poorly developed, low anterior nasal flaps and relatively large circular eyes. Caribbean reef sharks also have moderately long gill slits with the third gill slit lying above the origin of the pectoral fin. Comparison to similar sharks:
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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.[25][26]


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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