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.
Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library ~ Encyclopedia of Life (EOL) ~ ESA Online Journals ~ FishBase ~ Florida Museum of Natural History Ichthyology Department ~ GBIF ~ Google Scholar ~ ITIS ~ IUCN RedList (Threatened Status) ~ Marine Species Identification Portal ~ NCBI (PubMed, GenBank, etc.) ~ Ocean Biogeographic Information System ~ PLOS ~ SIRIS ~ Tree of Life Web Project ~ UNEP-WCMC Species Database ~ WoRMS
But another potential cause is that these sharks are skittish around people. So when too many people move into the area, the reef sharks flee to other coral reefs. Indeed, the researchers found far more sharks at small, isolated reefs than they expected. But this in itself is a danger to the reef sharks. With so many sharks concentrated in a small area, “if you really wanted to, you could fish out a few hundred sharks very easily,” said Friedlander.
Anchialine pool Archipelago Atoll Avulsion Ayre Barrier island Bay Baymouth bar Bight Bodden Brackish marsh Cape Channel Cliff Coast Coastal plain Coastal waterfall Continental margin Continental shelf Coral reef Cove Dune cliff-top Estuary Firth Fjard Fjord Förde Freshwater marsh Fundus Gat Geo Gulf Gut Headland Inlet Intertidal wetland Island Islet Isthmus Lagoon Machair Marine terrace Mega delta Mouth bar Mudflat Natural arch Peninsula Reef Regressive delta Ria River delta Salt marsh Shoal Shore Skerry Sound Spit Stack Strait Strand plain Submarine canyon Tidal island Tidal marsh Tide pool Tied island Tombolo Windwatt
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.
Reproduction is viviparous; once the developing embryos exhaust their supply of yolk, the yolk sac develops into a placental connection through which they receive nourishment from their mother. Mating is apparently an aggressive affair, as females are often found with biting scars and wounds on their sides. At the Fernando de Noronha Archipelago and Atol das Rocas off Brazil, parturition takes place at the end of the dry season from February to April, while at other locations in the Southern Hemisphere, females give birth during the Amazon summer in November and December. The average litter size is four to six, with a gestation period of one year. Females become pregnant every other year. The newborns measure no more than 74 cm (29 in) long; males mature sexually at 1.5–1.7 m (59–67 in) long and females at 2–3 m (79–118 in).
Socially, they are mostly loners unless living in a threatening ecosystem. These are the first and the only species of sharks that are known to “sleep” on the ocean floor or within reef caves. It is believed that these sharks are not actually sleeping but merely resting. These sharks have actually been given the nickname “sleeping sharks” because of their habit of lying motionless at the sea bottom. This is a somewhat unusual and unique behavior of these sharks.
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.