Silvertip shark

Species of shark

The silvertip shark (Carcharhinus albimarginatus) is a large species of requiem shark, in the family Carcharhinidae, with a fragmented distribution throughout the tropical Indian and Pacific Oceans. It is often encountered around offshore islands and coral reefs, and has been known to dive to a depth of The silvertip shark resembles a larger and bulkier grey reef shark (C. amblyrhynchos), but can be easily identified by the prominent white margins on its fins. It attains a maximum length of
An aggressive, powerful apex predator, the silvertip shark feeds on a wide variety of bony fishes, as well as eagle rays, smaller sharks, and cephalopods. This species dominates other requiem sharks of equal size when competing for food, and larger individuals are often heavily scarred from conflicts with others of its species. As with other members of its family, the silvertip shark is viviparous, with females giving birth to one to 11 pups in the summer. Silvertip sharks are regarded as potentially dangerous to humans, as they often approach divers quite closely. This slow reproducing species is taken by commercial fisheries for its meat, fins, skin, cartilage, and jaws and teeth, which has apparently led to local population declines or extirpations.

The silvertip shark was originally described as Carcharias albimarginatus by German naturalist Eduard Rüppell, in the 1837 Fische des Rothen Meeres (Fishes of the Red Sea). The name was later changed to the currently valid Carcharhinus albimarginatus. in reference to the distinct white fin margins. In 1960, a long immature male caught off Ras Muhammad in the Red Sea was designated as the type specimen. This interpretation was corroborated by Lavery (1992), based on allozyme data.

The silvertip shark is widely but not continuously distributed in the tropical Indian and Pacific Oceans. In the western Indian Ocean, this species occurs from the Red Sea to South Africa, including Madagascar, the Seychelles, the Aldabra Group, Mauritius and the Chagos Archipelago. In the western Pacific, it is known from off southern Japan to northern Australia, including Taiwan, the Philippines, Indonesia, Papua New Guinea, New Caledonia, Guam, Palau, the Solomon Islands, the Marshall Islands, the Phoenix Islands and Tahiti. In the eastern Pacific, it occurs from southern Baja California to Colombia, including the Cocos, Galapagos, and Revillagigedo Islands. Its presence in the Gulf of Mexico and the Caribbean Sea is unconfirmed. Silvertip sharks are found over continental and insular shelves at a depth of , occupying all levels of the water column. They are most common around isolated islands, coral banks, and reef drop offs. Juveniles frequent coastal shallows or lagoons, while adults occur in deeper water, with little overlap between the two age groups.

The silvertip shark is a robust and streamlined species with a moderately long, broad snout and large, round eyes. The five pairs of gill slits are short. It has 12–14 tooth rows on each side of both jaws, with one or two small teeth at the symphysis (middle of the jaws). The upper teeth are broad with oblique triangular cusps and coarse serrations near the base; the lower teeth have erect cusps with fine serrations. The first dorsal fin is large and triangular, originating above or slightly forward of the free pectoral fin tips. A ridge occurs between the first and second dorsal fins. The pectoral fins are proportionately longer than in most requiem sharks and falcate (sickle like) in shape, with pointed tips. The coloration is blue gray above with a bronze sheen, and white below. A subtle white band runs along the sides, with distinctive white tips and borders on all fins. Silvertip sharks can grow up to long, but typically measure in length. The maximum reported weight is They sometimes follow marine mammals such as bottlenose dolphins (Tursiops sp.) in open water, and are themselves followed by pilot fish (Naucrates ductor). Like the grey reef shark, the silvertip shark sometimes perform a stereotypical threat display if pursued by divers, warning that it is prepared to attack. The display begins with the shark accelerating away to a distance of , before turning and charging towards the perceived threat. At a distance of two body lengths, the shark brakes, turns broadside, drops its pectoral fins, gapes its jaws, lowers the posterior two thirds of its body, and "shivers". The last two elements of this display are unique to this species; the "shivering" may serve to emphasize its white fin markings. If the diver persists, the shark may rapidly close in and slash with its upper teeth.

The diet of the silvertip shark consists primarily of bony fishes, such as grouper, mackerel, tuna, escolars, lanternfish, flyingfish, wrasses, and soles. Eagle rays, smaller sharks, and octopus are occasionally taken.

Like other requiem sharks, the silvertip shark is viviparous; once the embryos exhaust their supply of yolk, the depleted yolk sac develops into a placental connection through which the mother delivers nourishment. In the Southern Hemisphere, mating and parturition both occur in summer. Females bear litters of one to 11 (usually five or six) young after a gestation period of about one year, on a biennial cycle. The newborns have been reported to measure and long by different authors, and are found in shallower water than adults. Males have been reported to be sexually mature at or long, and females at long. This species has also been known to circle or pursue divers. The silvertip shark is caught by commercial and artisan fisheries across its range using longlines, gillnets, and trawls, both intentionally and as bycatch. The fins are highly valued for shark fin soup and are sold on the export market, along with the skin and cartilage. The meat is marketed locally, fresh or dried and salted, as are the jaws and teeth. Silvertip sharks are known to be taken by fisheries in Indonesia, Myanmar, and the Philippines, as well as by various Indian Ocean nations with coral reef fisheries; it is also an increasingly important catch of pelagic fisheries, where it is often finned at sea. This species is susceptible to overfishing, due to its slow reproductive rate and tendency to stay in a certain area. It is believed to have been extirpated by Indonesian artisan fishers at Scott Reef off northern Australia, and is likely becoming rare in many other parts of its range. As a result, the International Union for Conservation of Nature has assessed the silvertip shark as vulnerable.