Silvertip Shark

Carcharhinus albimarginatus (Rüppell, 1837)

syn. Carcharhinus platyrhynchus, Carcharias albimarginatus, Carcharinus albimarginatus, Eulamia albimarginata, Eulamia platyrhynchus

2 - 3 m162 Kg30-800 mCITES IIDangerousVulnerable

1060

The silvertip shark (Carcharhinus albimarginatus) is a notable species within the requiem shark family, Carcharhinidae, characterized by its sporadic distribution throughout the tropical regions of the 🇮🇳 Indian and 🌊 Pacific Oceans. Frequently observed around offshore islands and coral reefs, this species has been documented diving to depths of up to 800 meters (2,600 feet). The silvertip shark is often likened to the grey reef shark (Carcharhinus amblyrhynchos) due to its larger and more robust physique but can be readily distinguished by the conspicuous white edges on its fins. The species reaches a maximum length of 3 meters (10 feet).

With a striking blue-gray hue on its dorsal side complemented by a bronze sheen, and a white ventral side, the silvertip shark features a subtle white band along its sides and distinct white tips and borders across its fins. Typically, these sharks measure between 2.0 and 2.5 meters (6.6 to 8.2 feet) in length, although they can grow as long as 3 meters (9.8 feet). Females generally surpass males in size, with recorded weights reaching up to 162.2 kilograms (358 pounds).

Silvertip sharks are robust apex predators, exhibiting aggressive behavior and preying on an assortment of bony fishes, eagle rays, smaller sharks, and cephalopods. This species demonstrates dominance over other requiem sharks of comparable size during food competition, often leading to observable scarring on larger individuals from intra-species conflicts. Reproductively, the silvertip shark is viviparous, with females producing litters of one to eleven pups primarily in the summer. Despite their formidable presence, silvertip sharks are deemed potentially hazardous to humans, as they are known to closely approach divers. Due to overfishing for their meat, fins, skin, cartilage, and jaws, localized population declines or extirpations have been reported.

First described by German naturalist Eduard Rüppell in 1837, the species was initially named Carcharias albimarginatus. The current taxonomy identifies it as Carcharhinus albimarginatus, with the specific epithet originating from the Latin terms "albi," meaning white, and "marginatus," meaning bordered, in reference to the distinctive fin coloration. A type specimen, an immature male measuring 103 centimeters (3.38 feet), was identified off Ras Muhammad in the 🌊 Red Sea in 1960. Studies by Garrick in 1982 and Lavery in 1992 suggest that the grey reef shark is the closest relative of the silvertip shark based on morphological and genetic data.

Geographically, the silvertip shark occupies a wide yet discontinuous range across the tropical 🇮🇳 Indian and 🌊 Pacific Oceans. It is present in regions spanning the 🌊 Red Sea to 🇿🇦 South Africa, including 🇲🇬 Madagascar, the 🇸🇨 Seychelles, and other surrounding areas. In the Pacific, its range extends from southern 🇯🇵 Japan to northern 🇦🇺 Australia and includes numerous islands and regions such as 🇹🇼 Taiwan, the 🇵🇭 Philippines, and the Galapagos. Despite reports, its existence in the 🌊 Gulf of Mexico and 🌊 Caribbean Sea remains unverified.

Inhabiting continental and insular shelf depths ranging from 30 to 800 meters (98 to 2,625 feet), silvertip sharks occupy varied water column levels, favoring isolated islands and reef drop-offs. Juvenile sharks typically reside in shallower waters, while adults are found in deeper areas, with minimal overlap between the two generations.

Morphologically, the silvertip shark exhibits a streamlined form with a moderately elongated snout and large round eyes. Its gill slits are short, and it possesses 12 to 14 tooth rows on each side of the jaws, with additional small teeth at the symphysis. The upper teeth display broad triangular cusps with coarse serrations, while the lower teeth are characterized by erect cusps with finer serrations. The prominent dorsal fin is triangular, with a noticeable ridge connecting it to the second dorsal fin, and the pectoral fins are notably long and falcate.

The diet of the silvertip shark predominantly comprises bony fishes such as groupers, mackerels, and tuna, along with rays, smaller sharks, and octopuses as occasional prey. Utilizing the distinctive dental structure of their jaws allows them effectively to grip and dismember prey. These sharks are often seen around ships, attracted to artificial, low-frequency sounds.

Considering their reproductive cycle, silvertip sharks are viviparous, with mating and birthing occurring in summer in the Southern Hemisphere. Courtship can involve the male biting the female to ensure copulation. On average, females produce one to eleven offspring after a gestation period of approximately one year, with reproduction occurring biennially.

Inquisitive and bold, particularly in the presence of food, silvertip sharks can pose a threat to humans. They have been observed approaching divers closely, which can be intimidating, as demonstrated by incidents involving diver pursuit and interactions with bait. As of 2008, the International Shark Attack File reported four non-lethal provoked attacks attributed to this species.

Commercial and artisan fisheries target silvertip sharks throughout their range, capturing them using longlines, gillnets, and trawls. Their fins are highly prized for shark fin soup in the export market, with the meat, skin, and other body parts also being utilized. These sharks face significant overfishing pressure due to their slow reproductive rate and territorial nature, with population reductions noted, particularly in areas like Northern 🇦🇺 Australia. Consequently, the International Union for Conservation of Nature has classified the silvertip shark as a vulnerable species.

Why it's threatened

Biological resource use

Intentional use: (subsistence/small scale) [harvest] · Intentional use: (large scale) [harvest] · Unintentional effects: (subsistence/small scale) [harvest] · Unintentional effects: (large scale) [harvest]

The Silvertip Shark is caught globally as target but mostly incidental catch in industrial, artisanal, and subsistence fisheries with pelagic longlines and purse seines, gillnet and demersal trawl, and a range of artisanal gear. It is generally retained for the meat and large fins (Ebert et al. 2021). Its migratory behaviour from the seafloor to shallow waters at night increases its susceptibility to capture in the pelagic tuna fisheries. Commercial at-vessel-mortality in pelagic longline fisheries is highly variable ranging from 15–47% (Ellis et al. 2017, White et al. 2019).

Coral reef-associated species such as the Silvertip Shark are important to fisheries in the Arabian Seas and adjacent waters and Western Indian Ocean region of East Africa and Madagascar. In these regions, elasmobranchs are most commonly taken as bycatch in non-target fisheries and in artisanal fisheries. For example, the Silvertip Shark is one of the most frequently caught sharks in traditional and artisanal fisheries of Madagascar and carcharhinids dominated the small-scale fisheries marine megafauna catches (elasmobranchs, marine mammals, and sea turtles) across Kenya, Zanzibar, and northern Madagascar from 2016–2017 (Cripps et al. 2015, Temple et al. 2019). Across the Western Indian Ocean (WIO), more than 60 million people reside within 100 km of the coast and there is great dependence on marine resources for food and employment (Obura et al. 2017). Marine fisheries catch in the WIO reported to the Food and Agriculture Organization (FAO) increased from the 1960s to the 1990s but have levelled off since 1999 suggesting stocks are fully fished. Artisanal catches are underreported and most small-scale, artisanal, and subsistence coastal fisheries within the Western Indian Ocean are considered to be fully- or overexploited, especially where they are found close to population centres.

The Silvertip Shark is landed in local markets in Indonesia, Papua New Guinea, Myanmar, the Philippines, and Papua New Guinea (SEAFDEC 2006, 2020; White 2007). In Papua New Guinea, the species was taken in the longline shark fishery that operated until 2014 and accounted for 0.5% by number of the shark catch young juveniles to large adults caught and retained, and is still caught by coastal fishers (White et al. 2017, White et al. 2019). It is not commonly landed in Taiwan (Ebert et al. 2013).

In the Great Barrier Reef (GBR), Queensland, Australia, the Silvertip Shark is taken incidentally in very low numbers by managed commercial and recreational line fisheries that target Coral Trout (Plectropomus leopardus; Heupel et al. 2009). The Silvertip Shark was previously taken by illegal fishers operating in northern Australian waters. The species accounted for 3.7% of fins by number of fins seized from Taiwanese vessels caught illegally fishing in Australia from 2006–2009 (Marshall 2011). However, the level of illegal catch since about 2009 has been relatively low and is typically conducted by small-scale fishers from neighboring countries. Most of these fishers operate close to Australia's maritime border and recently, these fishers have rarely come near to the Australian mainland, and Australia has a National Plan of Action to Prevent, Deter and Eliminate Illegal, Unreported, and Unregulated (IUU) Fishing (Department of Agriculture 2023).

Threat classification from the IUCN Red List.