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Silvertip Sharks, Carcharhinus albimarginatus

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Description & Behavior

Silvertip sharks, Carcharhinus albimarginatus (Rüppell, 1837), aka sharks, silver-tip reef sharks, silver-tip sharks and white fins, are large slender sharks with long and broadly rounded snouts that resemble gray reef sharks, C. amblyrhynchos, but can easily be distinguished by the prominent white margins on their fins. Their eyes are large and round, and they have an angular first dorsal fin and pectoral fins, triangular upper teeth; and an interdorsal ridge. Silvertips are dark gray or gray-brown above and white below; all fins have conspicuous white tips and posterior (rear) margins (hence their common name). They reach a maximum size of about 3 m (average 2-2.5 m) and a maximum weight of about 163 kg.

World Range & Habitat

Silvertip sharks, Carcharhinus albimarginatus, are found over or adjacent to continental and insular (island) shelves and offshore banks. They are thought to prefer offshore islands, coral reefs and banks to depths of 800 m. They have been found in the western Indian Ocean: the Red Sea and of East Africa, including Madagascar, Seychelles, Aldabra Group, Mauritius and the Chagos Archipelago. In the western Pacific they are found: off southern Japan to northern Australia and French Polynesia. In the eastern central Pacific they are found off southern Baja California, Mexico to Colombia, including the Cocos, Galápagos and Revillagigedo islands. Their range is: Tropical; 35°N-30°S.

Feeding Behavior (Ecology)

Silvertip sharks, Carcharhinus albimarginatus, are agressive apex predators which feed mainly on benthic and midwater fishes, also rays (including eagle rays), cephalopods, and small sharks.

Life History

Silvertips are Viviparous with 1-11 pups per litter (average 5-6). Gestation period is about one year, young are born in summer. Size at birth 55-80 cm. In the southern hemisphere, both breeding and pupping occur in summer. Distinct pairing with embrace.

Conservation Status & Comments

Silvertip sharks, Carcharhinus albimarginatus, are potentially dangerous and according to the International Shark Attack File they have been 4 provoked attacks by this species on humans, with no fatalities, since records began.

Silvertips are caught by commercial and artisan fisheries across their range using longlines, gillnets, and trawls, both intentionally and as bycatch. Their fins are highly valued for shark fin soup and are sold on the export market, along with their skin and cartilage.

This species is susceptible to overfishing (like almost all sharks are), due to its slow reproductive rate and tendency to stay in a certain area. The International Union for Conservation of Nature (IUCN) has assessed silvertip sharks as Near Threatened, and noted that they may be approaching the criteria for Vulnerable.

"Major Threat(s): This species is subjected to bycatch in high seas fisheries and in artisanal longline, gillnet and trawl fisheries throughout its range. The number of pelagic sharks landed by fishing fleets in all oceans has become increasingly important in recent years (Mejuto et al. 2006). However, catch statistics are not available (Holts 1988, Smith 1998) and where they are, they are under-reported. This is one of the nine principle species landed by high-seas longline and net fleets. The majority of these fleets target tunas in all of the world's oceans and as a result have a large bycatch of pelagic sharks (Fowler et al. 2005). This species was not considered in Clarke et al.?s (2006a) recent analysis of the global shark fin trade, although this species' fins have been identified in the trade (Clarke et al. 2006b). It is a known bycatch of western Pacific tuna fleets (Ward et al. 2004).

Coral reef associated species such as Silvertip Sharks are important in countries such as Eritrea, Sudan, Egypt, Saudi Arabia, Yemen, Maldives and Chagos, where reefs dominate coastal habitats (Anderson and Simpfendorfer 2005). In this region elasmobranchs are most commonly taken as bycatch in non-target fisheries or catch-all artisanal fisheries (Anderson and Simpfendorfer 2005). Finning and discarding of carcasses has been reported, especially in offshore and highseas fisheries targeting tuna (Anderson and Simpfendorfer 2005).

This Silvertip Shark is landed in local markets in Indonesia, Myanmar and the Philippines (SEAFDEC 2006). In the Philippines it is in the top ten most landed species by number (0.73%) and weight (2.6%) with individuals ranging in size from 210?240 cm TL and averaging 23 kg in weight (SEAFDEC 2006). Most sharks were landed by longliners (~65%) and gillnetters (~30%) in Indonesia, Philippines and Vietnam. In Malaysia, Thailand and Cambodia trawlers caught significant numbers of sharks, ~88%, 97% and 40%, respectively. Meat, jaws and teeth were sold in local markets and fins, cartilage, livers and skins entered the export markets (SEAFDEC 2006). It has been recorded in markets in Indonesia in small numbers (W. White, pers. comm. 2003). In a five year survey of Indonesian fish landing sites, only 95 individuals were observed out of a total of more than 21,000 sharks recorded (W. White pers. comm.).

There is evidence from northern Australia that finning can deplete and drive local populations to near extinction. Even remote populations are likely highly vulnerable to target fisheries for meat or fins, particularly given the limited dispersal and localised movement patterns (Stevens 1984). Acoustic and baited camera survey techniques were used to census shark abundance at two northern Australian reefs: Mermaid Reef in Rowley Shoals (a Commonwealth Marine Protected Area closed to all fishing) and Scott Reef (within MOU 1974 Box, where access by Indonesians using traditional artisanal fishing techniques is permitted). Shark abundance was an order of magnitude higher on Mermaid Reef (Meekan and Cappo 2004). Silvertip Sharks, noted to be the main target of shark finning fleets, were common on Mermaid Reef and absent at Scott (Meekan and Cappo 2004). Over-fishing is the most plausible explanation of differences in the composition and abundance of shark assemblages between Mermaid and Scott Reefs. Sharks preferentially targeted by fishermen, such as hammerheads and silvertip whalers were absent from counts at Scott Reef. Furthermore, catches of sharks in the local area (MOU74 Box) declined throughout the early 1990s to the point that Indonesian shark fishing vessels have been relatively uncommon in this area in recent years (Wallner and McLoughlin 1996, Fox and Sen 2002). There has been a large increase in the illegal, unregulated and unreported (IUU) fishing in northern Australia in the last few years (J. Stevens pers. obs.). Several initiatives are underway to identify which species are being taken and in what quantities. Some domestic boats are also suspected to be targeting species for their fins in the Northern Territory."

Resilience to fishing pressure: Very low, minimum population doubling time more than 14 years
Extinction vulnerability to fishing: High to very high vulnerability (74 of 100)

References & Further Research

Featured Elasmobranch - Silvertip Shark @ Pacific Shark Research Center at MLML
David Hall's Encounters in the Sea
Ken Bondy Photographer

Research Carcharhinus albimarginatus » Barcode of Life ~ BioOne ~ Biodiversity Heritage Library ~ CITES ~ Cornell Macaulay Library [audio / video] ~ 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

Search for Silvertip Sharks » ARKive ~ ~ Bing ~ dmoz ~ Flickr ~ Google ~ NatureFootage ~ Picsearch ~ Wikipedia ~ Yahoo! Images ~ YouTube

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