|Scientific Name:||Carcharhinus albimarginatus|
|Species Authority:||(Rüppell, 1837)|
Carcharias albimarginatus Rüppell, 1837
|Red List Category & Criteria:||Near Threatened ver 3.1|
|Assessor(s):||Pillans, R., Medina, E. & Dulvy, N.K.|
|Reviewer(s):||Stevens, J.D., Dudley, S., Pollard, D., Valenti, S.V., SSG Pelagic Shark Red List Workshop & Kyne, P.M. (Shark Red List Authority)|
The Silvertip Shark (Carcharhinus albimarginatus) has a wide but fragmented distribution throughout the tropical Indian and Pacific Oceans (reports in the western central Atlantic are as yet unconfirmed). It is a large, slow-growing whaler shark, which appears to be relatively site-specific, possibly with limited dispersion. This species is subjected to bycatch in high seas fisheries and in artisanal longline, gillnet and trawl fisheries throughout its range, and the number of pelagic sharks landed by fishing fleets in all oceans has become increasingly important in recent years. The meat, teeth and jaws are sold locally and fins, skin and cartilage are exported. Few data are available, however there is evidence to suggest that Indonesian fisheries have extirpated local populations of this species from Scott Reef in northern Australia and declines are suspected elsewhere. This species' site-specificity, fragmented populations and life history characteristics indicate that even remote populations are highly vulnerable to target shark fisheries. This information, combined with actual and potential levels of exploitation throughout its range result in a global assessment of Near Threatened, based on suspected overall population declines approaching 30% (close to meeting the criteria VU A2bd+A4bd). More information is needed on the status of separate populations throughout its range.
|Range Description:||Western Indian Ocean: occurs in the Red Sea, off South Africa, Mozambique, Kenya, Madagascar, Aldabra Islands, Mauritius, Seychelles, Chagos Archipelago (Compagno in prep.).
Western central Pacific: occurs off Indonesia, Taiwan (Province of China), Guam, New Caledonia, Philippines, Palau, Marshall, Solomon and Phoenix Islands, Tahiti, Tuvalu, Papua New Guinea (Compagno in prep). Also Northern Australian waters from Carnarvon (Western Australia) to Bundaberg (Queensland), with the exception of the Gulf of Carpentaria and Arafura Sea (Last and Stevens 1994, MIRC 2007, Jones et al. 1991).
Eastern central Pacific: from Southern Baja California, south to Guatemala and Colombia, including the Revillagigedo and Clipperton Islands, Cocos Island and Galapagos Islands (Compagno in prep).
Possibly also occurs in the western central Atlantic (Mexico, Gulf of Mexico and Caribbean Sea) (Compagno in prep.), although its presence in that region is unconfirmed (Grace 2001).
Native:Australia (Northern Territory, Queensland, Western Australia); British Indian Ocean Territory; Cocos (Keeling) Islands; Colombia; Ecuador (Galápagos); Egypt; Eritrea; French Polynesia (Society Is.); Guam; Guatemala; Indonesia (Kalimantan, Sulawesi); Kenya; Kiribati (Phoenix Is.); Madagascar; Marshall Islands; Mauritius; Mexico (Baja California Sur, Revillagigedo Is.); New Caledonia; Palau; Papua New Guinea; Philippines; Saudi Arabia; Seychelles (Aldabra, Seychelles (main island group)); Solomon Islands (Santa Cruz Is., South Solomons); South Africa (KwaZulu-Natal); Sudan; Taiwan, Province of China; Tuvalu; Yemen (North Yemen, South Yemen)
|FAO Marine Fishing Areas:||
Atlantic – western central; Indian Ocean – western; Pacific – eastern central; Pacific – western central
|Range Map:||Click here to open the map viewer and explore range.|
|Population:||Populations appear to be fragmented with apparently low potential for interchange among them.|
|Habitat and Ecology:||
This species occurs on the continental shelf, offshore islands, coral reefs and offshore banks, from surface waters to depths of 600-800 m (Compagno et al. 2005). It is also found inside lagoons, near drop offs and offshore (Compagno et al. 2005).
Reproduction is viviparous, with a yolk sac placenta (Compagno et al. 2005, White et al. 2006). Females give birth to 1-11 pups per litter (average six) biennially, after a 12 moth gestation period (Compagno et al. 2005, Last and Stevens 1994, White et al. 2006). Size at birth is reported at 63-68 cm total length (TL) (Compagno et al. 2005) and 73-81 cm TL (White et al. 2006). Young are found in shallow water closer to shore, whereas adults are more wide-ranging (Compagno et al. 2005). This is a large, slow-growing shark, which reaches a maximum size of 300 cm TL (Compagno et al. 2005). Compagno et al. (2005) report that males mature at 160-180 cm TL and females at 160-199 cm TL. White et al. (2006) report that males mature at 190-200 cm TL and females at ~195 cm TL.
This species may not disperse widely between sites, potentially making remote populations vulnerable to depletion (Compagno et al. 2005).
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.
|Conservation Actions:||No specific measures are in place for this species. Catch levels should be quantified and monitored throughout this species' range.|
|Citation:||Pillans, R., Medina, E. & Dulvy, N.K. 2009. Carcharhinus albimarginatus. The IUCN Red List of Threatened Species. Version 2015.2. <www.iucnredlist.org>. Downloaded on 03 August 2015.|
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