Species Details

Details of Silvertip Shark will be displayed below

Silvertip Shark   

Common Name: Silvertip shark
Scientific Name: Carcharhinus albimarginatus
Local Name: Kattafulhi miyaru
Dhivehi Name: ކަައްޓަފުޅި މިޔަރު
Animalia  (Kingdom)
Chordata  (Plylum)
Carcharhinidae  (Family)
Carcharhinus   (Genus)

Silvertip Shark's description

Distinctive Characters: snout moderately long and broadly rounded. Upper teeth broadly triangular. Second dorsal fin with a base less than twice height. Ridge between dorsal fins.
Colour: Grey above, pale below. First dorsal, pectoral, pelvic and caudal fins with extremely conspicuous white tips and posterior margins.

Silvertip Shark habitat

The Silvertip Shark 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). The species appears to be relatively site-specific for long periods with limited dispersion, particularly at remote and isolated coral reef habitats around tropical islands or atolls (Barnett et al. 2012, Espinoza et al. 2015). On the continental shelf, larger individuals of the species tend to be more mobile and use larger areas than other common reef shark species (Barnett et al. 2012, Espinoza et al. 2015). The Silvertip Shark also exhibits strong diel behaviour, moving closer to coral reefs and using shallower habitats at night.

Reproduction is viviparous, with a yolk sac placenta (Compagno et al. 2005, White et al. 2006, White 2007). Females give birth to 1-11 pups per litter (average six) biennially, after a 12 month gestation period (Compagno et al. 2005, White et al. 2006, Last and Stevens 2009). 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). 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. Growth appears to be fairly slow at about 9 cm per year for juveniles (Last and Stevens 2009). It reaches a maximum size of 300 cm TL (Compagno et al. 2005). No estimate of generation length is available for the species, although it can be inferred from its congener, the Pigeye Shark (C. amboinensis), which has a similar maximum size and an estimated generation length of 21.5 years (Tillett et al. 2011).

Silvertip Shark threats

The Silvertip Shark is a 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 increased in economic importance (Mejuto et al. 2006). However, catch statistics are generally not available (Holts 1988, Smith et al. 1998) and where they are, they are under-reported. The Silvertip Shark is one of the nine main 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); for example, the species is a known bycatch of western Pacific tuna fleets (Ward et al. 2004). The Silvertip Shark was not considered in Clarke et al.'s (2006a) analysis of the global shark fin trade, although fins of the species have been identified in the trade (Clarke et al. 2006b).

Coral reef-associated species such as the Silvertip Shark are important to fisheries in Eritrea, Sudan, Egypt, Saudi Arabia, Yemen, the Maldives, and Chagos Archipelago (500 km south of the Maldives in the Indian Ocean), where reefs dominate coastal habitats (Anderson and Simpfendorfer 2005). In this region elasmobranchs are most commonly taken as bycatch in non-target fisheries or catchall artisanal fisheries (Anderson and Simpfendorfer 2005). Finning and discarding of carcasses has been reported, especially in offshore and high seas fisheries targeting tuna (Anderson and Simpfendorfer 2005). The Silvertip Shark from the Chagos Archipelago is taken by the Mauritian Inshore Fishery, which targets grouper (subfamily Epinephelinae) and the Deepwater Snapper (Etelis carbunculus) and has operated in these waters since the early 1970s (Mees 1996). There is also an open-water fishery targeting tuna that commonly catches reef-associated sharks incidentally (Graham et al. 2010). Despite conservation measures in place in the Chagos Archipelago (see the Conservation section), illegal fishing is suspected to be a common activity in remote locations.

The Silvertip Shark is landed in local markets in Indonesia, Papua New Guinea, Myanmar, and the Philippines (Kumoru 2003, SEAFDEC 2006, White 2007). In the Philippines, it is in the top 10 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). In Papua New Guinea, the Silvertip Shark was taken in the longline shark fishery that operated close to seamounts and non-emergent reefs (Kumoru 2003). Based on observer data, the Silky Shark (C. falciformis) and the Oceanic Whitetip Shark (C. longimanus) dominated the shark catch (58%), but the Silvertip Shark (6.2%) was also taken in significant numbers (Kumoru 2003). Most Silvertip Shark individuals caught in this fishery were retained (88%) and the fins and meat marketable (Kumoru 2003). The fishery ceased in June 2014 due to the Western and Central Pacifc Fisheries Commission (WCPFC) requirement to not land or retain Silky Shark.

There is evidence from northern Australia that finning can cause localised depletion of shark populations. Remote populations of Silky Shark are likely highly sensitive to target fisheries for meat or fins, particularly given their limited dispersal and localised movement patterns (Barnett et al. 2012). 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 the Memorandum of Understanding [MOU] 1974 Box in the Timor Sea, where access by Indonesian fishers using traditional artisanal fishing techniques is permitted). Shark abundance was an order of magnitude higher on Mermaid Reef (Meekan and Cappo 2004). The Silvertip Shark, the main target of shark finning fleets in this area, was common on Mermaid Reef and absent at Scott Reef (Meekan and Cappo 2004). Fishing pressure is the most plausible explanation for differences in the composition and abundance of shark assemblages between Mermaid and Scott Reefs. Sharks preferentially targeted by fishermen, such as hammerheads (Sphyrna spp.) and the Silvertip Shark were absent from counts at Scott Reef. Furthermore, catches of reef sharks in the local area (MOU74 Box) declined throughout the early 1990s to the point that Indonesian shark fishing vessels have become relatively uncommon in this area (Wallner and McLoughlin 1996, Fox and Sen 2002, Ruppert et al. 2013). Several initiatives are underway to identify which species are being taken and in what quantities.

In the Great Barrier Reef (GBR), Queensland, Australia, the Silvertip Shark is not targeted by fisheries, but very low numbers are taken incidentally by commercial and recreational line fisheries that target Coral Trout (Plectropomus leopardus; Heupel et al. 2009). This may be a result of its strong diel and foraging behaviours around coral reefs at night when little fishing activity occurs (Espinoza et al. 2015). Conversely, poor reporting of species-specific shark landings may occur (Heupel et al. 2009), a common pattern observed in many fisheries where untargeted elasmobranch bycatch typically goes unidentified and/or unreported (Walsh et al. 2002). In addition, although most of the shark catch associated with the Coral Trout line fishery is not retained, sharks that interact with line fisheries may break off before landing or are released bearing hooks and traces, and it is unclear how this may affect the health and survival of Silvertip Sharks (Gallagher et al. 2014). However, catch-per-unit effort data from the period between 1989 and 2006 showed no evidence of increase or decline of sharks associated with the line fishery along the GBR (Heupel et al. 2009). The Silvertip Shark is not known to interact with the inshore gillnet fishery that operates in Queensland waters (Harry et al. 2011).

A ten-year survey (2000–2010) using baited remote underwater video stations (BRUVS) along the entire GBR showed that the Silvertip Shark was the second most commonly sighted species (12.2%) (Espinoza et al. 2014). This survey showed that the species is restricted to offshore coral reef habitats in the GBR. An examination of the GBR Marine Park Zoning showed higher abundances of the Silvertip Shark in reefs that were closed to fishing. Moreover, higher abundances of the species were observed in protected areas that had more and healthier coral cover, suggesting that the loss and degradation of coral reefs may negatively affect their populations (Espinoza et al. 2014). BRUVS data from 2004-2010 suggest that the abundance of the Silvertip Shark has not changed since the new re-zoning of the GBR Marine Park in 2004, despite an increase in the coverage of protected areas (Espinoza et al. 2014).

Silvertip Shark's status