The Silvertip Shark (Carcharhinus albimarginatus) is a large (to 300 cm total length) shark with a patchy distribution across the Indo-Pacific Ocean. It occurs on continental shelves, offshore islands, and coral reefs from the surface to depths of 800 m, can be relatively site-specific, and has slow population growth rates. The species is taken as target and bycatch in industrial, artisanal, and subsistence fisheries with pelagic longlines, gillnet, demersal trawl, and a range of artisanal gear, and is retained mainly for its large fins and meat. Declines in abundance of >50% have been noted in the Arabian Seas and adjacent waters and although it was previously common, it is now infrequently seen in the region. Significant declines of the species are also suspected in Southeast Asia and coral-reef associated shark species have globally declined by 60–73%. Populations of the Silvertip Shark are stable in protected areas and countries with managed fisheries, such as Australia. The species occurrence in upper continental slope habitats and deeper waters also provide it significant refuge from fisheries. Overall, while declines of >50% are noted in parts of its range, the population is stable in some areas, and it has significant refuge at depth across large parts of its range. Thus, it is suspected the population has undergone a reduction of 30–49% over the past three generation lengths (48 years) based on abundance data and levels of exploitation, and the Silvertip Shark is assessed as Vulnerable A2bd.

The Silvertip Shark has a patchy distribution across the Indo-Pacific Ocean. It ranges from South Africa north to the Arabian Seas and adjacent waters, east to Australia, north to Japan, and across the western and eastern Pacific to the Gulf of Mexico and south to Ecuador (White et al. 2006, Last et al. 2010, Jabado et al. 2017, Ebert et al. 2021, Dunn et al. 2022, Fricke et al. 2023). Since the previous assessment (Espinoza et al. 2021), the distribution map has been refined to map this species to its known bathymetric range.

There are no data available on the global population size of the Silky Shark. Genetic studies indicate no connectivity between the Western Indian Ocean and the southwest Pacific which is consistent with the Silvertip Shark's limited dispersion and reef-associated sharks rarely moving across large ocean basins (Green et al. 2019). Demographic analyses of the Silvertip Shark from the Indo-Pacific Ocean revealed that the population would decline with low to moderate levels of fishing mortality (F) across all age-classes with population declines of 4–6% per year for F=0.1 per year and population declines of 20% per year with F=0.3 per year (Smart et al. 2017a). This is indicative of the low resilience of this species to moderate levels of fishing effort due to its slow population growth rates (Smart et al. 2017a).

In the Arabian Seas and adjacent waters, there have been no dedicated surveys or population estimates for this species. Data from Eritrea from the 1980s and 1990s indicate that the Silvertip Shark was one of the most commonly caught species (Marshall 1996). In surveys of landings from the Saudi Arabian Red Sea, two juveniles were recorded in 2001 from a short survey (Bonfil 2003) and only three juvenile specimens were recorded in regular surveys from 2011–2013 (<1% of elasmobranch landings by number) (Spaet and Berumen 2015). It has not been observed in Baited Remote Underwater Video surveys (BRUVs) or Underwater Visual Census surveys, but it was observed on one occasion during longline surveys in this area (Kattan 2014, Spaet and Berumen 2015, Spaet et al. 2016). In the Yemeni Red Sea as well as the Gulf of Aden and around the Socotra Archipelago, it was reported as one of the dominant sharks in fisheries landings by number with both juveniles and adults recorded in 2003–2004 (Shaher 2007). More recent surveys over three seasons in Yemen have recorded very low numbers with 15 adult and subadult specimens landed but originating from Somalia (four specimens), Qusayr in Yemen (three specimens), and from Eritrea (eight specimens) (I. Elhassan pers. comm. 12 May 2017). These specimens represented <2% of shark landings by number. In Sudan, landings from illegal Yemeni fishermen contributed 2.5% by number of this species in 2002 but the Silvertip Shark has now become very uncommon at landing sites (I. Elhassan pers. comm. 12 May 2017). It is apparently very rare in Oman (A. Henderson pers. comm. 06 February 2017) and is rarely caught in India and Sri Lanka (Akhilesh K.V. and D. Fernando pers. comm. 06 February 2017). The species has undergone declines of ~70% in Pakistan since 1999 and is now among the rarest carcharhinids (M. Khan pers. comm. 04 September 2023). It was previously targeted in the Maldives through the gillnet and longline fisheries, and sharks in general underwent declines of at least 50% until the fisheries were halted in 2010 (Anderson and Ahmed 1993, Ali 2015).

In the Chagos Archipelago in the Western Indian Ocean, although the numbers of reef sharks observed on diver surveys from 1970–2006 severely declined by 90% over 36 years (likely due to inshore illegal fishing), there was a significant increase of 75% in the diver observed abundance of Silvertip Sharks during that same period (Graham et al. 2010). This was possibly due to their deeper occurrence and introduction of wire trace and finning regulations in the tuna longline fisheries in the area (Graham et al. 2010). Conversely, Ferretti (et al. 2018) reconstructed shark populations at this location and concluded that the Silvertip Shark population declined by 82% between the 1960s and 1990s but has been stable since the mid-1990s, and it is currently one of the dominant elasmobranchs in the area (Dunn et al. 2022). The decline was attributed to industrial offshore high-seas fisheries exploitation during that period followed by stability due to increasing protection of the area since 1991.

In the pelagic tuna fisheries of the Indian Ocean Tuna Commission (IOTC), the Silvertip Shark is reported to be taken in pelagic longline fisheries (Romanov et al. 2010) but is not among the seventeen main pelagic shark species reported catches or ecological risk assessments and thus is likely to be caught less frequently than those species. All shark catches in the Indian Ocean are under-reported as reconstructed catches indicate they account for 51% of unreported landings and discards in 2020 and all pelagic catches are estimated to be 30% higher than reported to the IOTC (Heidrich et al. 2023). In the pelagic tuna fisheries of the Western Central Pacific Fisheries Commission, Silvertip Shark is also not frequently encountered relative to some of the pelagic shark species and Silvertip Shark catch-per-unit-effort has remained low and stable over two decades from 1995–2015 (Tremblay-Boyer and Brouwer 2016). The species is mostly caught in the longline fishery with a total of 2,106 individuals taken from 1995–2015 compared to a total of 490 individuals taken during that same period in the purse seine fishery (Tremblay-Boyer and Brouwer 2016).

In Indonesia, fish markets surveys suggest that the Silvertip Shark has undergone large population declines with a five-year survey from 2001–2006 noting only 95 Silvertip Shark individuals out of a total of more than 21,000 sharks recorded (White 2007, W. White pers. comm. 14 February 2015). Landing site data indicate that in Malacca Strait less than 10 individuals per year have been recorded from 2017–2022 and in West Nusa Tenggara, numbers fluctuated from 24–137 individuals per year from 2014–2022 (B. Simeon unpub. data). Across Southeast Asia, surveys in 2003–2004 noted the Silvertip Shark was among the top 10–15 landed shark species in Indonesia, Myanmar, and the Philippines. However in similar surveys in 2015–2016, only five Silvertip Shark individuals were observed as landed and only in Indonesia, out of a total 13,504 sharks recorded across southeast Asia, i.e., the Silvertip Shark represented <0.1% of the recorded sharks (SEAFDEC 2006, 2020).

In Australia, a ten-year survey (2000–2010) using baited remote underwater video stations (BRUVS) along the entire Great Barrier Reef (GBR) Queensland, indicated the Silvertip Shark was the second most commonly sighted species with higher abundances of the species in reefs that were closed to fishing and in protected areas that had greater and healthier coral cover, suggesting that the loss and degradation of coral reefs may negatively affect their populations (Espinoza et al. 2014). The BRUVS data from 2004–2010 suggested a stable abundance of the Silvertip Shark over this period (Espinoza et al. 2014). Furthermore, catch-per-unit effort from 1989–2006 indicated stable populations of sharks, which includes the Silvertip Shark, caught in commercial and recreational line fisheries on the GBR that target Coral Trout (Plectropomus leopardus; Heupel et al. 2009).

In Costa Rica (Eastern Central Pacific), the Silvertip Shark has only been reported in oceanic waters around Cocos Island, and is not landed by the semi-industrial long-line fishery operating in the Economic Exclusive Zone of Costa Rica (M. Espinoza unpub. data 2023). Modelled diver observations of Silvertip Shark at Cocos Island over two decades (1993–2013) revealed an 87% decline in probability of occurrence that may have been associated with competition with the Blacktip Shark (Carcharhinus limbatus) and Galapagos Shark (C. galapagensis) which both increased during that period (White et al. 2015). A later five-year survey (2016–2020) using BRUVS at Cocos Island showed that the Silvertip Shark is a relatively common elasmobranch species in benthic habitats (34.2% occurrence; 397 stations), but rare in pelagic waters offshore (5.3% occurrence; 131 stations) (Espinoza et al. 2020, M. Espinoza unpub. data 2023). Furthermore, BRUVS data from 2016–2022 suggest a slight increase in the mean abundance of the Silvertip Shark over this period (M. Espinoza pers. comm. 2023).

Globally, coral reef associated sharks have declined dramatically due to overfishing, with a global survey of coral reefs revealing declines of 60–73% in five common resident reef shark species and that these reef sharks were not detected at 34–47% of surveyed reefs at which they had historically occurred (MacNeil et al. 2020, Simpfendorfer et al. 2023). While there is limited species-specific information available on the Silvertip Shark, its large size, large fins, slow population growth rates, and the presence of intensive and unregulated fisheries across most of its range mean that, like many other large carcharhinids and coral reef associated sharks, the species' population has declined. These declines are >50% in parts of the Arabian Seas and adjacent waters and Western Indian Ocean with similar levels of decline likely in Southeast Asia, with population stability in protected and managed areas such as Chagos Archipelago, Cocos Island, and Australia. The species' occurrence in upper continental slope habitats and deeper waters also provides it significant refuge from fisheries. Overall, across its entire range it is suspected the population has undergone a reduction of 30–49% over the past three generation lengths (48 years) based on abundance data and levels of exploitation.

The Silvertip Shark occurs on the continental shelf, offshore islands, coral reefs, and offshore banks, from the surface to depths of 800 m (Ebert et al. 2021). Limited tagging data reveals a mean depth range of 43 m and mean maximum depth of 441 m (Andrzejaczek et al. 2022). It is also found inside lagoons and near drop-offs, and young occur in shallower water among reefs while adults occur in deeper waters, but this is not an oceanic species (Ebert et al. 2021). The species appears to be relatively site-specific for long periods with limited movement, particularly at remote and isolated coral reef habitats around tropical islands or atolls (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 (Bond et al. 2015, Espinoza et al. 2015, Andrzejaczek et al. 2022). It reaches a maximum size of 300 cm total length (TL) with females mature at 160–209 cm TL and males mature at 160–200 cm TL (White et al. 2006, Smart et al. 2017b, Ebert et al. 2021). Reproduction is viviparous, with a yolk sac placenta, litter sizes of 1–11 (average 6) pups, a 12 month gestation period and biennial reproductive cycle, and size-at-birth of 63–81 cm TL (White et al. 2006, Ebert et al. 2021). Age parameters are available from Papua New Guinea with female age-at-maturity estimated as 14.8 years and maximum observed age is 18 years (though it may live longer); generation length is therefore at least 16 years (Smart et al. 2017b).

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).

The Silvertip Shark is used for its fins, meat, cartilage, liver, teeth, jaws, and skin (SEAFDEC 2006, Asbury et al. 2021, Ebert et al. 2021). The meat, teeth, and jaws are generally sold locally, whereas fins, skin, and cartilage are generally exported. The species is a relatively small component of the international fin trade, accounting for 0.35% and 0.10–0.13% of sampled fins traded in China and Hong Kong, respectively (Fields et al. 2018, Cardeñosa et al. 2020).

Currently there are no species-specific management measures in place. The Silvertip Shark is prohibited from targeted take in approximately 13% of the countries across its range, that is, those in which a 'Shark Sanctuary' has been declared and in other Marine Protected Areas (MPAs), such as the Chagos Archipelago and within MPAs of, for example, Australia and South Africa (Cardeñosa et al. 2022, Faure-Beaulieu et al. 2023). There are many general management measures that contribute to conserving this species in many range states. Marine Protected Areas that incorporate >20 km of coral reef can provide significant protections because of the limited movements observed in this species (Dwyer et al. 2020). Marine Protected Areas are common in coral reef areas throughout its range, but only those that are sufficiently large and well enforced provide refuge (MacNeil et al. 2020). Further research is needed on population size and trend, life history, and catch rates and future changes in fishing areas should be monitored.