Silvertip shark
Carcharhinus albimarginatus
The silvertip is a streamlined, large-bodied shark that dominates interactions with the other sharks it comes across, including the Galapagos shark. It is easily identifiable due to the white tips and borders on all of its fins.
IDENTIFICATION
Dark grey colouring on the dorsal side, with bronze sheen. Faint white band on flanks. White ventral side. Streamlined body. Large, broad, rounded snout. Upper teeth triangular and serrated, lower teeth pointed. First dorsal narrowly rounded. Striking white tips and white border on the trailing edge of all fins, except the second dorsal, which is tipped with black.
SPECIAL BEHAVIOUR
Silvertip sharks are agile and powerful hunters, targeting mid-water and bottom fishes like mackerel and smaller species of shark and ray. They have been observed darting into feeding frenzies and stealing fish from other sharks.
REPRODUCTION
Silvertip sharks are viviparous, with litters of up to 11 pups. They are thought to have a 1 year gestation period and reproduce biennially. Young are typically found in shallow water, whereas adults roam further offshore.
HABITAT AND GEOGRAPHICAL RANGE
Silvertip sharks are found on the continental shelf, and prefer offshore islands, offshore banks and remote coral reefs. They also occur near drop-offs and inside lagoons. The silvertip has a large vertical range, occurring from surface waters to depths of 800 m. They have a wide-ranging but fragmented distribution in the tropical Indo-Pacific.
DIET DESCRIPTION
Silvertip sharks feed on mid-water and bottom fishes, including bony fishes like mackerel, smaller sharks and rays, and sometimes cephalopods.
THREATS
Like many other sharks, the silvertip is slow to reproduce. It is also highly site-specific, tending not to disperse between sites. Both these traits make it vulnerable to external pressures. In the high seas, the silvertip is frequently caught as by-catch and is one of the nine main species landed by high seas longline and net fleets, which are mainly targeting tuna. They are also important to artisanal fisheries, particularly in the Western Indian Ocean. They are landed and sold for their meat, jaws, liver and cartilage. Silvertip fins have also been identified in the international fin trade.
RELATIONSHIP WITH HUMANS
Silvertip sharks are known to be a bold and dominant species, and may become aggressive if threatened.
CONSERVATION
As a member of the requiem shark family, the silvertip shark is listed on Appendix II of the Convention on the International Trade of Endangered Species (CITES), which means controls have been placed on the trade of this species. There are currently no other species-specific management measures in place, although the silvertip benefits from more generalised measures in certain parts of its range such as the banning of finning practices in the Chagos Archipelago (although illegal practices still continue in this region due to a lack of enforcement). Silvertip populations in remote coral reef habitats may also benefit from designated Marine Protected Areas.
FUN FACTS
Silvertip sharks have a tapetum lucidum, a layer of tissue in the eye that acts as a reflector, reflecting visible light back through the retina. This allows them to see and hunt in dark, murky waters.
They have been shown to make regular dives into deeper, colder waters, sometimes as far as 750 m beneath the surface. It’s thought they are following the daily migration of their prey – many other animals move down into the relative safety of the deep during the day, and return to the surface under the cover of darkness. The rapid dives of the silvertip sharks suggest they are capitalising on this resource, leaving the warmth of the reef in pursuit of food.
REFERENCES
IUCN Red List of Threatened Species. 2021. Silvertip shark.
David A. Ebert et al. 2021. Sharks of the World: A Complete Guide.
Florida Museum. Discover Fishes: Carcharhinus albimarginatus
DM Tickler et al. (2023) Pop-up archival tags reveal environmental influences on the vertical movements of silvertip sharks Carcharhinus albimarginatus. Marine Ecology Progress Series, 717, pp 85-105
