Silvertip Shark

The Silvertip Shark (Carcharhinus albimarginatus) is a robust and captivating reef shark, easily recognized by the distinctive white margins on its fins. This species is a powerful and agile predator, often encountered by divers in areas with strong currents that concentrate pelagic activity.

Found throughout the tropical Indo-Pacific, the Silvertip Shark prefers offshore islands, continental and insular shelves, coral reefs, and seamounts, frequently patrolling near drop-offs. While capable of diving to impressive depths of 800 m, they are often observed in shallower waters, making them accessible to divers. Juveniles typically inhabit more shallow, coastal areas, while adults range further offshore. Silvertip sharks are known for their bold and curious nature, sometimes approaching divers closely. They are considered apex predators within their habitat, often dominating interactions with other shark species of similar size.

This species is currently listed as Vulnerable by the IUCN, with populations facing threats primarily from bycatch in commercial fisheries, particularly longline and net fleets targeting tuna, and artisanal fisheries.

Identification

• Size: Silvertip Sharks are relatively large, reaching a maximum length of 3 meters (10 ft), though they commonly average between 1.8 and 2.4 meters (6-8 ft).
• Coloration: Their body is typically dark grey or blue-grey on the dorsal side, often with a bronze sheen, fading to a white ventral surface. A faint white band may be visible on their flanks.
• Fins: The most striking and diagnostic feature is the brilliant white tips and trailing margins on all fins, except for the second dorsal fin, which usually has a black or dusky tip. The first dorsal fin is large and narrowly rounded, originating over or slightly in front of the free rear tips of the pectoral fins. The pectoral fins are large and semi-falcate with pointed or narrowly rounded tips. An interdorsal ridge is present between the two dorsal fins.
• Head: They possess a streamlined body with a long, broadly rounded snout and distinct large, round eyes.
• Teeth: Both the upper and lower jaws contain 12-14 serrated teeth. The upper teeth are broad and triangular, while the lower teeth are narrower and more pointed.

Observed Dive Sites

Divers have the opportunity to encounter Silvertip Sharks at various dive sites known for their vibrant marine life and strong currents:

• Big Brother Island: Common
• Kandooma Thila: Rare
• Kuredu Express: Rare
• North Horn: Common
• Other notable locations include the Revillagigedo Archipelago (Mexico), Cocos Island (Costa Rica), Malpelo Island (Panama), Wolf and Darwin Islands (Galapagos), and the Tuamotu Archipelago (French Polynesia). They are also a highlight in Fiji, particularly around Beqa Lagoon and dive sites like The Colosseum.

The Silvertip Shark (Carcharhinus albimarginatus) is a striking species commonly encountered by divers in tropical waters. This large requiem shark is primarily associated with offshore environments, making it a thrilling sight for those exploring deeper reef systems.

Habitat and Distribution:

• The Silvertip Shark is widely distributed throughout the tropical Indian and Pacific Oceans, though its presence is fragmented across its range.
• In the western Indian Ocean, its range extends from the Red Sea and East Africa, including Madagascar, the Seychelles, and the Chagos Archipelago.
• In the western Pacific, it is found from southern Japan to northern Australia, encompassing regions like Taiwan, the Philippines, Indonesia, and the Solomon Islands.
• Its eastern Pacific distribution stretches from southern Baja California to Colombia, including notable locations such as Cocos, Galapagos, and Revillagigedo Islands.
• These sharks are typically found over or adjacent to continental and insular shelves and offshore banks. They show a strong preference for offshore islands, remote coral reefs, and areas near steep drop-offs. They can also be found inside lagoons.

Depth Range:

• Silvertip Sharks exhibit a considerable vertical range, from surface waters down to depths of 800 m.
• While adults are often found in deeper offshore waters, juveniles tend to remain in shallower reef areas, moving to deeper waters as they mature. Divers commonly encounter them on seaward reefs at depths greater than 30 m, though they may occasionally come shallower on steep slopes, especially if attracted by activities like spearfishing.

Ecosystem Associations:

• As apex predators, Silvertip Sharks play a crucial role in the health of coral reef ecosystems. They are known to dominate interactions with other shark species of similar size, such as Galapagos sharks and blacktip sharks, when competing for food.
• Their diet primarily consists of benthic and midwater fishes, including bony fishes like mackerel, as well as rays, cephalopods, and even smaller sharks.
• Silvertip Sharks are a significant draw for divers at various dive sites, including Big Brother Island and North Horn, where they are commonly observed.

The Silvertip Shark (Carcharhinus albimarginatus) is a robust and confident apex predator, often encountered by divers in tropical waters. Easily identified by the striking white tips and borders on all its fins, this species can reach a maximum size of 3 meters (10 ft).

Underwater Encounter Behavior

Silvertip Sharks are known for their bold and inquisitive nature, frequently approaching divers closely, which can lead to exhilarating encounters. They are often observed patrolling open water near steep walls, offshore islands, coral banks, and reef drop-offs, typically at depths from the surface down to 800 meters, though they are often found in shallower, diver-accessible depths. While generally not considered territorial, they are dominant among other reef sharks, including Galapagos and Blacktip sharks, and may display aggressive behavior towards members of their own species, often bearing combat scars. Should a Silvertip Shark perceive a threat, it may perform a "threat display." This involves accelerating away to about 15 meters, then turning and charging towards the perceived threat. At a distance of approximately two body lengths, the shark will brake, turn broadside, drop its pectoral fins, gape its jaws, lower the posterior two-thirds of its body, and "shiver" to emphasize its fins. If the threat persists, the shark may attack. Divers are advised to maintain a respectful distance and avoid actions that might be perceived as threatening, especially in the presence of bait.

Feeding Habits

As agile and powerful hunters, Silvertip Sharks are apex predators with a diverse diet. They primarily feed on a variety of bony fishes, including mackerel, tuna, wahoo, wrasses, lanternfish, flyingfish, and soles. They also prey on spotted eagle rays, smaller sharks, octopus, and squid. Silvertips are known to be aggressive feeders, often swimming at the periphery of groups of other feeding sharks and darting in to steal food. They possess differently shaped dentition in their upper and lower jaws, allowing them to grip and saw off chunks of large prey with violent twists. They exhibit a strong diel pattern in depth use, increasing their depth during daylight and on nights around the full moon, possibly related to foraging opportunities as they follow the daily migration of their prey.

Social Structure

Silvertip Sharks are typically observed alone or in pairs. However, small groups of adult females have been noted in deeper waters. While they are not considered highly social in large, tight schools, they are sometimes seen in loose aggregations, suggesting a complex social structure. They are known to be aggressive towards other Silvertip Sharks, and individuals often bear scars from these interactions. They may also form mixed-species aggregations with Grey Reef Sharks.

Notable Seasonal Patterns Relevant to Divers

Silvertip Sharks breed once a year during the summer months. Following a gestation period of approximately one year, females give birth to live young, typically 1 to 11 pups per litter. Juvenile sharks tend to inhabit shallower reef areas to avoid predation, moving to deeper waters as they mature. While Silvertip Sharks generally remain resident at coral reef habitats for long periods, studies indicate that adult males may show increased mobility during the austral summer (November and December), which is thought to correspond to their mating season. This increased movement could mean a higher chance of encountering them in different areas during these months. They have also been observed to make regular dives into deeper, colder waters, sometimes as far as 750 meters, thought to be related to following prey migrations. Their depth use varies cyclically with surface light levels, increasing during daylight and around the full moon. Silvertip Sharks are found in waters with a temperature range of approximately 22.5–30.9°C, often occupying a narrow ambient water temperature range around 27°C.