Featured Elasmobranch- Silvertip Shark
Category : Featured Elasmobranch
Photo Credit: David A. Ebert
Carcharhinus albimarginatus (Rüppell, 1837)
Family Carcharhinidae (Whaler or Requiem Sharks)
Identification: A medium-sized representative of the whaler shark family with a robust, fusiform body and a long, broadly rounded snout. First dorsal fin originates above or slightly anterior to the free rear tips of the pectoral fins; first dorsal tapers to a narrowly rounded apex. Second dorsal fin is much smaller than first and originates over or slightly posterior to anal fin origin. An interdorsal ridge is present between the dorsal fins. Upper teeth are broad with oblique triangular cusps and course serrations near the base; lower teeth more slender with erect cusps and fine serrations. Coloration is bronze to greyish on the dorsal surfaces, becoming lighter below. The fins are distinctively white tipped, with white margins along the trailing edges of the first dorsal, pectoral, and caudal fins.
Size: Silvertip sharks can grow up to 300 cm (9.8 ft) long, but typically measure from 200–250 cm (6.6–8.2 ft) in length. Relatively slow growth rates of about 9 cm per year for juveniles have been reported. Females are generally larger than males. Males become sexually mature around 170 cm (5.6 ft) and females at 195 cm (6.4 ft). Average size at birth ranges from 70–80 cm (27.6–31.5 inches). The maximum published weight is 162.2 kg (358 lbs).
Distribution: Eastern Pacific from off southern Baja California to Columbia including the Cocos, Galapagos, and Revillagigedo Islands. Elsewhere, widespread yet fragmented distribution throughout the tropical Indo-Pacific from East Africa to the eastern Pacific. No confirmed reports have been made from the Atlantic.
Habitat: The silvertip shark can be found inshore over continental shelves and coral reefs, but seem to prefer offshore islands, isolated banks, and reef ledges. Depth range is throughout the water column from the surface to depths of about 800 m. Juveniles of the species are known to enter lagoons and shallow estuaries while adults tend to remain in deeper water. Although silvertips are quite active swimmers, tagging studies of juveniles show that movements are restricted to fairly localized areas perhaps indicating territorial behavior or site fidelity. They generally are seen singly or in pairs.
Biology: Reproductive mode viviparous with internal nourishment of the embryos supported by a yolk-sac followed by limited histotrophy before placentation. Females can have up to 11 pups per litter but average 5 or 6 pups. Females give birth in the summer after a 12-month gestation period. The diet of the silvertip shark consists of a variety of pelagic and demersal bony fishes, eagle rays, smaller sharks, octopus, and squid. Differential dentition in the upper and lower jaws allows them to effectively grasp and cut through their prey. This species is attracted to certain artificial, low frequency sounds and has been known to approach boats.
General interest: The silvertip shark should be treated with caution as it has been known to approach divers aggressively, especially in the presence of food, however reported attacks are very rare. Throughout most of their range, silvertips are caught intentionally and as bycatch for their meat, fins, teeth, jaws, skin, and cartilage. They are taken in both commercial and artisanal fisheries’ using long-lines, gillnet, and trawls. In some parts of the Indo-Pacific, silvertips play an important role in diving tourism. The World Conservation Union (IUCN) Red List has assessed this species to be “Near Threatened” with their status approaching “Vulnerable” as isolated populations and high site-fidelity make them highly susceptible to overfishing.
By Jahnava Duryea
Graduate Student in Ichthyology
Moss Landing Marine Laboratories
8272 Moss Landing Road
Moss Landing, CA 95039