Silvertip Shark: Carcharhinus albimarginatus

Family: Carcharhinidae
Common name(s)

Silvertip Shark.

Identification

All fins (except second dorsal) have brilliant-white tips and posterior margins. Second dorsal small with black or dusky tip. First dorsal origin level with, or slightly anterior to free rear tip of pectoral fin. Second dorsal origin level with anal fin origin. Pectoral fins mildly falcate with pointed tips. Low interdorsal ridge present. Dorsal coloration coloration grey/brown; often with a bronzy sheen. Pelvic, anal, and caudal fins somewhat dusky (before white margin).

Size

Maximum length 275cm (Specimen recorded by Fourmanior in 1961). Size at maturity approx 160-199cm. Size at birth 63-80cm.

Habitat

A warm water species inhabiting coral and rocky reefs, offshore islands and seamounts. Will also enter coastal lagoons. Present from the surface to at least 600m.

Distribution

The silvertip shark is wide ranging throughout the tropical Indo-Pacific but not completely cosmopolitan. It is noticeably absent from the Red Sea and the Hawaiian Islands, among other places.

Conservation Status

VULNERABLE

The Silvertip Shark is subjected to high bycatch levels in high seas fisheries and in artisanal longline, gillnet, and trawl fisheries throughout its range, with its meat and fins marketable. Surveys of fish markets in Indonesia and Papua New Guinea suggest that the Silvertip Shark has undergone large declines in those waters. There is evidence that Indonesian fisheries have considerably reduced the numbers of the Silvertip Shark within the Memorandum of Understanding [MOU] 1974 Box in the Timor Sea. Catches of sharks in this area declined throughout the early 1990s to the level that Indonesian shark fishing vessels have become relatively uncommon. In the Indian Ocean there was an estimated decline in the abundance of several reef shark species (including the Silvertip Shark) of over 90% in the period between 1970 and 2006 and around the US Pacific Islands common reef sharks have declined to 3-10% of baseline levels. This species’ site-specificity, patchy population, and life history characteristics indicate that remote populations that are not currently managed are highly susceptible to depletion from direct shark fisheries and illegal practices. This information, combined with actual and potential levels of exploitation throughout its range results in a global assessment of Vulnerable, based on suspected overall population decline of greater than 30% over three generations (66 years) inferred from survey data. This assessment should be revisited when reliable catch data become available. In Australia, catch and survey data from the Great Barrier Reef suggest that this species is fairly common. The Silky Shark has limited interaction with fisheries operating in tropical Queensland and the Northern Territory an therefore, the species is listed as Least Concern in the regional Australian assessment.

Citations and References
Espinoza, M., González-Medina, E., Dulvy, N.K. & Pillans, R.D. 2016. Carcharhinus albimarginatusThe IUCN Red List of Threatened Species 2016: e.T161526A68611084. https://dx.doi.org/10.2305/IUCN.UK.2016-3.RLTS.T161526A68611084.en. Downloaded on 22 September 2020.

Reproduction

A viviparous species with yolk-sac placenta. 1-11 pups per litter. In the Mauritius-Sechelles area, birthing takes place in December or January after a gestation period of roughly 1 year.
Nurseries probably exist at many offshore islands where it occurs. At the Revillagigedo Archipelago (Socorro), small juveniles are often spotted at cleaning stations.

Diet

Diet consists of midwater and demersal bony fishes, small sharks, eagle rays, and cephalopods (octopuses).

Behavior

Cruises deeper reefs and drop-offs where schooling fish gather. Silvertip sharks are frequently sighted hunting amoung clouds of jacks and butterfish at Roca Partida (Socorro).
Considered an aggressive predator that dominates over similarly sized co-species such as Galapagos sharks and blacktip sharks where they occur.

Reaction to divers

Relatively easy to approach at some locations where resident silvertips are conditioned to seeing divers. Extremely bold and potentially aggressive in baited situations.

Diving logistics

In the Eastern Pacific, silvertip sharks can be encountered at most of the popular offshore archipelagos and islands. Due to their distance from the mainland, all must be visited by liveaboard dive boat.
At the Revillagigedo Archipelago in Mexico, juvenile silvertips are virtually always found at a dive site called The Canyon off of San Benedicto Island. Whereas, larger animals are regularly spotted at Roca Partida.
At Cocos Island in Costa Rica, silvertips are sporadically encountered on some deep wall dives. There used to be a particularly good spot for them at a cleaning station called Silverado but I have heard that they have moved off, and that particular dive site is now a better spot for tiger sharks (this needs confirmation).
Malpelo Island off of Panama also has random sightings. As do the current swept northern Galapagos dive sites at Wolf and Darwin.

In French Polynesia, silvertips are very common in the Tuamotu Archipelago. Divers often see them mixed in with the large aggregations of grey reef sharks that aggregate in the passes leading in and out of the atolls.
At the south pass of Fakarava, you are likely to see 400+ sharks on a good dive, of which maybe 5% are silvertips.
Rangiroa has similar passes but with smaller quantities of sharks. I once did a baited silvertip dive there, but chumming has since been banned across all of FP.

Back in the mid 1990’s, I visited Silvertip Bank in Myanmar. Even back then, the reef had been almost completely destroyed by dynamite fishing. There were very few fishes to be seen but we still managed to chum in a pair of large silvertip sharks. The sharks were extremely aggressive, repeatedly bumping our small group of divers, long after the bait had been consumed. Considering how easy it is to see this species at relatively close quarters in Pacific Mexico, French Polynesia, and elsewhere, the use of bait is clearly not necessary to encounter this species.

Similar species

Oceanic Whitetip Shark Although this species possesses white-tipped fins like the silvertip shark, it’s dappled countershading, and large spatulate pectoral fins looks significantly different.

Grey Reef Shark This similarly shaped species sometimes has an identical white margin on its first dorsal fin but none of its other finned are white-tipped.