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Characteristics, distribution and ecology
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Author: (Rüppell, 1837)

Field Marks:
A small, fairly slender grey requiem shark with brilliant, extremely conspicuous white tips (not entire posterior margins) on its first dorsal fin and upper caudal lobe (white tip sometimes present on the second dorsal, ventral caudal lobe, and underside of the pectoral fins), lighter undersides shading gradually into darker dorsal coloration, an extremely short, broad snout, horizontally oval eyes with posterior notches, downslanted mouth and prominent brow ridges that give its face a sardonic, disgusted look, prominent expanded, tubular anterior nasal flaps, a large second dorsal fin that is still considerably smaller than the first dorsal, and small smooth-edged teeth with strong cusplets in both jaws.

Diagnostic Features:
Body moderately slender. Head very broad and flattened but not trowel-shaped; snout broadly rounded or almost wedge-shaped in dorsoventral view and very short, with preoral length subequal to internarial space and much less than mouth width; eyes fairly small, usually with posterior notches; spiracles usually absent, or present as minute pore- or slitlike openings; no papillose gillrakers on internal gill openings; nostrils small, internarial space about 3 times the nostril width; anterior nasal flaps slightly elongated, distally truncated, and forming distinct tubes with the mesonarial flaps; labial furrows very short, essentially confined to mouth corners, with uppers shorter than lowers and with their ends falling far behind eyes; teeth similar in upper and lower jaws; anteroposteriors in both jaws with erect to semioblique, narrow cusps, strong, high proximal and distal cusplets, but no blades or serrations; cusps of lower teeth not protruding when mouth is closed; 42 to 50/42 to 48 rows of teeth. Interdorsal ridge absent; no lateral keels on caudal peduncle; upper precaudal pit transverse and crescentic. First dorsal origin well behind pectoral free rear tips, its midbase much closer to pelvic bases than pectorals and free rear tip slightly anterior, over, or slightly posterior to pelvic fin origins; second dorsal fin very large but distinctly smaller than first, its height 1/2 to 3/4 of first dorsal height; its origin about opposite or slightly anterior or posterior to anal origin; pectorals fin fairly broad and triangular, their lengths from origin to free rear tip between 3/ 5 to 2/3 of pectoral anterior margins; pectoral origins varying from under interspace between fourth and fifth gill slits to about under fifth gill slits; anal fin about as large as second dorsal, with short preanal ridges and a deeply notched posterior margin. Colour grey or brownish above, without a colour pattern other than variable dusky spots and brilliant white fin tips. Moderate-sized sharks, adults possibly reaching 2.2 m.

Geographical Distribution:
Wideranging in the Indo-Pacific. Indo-West and central Pacific: South Africa and Red Sea toPakistan, India, Sri Lanka, Burma, Indonesia, Viet Nam, Taiwan Island, Riu Kiu Islands, The Philippines, Australia (Queensland, north and Western Australia), New Guinea; widespread in Polynesia, Melanesia and Micronesia northward to the Hawaiian Islands and southwest to the Pitcairn group (see Randall, 1977 for details of the range of this species in Oceania). Eastern Pacific: Cocos and Galapagos Islands, Panama to Costa Rica.

Habitat and Biology:
A common tropical inshore shark of the continental shelves and island terraces, frequently found in shallow, clear water, on or near coral reefs; often at depths of 8 to 40 m but up to a metre or less or exceptionally down to 110 m or even 330 m; commonly occurring on or near the bottom, in crevices or caves in coral reefs, and in coral lagoons. It is often seen resting on the bottom, in caves and under ledges in coral and on sand. In Oceania, it is one of the commonest reef sharks, along with the blacktip reef shark, Carcharhinus melanopterus and the grey reef shark, C. amblyrhynchos. It does not frequent extremely shallow reef and sandy areas like the blacktip reef shark, nor does it range well above the substrate and near outer dropoffs like the grey reef shark.

This is a bottom-oriented shark that superficially resembles the sharks of the genus Triakis in its active, undulating swimming pattern, and like some of these triakids seldom comes to the surface and is readily capable of sitting motionless on the bottom for long periods. Tagging studies (including sonic tagging) indicate that these sharks have a diel and tidal activity pattern, being most active at night and at slack tides where strong currents occur. They aggregate in caves during daytime but are often more active during slack tides. Their usual routine may be interrupted by learned behaviour in areas where much spearfishing occurs, as they tend to come out of their caves when spearfishing starts, and search for speared prey. Apparently the sound of spearfishing activities, or even a boat dropping anchor, cues the sharks and arouses them.

Individual whitetip reef sharks return to the same caves in the day for long periods, but preferences for caves change periodically with given individuals, so that they vacate a given cave and rest in another after some time. These sharks have a narrow home range for their daily activities and can remain in a given small area for months or even years, but eventually may quit an area and wander for a time before fixating on a new area. Apparently these sharks are not territorial, but share their home range with other members of their species and other sharks without conflict. Distances travelled by given individuals have been from 0.3 to about 3 km in periods up to about a year, and an estimation of the sizes of home ranges of these sharks has been given as several square kilometres.

Data on growth in this species are limited, but from estimations by Randall (1977) the reef whitetip may take at least 5 years to reach maturity, and reach a maximum age of at least 25 years.

Viviparous, with 1 to 5 young per litter (commonly two or three). In French Polynesia, this shark apparently gives birth in autumn or winter, May to August, while at Enewetak Atoll they may give birth in July. Data from Randall (1977) from mature female sharks from Johnston Island and Enewetak Atoll suggests that this shark has a gestation period of at least 5 months, but this needs to be confirmed.

Unlike many carcharhinids, this shark is an inept pelagic predator, but is an efficient specialist in capturing bottom prey in crevices, holes and caves in coral heads and ledges. It apparently orients to olfactory and sonic cues but may have considerable difficulty finding cut baits. One or more whitetips may pursue a wounded, speared fish headfirst into a hole or crevice, and attempt to grab it. If they fail to immediately capture it they may rest with their bodies half out of the hole the prey is in, but sooner or later one will grab the prey. The shark then thrashes until it extracts or dismembers its victim. It feeds primarily on bony fishes, including eels (a moray was found in one), squirrelfishes, snappers, damselfishes, parrotfishes, surgeonfishes, triggerfishes, and goatfishes and octopi, but also spiny lobsters and crabs. One whitetipreef shark was found in the stomach of a giant grouper, and it is likely that other, larger carcharhinid sharks prey on it.

The whitetip reef shark often does not react to swimmers or divers unless approached, in which case it flees or keeps a distance between itself and the people involved. When spearfishing, other fish-collecting activity or deliberate baiting to lure sharks for photography is done by divers near the bottom where this shark occurs, it is readily attracted and seeks out potential food sources. Although whitetips may approach divers very closely under such conditions, they are rarely aggressive, and divers have been able to feed them by hand. On rare occasions, whitetips have bitten divers, but apparently in self-defence when molested, and especially when excited during spearfishing bouts. For example, Randall (1977) was attacked by one that he had speared and pursued. Other divers have had to repeatedly fend off excited and apparently attacking whitetips while contesting speared fishes with them. One spearfishing diver was bitten in the leg by a whitetip that had come up behind him, but was not greatly injured. Its small size, small teeth, and generally placid and unaggresive behaviour makes it far less dangerous than many other carcharhinids, but even this shark can be stimulated into attacking, like a domestic cat or dog. Randall (1977) regards the possibility of ciguatera poisoning from eating the meat of the whitetip as more of a danger than attack by it, although areas where whitetips are toxic are few and sporadic.

Size:
Maximum said to be about 213 cm but adults are very rare over 160 cm; males maturing at about 104 to 105 cm and reaching 168 cm, females maturing at 105 to 109+ cm and reaching at least 158 cm; size at birth about 52 to 60 cm.

Interest to Fisheries:
Details of fisheries involving this species are Sizetchy. It is apparently fished off Pakistan, India, Sri Lanka and Madagascar, and probably elsewhere where it occurs. It is fished with floating and fixed bottom gillnets and longlines, and its meat and liver utilized fresh for human consumption.

Remarks:
Randall (1977) presented a comprehensive survey of the life-history of this species, with a detailed review of its distribution.

The characters said by Whitley (1939) to separate his T. apicalis from the wide-ranging T. obesus apparently do not hold (Taniuchi, 1975; Bass, D'Aubrey and Kistnasamy, 1975b; Randall, 1977; Compagno, 1979), nor do eastern Pacific representatives of the species differ significantly from Indo-West Pacific sharks (Compagno, 1979).

Type material:
Lectotype: Naturmuseums Senckenberg, SMF 3149, 310 mm stuffed specimen, designated by Klausewitz (1960:291). Type Locality: Djedda, Saudi Arabia, Red Sea.

Whitetip reef shark (Triaenodon obesus)