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Characteristics, distribution and ecology
Taxonomische classification
Synonyms and common names
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Author: (Rüppell, 1837)

Field Marks:
A big, stocky, short-nosed, pale yellow-brown requiem shark with the second dorsal about as large as the first, and narrow, smooth-cusped teeth in both jaws. Very similar to the allopatric N. brevirostris, but usually has more falcate fins.

Diagnostic Features:
Dorsal, pectoral and pelvic fins usually more strongly falcate. Serrations weakly developed on blades of upper teeth in individuals 1.4 m long and larger, and absent in small individuals 0.7 m or less. Total vertebral counts 224 to 227.

Geographical Distribution:
Indo-West and central Pacific: South Africa, Mauritius, Scychelles, Madagascar, and Red Sea east to Pakistan, India, Thailand, Viet Nam, Malaysia, Indonesia, New Guinea, Australia (Queensland, Western Australia and probably northern Australia as well), New Caledonia, The Philippines, Palau, Marshall Islands, Tahiti.

Habitat and Biology:
This is a tropical insnore shark of continental and insular shelves and terraces, found on or near the bottom in the intertidal down to at least 30 m. It sometimes occurs near the ourface, particularly when stimulated by food. These sharks prefer bays, estuaries, sandy plateaus, outer reef shelves at moderate depths and reef lagoons, often in turbid, still water. Young sharks are commonly found on reef flats, in water sufficiently shallow to bare their dorsal fins. That they may occasionally venture into deeper water is suggested by the appearance of one in a film ("Blue water, White Death") well offshore, possibly near a dead sperm whale being eaten by oceanic whitetip sharks (Carcharhinus longimanus).

The-sicklefin lemon shark is described as a sluggish species, swimming slowly near the bottom or resting on it. It is hardy in captivity and has been kept in public aquaria and oceanaria.

Viviparous, number of fetuses in a litter 1 to 13. Depending on locality, young are born in October or November (Madagascar) or December or January (French Polynesia). Gestation period may be 10 or more months.

This lemon shark feeds on bottom-dwelling bony fishes, including porcupine fishes, and stingrays.

This shark is reported as being shy of divers and reluctant to approach them even when dead fish baits are placed to attract them. In one reported instance an adult was attracted to a dead speared grouper and repeatedly fled when divers nearby made the slightest movement, but eventually grabbed the fish in a rush after a half hour of approaches and departures; apparently this indicated strong approach-avoidance behaviour on the part of this particular lemon shark. In shallow water young sicklefin lemon sharks are said to be more aggressive and inquisitive, but the adults often leave the vicinity of divers after being approached to the limits of visibility. However, this shark responds promptly and aggressively when touched, poked, or speared, and will attack people or boats when accosted. One such attack involved a victim who sought refuge atop a coral head, but had the aroused shark circling the coral head and waiting for hours before departing. There have been instances of seemingly unprovoked attacks by this shark on divers, possibly after the divers approached too close or otherwise alarmed the shark. Because of its large size, bulky body, massive head, powerful jaws, large daggerlike teeth, and its propensity to vigorously defend itself, the sicklefin lemon shark should be treated with great respect as a dangerous species.

Size:
Maximum about 310 cm, males mature at 243 cm; size at birth about 45 to 80 cm.

Interest to Fisheries:
Caught in Pakistan, India, Thailand, and probably other places where it occurs, in anchored and floating gillnets and on longlines. Its meat is used fresh and dried salted for human consumption, its liver is used for vitamin oil, and its fins are processed for shark-fin soup base.

Remarks:
Vernacular names include 'sharp-toothed shark', 'South Pacific lemon shark', and 'Arava'.

Type material:
Lectotype: Naturmuseums Senckenberg, SMF 2825, 680 mm stuffed specimen, designated by Klausewitz (1960:292). Type Locality: Djedda, Saudi Arabia, Red Sea.

Sicklefin lemon shark (Negaprion acutidens)