suspended in open water. This species feeds mainly on bony fishes, including eels, squirrelfishes, snappers, damselfishes, parrotfishes, surgeonfishes, triggerfishes and goatfishes, as well as octopuses, spiny lobsters, and crabs. The whitetip reef shark is highly responsive to the olfactory, acoustic, and electrical cues given off by potential prey, while its visual system is attuned more to movement and/or contrast than to object details. It is especially sensitive to natural and artificial low-frequency sounds in the 25–100 Hz range, which evoke struggling fish. Whitetip reef sharks hunt primarily at night, when many fishes are asleep and easily taken. After dusk, groups of sharks methodically scour the reef, often breaking off pieces of coral in their vigorous pursuit of prey. Multiple sharks may target the same prey item, covering every exit route from a particular coral head. Each shark hunts for itself and in competition with the others in its group. Unlike blacktip reef sharks and grey reef sharks, whitetip reef sharks do not become more excited when feeding in groups and are unlikely to be stirred into a feeding frenzy. Despite their nocturnal habits, whitetip reef sharks will hunt opportunistically in daytime. Off Borneo, this species gathers around reef drop-offs to feed on food brought up by the rising current. Off Hawaii, they follow Hawaiian monk seals (Monachus schauinslandi) and attempt to steal their catches. A whitetip reef shark can survive for six weeks without food. Life history Like other members of its family, the whitetip reef shark is viviparous; once the developing embryos exhaust their supply of yolk, the yolk sac is converted into a placental connection through which the mother delivers nourishment for the remainder of gestation. Mature females have a single functional ovary, on the left side, and two functional uteruses. The reproductive cycle is biennial. Mating Mating is initiated when up to five males follow closely behind a female and bite at her fins and body, possibly cued by pheromones indicating the female's readiness. Each male attempts to seize the female by engulfing one of her pectoral fins; at times two males might grasp a female on both sides simultaneously. Once engaged, the sharks sink to the bottom, whereupon the male (or males) rotates one of his claspers forward, inflates the associated siphon sac (a subcutaneous abdominal organ that takes in seawater that is used to flush sperm into the female), and attempts to make contact with