Whitetip Reef Shark - Biology and Ecology

Biology and Ecology

The whitetip reef shark is one of the three most common sharks inhabiting the reefs of the Indo-Pacific, the other two being the blacktip reef shark (Carcharhinus melanopterus) and the grey reef shark (Carcharhinus amblyrhynchos). The habitat preferences of this species overlap those of the other two, though it does not tend to frequent very shallow water like the blacktip reef shark, nor the outer reef like the grey reef shark. The whitetip reef shark swims with strong undulations of its body, and unlike other requiem sharks can lie motionless on the bottom and actively pump water over its gills for respiration. This species is most active at night or during slack tide, and spends much of the day resting inside caves singly or in small groups, arranged in parallel or stacked atop one another. Off Hawaii, these sharks may be found sheltering inside underwater lava tubes, while off Costa Rica they are often seen lying in the open on sandy flats.

Whitetip reef sharks generally remain within a highly localized area; only rarely do they undertake long movements, wandering for a while before settling down somewhere new. One study at Johnston Atoll found that none of the sharks examined had moved more than 3 km (1.9 mi) away from their original capture location over periods of up to a year. Another study at Rangiroa Atoll in French Polynesia found that, after more than three years, around 40% of the originally tagged sharks were still present on the same reef where they were first captured. An individual shark may rest inside the same cave for months to years. The daytime home range of a whitetip reef shark is limited to approximately 0.05 km2 (0.019 sq mi); at night this range increases to 1 km2 (0.39 sq mi). These sharks are not territorial and share their home ranges with others of their species; they do not perform threat displays.

Important predators of the whitetip reef shark include tiger sharks (Galeocerdo cuvier), Galapagos sharks (Carcharhinus galapagensis), and possibly also silvertip sharks (Carcharhinus albimarginatus), though they usually occur at depths greater than those favored by whitetip reef sharks. An 80 cm (31 in) long whitetip reef shark has also been found in the stomach of a giant grouper (Epinephelus lanceolatus), though these groupers are unlikely to be significant predators of this species due to their rarity. Known parasites of the whitetip reef shark include the copepod Paralebion elongatus and the praniza (parasitic) larvae of the isopod Gnathia grandilaris. While resting during the day, these sharks have been observed being cleaned by the wrasse Bodianus diplotaenia and the goby Elacatinus puncticulatus. Unusually, there is also a report of seven whitetip reef sharks adopting a cleaning posture (mouth agape and gills flared) in the midst of a swarm of non-cleaning hyperiid amphipods; the mechanical stimulation from the moving amphipods are thought to have evoked this behavior through their similarity to actual cleaner organisms.