Blacktip Reef Shark - Biology and Ecology

Biology and Ecology

Along with the grey reef shark (C. amblyrhinchos) and the whitetip reef shark (Triaenodon obesus), the blacktip reef shark is one of the three most common sharks inhabiting coral reefs in the Indo-Pacific. This species predominates in shallow habitats, while the other two are mostly found deeper. Fast-swimming and active, the blacktip reef shark may be encountered alone or in small groups; large "social" aggregations have also been observed. For the most part, juvenile and adult sharks are not segregated by sex, save for the movements of pregnant females to give birth. Individuals exhibit strong fidelity to particular areas, where they may remain for several years.

A tracking study off Palmyra Atoll in the central Pacific has found the blacktip reef shark has a home range of around 0.55 km2 (0.21 sq mi), among the smallest of any shark species. The size and location of the range does not change with time of day. Within this range, 3–17% of the area constitute favored hunting patches that are disproportionately occupied by the resident shark. The sharks spend most of their time swimming back and forth along reef ledges, making occasional short forays onto sandy flats. Their average swimming speed decreases when the tide rises at night, possibly because the influx of cooler water reduces their metabolism, or the accompanying movement of prey fishes makes foraging easier. Blacktip reef sharks at Aldabra tend to be more mobile than those at Palmyra, with recorded individual movements of up to 2.5 km (1.6 mi) over 7 hours.

Blacktip reef sharks, particularly small individuals, fall prey to larger fishes, including groupers, grey reef sharks, tiger sharks (Galeocerdo cuvier), and members of their own species. At Palmyra Atoll, adults avoid patrolling tiger sharks by staying out of the central, deeper lagoon. Their known parasites include the tapeworms Anthobothrium lesteri, Nybelinia queenslandensis, Otobothrium alexanderi, and Platybothrium jondoeorum, a myxosporidian in the genus Unicapsula, and the monogenean Dermophthirius melanopteri. One of the few documented examples of infectious disease in a shark was a fatal case of hemorrhagic septicemia in a blacktip reef shark, caused by the bacterium Aeromonas salmonicida subsp. salmonicida.