Abundance, demography and population structure of the grey reef shark (Carcharhinus amblyrhynchos) and the white tip reef shark (Triaenodon obesus) (Fam. Charcharhinidae)\ud \ud

Reef sharks (fam. Carcharhinidae) are high-order predators, found throughout the Indo-\ud Pacific. I examined the abundance, growth, reproduction and demography of two\ud species of reef carcharhinid; the grey reef shark (Carcharhinus amblyrhynchos) and the\ud whitetip reef shark (Triaenodon obesus), and investigated the genetic stock structure of\ud T. obesus across the Indo-Pacific.\ud \ud Underwater visual census protocols were successfully developed, and provided realtime,\ud fisheries-independent estimates of reef carcharhinid abundances. Visual censusing\ud of a minimally-exploited reef system ascertained that reef crest was the preferred habitat\ud of T. obesus and C. amblyrhynchos, while the blacktip reef shark (C. melanopterus) was\ud more abundant in reef flat and lagoon habitats. Reef carcharhinid densities were low,\ud and even in the most abundant habitat, did not exceed 3.5 sharks hectare-1. Visual\ud censuses across reef systems in the Indian and Pacific Oceans found consistently low\ud numbers of reef sharks, with most regions having less than 0.5 sharks hectare-1. Closer\ud investigation of the Great Barrier Reef (Australia) revealed a significant effect of\ud fishing management on reef shark abundance. All levels of fishing pressure impacted\ud upon reef carcharhinid abundance, with reductions on fished reefs of up to 80% and\ud 97% for T. obesus and C. amblyrhynchos, respectively. This suggests that reef shark\ud populations are particularly vulnerable to population depletion. The inability of marine\ud protected areas to provide refuge for reef carcharhinids was highlighted and discussed.\ud \ud Age and growth characteristics of T. obesus and C. amblyrhynchos populations from the\ud Great Barrier Reef were examined through vertebral thin sections. Both shark species grew slowly, with longevities of 19 years. Females out-lived males in both species.\ud Both sexes of C. amblyrhynchos grew at similar rates, while sexually-dimorphic growth\ud rates were observed in older T. obesus. Age estimates were preliminarily validated\ud through oxytetracyclined recaptures of C. amblyrhynchos, while characterisation of the\ud vertebral edge provided strong evidence that T. obesus also lays annual growth bands.\ud \ud Females matured 1-2 years later than males, at 8 and 11 years for T. obesus and C.\ud amblyrhynchos, respectively. Mean litter sizes were comparable with smaller (