Journal of Fish Biology (2013) 82, 1192–1210 doi:10.1111/jfb.12057, available online at wileyonlinelibrary.com Population structure and residency patterns of the blacktip reef shark Carcharhinus melanopterus in turbid coastal environments A. Chin*†, A. J. Tobin*, M. R. Heupel*‡ and C. A. Simpfendorfer* *Centre for Sustainable Tropical Fisheries and Aquaculture & School of Earth and Environmental Sciences, James Cook University, Townsville, Qld 4811, Australia and ‡Australian Institute of Marine Science, Townsville, Qld 4810, Australia (Received 4 August 2012, Accepted 19 December 2012) This study examined the characteristics of a blacktip reef shark Carcharhinus melanopterus popula- tion in turbid coastal habitats through a multi-year fishery-independent sampling and tag–recapture programme. Results revealed a highly structured population comprised almost entirely of juve- niles and adult females with individuals between 850 and 1050 mm total length effectively absent. Mature males were also rarely encountered with adult sex ratio highly biased towards females (female:male = 7:1). Mating scars were observed on adult females between December and April, and parturition was observed from December to March. Regression analysis showed that catch rates were significantly higher during the summer wet season between November and May. Recapture data suggested a highly resident population with a recapture rate of 21% and a mean recapture distance of 0·8 km. In addition, 33% of recaptured animals were captured multiple times, indicating long-term residency. Most recaptures were, however, of adults with few juveniles recaptured. Widespread sampling at the study site and in adjacent areas suggested that the population was highly local- ized to a specific bay. The bimodal and sex-segregated population structure observed here differs from previous reports for this species, and in combination with reproductive observations, suggests population structuring to facilitate reproductive and recruitment success. These data also high- light the potential ecosystem functions performed by coastal habitats in sustaining C. melanopterus populations. © 2013 The Authors Journal of Fish Biology © 2013 The Fisheries Society of the British Isles Key words: catch per unit effort; dispersal; mangrove; reproduction; sex segregation; site attachment. INTRODUCTION Characteristics of fish populations, such as size and age structure, segregation by sex and maturity, movement, site attachment and habitat use patterns, are important aspects in understanding the biology and ecology of fishes (Cort´ es, 2007; Wear- mouth & Sims, 2008; Simpfendorfer et al ., 2011). Population characteristics can also reflect the ecosystem services that habitats may provide for fish populations, and can have important implications for management and conservation (Wearmouth †Author to whom correspondence should be addressed. Tel.: +61 7 4781 6796; email: andrew.chin@ jcu.edu.au 1192 © 2013 The Authors Journal of Fish Biology © 2013 The Fisheries Society of the British Isles