Blacktip Reef Sharks Carcharhinus Melanopterus Research Articles

Performance and detection range of acoustic receivers in mangrove habitats.

Acoustic telemetry has been used to monitor the movement of aquatic animals in a broad range of aquatic environments. Despite their importance, mangrove habitats are understudied for the spatial ecology of elasmobranchs, with acoustic telemetry rarely used inside mangrove habitats. One reason for this may be a general assumption that acoustic signals would not be able to be detected by receivers in such shallow, structurally complex, environments. This study tested whether acoustic receivers can be used inside mangrove habitats to track the movement of sharks and rays. Thirty-eight receivers were deployed in a mangrove system in Pioneer Bay, Orpheus Island, Great Barrier Reef, including inside mangroves, mangrove edges, and adjacent reef flat areas. The detection range and receiver performance metrics, such as code detection efficiency, rejection coefficient, and noise quotient, were examined and tested among habitats. The results highlighted that the signal from transmitters was successfully detected inside mangrove habitats as well as on the adjacent reef flat. The range to detect at least 50% of transmissions was up to 20 m inside mangroves and up to 120 m outside mangroves. The performance metrics of acoustic receivers inside the mangrove habitat were characterized by low background noise, low rejection rates, and reasonably high code detection efficiency. Furthermore, this study tested the application of this method on juvenile blacktip reef shark Carcharhinus melanopterus and mangrove whipray Urogymnus granulatus, and demonstrated that it can be used to successfully track animals inside mangrove habitat. This novel method could reveal further information on how sharks and rays use mangrove habitats.

Thermally insensitive physiological performance allows neonatal sharks to use coastal habitats as nursery areas

Coastal sharks can use shallow, nearshore habitats as nursery areas, which is a behaviour that may increase fitness. The ecological benefits of shark nursery areas are well studied; yet the physiological mechanisms that enable sharks to exploit coastal habitats, especially those that experience extreme and dynamic temperatures, remain understudied. We hypothesised that neonatal sharks are able to use thermally dynamic coastal habitats as nursery areas because temperature does not strongly affect their physiology. To test this hypothesis, we defined patterns of nursery area use and temperature-dependent physiological performance in 2 reef shark species. First, we determined whether 10 sites around the island of Moorea, French Polynesia, satisfied nursery area criteria for neonate populations of blacktip reef sharks Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens using 5 consecutive years of abundance surveys. We then quantified effects of thermal exposure in situ on growth in recaptured individuals and quantified the temperature dependence of metabolic rate ex situ using respirometry. We found several potential C. melanopterus nursery areas, but during different sampling years, and identified 1 N. acutidens nursery area that remained consistent during the entire 5 yr study. In support of our hypothesis, growth and metabolic performance were not strongly affected by temperature in either species. Thus, thermally insensitive physiological performance may be a trait that elasmobranchs exhibit in thermally variable coastal habitats, including shark nursery areas. Together, this approach demonstrates how physiological and ecological concepts complement each other to improve our understanding of nursery area use in coastal shark populations.

Human‐induced shifts in habitat use and behaviour of a marine predator: the effects of bait provisioning in the blacktip reef shark

AbstractWhile the negative effects of consumptive pressures on marine predators are well established, the effects of increasing non‐consumptive activities such as wildlife tourism are still understudied. As such, the long‐term effects of the provision of bait on shark behaviour are still unclear. Here, we assessed the effects of provisioning using a Control‐Impact design on the spatial use and level of residency of the blacktip reef shark Carcharhinus melanopterus over a 2‐year period. We used effect sizes to model the relative changes in residency between provisioning and non‐provisioning sites. Sharks showed a high degree of residency and significant changes in their habitat use which persisted overnight while the activity ceased. We suggest that provisioning activities can affect species with high level of residency such as the blacktip reef shark. Further research is needed to better understand how these behavioural modifications can alter the fitness of this species. It is important to adapt shark provisioning activities to limit the induced changes in habitat use.

At the Turn of the Tide: Space Use and Habitat Partitioning in Two Sympatric Shark Species Is Driven by Tidal Phase

Coexistence of ecologically similar species occupying the same geographic location (sympatry) poses questions regarding how their populations persist without leading to competitive exclusion. There is increasing evidence to show that micro-variations in habitat use may promote coexistence through minimising direct competition for space and resources. We used two sympatric marine predators that show high fidelity to a small, remote coral atoll as a model to investigate how temporally dynamic partitioning of space use may promote coexistence. Using novel methods (difference network analysis and dynamic space occupancy analysis), we revealed that even though blacktip reef sharks Carcharhinus melanopterus and sicklefin lemon sharks Negaprion acutidens both show focused use of the same atoll habitats, the spatio-temporal dynamics of their use was partitioned such that they only shared the same microhabitats 26% of the time. Moreover, the degree of overlap was strongly influenced by the tidal cycle, peaking at ~35% at higher tides as both species appear to target similar intertidal micro-habitats despite the increase in available space. Our work provides a rare example of how two marine predators with similar ecological roles and habitat preferences may coexist in the same place through dynamic segregation of habitat use in space and time, potentially reflecting adaptive behavioural traits for minimising interactions. The strong influence of small tidal variation on species habitat use and partitioning also raises concerns over how atoll ecosystem dynamics may be influenced by sea level rises that could alter tidal dynamics.

The hemisphere of fear: the presence of sharks influences the three dimensional behaviour of large mesopredators in a coral reef ecosystem

Predators can exert strong ecological effects on their prey either via consumption or by altering their behaviour and morphology. In marine systems, predators and their prey co‐occur in a three‐dimensional environment, but to date predator–prey studies have largely focussed on behaviours of prey on horizontal (distance from shelter) rather than vertical (height in water column) axes. We used life‐size shape‐models of a blacktip reef shark Carcharhinus melanopterus (threatening shape‐model), a juvenile coral trout Plectropomus leopardus (non‐threatening shape‐model) and a shape‐control to examine the impact of perceived instantaneous (measured by time to first feeding) versus sustained (measured by time to consume the entire bait) predation threats on the feeding behaviour and three‐dimensional use of space by mesopredatory reef fishes in a coral reef environment. We found that mesopredatory fishes such as red snapper Lutjanus bohar and spangled emperor Lethrinus nebulosus took longer to begin feeding and to consume predation assays (fish baits) at greater distances from the shelter of a patch reef across both horizontal and vertical axes and that this phenomenon was stronger in the vertical axis than the horizontal. The presence of a life‐size shape‐model of a shark, which we used to increase the perception of predator threat, magnified the instantaneous effect compared to non‐threatening models, but not the sustained effect. We found no evidence for a difference in the level of predation risk posed by the shape‐model of the juvenile coral trout (a non‐threatening reef fish) and a negative control (no shape‐model). Our study suggests that mesopredators modify their behaviours in response to the perceived risk of predation across both horizontal and vertical axes away from shelter, and that this response is most severe on the vertical axis, potentially limiting daytime foraging behaviour to a hemisphere around shelter sites.

Response of blacktip reef sharks Carcharhinus melanopterus to shark bite mitigation products

Globally, the frequency of shark bites is rising, resulting in an increasing demand for shark deterrents and measures to lessen the impact of shark bites on humans. Most existing shark protection measures are designed to reduce the probability of a bite, but fabrics that minimise injuries when a shark bite occurs can also be used as mitigation devices. Here, we assessed the ability of the Ocean Guardian Scuba7 and Kevlar material to reduce the likelihood of blacktip reef sharks, Carcharhinus melanopterus, from feeding, and to minimise injuries from shark bites. Sharks were enticed to consume a small piece of local reef fish (bait) placed between the two Scuba7 electrodes with the deterrents randomly being turned on or kept off. In the second experiment, the bait was attached to a small pouch made of either standard neoprene or neoprene with a protective layer of Kevlar around it. The Scuba7 reduced the proportion of baits being taken by 67%, (from 100% during control trials to 33%). Sharks also took more time to take the bait when the device was active (165 ± 20.40 s vs. 38.9 ± 3.35 s), approached at a greater distance (80.98 ± 1.72 cm vs. 38.88 ± 3.20 cm) and made a greater number of approaches per trial (19.38 ± 2.29 vs. 3.62 ± 0.53) than when the Scuba7 was inactive. The sizes of punctures from shark bites were significantly smaller on neoprene with Kevlar compared to standard neoprene (3.64 ± 0.26 mm vs. 5.88 ± 0.29 mm). The number of punctures was also fewer when Kevlar was used (14.92 ± 3.16 vs. 74.1 ± 12.44). Overall, the Ocean Guardian Scuba7 and Kevlar reduced the impact of blacktip reef shark bites. These findings may help consumers make informed decisions when purchasing shark deterring and protective products.

First photographic inland record of blacktip reef sharks Carcharhinus melanopterus (Carcharhiniformes: Carcharhinidae) in Indonesian waters

Blacktip reef sharks Carcharhinus melanopterus were caught and photographed by local people on 6 March 2019 during a flash flood in Sentani, Jayapura district, Papua province, Indonesia. The presence of C. melanopterus in Sentani represents the first inland record (c. 20 km) for this species in Indonesia. All individuals found were small-sized sharks (c. 500-600 mm), suggesting very young juveniles. We presume their occurence in Sentani a few hours after a flash flood is in response to seasonal freshwater inflow to estuarine environment.

Effects of anticoagulants on stable-isotope values (δ13 C and δ15 N) of shark blood components.

The effects of anticoagulant EDTA and sodium heparin (SH) on stable carbon δ13 C and nitrogen δ15 N isotopic values of red blood cells (RBC) and blood plasma in juvenile blacktip reef sharks Carcharhinus melanopterus were analysed. Plasma preserved with anticoagulants was not isotopically distinct from plasma stored in no-additive control tubes but RBC δ15 N values exhibited small enrichments when preserved with EDTA and SH. Results suggest EDTA and SH are viable anticoagulants for stable isotopic analyses of blood fractions but further studies are advised to validate results.

Similar bacterial communities on healthy and injured skin of black tip reef sharks

BackgroundSharks are in severe global decline due to human exploitation. The additional concern of emerging diseases for this ancient group of fish, however, remains poorly understood. While wild-caught and captive sharks may be susceptible to bacterial and transmissible diseases, recent reports suggest that shark skin may harbor properties that prevent infection, such as a specialized ultrastructure or innate immune properties, possibly related to associated microbial assemblages. To assess whether bacterial community composition differs between visibly healthy and insulted (injured) shark skin, we compared bacterial assemblages of skin covering the gills and the back from 44 wild-caught black-tip reef sharks (Carcharhinus melanopterus) from the Amirante Islands (Seychelles) via 16S rRNA gene amplicon sequencing.ResultsShark skin-associated bacterial communities were diverse (5971 bacterial taxa from 375 families) and dominated by three families of the phylum Proteobacteria typical of marine organisms and environments (Rhodobacteraceae, Alteromonadaceae, Halomonadaceae). Significant differences in bacterial community composition of skin were observed for sharks collected from different sites, but not between healthy or injured skin samples or skin type (gills vs. back). The core microbiome (defined as bacterial taxa present in ≥50% of all samples) consisted of 12 bacterial taxa, which are commonly observed in marine organisms, some of which may be associated with animal host health.ConclusionThe conserved bacterial community composition of healthy and injured shark skin samples suggests absence of severe bacterial infections or substantial pathogen propagation upon skin insult. While a mild bacterial infection may have gone undetected, the overall conserved bacterial community implies that bacterial function(s) may be maintained in injured skin. At present, the contribution of bacteria, besides intrinsic animal host factors, to counter skin infection and support rapid wound healing in sharks are unknown. This represents clear knowledge gaps that should be addressed in future work, e.g. by screening for antimicrobial properties of skin-associated bacterial isolates.

Fine-scale movements of juvenile blacktip reef sharks Carcharhinus melanopterus in a shallow nearshore nursery

Limited information is available on the fine-scale movements and habitat use of juvenile sharks in very shallow (<1 m) nearshore areas and the factors that drive these behaviours. Active acoustic tracking was used to investigate movements and habitat use of juvenile (683 +/- 58 mm total length; mean +/- SD) blacktip reef sharks Carcharhinus melanopterus at Orpheus Island, Australia. Six juveniles were tracked by foot and boat for over 62 h. Juveniles moved in synchrony with tidal cycles, always remaining within very shallow (<1 m) sandy reef flat or reef crest waters during outgoing, low and incoming tides, and using inundated mangrove habitat during higher tides, indicating that tidal fluctuations were a major driver of movement and habitat use. Individuals never left the bay where they were captured or entered deep water beyond the fringing reef, restricting their movements within water <60 cm deep. In general, linearity and rate of movement were significantly higher during incoming or outgoing tides, whereas these measures were significantly lower during higher tide heights when juveniles were occupying mangrove habitats. The observed behaviour was most likely a predator-avoidance strategy, highlighting the importance of mangrove root habitat use by juvenile blacktip reef sharks in coastal nursery areas and indicating that this may be an essential habitat for the young of this species.

Size frequency, dispersal distances and variable growth rates of young sharks in a multi-species aggregation.

During a mark-recapture survey from November 2014 until April 2017, 333 neonatal and juvenile blacktip reef sharks Carcharhinus melanopterus and 302 neonatal and juvenile sicklefin lemon sharks Negaprion acutidens were tagged and measured at the uninhabited and isolated St. Joseph Atoll (Republic of Seychelles). Both species demonstrated seasonal reproductive synchronicity and relatively large sizes at birth. Despite the extended times at liberty > 2.5 years, the majority of recaptures were found in close proximity to the initial tagging location (< 500 m). Annual growth rates of C. melanopterus (n = 24) and N. acutidens (n = 62) ranged from 6.6 to 31.7 cm year-1 (mean ± SE; 16.2 ± 1.2 cm year-1 ) and 0.2 to 32.2 cm year-1 (11.8 ± 1 cm year-1 ), respectively and are to date the most variable ever recorded in wild juvenile sharks. High abundances of both species coupled with long-term and repeated recaptures are indicative of a habitat where juveniles can reside for their first years of life. However, large variability in annual growth rates in both species may suggest high intra and interspecific competition induced by a possibly resource limited, isolated habitat.

Spatial distribution, seasonal abundance and exploitation status of shark species in Kenyan coastal waters

Efforts to conserve and manage shark populations are often hampered by a lack of basic data, such as species-specific landings and distribution ranges. We bridge this gap in coastal East Africa by providing data on the distributions, catch rates, morphometrics, and exploitation status of shark species in Kenyan coastal waters. Data were collected from artisanal fishers and from bycatch taken by shallow-water (10–50 m) prawn trawlers from Malindi-Ungwana Bay and demersal research trawlers (10–150-m depth) along the ∼640-km coastline, over a 12-month period (June 2012 to May 2013). A total of 1 893 individual sharks (representing 20 species and 11 families) were sampled from the artisanal fishery (n = 1 610) and the trawlers (n = 283). The demersal trawl bycatches were dominated by the African angelshark Squatina africana (2.39 kg h–1), shortnose spurdog shark Squalus megalops (1.48 kg h–1) and African spotted catshark Holohalaelurus punctatus (0.11 kg h–1). Catches of the scalloped hammerhead shark Sphyrna lewini (0.73 kg h–1), smooth hammerhead shark Sphyrna zygaena (0.60 kg h–1) and grey reef shark Carcharhinus amblyrhynchos (0.77 kg h–1) dominated in the prawn trawlers. Only a few species (S. lewini, C. amblyrhynchos, and blacktip reef shark Carcharhinus melanopterus) showed a coast-wide distribution in the artisanal fishery. Artisanal fishers harvested mostly immature specimens of S. lewini, C. melanopterus and blacktip shark Carcharhinus limbatus, suggesting that the fishery might be unsustainable in the long-term. The Endangered S. lewini is the most vulnerable to overexploitation on the Kenyan coast, with most specimens landed (>90%) being below the size at maturity. Data are also presented on morphometric relationships and observed or estimated exploitation reference points (maximum observed length Lmax, asymptotic length L∞, mean length at first maturity Lm, and optimum length Lopt) for the commonly landed species. A more comprehensive coast-wide National Plan of Action is recommended for the management of shark populations in Kenya.

Biological and environmental effects on activity space of a common reef shark on an inshore reef

Proximity to land and sources of freshwater expose fishes residing on inshore reefs to fluctuating environmental conditions (e.g. high freshwater run-off/low salinity events). However, site attachment in many reef residents, such as reef sharks, could mean that relocation in response to unfavourable environmental conditions may not be feasible. Passive acoustic telemetry was used to monitor movement and space use of 18 blacktip reef sharks Carcharhinus melanopterus on an inshore reef off the coast of Queensland, Australia, to determine their response to environmental change. Activity space of sharks was modelled against combinations of environmental (wind speed, rain, salinity and water temperature) and biological (size, sex) factors. Size was the most influential predictor of space use, with larger sharks having larger activity spaces. Sex also appeared in top-performing models, showing that juvenile males use more space than juvenile females, although effects were marginal. Model results also indicated a relationship between shark activity space and salinity, where space use increased with decreasing salinity. A similar but weaker relationship was observed with water temperature. These results show that blacktip reef sharks respond to minor changes in salinity, suggesting that they may be able to relocate when conditions are unfavourable, and help define the resilience of this species to disturbance and change.

First record of the blacktip reef shark &lt;i&gt;Carcharhinus melanopterus&lt;/i&gt; (Carcharhiniformes: Carcharhinidae) from the Tropical Eastern Pacific

The blacktip reef shark Carcharhinus melanopterus, is one of the most common Indo-Pacific reef sharks. On April 29, 2012, a juvenile male blacktip reef shark measuring 89 cm total length (TL), was incidentally caught during a research expedition in Chatham Bay, Isla del Coco National Park, Costa Rica, located in the Tropical Eastern Pacific. This is the first record of the species from Isla del Coco National Park, Costa Rica, and from the Tropical Eastern Pacific. Citation: López-Garro, A., I. Zanella, G. Golfín-Duarte &amp; M. Pérez-Montero. 2012. First record of the blacktip reef shark Carcharhinus melanopterus (Carcharhiniformes: Carcharhinidae) from the Eastern Tropical Pacific. Rev. Biol. Trop. 60 (Suppl. 3): 275-278. Epub 2012 Dec 01.

Using unmanned aerial vehicles (UAVs) to investigate shark and ray densities in a shallow coral lagoon

Unmanned aerial vehicles (UAVs) are being increasingly used in studies of marine fauna. Here, we tested the use of a UAV (DJI Phantom II®) to assess fine-scale variation in densities of 2 elasmobranchs (blacktip reef sharks Carcharhinus melanopterus and pink whiprays Himantura fai) on reef systems off Moorea (French Polynesia). We flew parallel transects designed to sample reef habitats (fringing, channel and sandflat habitats) across 2 survey blocks. Block 1 included a shark and ray provisioning site with potentially higher elasmobranch densities, whereas Block 2 most likely had lower densities with no provisioning activities. Across 10 survey days in July 2014, we flew 3 transects (400 m) within each survey block (n = 60 total transect passes). As expected, densities (animals ha−1) were significantly higher in Block 1 than in Block 2, particularly where provisioning activities occur. Differences between habitats surveyed were also found. Our study provides the first direct estimates of shark and ray densities in coral-reef ecosystems and demonstrates that UAVs can produce important fishery-independent data for elasmobranchs, particularly in shallow-water habitats.

Population organisation in reef sharks: new variations in coastal habitat use by mobile marine predators

Coastal habitats provide important functions for many species and may serve as nursery grounds for teleost fishes and sharks and rays. However, the importance of these habitats in sustaining marine species at seascape scales is debated, and their significance to reef shark populations is poorly understood. The blacktip reef shark Carcharhinus melanopterus is a widely distributed mobile marine predator; we explored its use of shallow, turbid coastal habitats in the Great Barrier Reef using tagging and acoustic telemetry. Residency and movement patterns of 23 individuals were monitored for up to 28 mo, revealing different patterns between sexes and sizes. Neonate/juveniles were short-term residents; adult females were long-term residents and preliminary data suggest that adult males were vagrants. Adult females and neonate/juveniles had small activity spaces (50% kernel utilisation distribution, KUD < 5 km²) and shared the same habitats and locations while adult males (when present) had larger activity spaces (50% KUD up to 14 km²). Population organisation, movement patterns and biological data suggest that blacktip reef sharks may use turbid coastal habitats for reproduction. This study reveals a new variation in coastal habitat use by sharks with habitat use patterns differing from those observed in other coastal sharks, and from conspecifics on coral reefs. These patterns do not conform to the characteristics of classical shark nurseries, and highlight the species' ecological flexibility. The study also demonstrates that shark behaviour and habitat use patterns can affect their vulnerability to fishing, habitat loss and climate change, and can affect the efficacy of marine protected areas.

Reef sharks: recent advances in ecological understanding to inform conservation.

Sharks are increasingly being recognized as important members of coral-reef communities, but their overall conservation status remains uncertain. Nine of the 29 reef-shark species are designated as data deficient in the IUCN Red List, and three-fourths of reef sharks had unknown population trends at the time of their assessment. Fortunately, reef-shark research is on the rise. This new body of research demonstrates reef sharks' high site restriction, fidelity and residency on coral reefs, their broad trophic roles connecting reef communities and their high population genetic structure, all information that should be useful for their management and conservation. Importantly, recent studies on the abundance and population trends of the three classic carcharhinid reef sharks (grey reef shark Carcharhinus amblyrhynchos, blacktip reef shark Carcharhinus melanopterus and whitetip reef shark Triaenodon obesus) may contribute to reassessments identifying them as more vulnerable than currently realized. Because over half of the research effort has focused on only these three reef sharks and the nurse shark Ginglymostoma cirratum in only a few locales, there remain large taxonomic and geographic gaps in reef-shark knowledge. As such, a large portion of reef-shark biodiversity remains uncharacterized despite needs for targeted research identified in their red list assessments. A research agenda for the future should integrate abundance, life history, trophic ecology, genetics, habitat use and movement studies, and expand the breadth of such research to understudied species and localities, in order to better understand the conservation requirements of these species and to motivate effective conservation solutions.

Complete mitochondrial genome of the blacktip reef shark Carcharhinus melanopterus (Carcharhiniformes: Carcharhinidae)

The complete mitochondrial genome of the blacktip reef shark Carcharhinus melanopterus is determined for the first time in this study. The gene composition and order in the mitogenome of C. melanopterus is identical to most vertebrates. The overall base composition is 31.3% A, 25.3% C, 13.3% G and 30.1% T. There are 29 bp overlaps and 21 bp short intergenic spaces in the mitogenome. Two start codons and three stop codons were found in protein-coding genes. The dihydrouridine arm of tRNA-Ser2 was replaced by a simple loop and the other tRNAs could be folded into the typical cloverleaf structure. The termination associated sequence (TAS) and the conserved sequence blocks (CSB1-3) are found in the control region.

Long-Term Changes in Species Composition and Relative Abundances of Sharks at a Provisioning Site

Diving with sharks, often in combination with food baiting/provisioning, has become an important product of today’s recreational dive industry. Whereas the effects baiting/provisioning has on the behaviour and abundance of individual shark species are starting to become known, there is an almost complete lack of equivalent data from multi-species shark diving sites. In this study, changes in species composition and relative abundances were determined at the Shark Reef Marine Reserve, a multi-species shark feeding site in Fiji. Using direct observation sampling methods, eight species of sharks (bull shark Carcharhinus leucas, grey reef shark Carcharhinus amblyrhynchos, whitetip reef shark Triaenodon obesus, blacktip reef shark Carcharhinus melanopterus, tawny nurse shark Nebrius ferrugineus, silvertip shark Carcharhinus albimarginatus, sicklefin lemon shark Negaprion acutidens, and tiger shark Galeocerdo cuvier) displayed inter-annual site fidelity between 2003 and 2012. Encounter rates and/or relative abundances of some species changed over time, overall resulting in more individuals (mostly C. leucas) of fewer species being encountered on average on shark feeding dives at the end of the study period. Differences in shark community composition between the years 2004–2006 and 2007–2012 were evident, mostly because N. ferrugineus, C. albimarginatus and N. acutidens were much more abundant in 2004–2006 and very rare in the period of 2007–2012. Two explanations are offered for the observed changes in relative abundances over time, namely inter-specific interactions and operator-specific feeding protocols. Both, possibly in combination, are suggested to be important determinants of species composition and encounter rates, and relative abundances at this shark provisioning site in Fiji. This study, which includes the most species from a spatially confined shark provisioning site to date, suggests that long-term provisioning may result in competitive exclusion among shark species.

Population structure and residency patterns of the blacktip reef shark Carcharhinus melanopterus in turbid coastal environments

This study examined the characteristics of a blacktip reef shark Carcharhinus melanopterus population 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 juveniles 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 localized 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 highlight the potential ecosystem functions performed by coastal habitats in sustaining C. melanopterus populations.