Grey Reef Sharks Carcharhinus Amblyrhynchos Research Articles

Sharks surf the slope: Current updrafts reduce energy expenditure for aggregating marine predators.

An animal's energy landscape considers the power requirements associated with residing in or moving through habitats. Within marine environments, these landscapes can be dynamic as water currents will influence animal power requirements and can change rapidly over diel and tidal cycles. In channels and along slopes with strong currents, updraft zones may reduce energy expenditure of negatively buoyant fishes that are also obligate swimmers. Despite marine predators often residing within high-current area, no study has investigated the potential role of the energetic landscape in driving such habitat selectivity. Over 500 grey reef sharks Carcharhinus amblyrhynchos reside in the southern channel of Fakarava Atoll, French Polynesia. We used diver observations, acoustic telemetry and biologging to show that sharks use regions of predicted updrafts and switch their core area of space use based on tidal state (incoming versus outgoing). During incoming tides, sharks form tight groups and display shuttling behaviour (moving to the front of the group and letting the current move them to the back) to maintain themselves in these potential updraft zones. During outgoing tides, group dispersion increases, swimming depths decrease and shuttling behaviours cease. These changes are likely due to shifts in the nature and location of the updraft zones, as well as turbulence during outgoing tides. Using a biomechanical model, we estimate that routine metabolic rates for sharks may be reduced by 10%-15% when in updraft zones. Grey reef sharks save energy using predicted updraft zones in channels and 'surfing the slope'. Analogous to birds using wind-driven updraft zones, negatively buoyant marine animals may use current-induced updraft zones to reduce energy expenditure. Updrafts should be incorporated into dynamic energy landscapes and may partially explain the distribution, behaviour and potentially abundance of marine predators.

Ecological redundancy between coral reef sharks and predatory teleosts

Reef sharks may be ecologically redundant, such that other mesopredatory fishes compensate for their functions when they decline in number, preventing trophic cascades. Oral jaw gape, hereafter referred to as gape, determines maximum prey size in many piscivores and therefore affects the size structure of prey assemblages. Here, we examine whether gape and maximum prey size differ between five species of reef shark and 21 species of teleost (n = 754) using data collected from 38 reefs in the Indo-Pacific. Sharks displayed relatively small gape dimensions compared to most teleost species and, at smaller sizes, the giant trevally Caranx ignobilis and other teleosts may be able to consume larger prey than similar-sized sharks. However, ecological redundancy between reef sharks and teleosts appears to decline at larger sizes, such that the grey reef shark Carcharhinus amblyrhynchos, for example, may be capable of consuming larger prey than any other reef predator at its largest sizes, regardless of prey body shape. Moreover, sharks may be able to consume proportionally larger prey as they grow, in contrast to reef teleosts, which may largely be limited by their gapes to ever-smaller prey as a proportion of their body size. Our results also suggest that reef sharks may be unable to swallow whole prey that are > 36% of their length, consistent with gut-content studies. Conservation of reef ecological function may therefore depend not only on the protection of sharks but also particular size classes and key components of the mesopredatory guild.

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.

Evidence for dynamic resource partitioning between two sympatric reef shark species within the British Indian Ocean Territory.

Stable‐isotope analyses (δ13C, δ15N and δ34S) of multiple tissues (fin, muscle, red blood cells and plasma), revealed ontogenetic shifts in resource use by grey reef sharks Carcharhinus amblyrhynchos and resource partitioning with silvertip sharks Carcharhinus albimarginatus within the British Indian Ocean Territory marine protected area (MPA). Resource partitioning varied temporally, with C. albimarginatus feeding on more pelagic prey during October to January, potentially attributable to an influx of pelagic prey from outside the MPA at that time. Reef sharks may therefore be affected by processes outside an MPA, even if the sharks do not leave the MPA.

Trophic niches determined from fatty acid profiles of sympatric coral reef mesopredators

Previous research has identified similar trophic levels in a wide range of coral reef sharks and large teleost fishes but has been unable to resolve the extent of dietary overlap and resource sharing that lead to interpretation of functional roles and, hence, adequately describe interaction strengths in food webs. We used fatty acid (FA) profiles of muscle and plasma reflecting the diet of several mesopredators to better understand the trophic structure and functioning of Great Barrier Reef ecosystems. Multivariate analysis identified significant dietary overlap between 2 shark species (whitetip reef shark Triaenodon obesus and grey reef shark Carcharhinus amblyrhynchos), but whitetip reef sharks occupied a smaller niche area than grey reef sharks. We also found clear niche separation between sharks and teleost fishes (red throat emperor, coral trout, and grass emperor). All mesopredators sampled had high proportions of polyunsaturated FAs linking them to carnivory, but differences among species in trophic biomarker ratios suggest distinctive dietary sources. However, based on a degree of niche overlap of species sharing common diet, reef-dwelling teleost fishes such as coral trout also derive nutrients from pelagic environments. A faster analytical method to determine FA profiles, proven highly useful in tuna, was tested and deemed viable for muscle tissue of tropical teleost fishes and sharks, while questions remain for use of FA extraction of plasma in ecological studies. These results demonstrate that fine-scale inter-specific differences in diet exist between mesopredators in coral reef ecosystems. Our results raise important questions about the ecological influences of these species and energy flow among mesopredators in coral reef ecosystems.

Tubbataha Reefs Natural Park: the first comprehensive elasmobranch assessment reveals global hotspot for reef sharks

Elasmobranchs are experiencing population declines worldwide because of anthropogenic stressors. Marine protected areas (MPAs) have been shown to benefit mesopredatory species of shark. The Tubbataha Reefs Natural Park (TRNP) is a United Nations Educational, Scientific and Cultural Organization World Heritage Site and the largest no-take MPA in the Philippines, yet information on the current status of elasmobranchs in the park is limited. Here, we investigate the abundance and biodiversity of elasmobranchs in TRNP using underwater visual census (UVC) and baited remote underwater video (BRUV) surveys. Twenty UVC were conducted in May 2015 (n = 10) and June 2016 (n = 10), documenting eight species of elasmobranchs with an average density of 7.18 sharks ha-1 for both years. A total of 113 successful BRUV surveys were conducted in TRNP between March–June 2015 (n = 47) and April–June 2016 (n = 66). The BRUV surveys recorded 14 species with an average catch per unit effort of 2.09 elasmobranchs per hour for both years. Both survey methods report some of the highest densities of the grey reef shark Carcharhinus amblyrhynchos and the whitetip reef shark Triaenodon obesus documented worldwide. This study underlines the importance of large, well-managed MPAs such as TRNP for the conservation of reef-associated elasmobranchs.

Misidentification of Carcharhinus galapagensis (Snodgrass & Heller, 1905) in the Southwest Pacific Ocean.

Although primarily a coral reef species the grey reef shark Carcharhinus amblyrhynchos has been recorded from a number of subtropical oceanic islands and reefs in the Southwest Pacific Ocean. Examination of all nominal C. amblyrhynchos voucher material collected from Lord Howe Island, Elizabeth and Middleton Reefs and Norfolk Island resulted in the re-identification of these specimens as Galapagos sharks, C. galapagensis. As C. amblyrhynchos superficially resembles C. galapagensis visual records of C. amblyrhynchos from Elizabeth and Middleton Reefs and the Kermadec Islands cannot be substantiated without voucher material. Carcharhinus amblyrhynchos therefore appears to be confined to waters north of about 25^o S in the Southwest Pacific. Precaudal vertebral counts should be used to confirm the identification of nominal C. amblyrhynchos specimens that have an interdorsal ridge.

Effects of Including Misidentified Sharks in Life History Analyses: A Case Study on the Grey Reef Shark Carcharhinus amblyrhynchos from Papua New Guinea.

Fisheries observer programs are used around the world to collect crucial information and samples that inform fisheries management. However, observer error may misidentify similar-looking shark species. This raises questions about the level of error that species misidentifications could introduce to estimates of species’ life history parameters. This study addressed these questions using the Grey Reef Shark Carcharhinus amblyrhynchos as a case study. Observer misidentification rates were quantified by validating species identifications using diagnostic photographs taken on board supplemented with DNA barcoding. Length-at-age and maturity ogive analyses were then estimated and compared with and without the misidentified individuals. Vertebrae were retained from a total of 155 sharks identified by observers as C. amblyrhynchos. However, 22 (14%) of these were sharks were misidentified by the observers and were subsequently re-identified based on photographs and/or DNA barcoding. Of the 22 individuals misidentified as C. amblyrhynchos, 16 (73%) were detected using photographs and a further 6 via genetic validation. If misidentified individuals had been included, substantial error would have been introduced to both the length-at-age and the maturity estimates. Thus validating the species identification, increased the accuracy of estimated life history parameters for C. amblyrhynchos. From the corrected sample a multi-model inference approach was used to estimate growth for C. amblyrhynchos using three candidate models. The model averaged length-at-age parameters for C. amblyrhynchos with the sexes combined were = 159 cm TL and = 72 cm TL. Females mature at a greater length (l50 = 136 cm TL) and older age (A50 = 9.1 years) than males (l50 = 123 cm TL; A50 = 5.9 years). The inclusion of techniques to reduce misidentification in observer programs will improve the results of life history studies and ultimately improve management through the use of more accurate data for assessments.

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.

Importance of environmental and biological drivers in the presence and space use of a reef‑associated shark

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 496:47-57 (2014) - DOI: https://doi.org/10.3354/meps10529 Theme Section: Tracking fitness in marine vertebrates Importance of environmental and biological drivers in the presence and space use of a reef‑associated shark M. R. Heupel1,2,*, C. A. Simpfendorfer2 1Australian Institute of Marine Science, PMB No 3, Townsville, Queensland 4810, Australia 2Centre for Sustainable Tropical Fisheries and Aquaculture and School of Earth and Environmental Sciences, James Cook University, Townsville, Queensland 4811, Australia *Corresponding author: m.heupel@aims.gov.au ABSTRACT: As coral reef ecosystems come under increasing pressure from fisheries and climate change, understanding how species that rely on these habitats respond to changes within their environment is increasingly important. The presence and movement of 28 grey reef sharks Carcharhinus amblyrhynchos were monitored for 15 mo in the southern Great Barrier Reef in relation to environmental conditions and biological factors. Twenty-eight models including water temperature, atmospheric pressure, wind speed, rainfall and time (week or month), size and sex were tested against presence and activity space data and compared using Akaike information criterion (AIC). Model results for presence of individuals in relation to environmental conditions indicated that temperature and wind speed had weak effects, likely related to detectability. Models using 3 different measures of activity space indicated no relationship between shark activity space and environmental parameters. Week was a significant factor in the top performing activity space models, with males showing increased activity space during weeks in September, when mating is believed to occur. These results suggest changes in movement were biologically rather than environmentally driven. It appears that C. amblyrhynchos are adapted to a wide range of environmental conditions in coral reef habitats and that movement between or away from reef platforms is likely related to biological factors such as prey density, competition, reproduction or dispersal rather than environmental or seasonal changes. KEY WORDS: Carcharhinus amblyrhynchos · Acoustic monitoring · AATAMS · Coral reef Full text in pdf format PreviousNextCite this article as: Heupel MR, Simpfendorfer CA (2014) Importance of environmental and biological drivers in the presence and space use of a reef‑associated shark. Mar Ecol Prog Ser 496:47-57. https://doi.org/10.3354/meps10529 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 496. Online publication date: January 27, 2014 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2014 Inter-Research.

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.

First Record of the Grey Reef Shark Carcharhinus amblyrhynchos, (Bleeker, 1856) (Carcharhiniformes: Carcharhinidae) from the Lakshadweep Sea, India

The Grey Reef Shark Carcharhinus amblyrhynchos is a moderately sized and fairly stocky species widely distributed in the Indian and Pacific Oceans from Easter Island and as far west as South Africa. In this paper, the first record of Grey reef shark (single specimen female 126cm in Total Length (TL)), caught from the Lakshadweep Sea (10o47 N and 72o09 E) by drift long line operation at 40m depth is reported.

Residency and Spatial Use by Reef Sharks of an Isolated Seamount and Its Implications for Conservation

Although marine protected areas (MPAs) are a common conservation strategy, these areas are often designed with little prior knowledge of the spatial behaviour of the species they are designed to protect. Currently, the Coral Sea area and its seamounts (north-east Australia) are under review to determine if MPAs are warranted. The protection of sharks at these seamounts should be an integral component of conservation plans. Therefore, knowledge on the spatial ecology of sharks at the Coral Sea seamounts is essential for the appropriate implementation of management and conservation plans. Acoustic telemetry was used to determine residency, site fidelity and spatial use of three shark species at Osprey Reef: whitetip reef sharks Triaenodon obesus, grey reef sharks Carcharhinus amblyrhynchos and silvertip sharks Carcharhinus albimarginatus. Most individuals showed year round residency at Osprey Reef, although five of the 49 individuals tagged moved to the neighbouring Shark Reef (∼14 km away) and one grey reef shark completed a round trip of ∼250 km to the Great Barrier Reef. Additionally, individuals of white tip and grey reef sharks showed strong site fidelity to the areas they were tagged, and there was low spatial overlap between groups of sharks tagged at different locations. Spatial use at Osprey Reef by adult sharks is generally restricted to the north-west corner. The high residency and limited spatial use of Osprey Reef suggests that reef sharks would be highly vulnerable to targeted fishing pressure and that MPAs incorporating no-take of sharks would be effective in protecting reef shark populations at Osprey and Shark Reef.