Academic literature on the topic 'Carcharhinus obscurus'

The dusky shark Carcharhinus obscurus and the bronze whaler Carcharhinus brachyurus are large-bodied, marine predators that inhabit coastal and shelf waters of southern Australia. C. obscurus is considered to be among the most vulnerable pelagic sharks to overexploitation. This study focussed on population metrics and movement patterns of these sympatric species. Litters from two pregnant C. brachyurus were examined; these comprised 20 and 24 embryos, respectively. Tagging data indicated that 75% of whaler sharks tagged in this region by recreational fishers were juveniles, and 58% of recaptures occurred within 50 km of the tagging locations. Fishery catch samples comprised 99% juvenile C. brachyurus and C. obscurus. Our findings suggested that semi-protected gulf waters represented ecologically significant habitats of juveniles. A fuzzy-logic model showed that in terms of relative vulnerability to fishing, C. brachyurus ranked in the mid to lower end of the spectrum, when compared with six sympatric pelagic shark species, including the white shark, Carcharodon carcharias. Our findings emphasised a need for improvement to management measures for these carcharhinids, which are likely to play a significant role in the functioning of the temperate gulf and shelf ecosystems.

The epidermal microbiome is a critical element of marine organismal immunity, but the epidermal virome of marine organisms remains largely unexplored. The epidermis of sharks represents a unique viromic ecosystem. Sharks secrete a thin layer of mucus which harbors a diverse microbiome, while their hydrodynamic dermal denticles simultaneously repel environmental microbes. Here, we sampled the virome from the epidermis of three shark species in the family Carcharhinidae: the genetically and morphologically similar Carcharhinus obscurus (n = 6) and Carcharhinus galapagensis (n = 10) and the outgroup Galeocerdo cuvier (n = 15). Virome taxonomy was characterized using shotgun metagenomics and compared with a suite of multivariate analyses. All three sharks retain species-specific but highly similar epidermal viromes dominated by uncharacterized bacteriophages which vary slightly in proportional abundance within and among shark species. Intraspecific variation was lower among C. galapagensis than among C. obscurus and G. cuvier. Using both the annotated and unannotated reads, we were able to determine that the Carcharhinus galapagensis viromes were more similar to that of G. cuvier than they were to that of C. obscurus, suggesting that behavioral niche may be a more prominent driver of virome than host phylogeny.

The diets of dusky (Carcharhinus obscurus), whiskery (Furgaleus macki) and gummy (Mustelus antarcticus) sharks from south-western Western Australia were examined by analysis of stomach contents. The majority of samples were obtained from catches of commercial gill-net fishers. Carcharhinus obscurus had a diverse diet dominated by pelagic teleosts and cephalopods. A wide range of demersal and benthic prey were also consumed, but represented only a small portion of the diet. As body size increased, importance of elasmobranchs in the diet of C. obscurus increased, while most other groups remained at similar levels. Furgaleus macki had a specialized diet, feeding almost exclusively on octopus and other cephalopods. The diet of M. antarcticus was dominated by benthic and epibenthic prey, including crabs, lobsters, tetraodontid fishes and octopus. As M. antarcticus increased in size there was an increase in the occurrence of rock lobster and a decrease in the occurrence of crabs in the diet. Differences in the diet were also noted between male and female M. antarcticus, but were confounded with differences between size classes.

Sumberdaya ikan adalah jenis ikan termasuk biota perairan laut lainnya yang merupakan sumber kekayaan alam yang memiliki daya pulih kembali secara alami, sehingga pemanfaatannya dapat dilakukan secara berkelanjutan. Pelabuhan perikanan merupakan tempat pendaratan hasil tangkapan dan awal pemasarannya. jenis ikan hasil tangkapan nelayan yang didaratkan di Pelabuhan Perikanan Pantai Tanjung Luar, Kabupaten Lombok Timur. Penelitian dilakukan dengan metode survey dan identifikasi. Berdasarkan penelitian diperoleh sebanyak 34 jenis ikan hasil tangkapan nelayan di Pelabuhan Perikanan Tanjung Luar, Pulau Lombok, yaitu: Naso brevisrostris, Chanos chanos, Parastromateus niger, Thallasoma purpureum, Siganus canaliculatus, Plectorhinchus polytaenia, Diodon holocanthus, Upeneus vittatus, Caesio cuning, Dermogenys sp, Epinephelus areolatus, Rastrelliger sp, Pomadasys argenteus, Lepturacanthus savala, Decapterus macrosoma, Sillago sihama, Eusphyra blochii, Carcharhinus brevipinna, Carcharhinus albimarginatus, Carcharhinus limbatus, Carcharhinus obscurus, Galeocerdo cuvier, Prionace glauca, Taeniura lymma, Priancanthus hamrur, Scolopsis sp, Scombermorus guttatus, Euthynnus affinis, Nemipterus japonicas, Sardinella sp, Lutjanus bitaeniatus, Secutor interruptus, Sphyraena jello, dan Caranx ignobilis

Abstract Reliable information for population assessments is rare for sharks. We quantified patterns in catch rates and mean size for numerous tropical and subtropical species from 15 years of fishery-independent surveys (2002–2017) in northwestern Australia. This study region represents an area of ~0.8 million km2 which was closed to commercial shark fishing from 1993 or 2005 onward due to the very high State-wide catches of sandbar (Carcharhinus plumbeus) and dusky (Carcharhinus obscurus) sharks. A total of 43 shark and ray species were sampled, with sandbar shark being the most commonly caught species, followed by milk (Rhizoprionodon acutus), spot-tail (Carcharhinus sorrah), tiger (Galeocerdo cuvier), blacktip (Carcharhinus limbatus and Carcharhinus tilstoni), dusky and sliteye (Loxodon macrorhinus) sharks, and scalloped hammerhead (Sphyrna lewini). For sandbar shark, catch rates increased between 2008 and 2017 whereas for other taxa catch rates were mostly stable (albeit fluctuating). Mean size at capture fluctuated across years with no particular trends. Unlike for other parts of the world, catch rates and mean size of northwestern Australian sharks have been stable or increased in recent years. Though most shark species have conservative life histories, when science, management and enforcement work synergistically, sustainable resource use, recovery and conservation outcomes can all be achieved.

Abstract Understanding the trophic interactions and the position of species within a foodweb is crucial if we want to understand the dynamics of marine communities and the impact individual components of the community have on trophic network compartments. Recent studies have indicated sharks and rays are important elements within foodwebs. In this study, we evaluated the ecological importance of sharks and rays in a subtropical ecosystem off the coast of southern Brazil by using topological analyses. We tested the hypotheses that some elasmobranchs can be considered key elements within the foodweb, and that large predators have topological importance (act as keystones), so that, when large predators are excluded, mesopredator elasmobranchs occupy higher topological positions. Our results indicate that Galeocerdo cuvier, Carcharhinus obscurus, Carcharias taurus, Sphyrna lewini and S. zygaena are species with large ecological function values and may exert a powerful influence over lower levels. These issues need to be considered by conservation and fishery management groups since it appears that ecosystem integrity may be compromised by reductions in the populations of large predators. Carcharhinus obscurus, S. zygaena and Zapteryx brevirostris were found to be the elasmobranchs with largest values of centrality, and can, therefore, be considered key elements in the topological structure.

Understanding the large-scale migrations of marine predators can allow better representation of their population dynamics. The migration biology of dusky sharks (Carcharhinus obscurus), a cosmopolitan large marine predator with very low resilience to fishing, was quantified using a large-scale network of acoustic receivers deployed across Western Australia. Time-series plotting of individual shark detections and modified logistic modelling were used to determine the timing of acoustically tagged sharks’ seasonal migration, the proportion of the population migrating, and the size at which sharks start to migrate. Large (>200 cm fork length) dusky sharks migrated between areas closed (north) and open (south) to commercial shark fishing. There was limited evidence that smaller sharks occurred in the northern study area, whereas several larger individuals of both sexes undertook repeated north–south displacements, moving between disparate ecosystems within the Indian Ocean (21.7°S–35.4°S) and covering round-trip distances of 2000–3000 km per migratory event. For migrating individuals, the probability of occurring in the north was high in the austral winter–spring and low (males) to moderate (females) during the austral summer–autumn.

Shark nets have been set off the beaches of KwaZulu–Natal, South Africa, since 1952 to reduce the risk of shark attack. The nets fish in fixed localities 400 m from shore and both directly affect local shark populations and act as fisheries-independent monitoring devices. Reliable catch information at the species level was available for the period 1978–2003. Trends in catch rate and size were used to assess the population status of 14 commonly caught shark species. In addition, a demographic modelling approach was used in conjunction with the catch information to assess the potential effect of the nets on populations. Catch rates of four species (Carcharhinus leucas, C. limbatus, Sphyrna lewini and S. mokarran) showed a significant decline, as did the mean or median length of three species (Carcharhinus amboinensis, C. limbatus and female Carcharodon carcharias). For three species that showed declining catch rates or length the potential effect of the shark nets was assessed to be low, suggesting that other sources of catch were responsible for the declining status. The potential effect of the shark nets was assessed to be high for two species (Carcharhinus obscurus and Carcharias taurus, neither of which showed declines in catch rate or length), because of very low intrinsic rates of population increase.

Understanding the role of predators is challenging but critical for ecosystem management. For community dynamics, predator-specific size-based variation in diet, trophic position, and habitat use are rarely accounted for. Using two applied tools (stable isotopes and stomach content data), we examined inter- and intra-species ontogenetic variability in diet (stomach contents), trophic position (TPSIA for δ15N and TPSCA for stomach contents), and habitat use (δ13C) of two large sharks, the scalloped hammerhead ( Sphyrna lewini ) and the dusky ( Carcharhinus obscurus ). Stomach contents identified size-based and gender-specific shifts in diet indicating resource partitioning for and between species. Calculated TP for the two sharks varied by method, either TPSIA or TPSCA and with species, size, and gender, but were complicated by differing baselines and broad functional prey groups, respectively. TP increased with size for S. lewini, but was low in large C. obscurus compared with small sharks. Size-based δ13C profiles indicated habitat partitioning by sex in S. lewini and a movement to shelf edge foraging in large C. obscurus. These results demonstrate that predators exert proportional size-based effects on multiple components of the marine system that are further complicated by species- and gender-specific strategies.

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Dados de captura por unidade de esforço (CPUE) aliados a telemetria acústica foram utilizados para acessar a abundância relativa, padrões de movimentação, utilização do habitat e interações inter- e intraespecíficas de tubarões do gênero Carcharhinus (C. falciformis, C. galapagensis e C. obscurus) no Arquipélago de São Pedro e São Paulo (ASPSP). A família Carcharhinidae respondeu por 90% da captura de tubarões (Carcharhinus falciformis: 66,9%, C. galapagensis: 16,5% e C. obscurus: 6,6%). Não foi observada tendência sazonal no comportamento reprodutivo de nenhuma das espécies, tendo sido encontrados indivíduos em todas as fases de desenvolvimento, embora sua maioria seja jovem nas três espécies. A maior média de comprimento total foi 198,4 (±23,2) para C. obscurus, seguido por C. galapagensis com 171,9 (±22,6) e C. falciformis 133,0 (±22,8). Durante o período de estudo, a CPUE média de C. falciformis foi igual a 0,43, para C. galapagensis 0,11 e 0,04 para C. obscurus. Para C. falciformis a CPUE se reduziu ao longo do tempo, enquanto a das outras duas espécies apresentou um forte crescimento a partir de 2012. Oito dos quinze tubarões marcados com transmissores acústicos (3 C. galapagensis e 5 C. falciformis) foram detectados pelos receptores instalados nas proximidades (Leste e Oeste) do ASPSP. O período de dias em sequência com detecções (C. galapagensis: 20,7 ± 3, n=3; C. falciformis: 4,6 ± 3,9; n=5) e o número total de detecções (C. galapagensis: 2194 ± 1314,2; C. falciformis: 352,6 ± 265,3) foram muito maiores para C. galapagensis do que para C. falciformis. As duas espécies apresentaram diferenças significativas no número de detecções entre os períodos do dia (ANOVA, C. falciformis: F = 23,56, p < 0,01 e C. galapagensis: F = 21,34, p < 0,01) e entre os lados leste e oeste da ilha (ANOVA, F = 311451, p < 0,01), indicando clara segregação espacial. A população local de C. galapagensis, em razão do seu comportamento muito mais residente, parece ter sofrido um declínio bem mais acentuado em razão da pesca no entorno do ASPSP, no período em que a mesma era permitida, do que C. falciformis, que têm comportamento muito mais migratório e oceânico, retornando diversas vezes ao ASPSP, mas nunca permanecendo por longo período nas proximidades dos receptores. Os dados de captura e telemetria aqui apresentados evidenciam que C. galapagensis não somente está presente no ASPSP, a despeito de trabalhos anteriores terem indicado a sua extinção no local, como está se tornando cada vez mais abundante desde a suspensão da pesca de elasmobrânquios nessa área.
Catch-per-unit-of-effort (CPUE) data associated with acoustic telemetry were analyzed to accessing relative abundance, patterns of movement, habitat use, residence, and inter- and intraspecific interactions of Carcharhinus sharks (C. falciformis, C. galapagensis and C. obscurus) in Saint Peter and Saint Paul Archipelago (SPSPA). Carcharhinidae family accounted 90% of shark capture, Carcharhinus falciformis being the predominant species (66.9%), followed by C. galapagensis (16.5%) and C. obscurus (6.6%). No clear trend was observed, between the reproductive behaviors of any of the species, having been found individuals in all stages of development, although, the majority of animals were juveniles in the three species. The total length followed the pattern described in literature, with the highest mean for C. obscurus 198.4 (± 23.2), followed by C. galapagensis 171.9 (± 22.6) and C. falciformis 133.0 (± 22.8). During the study period, the mean CPUE of C. falciformis was 0.43, for C. galapagensis 0.11 and 0.04 for C. obscurus. C. falciformis had it’s CPUE decreased over time, while the abundance of other two species shows a great growth since 2012. Eight of the fifteen sharks tagged with acoustic transmitters (3 C. galapagensis and 5 C. falciformis) were detected by the receivers installed in SPSPA proximities (East and West side). The period of days in a row with detections (C. galapagensis: 20.7 ± 3, n=3; C. falciformis: 4.6 ± 3.9; n=5) and the total number of detections (C. galapagensis: 2194 ± 1314.2; C. falciformis: 352.6 ± 265.3) were much bigger for C. galapagensis than C. falciformis. The two species showed significant differences in the number of detections between day’s periods (ANOVA, C. falciformis: F = 23.56, p < 0.01 and C. galapagensis: F = 21.34, p < 0.01) with afternoon and twilight periods presenting the highest detection frequency for both species. Detections were also significantly different between eastern and western sides of the island (ANOVA, F = 311451, p < 0.01), indicating clear spatial segregation. The local population of C. galapagensis, because of their high resident behavior, appears to have suffered higher decline as fishing around SPSPA result, in the period in which it was permitted, than C. falciformis, which has predominant migratory and oceanic behavior, returning many times to SPSPA, but never staying for a long period on receivers’ vicinity. Capture and telemetry data presented here evidence not only the presence of C. galapagensis in SPSPA vicinity, despite the fact that previous works have indicated that it has been extinguished, but its increase since elasmobranch fishery was banned on the area.

碩士
國立臺灣海洋大學
環境生物與漁業科學學系
92
Abstract This study deals with the fisheries biology of dusky shark, Carcharhinus obscurus. Samples, caught by longline in northeastern Taiwan waters from Sep. 2002 to Nov. 2003, were collected at Nan Fan Ao fish market. Specimens used for age and growth, reproduction, and stomach content analysis were 434, 320 and 322 individuals, respectively. Ranges were 110〜364 cm in total length. X-radiographs of vertebrae were viewed through a light box at 10 x magnification using transmitted light and growth bands were counted. Translucent and opaque bands on vertebra centra were formed once a year, and translucent bands were formed at September. The oldest individual aged in this study was 33 yrs. The parameters of von Bertalanffy growth equation based on age and observed length were est- imated as L∞=415.7 cm TL, k=0.056 yr-1, t0=-3.42 yr for both sexes combined. Males and females reached sexual maturity at about 16.1 yrs for males and 16.4 yrs for female. Gestation period of this species was estimated as 13 months. Litter size of dusky shark was 6〜16, and sex ratio of embryos was 1：1. Of 322 stomachs examined, 259 (80%) of them were empty. Stomach content analysis, indicated that teleosts were the most important food items, followed by mollusks, elasmobranches, crustaceans and marine mammals. Keywords：Carcharhinus obscurus, Fisheries biology, Age and growth, Reproduction, Stomach content analysis.

<em>Abstract.</em> —An assessment of the dusky shark <em>Carcharhinus obscurus </em> fishery in southwestern Australia was undertaken using demographic techniques. Current annual catches of <em>C. obscurus </em> by the fishery are 500–700 metric tons (live weight), most of which are recently born individuals (age-0). The best estimates of life history parameters indicate that the annual rate of population increase is 4.3% when unfished and that the <EM>F</EM>_MSY is 0.021. Tests indicate that the results are most sensitive to changes in values of natural mortality and age at maturity. Changes to the values of average litter size, reproductive periodicity, and longevity had little effect on the results. The inclusion in the analysis of age-specific exploitation rates from a tagging study indicate that at current levels of fishing the <em>C. obscurus </em> population in southwestern Australia is most likely to be sustainable. However, it must be noted that there is some unquantified mortality of older year-classes due to fishing operations outside of the managed fishery. The results indicate that it is possible to exploit long-lived, late-maturing, slow-reproducing marine animals by targeting the youngest age-classes. The results are discussed in relation to the dusky shark fishery in southwestern Australia and the exploitation of other long-lived marine species.

<em>Abstract.</em>—To identify and characterize shark nursery habitat in the coastal waters of Massachusetts, longline and shark angler surveys were conducted from 1989 to 2002 in the neritic waters of Nantucket Sound, Massachusetts. Additional samples and information were opportunistically collected from recreational and commercial fishermen, as well as published sources. A total of 123 longline sets of 5,591 hooks caught 372 sharks consisting of 344 (92.5%) smooth dogfish <em>Mustelus canis</em>, 23 (6.2%) sandbar sharks <em>Carcharhinus plumbeus</em>, and 5 (1.3%) dusky sharks <em>C. obscurus</em>. The sharks were taken during the period of 16 June–24 September in water temperature and depth ranges of 16.0–27.2°C and 1.2–27.1 m, respectively. Longline catch rates (number of sharks per longline set) were stratified by species, area, month, year, water temperature, and depth. Angler surveys reported the capture of 294 sharks, including sandbar sharks (72%) and smooth dogfish (28%). Data from 540 neonatal and adult smooth dogfish ranging 27.5–121.0 cm fork length (FL) support the conclusion that the neritic waters of southern Massachusetts serve as primary nursery habitat for this species. Size and sex data from 235 juvenile sandbar sharks ranging 61.0–157.0 cm FL indicate that this region provides secondary nursery habitat for this species. Opportunistic samples of juvenile sand tiger <em>Carcharias taurus</em>, white shark <em>Carcharodon carcharias</em>, basking shark <em>Cetorhinus maximus</em>, and tiger shark <em>Galeocerdo cuvier </em>provide evidence that these species utilize Massachusetts coastal waters for secondary nursery habitat.