46 resultados para Carcharhinus


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Pós-graduação em Ciências Biológicas (Zoologia) - IBB

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The ongoing decline in abundance and diversity of shark stocks, primarily due to uncontrolled fishery exploitation, is a worldwide problem. An additional problem for the development of conservation and management programmes is the identification of species diversity within a given area, given the morphological similarities among shark species, and the typical disembarkation of processed carcasses which are almost impossible to differentiate. The main aim of the present study was to identify those shark species being exploited off northern Brazil, by using the 12S-16S molecular marker. For this, DNA sequences were obtained from 122 specimens collected on the docks and the fish market in Bragança, in the Brazilian state of Pará. We identified at least 11 species. Three-quarters of the specimens collected were either Carcharhinus porosus or Rhizoprionodon sp, while a notable absence was the daggernose shark, Isogomphodon oxyrhyncus, previously one of the most common species in local catches. The study emphasises the value of molecular techniques for the identification of cryptic shark species, and the potential of the 12S-16S marker as a tool for phylogenetic inferences in a study of elasmobranchs.

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A comunidade de tubarões (Selachii:Galea) proveniente da Formação Pirabas pode ser considerada como uma das mais representativas e de maior diversidade entre as unidades do Neógeno da América do Sul. A presença de 8 gêneros permitiu elaborar hipóteses sobre a reconstrução da cadeia trófica envolvendo outros elementos da paleofauna de vertebrados, assim como também serviu como um indicador paleoecológico adicional que corrobora dados anteriores sobre a reconstituição dos parâmetros paleoambientais da unidade geológica. Foi realizado uma revisão taxonômica das espécies previamente conhecidos para a Formação Pirabas, cuja composição da paleocomun idade de tubarões foi a seguinte: Carcharhinus spl Carcharhinus sp2, Carcharhinus sp3, Carcharhinus priscus, Sphyma magna, Hemipristis serra, Carcharodon megalodon, Isurus sp, Ginglyrnostoma serra, Ginglymostoma obliquum. Novas coletas possibilitaram a expansão de 31 exemplares depositados em museus brasileiros para 231 novos indivíduos, incluindo material microscópico. Esta coleta serviu para aumentar o conhecimento sobre a diversidade e aspectos paleoecológicos dos grupos representados.

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Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

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Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

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Cathetocephalus thatcheri gen. et sp. n. is described from the spiral valve of the bull shark, Carcharhinus leucas (Valenciennes), taken in the Gulf of Mexico and the Atlantic coast of Florida. A new family is erected for the new genus. The species most closely resembles Pillersium owenium Southwell, 1927, in that both possess a scolex which is perpendicular to the long axis of the strobila. It differs, however, in having a single neck and holdfast organ rather than a bifurcate neck with two bothridia. Also, the surfaces of the scolex differ from those of P. owenium by possessing fleshy papilliform structures on the leading and trailing edges rather than leaflike folds. Specimens with several strobilae are figured and discussed.

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All immunoglobulins and T-cell receptors throughout phylogeny share regions of highly conserved amino acid sequence. To identify possible primitive immunoglobulins and immunoglobulin-like molecules, we utilized 3' RACE (rapid amplification of cDNA ends) and a highly conserved constant region consensus amino acid sequence to isolate a new immunoglobulin class from the sandbar shark Carcharhinus plumbeus. The immunoglobulin, termed IgW, in its secreted form consists of 782 amino acids and is expressed in both the thymus and the spleen. The molecule overall most closely resembles mu chains of the skate and human and a new putative antigen binding molecule isolated from the nurse shark (NAR). The full-length IgW chain has a variable region resembling human and shark heavy-chain (VH) sequences and a novel joining segment containing the WGXGT motif characteristic of H chains. However, unlike any other H-chain-type molecule, it contains six constant (C) domains. The first C domain contains the cysteine residue characteristic of C mu1 that would allow dimerization with a light (L) chain. The fourth and sixth domains also contain comparable cysteines that would enable dimerization with other H chains or homodimerization. Comparison of the sequences of IgW V and C domains shows homology greater than that found in comparisons among VH and C mu or VL, or CL thereby suggesting that IgW may retain features of the primordial immunoglobulin in evolution.

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Since the landmark contributions of Homer Smith and co-workers in the 1930s there has been a considerable advance in our knowledge regarding the osmoregulatory strategy of elasmobranch fish. Smith recognised that urea was retained in the body fluids as part of the 'osmoregulatory ballast' of elasmobranch fish so that body fluid osmolality is raised to a level that is iso- or slightly hyper-osmotic to that of the surrounding medium. From studies at that time he also postulated that many marine dwelling elasmobranchs were not capable of adaptation to dilute environments. However, more recent investigations have demonstrated that, at least in some species, this may not be the case. Gradual acclimation of marine dwelling elasmobranchs to varying environmental salinities under laboratory conditions has demonstrated that these fish do have the capacity to acclimate to changes in salinity through independent regulation of Na+, Cl- and urea levels. This suggests that many of the presumed stenohaline marine elasmobranchs could in fact be described as partially euryhaline. The contributions of Thomas Thorson in the 1970s demonstrated the osmoregulatory strategy of a fully euryhaline elasmobranch, the bull shark, Carcharhinus leucas, and more recent investigations have examined the mechanisms behind this strategy in the euryhaline elasmobranch, Dasyatis sabina. Both partially euryhaline and fully euryhaline species utilise the same physiological processes to control urea, Na+ and Cl- levels within the body fluids. The role of the gills, kidney, liver, rectal gland and drinking process is discussed in relation to the endocrine control of urea, Na+ and Cl- levels as elasmobranchs acclimate to different environmental salinities. (C) 2003 Elsevier Inc. All rights reserved.

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Passive electroreception is a complex and specialised sense found in a large range of aquatic vertebrates primarily designed for the detection of weak bioelectric fields. Particular attention has traditionally focused on cartilaginous fishes, but a range of teleost and non-teleost fishes from a diversity of habitats have also been examined. As more species are investigated, it has become apparent that the role of electroreception in fishes is not restricted to locating prey, but is utilised in other complex behaviours. This paper presents the various functional roles of passive electroreception in non-electric fishes, by reviewing much of the recent research on the detection of prey in the context of differences in species' habitat (shallow water, deep-sea, freshwater and saltwater). A special case study on the distribution and neural groupings of ampullary organs in the omnihaline bull shark, Carcharhinus leucas, is also presented and reveals that prey-capture, rather than navigation, may be an important determinant of pore distribution. The discrimination between potential predators and conspecifics and the role of bioelectric stimuli in social behaviour is discussed, as is the ability to migrate over short or long distances in order to locate environmentally favourable conditions. The various theories proposed regarding the importance and mediation of geomagnetic orientation by either an electroreceptive and/or a magnetite-based sensory system receives particular attention. The importance of electroreception to many species is emphasised by highlighting what still remains to be investigated, especially with respect to the physical, biochemical and neural properties of the ampullary organs and the signals that give rise to the large range of observed behaviours.

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We compared growth rates of the lemon shark, Negaprion brevirostris, from Bimini, Bahamas and the Marquesas Keys (MK), Florida using data obtained in a multi-year annual census. We marked new neonate and juvenile sharks with unique electronic identity tags in Bimini and in the MK we tagged neonate and juvenile sharks. Sharks were tagged with tiny, subcutaneous transponders, a type of tagging thought to cause little, if any disruption to normal growth patterns when compared to conventional external tagging. Within the first 2 years of this project, no age data were recorded for sharks caught for the first time in Bimini. Therefore, we applied and tested two methods of age analysis: ( 1) a modified 'minimum convex polygon' method and ( 2) a new age-assigning method, the 'cut-off technique'. The cut-off technique proved to be the more suitable one, enabling us to identify the age of 134 of the 642 previously unknown aged sharks. This maximised the usable growth data included in our analysis. Annual absolute growth rates of juvenile, nursery-bound lemon sharks were almost constant for the two Bimini nurseries and can be best described by a simple linear model ( growth data was only available for age-0 sharks in the MK). Annual absolute growth for age-0 sharks was much greater in the MK than in either the North Sound (NS) and Shark Land (SL) at Bimini. Growth of SL sharks was significantly faster during the first 2 years of life than of the sharks in the NS population. However, in MK, only growth in the first year was considered to be reliably estimated due to low recapture rates. Analyses indicated no significant differences in growth rates between males and females for any area.

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We used longline fishing to determine the effects of distance from the ocean, season, and short-term variation in abiotic conditions on the abundance of juvenile bull sharks (Carcharhinus leucas) in an estuary of the Florida Everglades, U.S.A. Logistic regression revealed that young-of-the-year sharks were concentrated at a protected site 20 km upstream and were present in greater abundance when dissolved oxygen (DO) levels were high. For older juvenile sharks (age 1+), DO levels had the greatest influence on catch probabilities followed by distance from the ocean; they were most likely to be caught at sites with .3.5 mg L21 DO and on the main branch of the river 20 km upstream. Salinity had a relatively small effect on catch rates and there were no seasonal shifts in shark distribution. Our results highlight the importance of considering DO as a possible driver of top predator distributions in estuaries, even in the absence of hypoxia. In Everglades estuaries hydrological drivers that affect DO levels (e.g., groundwater discharge, modification of primary productivity through nutrient fluxes) will be important in determining shark distributions, and the effects of planned ecosystem restoration efforts on bull sharks will not simply be mediated by changing salinity regimes and the location of the oligohaline zone. More generally, variation in DO levels could structure the nature and spatiotemporal pattern of top predator effects in the coastal Everglades, and other tropical and subtropical estuaries, because of interspecific variation in reliance on DO within the top predator guild.

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Stable-isotope values of a scalloped hammerhead Sphyrna lewini and blacktip shark Carcharhinus limbatus and their respective embryos were analysed. Embryos of both species were enriched in δ15N compared to their mothers (0·82 and 0·88‰, respectively), but fractionation of δ13C varied. Embryonic S. lewini were enriched (1·00‰) in δ13C while C. limbatus were depleted (0·27‰) relative to their mothers.

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Understanding how natural and anthropogenic drivers affect extant food webs is critical to predicting the impacts of climate change and habitat alterations on ecosystem dynamics. In the Florida Everglades, seasonal reductions in freshwater flow and precipitation lead to annual migrations of aquatic taxa from marsh habitats to deep-water refugia in estuaries. The timing and intensity of freshwater reductions, however, will be modified by ongoing ecosystem restoration and predicted climate change. Understanding the importance of seasonally pulsed resources to predators is critical to predicting the impacts of management and climate change on their populations. As with many large predators, however, it is difficult to determine to what extent predators like bull sharks (Carcharhinus leucas) in the coastal Everglades make use of prey pulses currently. We used passive acoustic telemetry to determine whether shark movements responded to the pulse of marsh prey. To investigate the possibility that sharks fed on marsh prey, we modelled the predicted dynamics of stable isotope values in bull shark blood and plasma under different assumptions of temporal variability in shark diets and physiological dynamics of tissue turnover and isotopic discrimination. Bull sharks increased their use of upstream channels during the late dry season, and although our previous work shows long-term specialization in the diets of sharks, stable isotope values suggested that some individuals adjusted their diets to take advantage of prey entering the system from the marsh, and as such this may be an important resource for the nursery. Restoration efforts are predicted to increase hydroperiods and marsh water levels, likely shifting the timing, duration and intensity of prey pulses, which could have negative consequences for the bull shark population and/or induce shifts in behaviour. Understanding the factors influencing the propensity to specialize or adopt more flexible trophic interactions will be an important step in fully understanding the ecological role of predators and how ecological roles may vary with environmental and anthropogenic changes.

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1. Apex predators are often assumed to be dietary generalists and, by feeding on prey from multiple basal nutrient sources, serve to couple discrete food webs. But there is increasing evidence that individual level dietary specialization may be common in many species, and this has not been investigated for many marine apex predators. 2. Because of their position at or near the top of many marine food webs, and the possibility that they can affect populations of their prey and induce trophic cascades, it is important to understand patterns of dietary specialization in shark populations. 3. Stable isotope values from body tissues with different turnover rates were used to quantify patterns of individual specialization in two species of ‘generalist’ sharks (bull sharks, Carcharhinus leucas, and tiger sharks, Galeocerdo cuvier). 4. Despite wide population-level isotopic niche breadths in both species, isotopic values of individual tiger sharks varied across tissues with different turnover rates. The population niche breadth was explained mostly by variation within individuals suggesting tiger sharks are true generalists. In contrast, isotope values of individual bull sharks were stable through time and their wide population level niche breadth was explained by variation among specialist individuals. 5. Relative resource abundance and spatial variation in food-predation risk tradeoffs may explain the differences in patterns of specialization between shark species. 6. The differences in individual dietary specialization between tiger sharks and bull sharks results in different functional roles in coupling or compartmentalizing distinct food webs. 7. Individual specialization may be an important feature of trophic dynamics of highly mobile marine top predators and should be explicitly considered in studies of marine food webs and the ecological role of top predators.

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This stock assessment provides detailed results for the most common sharks encountered by Queensland commercial fishers. These sharks come from the whaler (Carcharhinidae) and hammerhead (Sphyrnidae) families and comprise sharpnose sharks (Rhizoprionodon taylori and R. oligolinx), the milk shark (R. acutus), the creek whaler (Carcharhinus fitzroyensis), the hardnose shark (C. macloti), the spot-tail shark (C. sorrah), the Australian blacktip shark (C. tilstoni), the common blacktip shark (C. limbatus), the spinner shark (C. brevipinna), bull and pigeye sharks (C. leucas and C. amboinensis), the winghead shark (Eusphyra blochii), the scalloped hammerhead (Sphyrna lewini) and the great hammerhead (S. mokarran). Reef sharks were excluded because fishery observer data indicated that they were largely spatially segregated from sharks caught in the inshore net fisheries. The three common species of reef sharks in Queensland, which are all whaler sharks, are the grey reef shark Carcharhinus amblyrhynchos, the blacktip reef shark C. melanopterus and the whitetip reef shark Triaenodon obesus.