Dissertations / Theses on the topic 'Carcharhinus plumbeus'

Toward developing a comprehensive understanding of the molecular origins and changes to the recombining segmental antibody gene, I submit the present examination of the changes in immunoglobulin heavy chain coding segments over the 180-million year span separating carcharine from horned sharks. In this study, nucleic acid sequences from Carcharhinus plumbeus (sandbar shark) immunoglobulin heavy chain constant and post-Joining regions are given along with a restriction map showing the arrangement of these components within a single genomic heavy chain fragment. These sequences and map are compared with those from the horned shark, Heterodontus francisci and the nurse shark, Ginglymostoma cirratum. Shark immunoglobulin nucleic acid segments are also compared with known sequences of rat and skate, and corresponding amino acid sequences aligned with those of toad, chicken, mouse and man.

In order to understand the evolution of the rearranging immunoglobulin system, it is necessary to examine living representatives of the most primitive vertebrate phyla. Immunoglobulins are the major recognition and defense molecules of the humoral immune response and are found in all vertebrates. While early studies demonstrated that the general structure of immunoglobulins has remained relatively unchanged throughout evolution, the organization of their encoding genes differs dramatically. Elasmobranchs, which include the sharks, skates, and rays, are the most ancient phylogenetic class of vertebrates from which immunoglobulin DNA sequences have been obtained. The Carcharhinoid sharks are of considerable interest for evolutionary studies because they are an old order whose ancestors date back to the Jurassic period. Immunoglobulin light chain genes of the sandbar shark (Carcharhinus plumbeus) were characterized as to their DNA sequence as well as their number and arrangement within the genome. Sequence of a cDNA clone encoding sandbar shark light chain demonstrates that their Ig light chains are homologous to mammalian λ chains with shark sequences sharing ∼40-50% identity with human λ chains. Analysis of sandbar shark genomic light chain clones by mapping and DNA sequencing demonstrates that sharks have a unique Ig gene arrangement system in which the genes are organized into clusters or cassettes spanning 4.3 to 6 kilobases and contain a single variable (V), joining (J), and constant (C) gene. The light chain clusters can be divided into two patterns based upon spacing differences between the J and C genes. A unique finding of this study is that the V and J genes are fused within the germline. PCR analysis of genomic DNA extends this finding, demonstrating that VJ fusion is the predominant organizational feature of sandbar shark immunoglobulin light chain genes. This finding raises questions concerning the necessity of recombination to produce an antibody repertoire capable of reacting against a diverse array of antigens. While such fusion may initially suggest a lack of light chain diversity in these animals, the results of this study strongly supports the hypothesis that sandbar sharks can potentially express a highly diverse light chain repertoire.

Numbers of sandbar sharks, Carcharhinus plumbeus, in the Northwest Atlantic have experienced drastic declines since the early 1980's reaching their minima during the early 1990's. Catch rates in the early 1990's were a mere 25% of those during the 1980's. Such drastic reductions in other fish stocks have often caused compensatory responses, most notably the cod stocks in the Northwest Atlantic. Compensatory responses in depressed populations may include decreased natural mortality, increased fecundity, or increased growth rates. Compensation for population fluctuations below carrying capacities have been recognized for many terrestrial and oceanic r-selected organisms, but few instances have been noted for K-selected species. Due to slow-growth and late maturity, compensatory responses in K-selected species such as the sandbar shark probably require generation-scale time periods to become evident. A previous age and growth study discovered slight increases in juvenile sandbar shark growth rates when vertebral centra samples obtained in 1980-81 and 1990-1992 were compared. The Virginia Institute of Marine Science shark long-line survey reported the lowest abundance of sandbar sharks in 1992. Animals pupped during this time may display greater differences in growth rates due to drastically reduced population size. Samples obtained over the 2001-2004 time period were compared to the aforementioned time periods to investigate potential compensatory responses in the sandbar shark population in the Northwest Atlantic. Growth estimates for the sandbar shark, Carcharhinus plumbeus, in the Northwestern Atlantic were estimated using a reparameterized von Bertalanffy growth model. Sharks were tagged in Virginia waters with roto-tags and double return nylon dart tags from 1992 to 2006 by the shark longline survey of the Virginia Institute of Marine Science. Captured sharks were measured, tagged, and released by VIMS scientists. Age and growth estimates were determined for the sandbar shark, Carcharhinus plumbeus, from Oahu, Hawaii in the central Pacific Ocean. Age estimates were obtained through vertebral centra analysis of 187 sharks. We verified our age estimates through marginal increment analysis of centra and oxytetracycline marking methods of at-liberty sandbar sharks. Sizes of sampled sharks ranged from 46 cm to 147 cm pre-caudal length. Four growth models were fitted to length-at-age data; two forms of the von Bertalanffy growth model, the Gompertz growth model, and a logistic growth model. Males and females exhibited statistically significant differences in growth, indicating that females grow slower and attain larger sizes than males. Growth parameter estimates revealed slower growth rates than previously estimated (based on captive specimens) for Hawaiian sandbar sharks. The von Bertalanffy growth model using empirical length-at-birth provided the best biological and statistical fit to the data. This model gave parameter estimates of L infinity .=138.5 cm PCL and k=0.12 year-1 for males and Linfinity=152.8 cm PCL, k=0.10 year-1 for females. Male and female sandbar sharks mature at approximately 8 and 10 years of age respectively. The population of sandbar sharks in the Hawaiian Islands is an unfished population. The presents a unique opportunity to conduct demographic analyses on a virgin population of sandbar sharks. Most populations of sandbar sharks have been heavily exploited due to near coastal and estuarine habitat preferences and high demand for fins. Conversely the population of sandbar sharks in the Northwest Atlantic (NWA) has suffered severe declines since the early 1980's. Previous studies have suggested compensatory growth is occurring within this population, but the true effect at the population level has not been estimated. Life history parameters estimated for the Hawaii population, the NWA population in 1980-1981 and 2000-2004 time periods were used in stochastic age-based life tables and Leslie matrices to estimate demographic parameters. Yield recruit-1 relationships were estimated for the Hawaii population to determine optimal harvest strategies that would maintain a population at equilibrium. Population growth for the Hawaii population was estimated to be 1.014 year-1. Yield recruit-1 analyses suggested harvest of sharks 15 years of age and older would provide the greatest yield while not causing population decline. Population growth for sandbar sharks in the NWA was 1.009-1 year for the 1980-1981 time period and 1.030-1 year for the 2000-2004 time period. (Abstract shortened by UMI.).

The objectives of my research were to test the hypothesis that compensatory (density-dependent) growth of sandbar shark (Carcharhinus plumbeus) occurred after severe population reduction, to describe the juvenile sandbar shark fauna present in the Chesapeake Bay during 1980-81 and 1990-93, and to perform demographic analyses to examine potential population growth. Age and growth of sandbar sharks were investigated by counting rings in vertebral samples collected in 1980-81 and 1991-92. Age at maturity was 15-16 years for both sample periods and both sexes. For sexes combined, the von Bertalanffy growth parameters were L&\sb{lcub}\infty{rcub}& = 199 cm precaudal length (PCL), K = 0.057, t&\sb{lcub}\rm o{rcub}& = &-&4.9 years for the 1980-81 sample and L&\sb{lcub}\infty{rcub}& = 164 cm PCL, K = 0.089, t&\sb{lcub}\rm o{rcub}& = &-&3.8 years for the 1991-92 sample. Significant differences in size at age and annual incremental growth of juveniles suggest a small increase in juvenile sandbar shark growth rate between the two sampling periods. Annual catches of sharks &>&105 cm PCL declined substantially between survey periods. Males and females were present in a 1:1 ratio. During 1980-81 juveniles ranged in age from 0-7 yr, but in 1990-93 few sandbar sharks over age 4 were taken. Based on the best estimate of fishing mortality the population ranged from 10,087 to 8509 sharks from 1989-1993. Annual year-class size was variable but all estimates were within one order of magnitude. Juvenile sandbar sharks declined in abundance by approximately 15% between 1989 and 1993. The annual population growth rate was highest under a scenario of natural mortality (M) = 0.05 and maximum age of 30 yr, but was only 11.9%/yr. at higher juvenile mortality rates and adult M fixed at 0.10, the best estimate of M for sandbar sharks, population growth rate was only 2.6%/yr. Adding fishing mortality (F) at immature ages caused the population to decline unless F levels were &<&0.10 and 0.05 at maximum age = 30 and 60 yr, respectively. It is apparent that sandbar shark populations will decline under any substantial fishing mortality on immature ages, and mature fish can only be exploited at very low levels of fishing mortality.

Chesapeake Bay is possibly the largest summer nursery for Carcharhinus plumbeus in the western Atlantic. Longline sampling conducted from 1990--1999 was used to delineate this nursery spatially and temporally. Catch data from 83 longline stations sampled throughout the Virginia Chesapeake Bay were analyzed as a function of nine physical and environmental variables to delineate this nursery spatially. Tree-based models determined which variables best discriminated between stations with high and low catches and indicated that complex distribution patterns could be adequately modeled with few variables. The highest abundance of juvenile sharks was predicted where salinity was greater than 20.5 and depth was greater than 5.5 meters. Longline data from 100 sets made at two standard stations in the lower Bay indicated that immigration occurred in late May and early June and was highly correlated with increasing water temperature. Emigration from the estuary occurred in late September and early October and was highly correlated with decreasing day length. Between 1995 and 2000, 1846 juvenile C. plumbeus were tagged. With two exceptions, recaptures made in summer months were within 50 kilometers of the tagging location. Those recaptured in winter months were caught between 200 and 830 kilometers from the tagging location and indicated that the coastal waters of North Carolina and South Carolina serve as important winter nurseries from late October until May. Tag recaptures made in subsequent summers suggest that most juvenile sandbar sharks return to the same summer nurseries annually. Ultrasonic telemetry was used in investigate the diel activity patterns of juvenile C. plumbeus in Chesapeake Bay. Ten sharks were tracked for 10 to 50 consecutive hours. Swimming direction was correlated with mean direction of 2 tidal currents. Mean activity space was conservatively estimated to be 110 km2, which is two orders of magnitude greater than that reported for other carcharhiniform species. Swimming depth ranged from surface to 40 meters and was significantly deeper during the day (12.8 meters) than during the night (8.5 meters). This diel activity pattern and large activity space is hypothesized to be an adaptation for foraging on patchy prey in a productive, yet dynamic, temperate estuary.

The sandbar shark (Carchrarhinus plumbeus) is a commercially important shark species to fisheries around the world but is known to be highly susceptible to over·fishing. During the late 1990s, changes in the targeting practices of Western Australian demersal gillnet fishing vessels, and an expansion of targeted demersal longlining in the north of the State, caused a rapid escalation in C. plumbeus catches. This study therefore aimed to collect the biological and fishery data necessary to assess the impacts of increasing exploitation of the species and to develop biologically appropriate techniques for assessing the sustainability of these fishery developments.

The identification and delineation of nursery areas and areas of aggregation of north Atlantic sharks has been identified as an important information need for future management efforts. The objectives of this project were to use a fishery-independent method to study the overwintering area of juvenile sandbar sharks, to spatially delineate the Eastern Shore nursery area, and to examine movement patterns and space use within this nursery area. Data from 21 satellite transmitters attached to large juvenile sandbar sharks revealed that these sharks primarily occurred off the outer banks of North Carolina, at deeper depths and colder water temperatures during the overwintering period (after November 1). The data from this project support the size and scope of the closed area currently enacted by the Fishery Management Plan. The Eastern Shore of Virginia was found to be an important primary and secondary nursery area for this population of sandbar sharks. Within this nursery area sharks were most concentrated in Great Machipongo Inlet. Abundance of juvenile sandbar sharks was positively correlated to distance from the inlet and water temperature. Smaller juvenile sharks were more concentrated farther from the inlets and were more prevalent in the southern inlets. Juvenile sandbar shark movements were studied using passive acoustic telemetry. Juveniles tended to spend significantly more time farther from the inlets and their space use was positively correlated to time of day with a greater proportion of time spent in the acoustic array during the night time hours. Tidal currents were positively correlated with small scale movements but were unrelated to overall space use. The sharks tracked returned or remained within the array to a greater extent than would be predicted by random movements alone indicating these animals have some site attachment to these areas. Smaller sharks remained within the array area to a greater extent than larger sharks indicating they likely have smaller activity spaces. This study emphasizes the importance of both the Eastern Shore of Virginia nursery area and the overwintering area that occurs off the central coast of North Carolina as essential habitat for the north Atlantic population of sandbar sharks.

The sandbar shark, Carcharhinus plumbeus, has a discontinuous cosmopolitan distribution and is exploited throughout much of its range. In the western North Atlantic, it constitutes the majority of the directed commercial fishery. The stock has declined greatly since the fisheries' inception and has not shown signs of recovery despite the implementation of management practices. Like many highly vagile marine species, it is difficult to obtain information about the sandbar shark through direct observation. Therefore, the goal of this dissertation is to use a molecular approach to examine aspects of behavior and reproduction, providing information useful in conservation and management. to this end, I examine the prevalence of genetic polyandry in the western North Atlantic and estimate effective population size and effective number of breeders for the Delaware Bay and Eastern Shore of Virginia nursery grounds. In addition, I look at patterns of philopatry and reproductive periodicity, while on a worldwide scale, assessing both historical and contemporary gene flow. Paternity analysis using microsatellite markers reveals that most females are mate with multiple males during one reproductive period. Despite the high prevalence of genetic polyandry, no direct benefits are detected. The data, however, suggest that males benefit by excluding other males from mating, intimating strong intrasexual competition. The effective number of breeders per nursery ground, estimated using the linkage disequilibrium method, is fairly consistent across years. Comparisons with census size estimates made for Delaware Bay reveal that the two measurements are tightly coupled. The ratio of effective size to census size is 0.45 or higher. This suggests that monitoring of effective population size may be a useful methodology for tracking abundance, and that exploitation may have a direct negative impact on the level of genetic variance. The results suggest that females may stray between nursery grounds found in Delaware Bay, the Eastern Shore lagoons and Chesapeake Bay, as phi st values are nonsignificant and kin groups are detected between as well as within samples. However, true kin groups can not be distinguished from erroneous kin groups because sample size is too small and the loci employed do not have enough power. Even so, the results suggest that female reproductive periodicity in this species needs to be reevaluated. Different patterns of historical dispersal and contemporary gene flow are observed when markers with different modes of inheritance are used to evaluate historical phylogeography. The results suggest that, although females show regional phylopatry, pulses of female dispersal during the Pleistocene may have created the species' current distribution. This dynamic may have been mediated by the changing distribution of nursery habitat caused by the rise and fall of sea level associated with climate change rather than by fluctuating temperature. This idea is supported by the results, which suggest that male mediated gene flow persists long after female gene flow has stopped.

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Universidade do Estado da Bahia
O presente trabalho relata a biologia de 3 espécies de tubarões, o Carcharhinus falciformis, Carcharhinus plumbeus e o Pseudocarcharias kamoharai, além da ecologia da raia prego, Dasyatis americana. Primeiramente foi estudada a biologia reprodutiva do C. falciformis, sendo examinado um total de 96 indivíduos, sendo 48 machos e 48 fêmeas, capturados na região Equatorial do Oceano Atlântico, nas proximidades do Arquipélago de São Pedro e São e São Paulo (0°55 10 N;29°20 33 W). O comprimento total (CT) dos indivíduos variou entre 83,0 e 272,0cm, para as fêmeas e entre 75,0 e 295,0 para os machos. Estes dados sugerem um tamanho de primeira maturação sexual para o tubarão lombo-preto, em águas equatoriais, de aproximadamente 230,0cm, para as fêmeas e de 210,0 a 230,0cm para os machos. A distribuição mensal das fases sexuais ao longo do ano das fêmeas, não apresentaram uma tendência clara, sugerindo que pelo menos, na área estudada, esta espécie, não apresenta um ciclo gestacional anual claro. A proporção sexual dos embriões foi igual a 1:1,4 (macho:fêmea), com uma fecundidade de 4 a 15 embriões por período gestacional. Outra espécie que também teve os aspectos da sua biologia reprodutiva investigados foi o C. plumbeus, que durante o período de dezembro de 1994 a janeiro de 1996, teve, um total de 28 tubarões, sendo 11 machos e 17 fêmeas, capturados na região Nordeste do Brasil, na área de talude continental, em frente à costa do Estado de Pernambuco. O CT variou entre 154,0 e 196,0cm para os machos e entre 108,5 e 208,0cm para as fêmeas. A distribuição mensal dos estágios sexuais demonstraram que o parto e a ovulação ocorrem nos mesmos meses, sugerindo um ciclo de gestacional de 12 meses, em anos alternados. O número de embriões por fêmea grávida, variou entre 7 e 10 indivíduos, com um valor médio de 8,6, apresentando os mesmos uma proporção sexual de 1:1,4(macho:fêmea). Uma terceira e ultima espécie ainda teve a biologia reprodutiva investigada, no período de fevereiro de 2005 a setembro de 2007 foram capturados, por barcos da frota comercial arrendada, 490 exemplares de tubarão cachorro, Pseudocarcharias kamoharai, no Atlântico Tropical (06º 45 N e 23º 36 S e 018º 44 W e 053º 13 W). Em laboratório, os indivíduos capturados foram identificados e tiveram seus principais comprimentos aferidos, e seus aparelhos reprodutores coletados e fixados em formol a 10%. Dos 490 espécimes de tubarão cachorro analisados, 313 (63,9%) eram fêmeas, com CT variando de 75,0 a 122,0 cm, e 177(36,1%) eram machos, com CT entre 65,5 e 109,0 cm. As fêmeas apresentaram 6 classes de estágios maturacionais, enquanto que os machos apenas 2 classes. A distribuição de freqüência de comprimento apresentou uma moda para as fêmeas de entre 90,1 e 100,0 cm, sendo igual para os machos. O peso médio da glândula oviducal nos jovens apresentou diferença estatisticamente significantes em relação aos outros estágios (Kruskal-Wallis, F=2.34; P = 0.004). As fêmeas classificadas como adultas, exibiam todo o aparelho reprodutor desenvolvido, contudo, sempre, com peso do ovário e largura dos úteros menores que os outros estágios, excetuando-se as juvenis. As fêmeas prenhes, cujo CT variou entre 87,5 e 118,6 cm, foram classificadas em quatro estágios distintos, prenhe I, II, III e IV (a termo), pois, embora estivessem na mesma condição, exibiam características particulares, principalmente no que tange as condições dos úteros e ovários. As fêmeas classificadas como prenhe II apresentavam os ovários com características semelhantes aos da prenhe I, contudo com um peso médio um pouco maior e com intensa atividade vitelogênica. Os espécimes classificados como prenhe III, continham em seus úteros apenas embriões, com comprimento total sempre inferior a 30 cm. Os espécimes classificados no estágio de prenhes IV (a termo) exibiam os ovários nitidamente em processo de reabsorção, não se encontrando mais em ovulação, o que pode ser verificado pela diminuição de seu peso. Apresentavam ainda em ambos os úteros embriões com CT superior a 30,0 cm. As relações entre o comprimento total e a largura dos úteros e o peso das glândulas oviducais apontam para um tamanho de 1º maturação sexual em torno de 90,0 cm de CT. Entre os 177 machos examinados 37 (20,9%) encontravam-se juvenis, com CT variando entre 65,5 94,0 cm e 140 (70,1%), eram adultos, exibindo CT entre 80,0 109,0 cm. As relações entre CT e a largura, comprimento e peso do aparelho reprodutor da espécie, apontam para um tamanho de primeira maturação sexual entre 80,0 e 94,0 cm de CT. Também foi realizado um estudo de ocorrência do Rynchodon typus no Arquipélago de São Pedro e São Paulo, por se tratar de um importante local de concentração de tubarões-baleia. Os animais foram vistos ao longo de todo ano, próximos às embarcações de pesca nas adjacências das ilhas. Em avistagens registradas entre fevereiro de 2000 e novembro de 2005, os comprimentos dos indivíduos variaram entre 1,8 m e 14 m. As causas destas concentrações no arquipélago ainda não são claras, uma vez que não há há ressurgências e grandes concentrações de plâncton no arquipélago, e também não foram observadas atividades reprodutivas. No entanto, podem estar associadas ao período de desova dos peixes-voadores, marcadamente no primeiro semestre, quando as aparições são mais freqüentes. Finalizando, foi realizado na Reserva Biológica do Atol das Rocas o trabalho de ecologia populacional e uso do habitat da Dasyatis americana, sendo avistadas 184 raias, durante as incursões subaquáticas, no período de agosto de 2003 a dezembro de 2005. O tamanho dos indivíduos variou entre 29,0 e 113,0 cm de largura de disco (LD). A maioria dos espécimes observados encontravam-se na faixa de 80,0 a 89,0 cm de LD, representando cerca de 25% do total. As fêmeas foram mais abundantes que os machos, com uma proporção sexual de 5,7♀:1♂ (fêmea:macho). O tamanho da população foi estimada em 99,2±17,1 e 94,4±10,3 indivíduos, utilizando Petersen-Bayley e Jolly-Saber, como estimadores probabilísticos, respectivamente. Os espécimes observados apresentaram comportamentos de alimentação e movimentação altamente relacionados com o severo ciclo de mares imposto pelo Atol