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John E. Graves - One of the best experts on this subject based on the ideXlab platform.
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world phylogeography and male mediated gene flow in the Sandbar Shark carcharhinus plumbeus
Molecular Ecology, 2010Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Edward J Heist, John E. GravesAbstract:The Sandbar Shark, Carcharhinus plumbeus, is a large, cosmopolitan, coastal species. Females are thought to show philopatry to nursery grounds while males potentially migrate long distances, creating an opportunity for male-mediated gene flow that may lead to discordance in patterns revealed by mitochondrial DNA (mtDNA) and nuclear markers. While this dynamic has been investigated in elasmobranchs over small spatial scales, it has not been examined at a global level. We examined patterns of historical phylogeography and contemporary gene flow by genotyping 329 individuals from nine locations throughout the species’ range at eight nuclear microsatellite markers and sequencing the complete mtDNA control region. Pairwise comparisons often resulted in fixation indices and divergence estimates of greater magnitude using mtDNA sequence data than microsatellite data. In addition, multiple methods of estimation suggested fewer populations based on microsatellite loci than on mtDNA sequence data. Coalescent analyses suggest divergence and restricted migration among Hawaii, Taiwan, eastern and western Australia using mtDNA sequence data and no divergence and high migration rates, between Taiwan and both Australian sites using microsatellite data. Evidence of secondary contact was detected between several localities and appears to be discreet in time rather than continuous. Collectively, these data suggest complex spatial ⁄temporal relationships between Shark populations that may feature pulses of female dispersal and more continuous male-mediated gene flow.
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Effective size closely approximates the census size in the heavily exploited western Atlantic population of the Sandbar Shark, Carcharhinus plumbeus
Conservation Genetics, 2008Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Camilla T. Mccandless, John E. GravesAbstract:The Sandbar Shark, Carcharhinus plumbeus, is a long-lived species with low lifetime fecundity that is heavily fished in the western North Atlantic. Inshore nursery grounds increase survivorship of Sandbar Shark pups and the principal nurseries are in the mid-Atlantic region. We calculated effective number of breeders (Nb) and effective population size (Ne) for adults utilizing the nursery grounds of the Delaware Bay and the Eastern Shore of Virginia by genotyping 902 animals across five cohorts at eight microsatellite loci. Estimates of Nb and Ne were compared to estimates of census size (Nc) of cohorts obtained from Delaware Bay. The estimated Ne/Nc and Nb/Nc ratios were 0.45 or higher whether the Delaware Bay cohorts were considered as distinct year classes or combined. This is in contrast to estimated Ne/Nc ratios in other exploited marine fishes, which are several orders of magnitude smaller. Instead, the Ne/Nc ratio of Sandbar Sharks is similar to that found in marine and terrestrial mammals.
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genetic polyandry and sexual conflict in the Sandbar Shark carcharhinus plumbeus in the western north atlantic and gulf of mexico
Molecular Ecology, 2006Co-Authors: David S. Portnoy, John A. Musick, George H Burgess, Andrew N Piercy, John E. GravesAbstract:To investigate patterns of polyandry in the Sandbar Shark (Carcharhinus plumbeus), 20 pregnant females were sampled from the western North Atlantic and Gulf of Mexico. Five species-specific microsatellite markers were used to genotype each Shark and its litter. Of 20 litters, 17 (85%) were shown to have multiple sires. In multiply sired litters, the estimated minimum number of sires ranged from two to five with an average of 2.3 males per litter. Regression analysis did not demonstrate a significant relationship between female reproductive success and female body size or sire number and female body size. There was a high incidence of reproductive skew noted in litters, and two groups of males with significantly different mean reproductive success were observed. Analyses using Bateman's principles suggest that there is less direct benefit for females that acquire multiple mates than for males who bias paternity within litters. In light of past morphological and behavioural studies, these data suggest that patterns of polyandry in elasmobranchs may be determined by coercive mating, and that breeding behaviour has likely evolved in the context of sexual conflict.
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Isolation and characterization of five dinucleotide microsatellite loci in the Sandbar Shark, Carcharhinus plumbeus
Molecular Ecology Notes, 2006Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Kevin A. Thompson, John E. GravesAbstract:Five dinucleotide markers were isolated and optimized from a microsatellite-enriched genomic library obtained from the Sandbar Shark, Carcharhinus plumbeus. Genotypic distributions of all markers were found to be in conformance with the expectations of Hardy–Weinberg equilibrium with four to 39 alleles present per locus. We amplified these loci in two female Sharks and their litters. A maternal allele was recovered at each locus in all progeny indicating reliable amplification. More than two paternal alleles were recovered across both litters indicating genetic polyandry. Additionally, these markers were amplified across 10 carcharhiniform species to examine their utility in other studies.
Richard W Brill - One of the best experts on this subject based on the ideXlab platform.
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The effects of elevated potassium, acidosis, reduced oxygen levels, and temperature on the functional properties of isolated myocardium from three elasmobranch fishes: clearnose skate (Rostroraja eglanteria), smooth dogfish (Mustelus canis), and sand
Journal of Comparative Physiology B, 2021Co-Authors: Gail D. Schwieterman, Heather M Marshall, Peter G Bushnell, Diego Bernal, Maggie M. Winchester, Holly A. Shiels, Richard W BrillAbstract:Elevated plasma potassium levels (hyperkalemia), reduced plasma pH (acidosis), reduced blood oxygen content, and elevated temperatures are associated with species-specific rates of at-vessel and post-release mortality in elasmobranch fishes. The mechanism linking these physiological disturbances to mortality remains undetermined however, and we hypothesize that the proximate cause is reduced myocardial function. We measured changes in the functional properties of isolated ventricular myocardial strips from clearnose skate ( Rostroraja eglanteria ), smooth dogfish ( Mustelus canis ), and Sandbar Shark ( Carcharhinus plumbeus ) when subjected to the following stressors (both in isolation and in combination): hyperkalemia (7.4 mM K^+), acidosis (from 7.9 to 7.1), and reduced oxygen (to 31% O_2 saturation) applied at temperatures 5 °C above and below holding temperatures. We selected these species based on phylogenetic distance, diverse routine activity levels, and their tolerance to capture and transport. Stressors had a few significant species-specific detrimental impacts on myocardial function (e.g., a 33–45% decrease in net force under acidosis + low O_2). Net force production of myocardial strips from clearnose skate and smooth dogfish approximately doubled following exposure to isoproterenol, demonstrating that these species possess beta-adrenergic receptors and that their stimulation could provide a mechanism for preservation of cardiac function during stress. Our results suggest that disruption of physiological homeostasis associated with capture may fatally impair cardiac function in some elasmobranch species, although research with more severe stressors is needed.
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The impacts of warming and hypoxia on the performance of an obligate ram ventilator.
Conservation physiology, 2019Co-Authors: Daniel P. Crear, Richard W Brill, Peter G Bushnell, Robert J. Latour, Gail D. Schwieterman, Rachel M. Steffen, Kevin C. WengAbstract:Climate change is causing the warming and deoxygenation of coastal habitats like Chesapeake Bay that serve as important nursery habitats for many marine fish species. As conditions continue to change, it is important to understand how these changes impact individual species' behavioral and metabolic performance. The Sandbar Shark (Carcharhinus plumbeus) is an obligate ram-ventilating apex predator whose juveniles use Chesapeake Bay as a nursery ground up to 10 years of age. The objective of this study was to measure juvenile Sandbar Shark metabolic and behavioral performance as a proxy for overall performance (i.e. fitness or success) when exposed to warm and hypoxic water. Juvenile Sandbar Sharks (79.5-113.5 cm total length) were collected from an estuary along the eastern shore of Virginia and returned to lab where they were fitted with an accelerometer, placed in a respirometer and exposed to varying temperatures and oxygen levels. Juvenile Sandbar Shark overall performance declined substantially at 32°C or when dissolved oxygen concentration was reduced below 3.5 mg l-1 (51% oxygen saturation between 24-32°C). As the extent of warm hypoxic water increases in Chesapeake Bay, we expect that the available Sandbar Shark nursery habitat will be reduced, which may negatively impact the population of Sandbar Sharks in the western Atlantic as well as the overall health of the ecosystem within Chesapeake Bay.
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Microprocessor-based prototype bycatch reduction device reduces bait consumption by spiny dogfish and Sandbar Shark
ICES Journal of Marine Science, 2018Co-Authors: Sunkita Howard, Richard W Brill, Christopher D. Hepburn, Jenny RockAbstract:Abstract Elasmobranchs contribute heavily to bycatch in longline fisheries globally, and an effective method of deterring them from baited fishing gear is needed. Electrosensory stimulus holds promise as a method of disrupting elasmobranch close-range feeding responses as their electric sense guides their final strike during prey capture. We used laboratory experiments to test the hypothesis that weak electric stimuli generated by a prototype electronic bycatch reduction device (BRD) could deter Sandbar Shark (Carcharhinus plumbeus) and spiny dogfish (Squalus acanthias) from eating bait. Voltage gradients <1 mV cm−1 at the location of bait were produced by an Arduino microcontroller powered by a 9 V battery and attached to carbon electrodes. Median bait consumption by groups of juvenile Sandbar Shark declined by 74% when bait was located 10 cm vs. 2 m from active electrodes. Spiny dogfish median bait consumption halved when bait was located 10 cm from active vs. inactive electrodes. Although laboratory studies often produce a larger effect for electrosensory Shark deterrents than can be demonstrated during field trials, if the effects seen in our laboratory studies produced similar effects in the field, it could meet fishermen’s requirements for a BRD.
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the effects of pop up satellite archival tags psats on the metabolic rate and swimming kinematics of juvenile Sandbar Shark carcharhinus plumbeus
Fisheries Research, 2017Co-Authors: Scott D Lynch, Benjamin J Marcek, Heather M Marshall, Peter G Bushnell, Diego Bernal, Richard W BrillAbstract:Abstract Pop-up satellite archival tags (PSATs) have been used since the 1990s to document the movements and post-release survival of numerous fish species. The effects of PSAT attachment on metabolic rate, cost of transport, and swimming kinematics have, however, not been broadly investigated. We therefore quantified the acute effects of PSAT attachment on these parameters in juvenile (47–87 cm fork length) Sandbar Shark Carcharhinus plumbeus. Using a water tunnel, we also measured the lift and drag forces of PSATs from three manufacturers which allowed us to calculate the theoretical power costs of towing these devices. We found no evidence that PSAT attachment results in increases in metabolic rate or cost of transport, or influences swimming kinematics of juvenile Sandbar Shark at volitional swimming speeds. Applying drag force measurements obtained for PSATs to our data showed that the predicted fractional increase in metabolic rate engendered by towing one of these devices at a specified velocity, normalized by the metabolic rate when swimming at that velocity minus the standard metabolic rate, would be below 5%. Our results are therefore congruent and suggest that PSAT attachment does not negatively impact juvenile Sandbar Shark (and by extension other elasmobranch species of equivalent or larger body sizes and employing a similar swimming mode).
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validation of the i stat system for the analysis of blood gases and acid base status in juvenile Sandbar Shark carcharhinus plumbeus
Conservation Physiology, 2015Co-Authors: Till S Harter, Phillip R Morrison, John W Mandelman, Jodie L Rummer, Anthony P Farrell, Richard W Brill, Colin J BraunerAbstract:Accurate measurements of blood gases and acid–base status require an array of sophisticated laboratory equipment that is typically not available during field research; such is the case for many studies on the stress physiology, ecology and conservation of elasmobranch fish species. Consequently, researchers have adopted portable clinical analysers that were developed for the analysis of human blood characteristics, but often without thoroughly validating these systems for their use on fish. The aim of our study was to test the suitability of the i-STAT system, the most commonly used portable clinical analyser in studies on fish, for analysing blood gases and acid–base status in elasmobranchs, over a broad range of conditions and using the Sandbar Shark (Carcharhinus plumbeus) as a model organism. Our results indicate that the i-STAT system can generate useful measurements of whole blood pH, and the use of appropriate correction factors may increase the accuracy of results. The i-STAT system was, however, unable to generate reliable results for measurements of partial pressure of oxygen (PO2) and the derived parameter of haemoglobin O2 saturation. This is probably due to the effect of a closed-system temperature change on PO2 within the i-STAT cartridge and the fact that the temperature correction algorithms used by i-STAT assume a human temperature dependency of haemoglobin–O2 binding; in many ectotherms, this assumption will lead to equivocal i-STAT PO2 results. The in vivo partial pressure of CO2 (PCO2) in resting Sandbar Sharks is probably below the detection limit for PCO2 in the i-STAT system, and the measurement of higher PCO2 tensions was associated with a large measurement error. In agreement with previous work, our results indicate that the i-STAT system can generate useful data on whole blood pH in fishes, but not blood gases.
John A. Musick - One of the best experts on this subject based on the ideXlab platform.
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DRAFT
2013Co-Authors: Jason G. Romine, John A. MusickAbstract:The Sandbar Shark, Carcharhinus plumbeus, is a common large coastal Shark that inhabits temperate and subtropical waters world wide and attains lengths greater than 2 meters (Compagno 1984). In the western North Atlantic the species inhabits near-shore waters out to the edge of the continental shelf from Cape Cod to Brazil (Bigelow 1948
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Compensatory Growth of the Sandbar Shark in the Western North Atlantic Including the Gulf of Mexico
Marine and Coastal Fisheries, 2013Co-Authors: Jason G. Romine, John A. Musick, R. A. JohnsonAbstract:Abstract The number of Sandbar Sharks Carcharhinus plumbeus in the western North Atlantic Ocean has experienced a drastic decline since the early 1980s, reaching a minimum during the early 1990s. Catch rates in the early 1990s were a mere 25% of those during the 1980s. According to several fishery-independent surveys, the low point in Sandbar Shark abundance followed a period of high exploitation. Growth models fit to age–length data collected from 1980 to 1983 and from 2001 to 2004 were compared to investigate potential changes in parameter estimates that might reveal compensatory responses in the Sandbar Shark population. Statistical differences were found between the model parameters for the two time periods, but the differences in growth rates were minimal. The parameters from the three-parameter von Bertalanffy growth model for female Sharks during the 1980–1983 and 2000–2004 time periods were as follows: L∞ = 188.4 and 178.3 cm FL; k = 0.084 and 0.106; and t 0 = −4.097 and −3.41. For males the growt...
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world phylogeography and male mediated gene flow in the Sandbar Shark carcharhinus plumbeus
Molecular Ecology, 2010Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Edward J Heist, John E. GravesAbstract:The Sandbar Shark, Carcharhinus plumbeus, is a large, cosmopolitan, coastal species. Females are thought to show philopatry to nursery grounds while males potentially migrate long distances, creating an opportunity for male-mediated gene flow that may lead to discordance in patterns revealed by mitochondrial DNA (mtDNA) and nuclear markers. While this dynamic has been investigated in elasmobranchs over small spatial scales, it has not been examined at a global level. We examined patterns of historical phylogeography and contemporary gene flow by genotyping 329 individuals from nine locations throughout the species’ range at eight nuclear microsatellite markers and sequencing the complete mtDNA control region. Pairwise comparisons often resulted in fixation indices and divergence estimates of greater magnitude using mtDNA sequence data than microsatellite data. In addition, multiple methods of estimation suggested fewer populations based on microsatellite loci than on mtDNA sequence data. Coalescent analyses suggest divergence and restricted migration among Hawaii, Taiwan, eastern and western Australia using mtDNA sequence data and no divergence and high migration rates, between Taiwan and both Australian sites using microsatellite data. Evidence of secondary contact was detected between several localities and appears to be discreet in time rather than continuous. Collectively, these data suggest complex spatial ⁄temporal relationships between Shark populations that may feature pulses of female dispersal and more continuous male-mediated gene flow.
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Effective size closely approximates the census size in the heavily exploited western Atlantic population of the Sandbar Shark, Carcharhinus plumbeus
Conservation Genetics, 2008Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Camilla T. Mccandless, John E. GravesAbstract:The Sandbar Shark, Carcharhinus plumbeus, is a long-lived species with low lifetime fecundity that is heavily fished in the western North Atlantic. Inshore nursery grounds increase survivorship of Sandbar Shark pups and the principal nurseries are in the mid-Atlantic region. We calculated effective number of breeders (Nb) and effective population size (Ne) for adults utilizing the nursery grounds of the Delaware Bay and the Eastern Shore of Virginia by genotyping 902 animals across five cohorts at eight microsatellite loci. Estimates of Nb and Ne were compared to estimates of census size (Nc) of cohorts obtained from Delaware Bay. The estimated Ne/Nc and Nb/Nc ratios were 0.45 or higher whether the Delaware Bay cohorts were considered as distinct year classes or combined. This is in contrast to estimated Ne/Nc ratios in other exploited marine fishes, which are several orders of magnitude smaller. Instead, the Ne/Nc ratio of Sandbar Sharks is similar to that found in marine and terrestrial mammals.
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The Sandbar Shark Summer Nursery within Bays and Lagoons of the Eastern Shore of Virginia
Transactions of the American Fisheries Society, 2007Co-Authors: Christina L. Conrath, John A. MusickAbstract:Abstract We sought to examine the spatial use of coastal bays and lagoons associated with the Eastern Shore of Virginia (i.e., the Atlantic shoreline north of the mouth of the Chesapeake Bay) as nursery habitat for Sandbar Sharks Carcharhinus plumbeus. Generalized linear mixed models were used to examine the relationship between physical factors and the abundance of neonate and juvenile Sandbar Sharks within the study area. Neonates, small juveniles, and large juveniles were present throughout the sampling area in relatively high abundance throughout the months of June-September. Abundances of neonates and small juveniles were correlated with sampling distance from the inlet; larger fractions of these groups were captured as distance from the inlet increased. Large-juvenile abundance was not significantly correlated with any physical factor. The catch rates of neonate and juvenile Sandbar Sharks within this area were comparable with those observed in nearby Chesapeake Bay, although a larger number of juve...
David S. Portnoy - One of the best experts on this subject based on the ideXlab platform.
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world phylogeography and male mediated gene flow in the Sandbar Shark carcharhinus plumbeus
Molecular Ecology, 2010Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Edward J Heist, John E. GravesAbstract:The Sandbar Shark, Carcharhinus plumbeus, is a large, cosmopolitan, coastal species. Females are thought to show philopatry to nursery grounds while males potentially migrate long distances, creating an opportunity for male-mediated gene flow that may lead to discordance in patterns revealed by mitochondrial DNA (mtDNA) and nuclear markers. While this dynamic has been investigated in elasmobranchs over small spatial scales, it has not been examined at a global level. We examined patterns of historical phylogeography and contemporary gene flow by genotyping 329 individuals from nine locations throughout the species’ range at eight nuclear microsatellite markers and sequencing the complete mtDNA control region. Pairwise comparisons often resulted in fixation indices and divergence estimates of greater magnitude using mtDNA sequence data than microsatellite data. In addition, multiple methods of estimation suggested fewer populations based on microsatellite loci than on mtDNA sequence data. Coalescent analyses suggest divergence and restricted migration among Hawaii, Taiwan, eastern and western Australia using mtDNA sequence data and no divergence and high migration rates, between Taiwan and both Australian sites using microsatellite data. Evidence of secondary contact was detected between several localities and appears to be discreet in time rather than continuous. Collectively, these data suggest complex spatial ⁄temporal relationships between Shark populations that may feature pulses of female dispersal and more continuous male-mediated gene flow.
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Effective size closely approximates the census size in the heavily exploited western Atlantic population of the Sandbar Shark, Carcharhinus plumbeus
Conservation Genetics, 2008Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Camilla T. Mccandless, John E. GravesAbstract:The Sandbar Shark, Carcharhinus plumbeus, is a long-lived species with low lifetime fecundity that is heavily fished in the western North Atlantic. Inshore nursery grounds increase survivorship of Sandbar Shark pups and the principal nurseries are in the mid-Atlantic region. We calculated effective number of breeders (Nb) and effective population size (Ne) for adults utilizing the nursery grounds of the Delaware Bay and the Eastern Shore of Virginia by genotyping 902 animals across five cohorts at eight microsatellite loci. Estimates of Nb and Ne were compared to estimates of census size (Nc) of cohorts obtained from Delaware Bay. The estimated Ne/Nc and Nb/Nc ratios were 0.45 or higher whether the Delaware Bay cohorts were considered as distinct year classes or combined. This is in contrast to estimated Ne/Nc ratios in other exploited marine fishes, which are several orders of magnitude smaller. Instead, the Ne/Nc ratio of Sandbar Sharks is similar to that found in marine and terrestrial mammals.
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genetic polyandry and sexual conflict in the Sandbar Shark carcharhinus plumbeus in the western north atlantic and gulf of mexico
Molecular Ecology, 2006Co-Authors: David S. Portnoy, John A. Musick, George H Burgess, Andrew N Piercy, John E. GravesAbstract:To investigate patterns of polyandry in the Sandbar Shark (Carcharhinus plumbeus), 20 pregnant females were sampled from the western North Atlantic and Gulf of Mexico. Five species-specific microsatellite markers were used to genotype each Shark and its litter. Of 20 litters, 17 (85%) were shown to have multiple sires. In multiply sired litters, the estimated minimum number of sires ranged from two to five with an average of 2.3 males per litter. Regression analysis did not demonstrate a significant relationship between female reproductive success and female body size or sire number and female body size. There was a high incidence of reproductive skew noted in litters, and two groups of males with significantly different mean reproductive success were observed. Analyses using Bateman's principles suggest that there is less direct benefit for females that acquire multiple mates than for males who bias paternity within litters. In light of past morphological and behavioural studies, these data suggest that patterns of polyandry in elasmobranchs may be determined by coercive mating, and that breeding behaviour has likely evolved in the context of sexual conflict.
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Isolation and characterization of five dinucleotide microsatellite loci in the Sandbar Shark, Carcharhinus plumbeus
Molecular Ecology Notes, 2006Co-Authors: David S. Portnoy, John A. Musick, Jan R. Mcdowell, Kevin A. Thompson, John E. GravesAbstract:Five dinucleotide markers were isolated and optimized from a microsatellite-enriched genomic library obtained from the Sandbar Shark, Carcharhinus plumbeus. Genotypic distributions of all markers were found to be in conformance with the expectations of Hardy–Weinberg equilibrium with four to 39 alleles present per locus. We amplified these loci in two female Sharks and their litters. A maternal allele was recovered at each locus in all progeny indicating reliable amplification. More than two paternal alleles were recovered across both litters indicating genetic polyandry. Additionally, these markers were amplified across 10 carcharhiniform species to examine their utility in other studies.
Mohamed Nejmeddine Bradai - One of the best experts on this subject based on the ideXlab platform.
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Effects of fishing practice changes on pelagic Shark longline captures in the Gulf of Gabes, Tunisia
Aquatic Conservation: Marine and Freshwater Ecosystems, 2019Co-Authors: Bechir Saidi, Sami Karaa, Samira Enajjar, Mohamed Nejmeddine BradaiAbstract:In order to increase their catches, longliners targeting Sharks in the Gulf of Gabes, Tunisia, have increased the number of hooks per basket and have included new bait types instead of mackerel (Scomber scombrus). This paper reports the effects of these changes on catch composition, catch rates, size distribution, life‐stage captures, and mortality at haulback. Data from 48 and 96 longline sets, carried out during the Shark fishing seasons of 2007 and 2008, with two hooks per basket, and 2016 and 2017, with five hooks per basket, respectively, were examined to assess the effect of gear change. Moreover, the effects of bait types were inspected based on 33 fishing sets using whole mackerel, 19 using salema (Sarpa salpa) halves, and 27 using pieces of stingray (Dasyatis spp.), sampled during 2016 and 2017. The species composition indicated that longliners expand the vertical distribution of their hooks to operate from the surface to the bottom. The catches with both longline designs were dominated by Sandbar Shark (Carcharhinus plumbeus). Despite gear changes, the catch rate of C. plumbeus decreased by 42.21%, suggesting population decline. The size composition indicated a shift towards larger specimens, mainly adult females, which could jeopardize the Shark population. Moreover, the mortality of the main species at haulback seems to be affected by the design of the longline. The bait used, mainly pieces of stingray, significantly increased the catch rate of Sandbar Shark, which suggests a greater attractiveness of the new bait; however, fish size and mortality rates at haulback were unchanged in response to bait variation. The fishery operates in Shark nursery grounds, which exposes these fish (principally C. plumbeus) to considerable exploitation pressure. The new fishing practices intensified the pressure and thus the risk of a rapid depletion of populations. To preserve the Shark species in the area, the use of new gear and attractive bait should be banned.
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Atypical characteristics of an albino embryo of Carcharhinus plumbeus (Chondrichthyes: Carcharhinidae) from the Gulf of Gabès (southern Tunisia, central Mediterranean)
Acta Adriatica: International Journal of Marine Sciences, 2006Co-Authors: Bechir Saidi, Mohamed Nejmeddine Bradai, Sondes Marouani, Olivier Guelorget, Christian CapapéAbstract:An abnormal partially-albino embryo with atypical characteristics was removed from a pregnant female Sandbar Shark, Carcharhinus plumbeus, caught in the Gulf of Gabes in southern Tunisian, central Mediterranean. The specimen is described and atypical characteristics and albinism in Shark species is reviewed.
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The reproductive biology of the Sandbar Shark, Carcharhinus plumbeus (Chondrichthyes: Carcharhinidae), from the Gulf of Gabès (southern Tunisia, central Mediterranean)
Acta Adriatica: International Journal of Marine Sciences, 2005Co-Authors: Béchir Saïumldi, Mohamed Nejmeddine Bradai, Abderrahman Bouaïumln, Olivier Guéacutelorget, Christian CapapéAbstract:The Sandbar Shark, Carcharhinus plumbeus, is commonly captured in the Gulf of Gabes (southern Tunisia). Of 932 specimens collected from January 2001 to May 2004, the smallest mature male was 1545 mm total length and the largest male was 1935 mm. All males above 1600 mm were mature. Adult females ranged 1660-2815 mm, while all females above 1720 mm were mature. The pupping season occurred in spring and early summer, with parturition in July. Gestation was estimated at twelve months, with females appearing to reproduce in alternate years. The diameter of the largest yellow-yolked oocytes ranged 29-32 mm (mean 30.3±1.2) with the mass ranging 9.1-13.3 g (mean 11.9±1.3). Both uteri were compartmentalized into chambers and a single embryo developed in each chamber. Length and weight at birth, based on near-term embryos, were estimated at 450-650 mm and 532-1458 g. The chemical balance of development, based on the mean dry masses of the largest yellow-yolked oocytes and near-term embryos, was 40.3, showing that C. plumbeus is a matrotrophic species. Ovarian fecundity was slightly higher than uterine fecundity. There was a positive relationship between uterine fecundity and total length of females. Litter sizes ranged 4-10 (mean 6.9±1.1). Embryos and free-swimming juvenile and adult females significantly outnumbered males.
