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Mahmood S Shivji - One of the best experts on this subject based on the ideXlab platform.
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Restricted connectivity and population genetic fragility in a globally endangered Hammerhead Shark
Reviews in Fish Biology and Fisheries, 2020Co-Authors: Danillo Pinhal, Mahmood S Shivji, Rodrigo R. Domingues, Christine C. Bruels, Bruno L. S. Ferrette, Otto B. F. Gadig, Cesar MartinsAbstract:Vagile, large-bodied marine organisms frequently have wide range dispersion but also dependence on coastal habitats for part of their life history. These characteristics may induce complex population genetic structure patterns, with resulting implications for the management of exploited populations. The scalloped Hammerhead, Sphyrna lewini , is a cosmopolitan, migratory Shark in tropical and warm temperate waters, inhabiting coastal bays during parturition and juvenile development, and the open ocean as adults. Here, we investigated the genetic connectivity and diversity of S. lewini in the western Atlantic using large sample coverage (N = 308), and data from whole mitochondrial control region (mtCR) sequences and ten nuclear microsatellite markers We detected significant population genetic structure with both mtCR and microsatellites markers (mtCR: Φ_ST = 0.60; p
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Complete mitogenome sequences of smooth Hammerhead Sharks, Sphyrna zygaena, from the eastern and western Atlantic
Mitochondrial DNA Part B, 2017Co-Authors: Cassandra L Ruck, Jose V. Lopez, Mahmood S ShivjiAbstract:AbstractWe report the first mitogenome sequences of the circumglobally distributed, highly mobile, smooth Hammerhead Shark, Sphyrna zygaena, from the eastern and western Atlantic. Both genomes were...
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the complete mitochondrial genome of the endangered great Hammerhead Shark sphyrna mokarran
Mitochondrial DNA Part B, 2017Co-Authors: Cassandra L Ruck, Mahmood S Shivji, Nicholas J Marra, Michael J StanhopeAbstract:AbstractWe present the first mitochondrial genome sequence of the great Hammerhead Shark, Sphyrna mokarran. This species is of considerable conservation concern throughout its global distribution, and currently listed as Endangered on the IUCN Red List. The mitochondrial genome is 16,719 bp in length with 13 protein-coding genes, 22 tRNA genes, 2 rRNA genes and a non-coding control region. The gene arrangement is congruent with other Shark and most vertebrate species. This S. mokarran mitogenome provides a genomic resource for assisting with population studies and conservation efforts for this highly depleted species.
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cryptic Hammerhead Shark lineage occurrence in the western south atlantic revealed by dna analysis
Marine Biology, 2012Co-Authors: Danillo Pinhal, Demian D Chapman, Mahmood S Shivji, Marcelo Vallinoto, Otto Bismarck Fazzano Gadig, Cesar MartinsAbstract:A cryptic lineage of Hammerhead Shark closely related to but evolutionarily distinct from the scalloped Hammerhead (Sphyrna lewini) was recently documented in the western North Atlantic Ocean. Here, we demonstrate using nuclear and mitochondrial DNA sequences that this cryptic lineage also occurs in the western South Atlantic Ocean, extending its distribution >7,000 km from its only previously reported location. Our results also further validate the existence of this evolutionarily distinct Hammerhead Shark lineage. The southern hemisphere cryptic individuals were 1.6 and 5.8% divergent from S. lewini (sensu stricto) for the nuclear internal transcribed spacer 2 (ITS2) and mitochondrial control region loci, respectively, and formed a strongly supported, reciprocally monophyletic sister group to sympatric S. lewini. Coalescent analysis (ITS2 locus) yielded a divergence estimate of ~4.5 million years between S. lewini and the cryptic lineage. Given expanding concerns about overfishing of the large-bodied Hammerhead Sharks, this cryptic lineage needs to be formally recognized and incorporated into Shark management and conservation planning to avoid the inadvertent, potential extirpation of a unique Hammerhead lineage.
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virgin birth in a Hammerhead Shark
Biology Letters, 2007Co-Authors: Demian D Chapman, Mahmood S Shivji, Ed Louis, Julie Sommer, Hugh L Fletcher, Paulo A ProdohlAbstract:Parthenogenesis has been documented in all major jawed vertebrate lineages except mammals and cartilaginous fishes (class Chondrichthyes: Sharks, batoids and chimeras). Reports of captive female Sharks giving birth despite being held in the extended absence of males have generally been ascribed to prior matings coupled with long-term sperm storage by the females. Here, we provide the first genetic evidence for chondrichthyan parthenogenesis, involving a Hammerhead Shark (Sphyrna tiburo). This finding also broadens the known occurrence of a specific type of asexual development (automictic parthenogenesis) among vertebrates, extending recently raised concerns about the potential negative effect of this type of facultative parthenogenesis on the genetic diversity of threatened vertebrate species.
Austin J. Gallagher - One of the best experts on this subject based on the ideXlab platform.
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The biology and conservation status of the large Hammerhead Shark complex: the great, scalloped, and smooth Hammerheads
Reviews in Fish Biology and Fisheries, 2018Co-Authors: Austin J. Gallagher, A. Peter KlimleyAbstract:Hammerhead Sharks are among the most intriguing yet imperiled groups of large Sharks globally. Until recently, our understanding of their biology, movements, diet, and life histories was challenged by a lack of studies. In recent years there has been a surge of published studies on this group of Sharks, incorporating new information on age and growth, behavior, and the threats they face. Here we summarize and compare what is known on the biology and conservation of the three largest species of Hammerhead Sharks: the great Hammerhead ( Sphyrna mokarran ), the scalloped Hammerhead ( Sphyrna lewini ), and the smooth Hammerhead ( Sphyrna zygaena ). We chose these species since they are the most well-studied of the Hammerheads, and also because they are commonly captured in target and non-target fisheries worldwide. Thus, we also discuss population trends and the vulnerabilities of each species, and make recommendations for future studies on these fascinating and complex elasmobranch fishes.
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Shallow water tidal flat use and associated specialized foraging behavior of the great Hammerhead Shark (Sphyrna mokarran)
Marine and Freshwater Behaviour and Physiology, 2016Co-Authors: Robert P. Roemer, Austin J. Gallagher, Neil HammerschlagAbstract:AbstractEvidence suggests the great Hammerhead Shark, Sphyrna mokarran, is vulnerable to a variety of anthropogenic stressors, and is an understudied species of Shark due to its cryptic nature and wide-ranging movements. While recognized as both a pelagic-coastal and a highly mobile predator, minimal anecdotal evidence exist describing shallow water habitat use by this species. This report describes six cases in which a great Hammerhead Shark utilizes an inshore shallow water flats environment (
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shallow water tidal flat use and associated specialized foraging behavior of the great Hammerhead Shark sphyrna mokarran
Marine and Freshwater Behaviour and Physiology, 2016Co-Authors: Robert P. Roemer, Austin J. Gallagher, Neil HammerschlagAbstract:AbstractEvidence suggests the great Hammerhead Shark, Sphyrna mokarran, is vulnerable to a variety of anthropogenic stressors, and is an understudied species of Shark due to its cryptic nature and wide-ranging movements. While recognized as both a pelagic-coastal and a highly mobile predator, minimal anecdotal evidence exist describing shallow water habitat use by this species. This report describes six cases in which a great Hammerhead Shark utilizes an inshore shallow water flats environment (<1.5 m in depth), five of which involve prey capture. These observations permitted identification of two novel behaviors that may allow great Hammerheads to inhabit these shallow habitats: a (1) prey-capture technique termed ‘grasp-turning’ that involves burst swimming at tight turning angles while grasping prey and (2) a post-predation recovery period whereby the Shark maintains head-first orientation into the current that may facilitate respiration and prey consumption. These behavioral observations provide insig...
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range extension of the endangered great Hammerhead Shark sphyrna mokarran in the northwest atlantic preliminary data and significance for conservation
Endangered Species Research, 2011Co-Authors: Neil Hammerschlag, Austin J. Gallagher, Dominique M Lazarre, Curt SlonimAbstract:We provide pilot data from a satellite-tracked great Hammerhead Shark Sphyrna mokar- ran in the Atlantic, representing the first such data on this species in the literature. The 250 cm Shark was tagged off the coast of the middle-Florida Keys (USA) and transmitted for 62 d. During this time it migrated a minimum distance of ~1200 km northeast from the coast of Florida, into pelagic interna- tional waters of the Northwest Atlantic. When compared to the primary literature, this migration rep- resented a northeasterly range extension for this species off the continental slope in the Atlantic. The significance of this range extension is discussed in terms of the vulnerability of S. mokarran to target and non-target fisheries.
Rui Coelho - One of the best experts on this subject based on the ideXlab platform.
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distribution patterns and indicators of the smooth Hammerhead Shark sphyrna zygaena in the atlantic ocean
Fisheries Research, 2019Co-Authors: Catarina C Santos, Rui CoelhoAbstract:Abstract The smooth Hammerhead Shark, Sphyrna zygaena, is a pelagic Shark occasionally captured as bycatch by industrial pelagic longline fleets in the Atlantic Ocean. Data for this study were collected by fishery observers, between 2003 and 2016. Datasets analyzed included information on catches per unit effort (CPUE), size and sex of smooth Hammerhead Sharks bycaught by the Portuguese pelagic longline fishery in the Atlantic Ocean. A total effort of 2 523 288 hooks yielded 638 Sharks, ranging in size from 123 to 275 cm fork length. Larger Sharks tended to occur in open ocean habitats and smaller specimens in coastal areas. Results confirmed the wide latitudinal range of the species (45 °N–35 °S), although CPUE was higher closer inshore within the Tropical North and Equatorial regions. An overall sex ratio of 1.4 males for each female was observed, with more males in both inshore and offshore waters. Significant differences in CPUE and size distribution were found between regions, years and quarters of the year. Mean CPUE increased and mean specimen size decreased in the Equatorial region from 2012 onwards. In order to remove fishery-dependent effects from CPUE data, a Tweedie Generalized Linear Model (GLM) was used to create a relative index of abundance (standardized CPUE). The index showed some oscillations in the initial years (2008–2010), followed by a decreasing trend until 2013 and then an increasing trend in more recent years, until 2016. The distributional patterns and indicators presented in this study provide a better understanding of the smooth Hammerhead Shark’s spatio-temporal dynamics and population structure in the Atlantic Ocean and can be used to improve management and conservation measures for this species.
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migrations and habitat use of the smooth Hammerhead Shark sphyrna zygaena in the atlantic ocean
PLOS ONE, 2018Co-Authors: Catarina C Santos, Rui CoelhoAbstract:The smooth Hammerhead Shark, Sphyrna zygaena, is a cosmopolitan semipelagic Shark captured as bycatch in pelagic oceanic fisheries, especially pelagic longlines targeting swordfish and/or tunas. From 2012 to 2016, eight smooth Hammerheads were tagged with Pop-up Satellite Archival Tags in the inter-tropical region of the Northeast Atlantic Ocean, with successful transmissions received from seven tags (total of 319 tracking days). Results confirmed the smooth Hammerhead is a highly mobile species, as the longest migration ever documented for this species (> 6600 km) was recorded. An absence of a diel vertical movement behavior was noted, with the Sharks spending most of their time at surface waters (0–50 m) above 23°C. The operating depth of the pelagic longline gear was measured with Minilog Temperature and Depth Recorders, and the overlap with the species vertical distribution was calculated. The overlap is taking place mainly during the night and is higher for juveniles (~40% of overlap time). The novel information presented can now be used to contribute to the provision of sustainable management tools and serve as input for Ecological Risk Assessments for smooth Hammerheads caught in Atlantic pelagic longline fisheries.
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age and growth of the smooth Hammerhead Shark sphyrna zygaena in the eastern equatorial atlantic ocean using vertebral sections
Aquatic Living Resources, 2011Co-Authors: Rui Coelho, Joana Fernandezcarvalho, Sergio Amorim, Miguel N SantosAbstract:The smooth Hammerhead Shark Sphyrna zygaena (Sphyrnidae) is regularly caught as bycatch in pelagic longline fisheries, but is one of the least studied of all pelagic Sharks. Recently, ICCAT (International Commission for the Conservation of Atlantic Tunas) issued recommendations underlining the need for more studies on the life history parameters of this and other pelagic Shark species. To this end, the age and growth of S. zygaena were studied in the Eastern Equatorial Atlantic Ocean, in an area where growth parameters were not yet available for this species. Data from 139 specimens, caught between June and September 2009, ranging in size from 136 to 233 cm fork length (FL), were analysed. Preliminary trials were carried out to assess the most efficient growth band enhancement technique. These indicated that sectioning the vertebrae into 500 μ m sections followed by staining with crystal violet produced the best results. Growth models were fitted using the traditional von Bertalanffy growth equation and a modification of this equation using a known size at birth. Growth models were compared using the Akaike information criterion (AIC). The von Bertalanffy growth equation seemed to be the most adequate model to describe growth in this species, with resulting growth parameters of L inf = 272 cm FL, k = 0.06 year for males and L inf = 285 cm FL, k = 0.07 year for females. In the first four years of life, S. zygaena grows 25 cm per year on average, but its growth slows down in later life. Future stock assessment models should incorporate these age and growth parameters for species management and conservation.
Neil Hammerschlag - One of the best experts on this subject based on the ideXlab platform.
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Shallow water tidal flat use and associated specialized foraging behavior of the great Hammerhead Shark (Sphyrna mokarran)
Marine and Freshwater Behaviour and Physiology, 2016Co-Authors: Robert P. Roemer, Austin J. Gallagher, Neil HammerschlagAbstract:AbstractEvidence suggests the great Hammerhead Shark, Sphyrna mokarran, is vulnerable to a variety of anthropogenic stressors, and is an understudied species of Shark due to its cryptic nature and wide-ranging movements. While recognized as both a pelagic-coastal and a highly mobile predator, minimal anecdotal evidence exist describing shallow water habitat use by this species. This report describes six cases in which a great Hammerhead Shark utilizes an inshore shallow water flats environment (
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shallow water tidal flat use and associated specialized foraging behavior of the great Hammerhead Shark sphyrna mokarran
Marine and Freshwater Behaviour and Physiology, 2016Co-Authors: Robert P. Roemer, Austin J. Gallagher, Neil HammerschlagAbstract:AbstractEvidence suggests the great Hammerhead Shark, Sphyrna mokarran, is vulnerable to a variety of anthropogenic stressors, and is an understudied species of Shark due to its cryptic nature and wide-ranging movements. While recognized as both a pelagic-coastal and a highly mobile predator, minimal anecdotal evidence exist describing shallow water habitat use by this species. This report describes six cases in which a great Hammerhead Shark utilizes an inshore shallow water flats environment (<1.5 m in depth), five of which involve prey capture. These observations permitted identification of two novel behaviors that may allow great Hammerheads to inhabit these shallow habitats: a (1) prey-capture technique termed ‘grasp-turning’ that involves burst swimming at tight turning angles while grasping prey and (2) a post-predation recovery period whereby the Shark maintains head-first orientation into the current that may facilitate respiration and prey consumption. These behavioral observations provide insig...
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range extension of the endangered great Hammerhead Shark sphyrna mokarran in the northwest atlantic preliminary data and significance for conservation
Endangered Species Research, 2011Co-Authors: Neil Hammerschlag, Austin J. Gallagher, Dominique M Lazarre, Curt SlonimAbstract:We provide pilot data from a satellite-tracked great Hammerhead Shark Sphyrna mokar- ran in the Atlantic, representing the first such data on this species in the literature. The 250 cm Shark was tagged off the coast of the middle-Florida Keys (USA) and transmitted for 62 d. During this time it migrated a minimum distance of ~1200 km northeast from the coast of Florida, into pelagic interna- tional waters of the Northwest Atlantic. When compared to the primary literature, this migration rep- resented a northeasterly range extension for this species off the continental slope in the Atlantic. The significance of this range extension is discussed in terms of the vulnerability of S. mokarran to target and non-target fisheries.
Felipe Galván-magaña - One of the best experts on this subject based on the ideXlab platform.
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Population genetic divergence as consequence of past range expansion of the smooth Hammerhead Shark Sphyrna zygaena
Hydrobiologia, 2019Co-Authors: Nataly Bolaño-martínez, Felipe Galván-magaña, Sebastián Hernández-muñoz, Manuel Uribe-alcocer, Peter A. Ritchie, Francisco Javier García-de León, Píndaro Díaz-jaimesAbstract:The Smooth Hammerhead Shark Sphyrna zygaena is a species with anti-tropical distribution in the eastern Pacific from California USA, to southern Chile with a remarkably gap in abundance in equatorial areas between southern Mexico and Central America. For temperate species, warm waters can represent oceanographic barriers limiting the gene flow between adjacent populations. The mtDNA control region was used to infer the phylogeography and historical demography of the Smooth Hammerhead in the eastern Pacific. An AMOVA comparing locations grouped into northern and southern eastern Pacific equatorial areas indicated significant genetic differentiation. Each population had a common haplotype separated by two mutational differences suggesting that divergence occurred very recently. The pattern of genetic differences matches with the anti-tropical distribution of S. zygaena in the eastern Pacific. Gene diversity was lower in the northern population when compared to the southern area, a pattern indicative of a recent founder event. Broadly, this pattern suggests a recent population expansion occurring 25,000–10,000 years. bp, during the last glacial cycle, when the drop of surface sea temperatures created favorable conditions at equatorial latitudes to cross the thermal barrier imposed by warm waters at equatorial latitudes. These genetically distinct population groups might lead to delineate a management plan that considers two separated stocks in the eastern Pacific.
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Feeding habits and trophic level of the smooth Hammerhead Shark, Sphyrna zygaena (Carcharhiniformes: Sphyrnidae), off Ecuador
Journal of the Marine Biological Association of the United Kingdom, 2018Co-Authors: Colombo Estupiñán-montaño, Felipe Galván-magaña, Luis G. Cedeño-figueroa, José F. Estupiñán-ortiz, Alejandro Sandoval-londoño, David Castañeda-suarez, Carlos Polo-silvaAbstract:As apex predators, Sharks are known to play an important role in marine food webs. Detailed information on their diet and trophic level is however needed to make clear inferences about their role in the ecosystem. A total of 335 stomachs of smooth Hammerhead Sharks, Sphyrna zygaena, were obtained from commercial fishing vessels operating in the Ecuadorian Pacific between January and December 2004. A total of 53 prey items were found in the stomachs. According to the Index of Relative Importance (%IRI), cephalopods were the main prey (Dosidicus gigas, Sthenoteuthis oualaniensis, Ancistrocheirus lesueurii and Lolliguncula [Loliolopsis] diomedeae). Sphyrna zygaena was thus confirmed to be a teutophagous species. The estimated trophic level of S. zygaena was between 4.6 and 5.1 (mean ± SD: 4.7 ± 0.16; males: 4.7; females: 4.8). Levin's index (BA) was low (overall: 0.07; males: 0.08; females: 0.09), indicating a narrow trophic niche. We found that Sharks <150 cm in total length consumed prey of coastal origin, whereas Sharks ≥150 cm foraged in oceanic waters and near the continental shelf. The analyses indicate that S. zygaena is a specialized predator consuming mainly squids.
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Population and individual foraging patterns of two Hammerhead Sharks using carbon and nitrogen stable isotopes
Rapid Communications in Mass Spectrometry, 2015Co-Authors: Peggy Loor-andrade, Felipe Galván-magaña, Fernando R. Elorriaga-verplancken, Carlos Polo-silva, Antonio Delgado-huertasAbstract:Rationale Individual foraging behavior is an important variable of predators commonly studied at the population level. Some Hammerhead Shark species play a significant role in the marine ecosystem as top consumers. In this context, stable isotope analysis allows us to infer some ecological metrics and patterns that cannot usually be obtained using traditional methods. Methods We determined the isotopic composition (δ13C and δ15N values) of dorsal muscle and vertebrae of Sphyrna lewini and Sphyrna zygaena using a continuous-flow system consisting of an elemental analyzer combined with a Delta Plus XL mass spectrometer. Foraging variability by sex and by individual was inferred from the isotopic values. Results There were no significant differences in the isotopic values of muscle samples between sexes, but there were differences between species. The trophic niche breadth of the two species was similar and overlap was low. A low niche overlap was observed between S. lewini individual vertebrae. We found differences in the δ15N values of S. zygaena vertebrae, with lower values in the first group of samples. Conclusions Despite these Hammerhead Shark species inhabiting the same area, there was low trophic niche overlap between species and individuals, due to different individual foraging strategies, according to the carbon and nitrogen isotopic profiles obtained. The use of tissues that retain lifetime isotopic information is useful to complement studies on trophic ecology. Copyright © 2015 John Wiley & Sons, Ltd.
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Mercury and selenium bioaccumulation in the smooth Hammerhead Shark, Sphyrna zygaena Linnaeus, from the Mexican Pacific Ocean.
Bulletin of Environmental Contamination and Toxicology, 2010Co-Authors: Ofelia Escobar-sánchez, Felipe Galván-magaña, Rene Rosiles-martínezAbstract:We analyzed total mercury and selenium bioaccumulation in muscle tissue and cartilage fibers (fins) from smooth Hammerhead Shark, Sphyrna zygaena, caught off Baja California Sur, Mexico. In muscle tissue, the mercury concentration ranged from 0.005 to 1.93 μg g−1 ww (wet weight), which falls within the safety limits for food set by international agencies (Hg > 1.0 μg g−1 ww). Only one specimen showed a mercury value that exceeded this limit. In fins, the mercury bioaccumulation was lower (
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Stomach content analysis of juvenile, scalloped Hammerhead Shark Sphyrna lewini captured off the coast of Mazatlán, Mexico
Aquatic Ecology, 2009Co-Authors: Yassir Eden Torres-rojas, Felipe Galván-magaña, Agustín Hernández-herrera, Vanessa Alatorre-ramírezAbstract:We quantified the diet of juvenile, scalloped Hammerhead Shark Sphyrna lewini in the area off Mazatlan, Sinaloa, Mexico, to understand their feeding ecology this Shark. The prey species of Sphyrna lewini were identified and quantified from stomach content analysis. In addition, we determined the variations between genders. During two fishing seasons (2000–2001 and 2001–2002), we analyzed 232 stomachs, of which 85% contained food. The trophic spectrum was composed of three species of cephalopods, six of crustaceans and 19 species of fish from mainly pelagic and benthic habitats. According to the Index of Relative Importance (%IRI), the cephalopod Loliolopsis diomedeae with IRI = 18%, fish of the family Carangidae IRI = 25% and family Synodontidae IRI = 19% constituted the main prey in general. The trophic niche width was
