The Experts below are selected from a list of 1122 Experts worldwide ranked by ideXlab platform
Sébastien Jaquemet - One of the best experts on this subject based on the ideXlab platform.
-
genetic population structure and demography of an apex predator the tiger shark Galeocerdo cuvier
Ecology and Evolution, 2019Co-Authors: Agathe Pirog, Sébastien Jaquemet, Bonnie J Holmes, Virginie Ravigne, Geremy Cliff, Eric Clua, Nigel E Hussey, John E G Nevill, Andrew J Temple, Per BerggrenAbstract:Population genetics has been increasingly applied to study large sharks over the last decade. Whilst large shark species are often difficult to study with direct methods, improved knowledge is needed for both population management and conservation, especially for species vulnerable to anthropogenic and climatic impacts. The tiger shark, Galeocerdo cuvier, is an apex predator known to play important direct and indirect roles in tropical and subtropical marine ecosystems. While the global and Indo‐West Pacific population genetic structure of this species has recently been investigated, questions remain over population structure and demographic history within the western Indian (WIO) and within the western Pacific Oceans (WPO). To address the knowledge gap in tiger shark regional population structures, the genetic diversity of 286 individuals sampled in seven localities was investigated using 27 microsatellite loci and three mitochondrial genes (CR, COI, and cytb). A weak genetic differentiation was observed between the WIO and the WPO, suggesting high genetic connectivity. This result agrees with previous studies and highlights the importance of the pelagic behavior of this species to ensure gene flow. Using approximate Bayesian computation to couple information from both nuclear and mitochondrial markers, evidence of a recent bottleneck in the Holocene (2,000–3,000 years ago) was found, which is the most probable cause for the low genetic diversity observed. A contemporary effective population size as low as 111 [43,369] was estimated during the bottleneck. Together, these results indicate low genetic diversity that may reflect a vulnerable population sensitive to regional pressures. Conservation measures are thus needed to protect a species that is classified as Near Threatened.
-
seasonal variability of bull and tiger shark presence on the west coast of reunion island western indian ocean
African Journal of Marine Science, 2015Co-Authors: Antonin Blaison, Sébastien Jaquemet, David Guyomard, Geremy Cliff, G Vangrevelynghe, T Gazzo, P Cotel, Marc SoriaAbstract:A fisheries‑independent survey using longlines and drumlines, and an acoustic telemetry study, revealed that bull sharks Carcharhinus leucas and tiger sharks Galeocerdo cuvier occur throughout the year off the west coast of Reunion Island. The research, which commenced in 2011, was conducted in response to an increase in the rate of shark attacks. Juvenile, subadult and young adult tiger sharks of 111–390 cm total length (TL) were caught in all months except July; the sex ratio was 1:1 (M:F; n = 61). All bull sharks taken, except one (183 cm TL), were mature (205–329 cm TL), with a sex ratio of 0.7:1 (M:F; n = 54), and catches occurred throughout the year except in May and August, with the highest CPUE in September. Presence/absence of a total of 46 tagged tiger sharks and 36 tagged bull sharks was monitored by means of 42 acoustic receivers distributed along the west coast of the island. Tagged tiger sharks were detected in all months, with seasonal variation between sexes. Detections of males remained l...
-
Isolation and characterization of 20 microsatellite markers from Carcharhinus leucas (bull shark) and cross-amplification in Galeocerdo cuvier (tiger shark), Carcharhinus obscurus (dusky shark) and Carcharhinus plumbeus (sandbar shark)
Conservation Genetics Resources, 2015Co-Authors: Agathe Pirog, Antonin Blaison, Sébastien Jaquemet, Marc Soria, Hélène MagalonAbstract:With the development of genetics methods, it becomes possible to study the population structure and some aspects of the reproductive behaviour of endangered sharks. Here we describe the isolation of 20 polymorphic microsatellite markers in the bull shark Carcharhinus leucas (Carcharhinidae) and their characteristics. Two to 10 alleles per locus were detected. Observed and expected heterozygosities ranged from 0.00 to 0.78 and from 0.05 to 0.80, respectively. Four markers showed deviations from Hardy–Weinberg equilibrium; among them, three showed presence of null alleles. No linkage disequilibrium was detected among any of the loci. Moreover, four, 11 and 19 of these 20 markers successfully cross-amplified in the tiger shark Galeocerdo cuvier, the sandbar shark Carcharhinus plumbeus and the dusky shark Carcharhinus obscurus, respectively.
-
First Observation of a Pregnant Tiger Shark (Galeocerdo cuvier) at Reunion Island, Western Indian Ocean
Western Indian Ocean Journal of Marine Science, 2012Co-Authors: Sébastien Jaquemet, Antonin Blaison, Malcom Smale, David Guyomard, Marc SoriaAbstract:The tiger shark Galeocerdo cuvier is a common predator in tropical oceans although its biology is still not well documented, especially in the western Indian Ocean. We report the first observation of a pregnant tiger shark captured at Reunion Island in November 2012. A total of 42 embryos without external yolksacs, measuring 750-846 mm in total length, were found in the two uteri. The sex ratio was nearly 1:1 and males and females did not differ in size or weight. Although the embryos were fully formed, the teeth had not yet erupted through the gums, suggesting that birth would take place a few weeks later. This information is in agreement with observations made in other locations, including the limited data available for this region, suggesting that mating occurs in late winter and parturition in summer
Agathe Pirog - One of the best experts on this subject based on the ideXlab platform.
-
genetic population structure and demography of an apex predator the tiger shark Galeocerdo cuvier
Ecology and Evolution, 2019Co-Authors: Agathe Pirog, Sébastien Jaquemet, Bonnie J Holmes, Virginie Ravigne, Geremy Cliff, Eric Clua, Nigel E Hussey, John E G Nevill, Andrew J Temple, Per BerggrenAbstract:Population genetics has been increasingly applied to study large sharks over the last decade. Whilst large shark species are often difficult to study with direct methods, improved knowledge is needed for both population management and conservation, especially for species vulnerable to anthropogenic and climatic impacts. The tiger shark, Galeocerdo cuvier, is an apex predator known to play important direct and indirect roles in tropical and subtropical marine ecosystems. While the global and Indo‐West Pacific population genetic structure of this species has recently been investigated, questions remain over population structure and demographic history within the western Indian (WIO) and within the western Pacific Oceans (WPO). To address the knowledge gap in tiger shark regional population structures, the genetic diversity of 286 individuals sampled in seven localities was investigated using 27 microsatellite loci and three mitochondrial genes (CR, COI, and cytb). A weak genetic differentiation was observed between the WIO and the WPO, suggesting high genetic connectivity. This result agrees with previous studies and highlights the importance of the pelagic behavior of this species to ensure gene flow. Using approximate Bayesian computation to couple information from both nuclear and mitochondrial markers, evidence of a recent bottleneck in the Holocene (2,000–3,000 years ago) was found, which is the most probable cause for the low genetic diversity observed. A contemporary effective population size as low as 111 [43,369] was estimated during the bottleneck. Together, these results indicate low genetic diversity that may reflect a vulnerable population sensitive to regional pressures. Conservation measures are thus needed to protect a species that is classified as Near Threatened.
-
Isolation and characterization of 20 microsatellite markers from Carcharhinus leucas (bull shark) and cross-amplification in Galeocerdo cuvier (tiger shark), Carcharhinus obscurus (dusky shark) and Carcharhinus plumbeus (sandbar shark)
Conservation Genetics Resources, 2015Co-Authors: Agathe Pirog, Antonin Blaison, Sébastien Jaquemet, Marc Soria, Hélène MagalonAbstract:With the development of genetics methods, it becomes possible to study the population structure and some aspects of the reproductive behaviour of endangered sharks. Here we describe the isolation of 20 polymorphic microsatellite markers in the bull shark Carcharhinus leucas (Carcharhinidae) and their characteristics. Two to 10 alleles per locus were detected. Observed and expected heterozygosities ranged from 0.00 to 0.78 and from 0.05 to 0.80, respectively. Four markers showed deviations from Hardy–Weinberg equilibrium; among them, three showed presence of null alleles. No linkage disequilibrium was detected among any of the loci. Moreover, four, 11 and 19 of these 20 markers successfully cross-amplified in the tiger shark Galeocerdo cuvier, the sandbar shark Carcharhinus plumbeus and the dusky shark Carcharhinus obscurus, respectively.
Bonnie J Holmes - One of the best experts on this subject based on the ideXlab platform.
-
genetic population structure and demography of an apex predator the tiger shark Galeocerdo cuvier
Ecology and Evolution, 2019Co-Authors: Agathe Pirog, Sébastien Jaquemet, Bonnie J Holmes, Virginie Ravigne, Geremy Cliff, Eric Clua, Nigel E Hussey, John E G Nevill, Andrew J Temple, Per BerggrenAbstract:Population genetics has been increasingly applied to study large sharks over the last decade. Whilst large shark species are often difficult to study with direct methods, improved knowledge is needed for both population management and conservation, especially for species vulnerable to anthropogenic and climatic impacts. The tiger shark, Galeocerdo cuvier, is an apex predator known to play important direct and indirect roles in tropical and subtropical marine ecosystems. While the global and Indo‐West Pacific population genetic structure of this species has recently been investigated, questions remain over population structure and demographic history within the western Indian (WIO) and within the western Pacific Oceans (WPO). To address the knowledge gap in tiger shark regional population structures, the genetic diversity of 286 individuals sampled in seven localities was investigated using 27 microsatellite loci and three mitochondrial genes (CR, COI, and cytb). A weak genetic differentiation was observed between the WIO and the WPO, suggesting high genetic connectivity. This result agrees with previous studies and highlights the importance of the pelagic behavior of this species to ensure gene flow. Using approximate Bayesian computation to couple information from both nuclear and mitochondrial markers, evidence of a recent bottleneck in the Holocene (2,000–3,000 years ago) was found, which is the most probable cause for the low genetic diversity observed. A contemporary effective population size as low as 111 [43,369] was estimated during the bottleneck. Together, these results indicate low genetic diversity that may reflect a vulnerable population sensitive to regional pressures. Conservation measures are thus needed to protect a species that is classified as Near Threatened.
-
a perspective on future tiger shark research
Frontiers in Marine Science, 2019Co-Authors: Kim N Holland, James M Anderson, Daniel M Coffey, Bonnie J Holmes, Carl G Meyer, Mark A RoyerAbstract:This ‘Perspectives’ paper identifies aspects of tiger shark (Galeocerdo cuvier) biology that are currently unknown or for which additional data are needed to improve interpretive power. Some of these data gaps may be regional. Technical or methodological approaches to acquiring these data are suggested. Some of these technologies already exist, some are in development and some exist in concept only. Reproductive biology and behavior, social interactions and the behavioral ecology of sub-adults are among the areas identified as deserving of future research effort
-
lack of multiple paternity in the oceanodromous tiger shark Galeocerdo cuvier
Royal Society Open Science, 2018Co-Authors: Bonnie J Holmes, M. B. Bennett, Ian R Tibbetts, Lisa C Pope, Samuel M Williams, J. R. OvendenAbstract:Multiple paternity has been documented as a reproductive strategy in both viviparous and ovoviviparous elasmobranchs, leading to the assumption that multiple mating may be ubiquitous in these fishes. However, with the majority of studies conducted on coastal and nearshore elasmobranchs that often form mating aggregations, parallel studies on pelagic, semi-solitary species are lacking. The tiger shark (Galeocerdo cuvier) is a large pelagic shark that has an aplacental viviparous reproductive mode which is unique among the carcharhinids. A total of 112 pups from four pregnant sharks were genotyped at nine microsatellite loci to assess the possibility of multiple paternity or polyandrous behaviour by female tiger sharks. Only a single pup provided evidence of possible multiple paternity, but with only seven of the nine loci amplifying for this individual, results were inconclusive. In summary, it appears that the tiger sharks sampled in this study were genetically monogamous. These findings may have implications for the genetic diversity and future sustainability of this population.
-
the trophic role of a large marine predator the tiger shark Galeocerdo cuvier
Scientific Reports, 2017Co-Authors: Bonnie J Holmes, Luciana C. Ferreira, Michele Thums, Adam Barnett, Katya G Abrantes, Lara Marcus Zamora, Ashley J FrischAbstract:Tiger sharks were sampled off the western (Ningaloo Reef, Shark Bay) and eastern (the Great Barrier Reef; GBR, Queensland and New South Wales; NSW) coastlines of Australia. Multiple tissues were collected from each shark to investigate the effects of location, size and sex of sharks on δ13C and δ15N stable isotopes among these locations. Isotopic composition of sharks sampled in reef and seagrass habitats (Shark Bay, GBR) reflected seagrass-based food-webs, whereas at Ningaloo Reef analysis revealed a dietary transition between pelagic and seagrass food-webs. In temperate habitats off southern Queensland and NSW coasts, shark diets relied on pelagic food-webs. Tiger sharks occupied roles at the top of food-webs at Shark Bay and on the GBR, but not at Ningaloo Reef or off the coast of NSW. Composition of δ13C in tissues was influenced by body size and sex of sharks, in addition to residency and diet stability. This variability in stable isotopic composition of tissues is likely to be a result of adaptive foraging strategies that allow these sharks to exploit multiple shelf and offshore habitats. The trophic role of tiger sharks is therefore both context- and habitat-dependent, consistent with a generalist, opportunistic diet at the population level.
-
age and growth of the tiger shark Galeocerdo cuvier off the east coast of australia
Journal of Fish Biology, 2015Co-Authors: Bonnie J Holmes, Ian R Tibbetts, Victor M Peddemors, Adrian N Gutteridge, Pascal T Geraghty, Ricky W K Chan, M. B. BennettAbstract:Total lengths (L(T)) at age and growth rates for south-west Pacific Galeocerdo cuvier were estimated from vertebral growth-band counts of 202 sagitally sectioned centra from 112 females (71-430 cm L(T)), 79 males (72-351 cm L(T)) and 11 of unknown sex. Captive growth data were also examined to complement vertebral age estimations. The sexes combined modelled growth coefficient (k = 0.08) was smaller than previously reported for G. cuvier populations elsewhere. Split-band and narrow banding patterns were identified as potential sources of age underestimation in this species.
Geremy Cliff - One of the best experts on this subject based on the ideXlab platform.
-
genetic population structure and demography of an apex predator the tiger shark Galeocerdo cuvier
Ecology and Evolution, 2019Co-Authors: Agathe Pirog, Sébastien Jaquemet, Bonnie J Holmes, Virginie Ravigne, Geremy Cliff, Eric Clua, Nigel E Hussey, John E G Nevill, Andrew J Temple, Per BerggrenAbstract:Population genetics has been increasingly applied to study large sharks over the last decade. Whilst large shark species are often difficult to study with direct methods, improved knowledge is needed for both population management and conservation, especially for species vulnerable to anthropogenic and climatic impacts. The tiger shark, Galeocerdo cuvier, is an apex predator known to play important direct and indirect roles in tropical and subtropical marine ecosystems. While the global and Indo‐West Pacific population genetic structure of this species has recently been investigated, questions remain over population structure and demographic history within the western Indian (WIO) and within the western Pacific Oceans (WPO). To address the knowledge gap in tiger shark regional population structures, the genetic diversity of 286 individuals sampled in seven localities was investigated using 27 microsatellite loci and three mitochondrial genes (CR, COI, and cytb). A weak genetic differentiation was observed between the WIO and the WPO, suggesting high genetic connectivity. This result agrees with previous studies and highlights the importance of the pelagic behavior of this species to ensure gene flow. Using approximate Bayesian computation to couple information from both nuclear and mitochondrial markers, evidence of a recent bottleneck in the Holocene (2,000–3,000 years ago) was found, which is the most probable cause for the low genetic diversity observed. A contemporary effective population size as low as 111 [43,369] was estimated during the bottleneck. Together, these results indicate low genetic diversity that may reflect a vulnerable population sensitive to regional pressures. Conservation measures are thus needed to protect a species that is classified as Near Threatened.
-
diet and trophic ecology of the tiger shark Galeocerdo cuvier from south african waters
PLOS ONE, 2017Co-Authors: Matthew Laurence Dicken, Geremy Cliff, Nigel E Hussey, Heather M Christiansen, Malcolm J Smale, Nomfundo Nkabi, Sabine P WintnerAbstract:Knowledge of the diet and trophic ecology of apex predators is key for the implementation of effective ecosystem as well as species-based management initiatives. Using a combination of stomach content data and stable isotope analysis (δ15N and δ13C) the current study provides information on size-based and sex-specific variations in diet, trophic position (TP) and foraging habitat of tiger sharks (Galeocerdo cuvier) caught in the KwaZulu-Natal Sharks Board bather protection program. This study presents the longest time-series and most detailed analysis of stomach content data for G. cuvier worldwide. Prey identified from 628 non-empty stomachs revealed a size-based shift in diet. Reptiles, birds, mysticetes, and large shark species increased in dietary importance with G. cuvier size, concomitant with a decrease in smaller prey such as batoids and teleosts. Seasonal and decadal shifts in diet driven primarily by changes in the importance of elasmobranchs and mammal (cetacean) prey were recorded for medium sized (150–220 cm) G. cuvier. Both stomach content and stable isotope analysis indicated that G. cuvier is a generalist feeder at the population level. Size-based δ13C profiles indicated a movement to offshore foraging habitats by larger G. cuvier. Calculated TP varied by method ranging from 4.0 to 5.0 (TPSCA for stomach contents) and from 3.6 to 4.5 (TPscaled and TPadditive for δ15N). Large (> 220 cm) G. cuvier did not feed at discrete trophic levels, but rather throughout the food web. These data provide key information on the ecological role of G. cuvier to improve the accuracy of regional food web modelling. This will enable a better understanding of the ecological impacts related to changes in the abundance of this predator.
-
sharks caught in the kwazulu natal bather protection programme south africa 13 the tiger shark Galeocerdo cuvier
African Journal of Marine Science, 2016Co-Authors: M L Dicken, Geremy Cliff, Henning WinkerAbstract:The current study provides long-term catch rate and biological data for tiger sharks Galeocerdo cuvier caught in the KwaZulu-Natal bather protection programme. Between 1978 and 2014, 1 760 G. cuvier were caught in nets and between 2007 and 2014, 108 G. cuvier were caught on drumlines. Standardised catch rates increased significantly over time (p 180 cm). There was also a significant temporal increase in the mean size of sharks across gear types (p < 0.001). A quasi-Poisson generalised additive mixed model showed that the deployment of drumlines had no significant effect on the catch rate of sharks in nets. The nets, however, caught significantly larger sharks (mean 184.5 cm, SD 39) than did drumlines (mean 138.6 cm, SD 36.5; p < 0.001). The size frequency of the catch was unimodal and females significantly outnumbered males in both gear types. Few young-of-the-year (0.8%) or mature sharks (1.8%) were caught. Only 23 (4.7%) of the 4...
-
seasonal variability of bull and tiger shark presence on the west coast of reunion island western indian ocean
African Journal of Marine Science, 2015Co-Authors: Antonin Blaison, Sébastien Jaquemet, David Guyomard, Geremy Cliff, G Vangrevelynghe, T Gazzo, P Cotel, Marc SoriaAbstract:A fisheries‑independent survey using longlines and drumlines, and an acoustic telemetry study, revealed that bull sharks Carcharhinus leucas and tiger sharks Galeocerdo cuvier occur throughout the year off the west coast of Reunion Island. The research, which commenced in 2011, was conducted in response to an increase in the rate of shark attacks. Juvenile, subadult and young adult tiger sharks of 111–390 cm total length (TL) were caught in all months except July; the sex ratio was 1:1 (M:F; n = 61). All bull sharks taken, except one (183 cm TL), were mature (205–329 cm TL), with a sex ratio of 0.7:1 (M:F; n = 54), and catches occurred throughout the year except in May and August, with the highest CPUE in September. Presence/absence of a total of 46 tagged tiger sharks and 36 tagged bull sharks was monitored by means of 42 acoustic receivers distributed along the west coast of the island. Tagged tiger sharks were detected in all months, with seasonal variation between sexes. Detections of males remained l...
Tristan L Guttridge - One of the best experts on this subject based on the ideXlab platform.
-
evidence of shark attacks on atlantic spotted dolphins stenella frontalis off bimini the bahamas
Marine Mammal Science, 2014Co-Authors: Kelly Melillosweeting, Stephen D Turnbull, Tristan L GuttridgeAbstract:The rate of shark predation on small cetaceans is poorly understood, but information is increasing as more long-term cetacean and shark studies are conducted. Resident Atlantic spotted dolphins (Stenella frontalis), off the coast of Bimini, The Bahamas, have been the subject of ongoing photo-ID and behavioral studies since 2001. Sharks in this area have also been systematically documented for decades. Despite these efforts, an actual shark attack on a dolphin has not been observed in Bimini and such an observation is rare anywhere in the world. Because of this, photo-ID records were analyzed for evidence of shark-induced injuries, often in the form of a crescent-shaped injury or scar. Fifteen percent of cataloged individuals within the Bimini dolphin population exhibit evidence of a shark attack. Patterns in the location on the body of the attack and trends related to age and sex were calculated. There were few injuries to the ventral portion of the body, where most attacks would likely be fatal. Although the level of healing prevented most scars from being linked to a specific shark species, we suspect bull (Carcharhinus leucas), tiger (Galeocerdo cuvieri), shortfin mako (Isurus oxyrinchus) and dusky sharks (Carcharhinus obscures) to be possible predators of dolphins near Bimini. This study does not estimate the frequency of attacks on dolphins; here, we estimate the occurrence of unsuccessful attacks. Introduction: The amount of information on shark predation on small cetaceans is increasing as longitudinal cetacean projects and anecdotal information are compiled. Stomach content studies have shown delphinid species consumed by the following shark species: Zambesi/bull (Carcharhinus leucas), tiger (Galeocerdo cuvieri), great white (Carcharodon carcharias), and dusky (Carcharhinus obscures)(Cockcroft et al., 1989). First hand observations are rare (Mann & Barnett, 1999; Maldini, 2003) so alternative methods for assessing shark predation must be developed. One method is by assessing failed attempts; that is, documenting fresh injuries and scars on known dolphins that can be attributed to sharks, as was done in this study. Here, the percentage of Atlantic spotted dolphins, from a known population, with evidence of past shark attacks was determined and compared to other dolphin populations. Patterns in the body location of these scars as well as differences between ages and sexes were considered. Potential shark species responsible for the attacks are discussed.
