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Adam Barnett - One of the best experts on this subject based on the ideXlab platform.
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Evidence of historical isolation and genetic structuring among Broadnose Sevengill Sharks (Notorynchus cepedianus) from the world’s major oceanic regions
Reviews in Fish Biology and Fisheries, 2021Co-Authors: Alicia C. J. Schmidt-roach, Adam Barnett, David A. Ebert, Christine C. Bruels, Adam D. Miller, Craig D. H. Sherman, Sebastian Schmidt-roach, Charlene Da Silva, Christopher G. Wilke, Craig ThorburnAbstract:Cosmopolitan marine pelagic species display variable patterns of population connectivity among the world’s major oceans. While this information is crucial for informing management, information is lacking for many ecologically important species, including apex predators. In this study we examine patterns of genetic structure in the Broadnose Sevengill Shark, Notorynchus cepedianus across its global distribution. We estimate patterns of connectivity among Broadnose Sevengill Shark populations from three major oceanic regions (South Atlantic, Oceania and Eastern Pacific) by contrasting mitochondrial and nuclear DNA haplotype frequencies. We also produced time calibrated Bayesian Inference phylogenetic reconstructions to analyses global phylogeographic patterns and estimate divergence times among distinctive Shark lineages. Our results demonstrate significant genetic differentiation among oceanic regions ( Φ _ST = 0.9789, P
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Integrating acoustic telemetry into mark–recapture models to improve the precision of apparent survival and abundance estimates
Oecologia, 2015Co-Authors: Christine L. Dudgeon, Jayson M. Semmens, Kenneth H. Pollock, J. Matias Braccini, Adam BarnettAbstract:Capture–mark–recapture models are useful tools for estimating demographic parameters but often result in low precision when recapture rates are low. Low recapture rates are typical in many study systems including fishing-based studies. Incorporating auxiliary data into the models can improve precision and in some cases enable parameter estimation. Here, we present a novel application of acoustic telemetry for the estimation of apparent survival and abundance within capture–mark–recapture analysis using open population models. Our case study is based on simultaneously collecting longline fishing and acoustic telemetry data for a large mobile apex predator, the Broadnose Sevengill Shark ( Notorhynchus cepedianus ), at a coastal site in Tasmania, Australia. Cormack–Jolly–Seber models showed that longline data alone had very low recapture rates while acoustic telemetry data for the same time period resulted in at least tenfold higher recapture rates. The apparent survival estimates were similar for the two datasets but the acoustic telemetry data showed much greater precision and enabled apparent survival parameter estimation for one dataset, which was inestimable using fishing data alone. Combined acoustic telemetry and longline data were incorporated into Jolly–Seber models using a Monte Carlo simulation approach. Abundance estimates were comparable to those with longline data only; however, the inclusion of acoustic telemetry data increased precision in the estimates. We conclude that acoustic telemetry is a useful tool for incorporating in capture–mark–recapture studies in the marine environment. Future studies should consider the application of acoustic telemetry within this framework when setting up the study design and sampling program.
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Integrating acoustic telemetry into mark-recapture models to improve the precision of apparent survival and abundance estimates
Oecologia, 2015Co-Authors: Christine L. Dudgeon, Jayson M. Semmens, Kenneth H. Pollock, J. Matias Braccini, Adam BarnettAbstract:Capture–mark–recapture models are useful tools for estimating demographic parameters but often result in low precision when recapture rates are low. Low recapture rates are typical in many study systems including fishing-based studies. Incorporating auxiliary data into the models can improve precision and in some cases enable parameter estimation. Here, we present a novel application of acoustic telemetry for the estimation of apparent survival and abundance within capture–mark–recapture analysis using open population models. Our case study is based on simultaneously collecting longline fishing and acoustic telemetry data for a large mobile apex predator, the Broadnose Sevengill Shark (Notorhynchus cepedianus), at a coastal site in Tasmania, Australia. Cormack–Jolly–Seber models showed that longline data alone had very low recapture rates while acoustic telemetry data for the same time period resulted in at least tenfold higher recapture rates. The apparent survival estimates were similar for the two datasets but the acoustic telemetry data showed much greater precision and enabled apparent survival parameter estimation for one dataset, which was inestimable using fishing data alone. Combined acoustic telemetry and longline data were incorporated into Jolly–Seber models using a Monte Carlo simulation approach. Abundance estimates were comparable to those with longline data only; however, the inclusion of acoustic telemetry data increased precision in the estimates. We conclude that acoustic telemetry is a useful tool for incorporating in capture–mark–recapture studies in the marine environment. Future studies should consider the application of acoustic telemetry within this framework when setting up the study design and sampling program.
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Markov models and network analysis reveal sex-specific differences in the space-use of a coastal apex predator
Oikos, 2014Co-Authors: Kilian M. Stehfest, Adam Barnett, Toby A. Patterson, Jayson M. SemmensAbstract:Understanding the links between external variables such as habitat and interactions with conspecifics and animal space-use is fundamental to developing effective management measures. In the marine realm, automated acoustic tracking has become a widely used method for monitoring the movement of free-ranging animals, yet researchers generally lack robust methods for analysing the resulting spatial-usage data. In this study, acoustic tracking data from male and female Broadnose Sevengill Sharks Notorynchus cepedianus, collected in a system of coastal embayments in southeast Tasmania were analyzed to examine sex-specific differences in the Sharks' coastal space-use and test novel methods for the analysis of acoustic telemetry data. Sex-specific space-use of the Broadnose Sevengill Shark from acoustic telemetry data was analysed in two ways: The recently proposed spatial network analysis of between-receiver movements was employed to identify sex-specific space-use patterns. To include the full breadth of temporal information held in the data, movements between receivers were furthermore considered as transitions between states of a Markov chain, with the resulting transition probability matrix allowing the ranking of the relative importance of different parts of the study area. Both spatial network and Markov chain analysis revealed sex-specific preferences of different sites within the study area. The identification of priority areas differed for the methods, due to the fact that in contrast to network analysis, our Markov chain approach preserves the chronological sequence of detections and accounts for both residency periods and movements. In addition to adding to our knowledge of the ecology of a globally distributed apex predator, this study presents a promising new step towards condensing the vast amounts of information collected with acoustic tracking technology into straightforward results which are directly applicable to the management and conservation of any species that meet the assumptions of our model.
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Non-lethal assessment of the reproductive status of Broadnose Sevengill Sharks (Notorynchus cepedianus) to determine the significance of habitat use in coastal areas
Conservation physiology, 2014Co-Authors: Ca Awruch, Susan M. Jones, Martín García Asorey, Adam BarnettAbstract:Identification of the importance of habitats that are frequently used by any species is essential to a complete understanding of the species' biology and to incorporate their ecological role into conservation and management programmes. In this context, the present study investigated whether Tasmanian coastal waters have any reproductive relevance for the Broadnose Sevengill Shark (Notorynchus cepedianus). Although this species is a large coast-associated apex predator in these areas, there is a complete gap in understanding the role that these coastal systems could play in its reproduction. Reproductive hormones were used as a non-lethal method to address the reproductive biology of this species. Females seemed to have at least a bi-annual reproductive cycle, being pregnant for ∼1 year and spending at least 1 year non-pregnant, with the ovulatory cycle separated from gestation. Mature females were found to be ovulating, in the initial stages of pregnancy, resting or starting a new vitellogenic cycle. Notorynchus cepedianus did not use these coastal habitats for mating or as a pupping ground. Although the mating season was distinguished between September to April, only 22% of males showed mating scars during the peak of the mating period and no near-term pregnant females were observed. Thus, despite these coastal waters being an important foraging ground for this species, these areas did not have any reproductive relevance. In consequence, future management and conservation planning programmes need to identify whether there are other areas in Tasmania that play a critical role for reproductive purposes in this species. Finally, although previous studies have linked reproductive hormones with external examination of the gonads to validate the use of steroids as a non-lethal tool to address reproduction, the present study used this methodology without killing any animals. This has important implications for conservation programmes of threatened and endangered species worldwide where the methodology cannot be validated.
Jayson M. Semmens - One of the best experts on this subject based on the ideXlab platform.
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Integrating acoustic telemetry into mark–recapture models to improve the precision of apparent survival and abundance estimates
Oecologia, 2015Co-Authors: Christine L. Dudgeon, Jayson M. Semmens, Kenneth H. Pollock, J. Matias Braccini, Adam BarnettAbstract:Capture–mark–recapture models are useful tools for estimating demographic parameters but often result in low precision when recapture rates are low. Low recapture rates are typical in many study systems including fishing-based studies. Incorporating auxiliary data into the models can improve precision and in some cases enable parameter estimation. Here, we present a novel application of acoustic telemetry for the estimation of apparent survival and abundance within capture–mark–recapture analysis using open population models. Our case study is based on simultaneously collecting longline fishing and acoustic telemetry data for a large mobile apex predator, the Broadnose Sevengill Shark ( Notorhynchus cepedianus ), at a coastal site in Tasmania, Australia. Cormack–Jolly–Seber models showed that longline data alone had very low recapture rates while acoustic telemetry data for the same time period resulted in at least tenfold higher recapture rates. The apparent survival estimates were similar for the two datasets but the acoustic telemetry data showed much greater precision and enabled apparent survival parameter estimation for one dataset, which was inestimable using fishing data alone. Combined acoustic telemetry and longline data were incorporated into Jolly–Seber models using a Monte Carlo simulation approach. Abundance estimates were comparable to those with longline data only; however, the inclusion of acoustic telemetry data increased precision in the estimates. We conclude that acoustic telemetry is a useful tool for incorporating in capture–mark–recapture studies in the marine environment. Future studies should consider the application of acoustic telemetry within this framework when setting up the study design and sampling program.
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Integrating acoustic telemetry into mark-recapture models to improve the precision of apparent survival and abundance estimates
Oecologia, 2015Co-Authors: Christine L. Dudgeon, Jayson M. Semmens, Kenneth H. Pollock, J. Matias Braccini, Adam BarnettAbstract:Capture–mark–recapture models are useful tools for estimating demographic parameters but often result in low precision when recapture rates are low. Low recapture rates are typical in many study systems including fishing-based studies. Incorporating auxiliary data into the models can improve precision and in some cases enable parameter estimation. Here, we present a novel application of acoustic telemetry for the estimation of apparent survival and abundance within capture–mark–recapture analysis using open population models. Our case study is based on simultaneously collecting longline fishing and acoustic telemetry data for a large mobile apex predator, the Broadnose Sevengill Shark (Notorhynchus cepedianus), at a coastal site in Tasmania, Australia. Cormack–Jolly–Seber models showed that longline data alone had very low recapture rates while acoustic telemetry data for the same time period resulted in at least tenfold higher recapture rates. The apparent survival estimates were similar for the two datasets but the acoustic telemetry data showed much greater precision and enabled apparent survival parameter estimation for one dataset, which was inestimable using fishing data alone. Combined acoustic telemetry and longline data were incorporated into Jolly–Seber models using a Monte Carlo simulation approach. Abundance estimates were comparable to those with longline data only; however, the inclusion of acoustic telemetry data increased precision in the estimates. We conclude that acoustic telemetry is a useful tool for incorporating in capture–mark–recapture studies in the marine environment. Future studies should consider the application of acoustic telemetry within this framework when setting up the study design and sampling program.
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Markov models and network analysis reveal sex-specific differences in the space-use of a coastal apex predator
Oikos, 2014Co-Authors: Kilian M. Stehfest, Adam Barnett, Toby A. Patterson, Jayson M. SemmensAbstract:Understanding the links between external variables such as habitat and interactions with conspecifics and animal space-use is fundamental to developing effective management measures. In the marine realm, automated acoustic tracking has become a widely used method for monitoring the movement of free-ranging animals, yet researchers generally lack robust methods for analysing the resulting spatial-usage data. In this study, acoustic tracking data from male and female Broadnose Sevengill Sharks Notorynchus cepedianus, collected in a system of coastal embayments in southeast Tasmania were analyzed to examine sex-specific differences in the Sharks' coastal space-use and test novel methods for the analysis of acoustic telemetry data. Sex-specific space-use of the Broadnose Sevengill Shark from acoustic telemetry data was analysed in two ways: The recently proposed spatial network analysis of between-receiver movements was employed to identify sex-specific space-use patterns. To include the full breadth of temporal information held in the data, movements between receivers were furthermore considered as transitions between states of a Markov chain, with the resulting transition probability matrix allowing the ranking of the relative importance of different parts of the study area. Both spatial network and Markov chain analysis revealed sex-specific preferences of different sites within the study area. The identification of priority areas differed for the methods, due to the fact that in contrast to network analysis, our Markov chain approach preserves the chronological sequence of detections and accounts for both residency periods and movements. In addition to adding to our knowledge of the ecology of a globally distributed apex predator, this study presents a promising new step towards condensing the vast amounts of information collected with acoustic tracking technology into straightforward results which are directly applicable to the management and conservation of any species that meet the assumptions of our model.
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Intraspecific differences in movement, dive behavior and vertical habitat preferences of a key marine apex predator
Marine Ecology Progress Series, 2014Co-Authors: Kilian M. Stehfest, Adam Barnett, Toby A. Patterson, Jayson M. SemmensAbstract:Understanding the patterns of large-scale movements of highly mobile marine predators is essential to understanding the impacts of anthropogenic pressures on the animals and the ecosystems they frequent. The Broadnose Sevengill Shark Notorynchus cepedianus is one of the most important apex predators in temperate coastal areas around the world, yet little is known of its seasonal large-scale movements. Five male and five female Sevengill Sharks were equipped with pop-up satellite archival tags (PSATs) in a coastal embayment in southern Tasmania, that collected depth and temperature data during winter, when the animals leave the coastal embayment, resulting in a dataset covering a total of 818 d. Animal tracks indicated that males moved northwards into warmer waters, whereas females remained in southern waters. Three of the females stayed in the Tasmanian coastal areas while the other two left, with one of them moving into deeper waters of up to 360 m depth at the southern edge of the Tasmanian shelf before returning to the Tasmanian coast. These sex-specific differences in large-scale movement could potentially lead to the differential exploitation of the sexes when the Sharks leave the protected areas where they were tagged. Both males and females switched between diel vertical migration and reverse diel vertical migration over the course of their tracks and displayed oscillatory vertical movements, probably linked to foraging. These vertical movements persisted throughout the tracks, suggesting that Sevengill Sharks foraged continuously during their migration rather than switching between transiting and foraging modes.
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Fine-Scale Movements of the Broadnose Sevengill Shark and Its Main Prey, the Gummy Shark
2013Co-Authors: Adam Barnett, John D. Stevens, Kátya G. Abrantes, Barry D. Bruce, Jayson M. SemmensAbstract:Information on the fine-scale movement of predators and their prey is important to interpret foraging behaviours and activity patterns. An understanding of these behaviours will help determine predator-prey relationships and their effects on community dynamics. For instance understanding a predator’s movement behaviour may alter pre determined expectations of prey behaviour, as almost any aspect of the prey’s decisions from foraging to mating can be influenced by the risk of predation. Acoustic telemetry was used to study the fine-scale movement patterns of the Broadnose Sevengill Shark Notorynchus cepedianus and its main prey, the Gummy Shark Mustelus antarcticus, in a coastal bay of southeast Tasmania. Notorynchus cepedianus displayed distinct diel differences in activity patterns. During the day they stayed close to the substrate (sea floor) and were frequently inactive. At night, however, their swimming behaviour continually oscillated through the water column from the substrate to near surface. In contrast, M. antarcticus remained close to the substrate for the entire diel cycle, and showed similar movement patterns for day and night. For both species, the possibility that movement is related to foraging behaviour is discussed. For M. antarcticus, movement may possibly be linked to a diet of predominantly slow benthic prey. On several occasions, N. cepedianus carried out a sequence of burst speed events (increased rates of movement) that could be related to chasing prey. All burst speed events during the day were across the substrate, while at night these occurred in the water column. Overall, diel differences in water column use, along with th
John D. Stevens - One of the best experts on this subject based on the ideXlab platform.
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Fine-Scale Movements of the Broadnose Sevengill Shark and Its Main Prey, the Gummy Shark
2013Co-Authors: Adam Barnett, John D. Stevens, Kátya G. Abrantes, Barry D. Bruce, Jayson M. SemmensAbstract:Information on the fine-scale movement of predators and their prey is important to interpret foraging behaviours and activity patterns. An understanding of these behaviours will help determine predator-prey relationships and their effects on community dynamics. For instance understanding a predator’s movement behaviour may alter pre determined expectations of prey behaviour, as almost any aspect of the prey’s decisions from foraging to mating can be influenced by the risk of predation. Acoustic telemetry was used to study the fine-scale movement patterns of the Broadnose Sevengill Shark Notorynchus cepedianus and its main prey, the Gummy Shark Mustelus antarcticus, in a coastal bay of southeast Tasmania. Notorynchus cepedianus displayed distinct diel differences in activity patterns. During the day they stayed close to the substrate (sea floor) and were frequently inactive. At night, however, their swimming behaviour continually oscillated through the water column from the substrate to near surface. In contrast, M. antarcticus remained close to the substrate for the entire diel cycle, and showed similar movement patterns for day and night. For both species, the possibility that movement is related to foraging behaviour is discussed. For M. antarcticus, movement may possibly be linked to a diet of predominantly slow benthic prey. On several occasions, N. cepedianus carried out a sequence of burst speed events (increased rates of movement) that could be related to chasing prey. All burst speed events during the day were across the substrate, while at night these occurred in the water column. Overall, diel differences in water column use, along with th
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Fine-Scale Movements of the Broadnose Sevengill Shark and Its Main Prey, the Gummy Shark
PloS one, 2010Co-Authors: Adam Barnett, John D. Stevens, Kátya G. Abrantes, Barry D. Bruce, Jayson M. SemmensAbstract:Information on the fine-scale movement of predators and their prey is important to interpret foraging behaviours and activity patterns. An understanding of these behaviours will help determine predator-prey relationships and their effects on community dynamics. For instance understanding a predator's movement behaviour may alter pre determined expectations of prey behaviour, as almost any aspect of the prey's decisions from foraging to mating can be influenced by the risk of predation. Acoustic telemetry was used to study the fine-scale movement patterns of the Broadnose Sevengill Shark Notorynchus cepedianus and its main prey, the Gummy Shark Mustelus antarcticus, in a coastal bay of southeast Tasmania. Notorynchus cepedianus displayed distinct diel differences in activity patterns. During the day they stayed close to the substrate (sea floor) and were frequently inactive. At night, however, their swimming behaviour continually oscillated through the water column from the substrate to near surface. In contrast, M. antarcticus remained close to the substrate for the entire diel cycle, and showed similar movement patterns for day and night. For both species, the possibility that movement is related to foraging behaviour is discussed. For M. antarcticus, movement may possibly be linked to a diet of predominantly slow benthic prey. On several occasions, N. cepedianus carried out a sequence of burst speed events (increased rates of movement) that could be related to chasing prey. All burst speed events during the day were across the substrate, while at night these occurred in the water column. Overall, diel differences in water column use, along with the presence of oscillatory behaviour and burst speed events suggest that N. cepedianus are nocturnal foragers, but may opportunistically attack prey they happen to encounter during the day.
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seasonal occurrence and population structure of the Broadnose Sevengill Shark notorynchus cepedianus in coastal habitats of south east tasmania
Journal of Fish Biology, 2010Co-Authors: Adam Barnett, John D. Stevens, Stewart Frusher, Jayson M. SemmensAbstract:Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the Broadnose Sevengill Shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (LT) classes (<80 cm) from the catches suggests that N. cepedianus are not using these coastal habitats as nursery areas. Of the 457 individuals tagged, 68 (15%) were recaptured. Time at liberty ranged from 6 days to almost 4 years and all but one of the recaptures were caught in its original tagging location, suggesting site fidelity. The large number of N. cepedianus in these coastal systems over summer indicates that these areas are important habitats for this species and that N. cepedianus may have a significant influence on community dynamics through both direct and indirect predator–prey interactions.
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Seasonal occurrence and population structure of the Broadnose Sevengill Shark Notorynchus cepedianus in coastal habitats of south-east Tasmania
Journal of fish biology, 2010Co-Authors: Adam Barnett, John D. Stevens, Stewart Frusher, Jayson M. SemmensAbstract:Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the Broadnose Sevengill Shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (LT) classes (
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Predator–prey relationships and foraging ecology of a marine apex predator with a wide temperate distribution
Marine Ecology Progress Series, 2010Co-Authors: Adam Barnett, John D. Stevens, Stewart Frusher, Kátya G. Abrantes, Jonah L. Yick, Jayson M. SemmensAbstract:The diet of the Broadnose Sevengill Shark Notorynchus cepedianus was investigated over 3 years from 2 coastal locations in south-east Tasmania: the Derwent Estuary and Norfolk Bay. In general, individuals from both locations consumed the same broad dietary categories (Sharks, batoids, teleosts and mammals). However, within these categories, species composition differed. Variations in chondrichthyan prey consumed matched estimations of prey abundance: Mustelus antarcticus was the primary prey in Norfolk Bay, where it was also the most abundant prey species; similarly, Squalus acanthias was an important prey and the most abundant in the Derwent Estuary. A decline in the catch rates of N. cepedianus and elasmobranch prey, in particular M. antarcticus over 3 years coincided with declines in dietary occurrence of M. antarcticus. Also, N. cepedianus and M. antarcticus abundances were both higher in Norfolk Bay than the Derwent Estuary. The correla- tion with diet and estimations of predator and prey relative abundance suggests N. cepedianus may move into coastal areas to exploit regular seasonal abundant resources, but they can also be versatile opportunistic predators that exploit a temporarily abundant resource.
David A. Ebert - One of the best experts on this subject based on the ideXlab platform.
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Evidence of historical isolation and genetic structuring among Broadnose Sevengill Sharks (Notorynchus cepedianus) from the world’s major oceanic regions
Reviews in Fish Biology and Fisheries, 2021Co-Authors: Alicia C. J. Schmidt-roach, Adam Barnett, David A. Ebert, Christine C. Bruels, Adam D. Miller, Craig D. H. Sherman, Sebastian Schmidt-roach, Charlene Da Silva, Christopher G. Wilke, Craig ThorburnAbstract:Cosmopolitan marine pelagic species display variable patterns of population connectivity among the world’s major oceans. While this information is crucial for informing management, information is lacking for many ecologically important species, including apex predators. In this study we examine patterns of genetic structure in the Broadnose Sevengill Shark, Notorynchus cepedianus across its global distribution. We estimate patterns of connectivity among Broadnose Sevengill Shark populations from three major oceanic regions (South Atlantic, Oceania and Eastern Pacific) by contrasting mitochondrial and nuclear DNA haplotype frequencies. We also produced time calibrated Bayesian Inference phylogenetic reconstructions to analyses global phylogeographic patterns and estimate divergence times among distinctive Shark lineages. Our results demonstrate significant genetic differentiation among oceanic regions ( Φ _ST = 0.9789, P
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RESEARCH ARTICLE Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries
2016Co-Authors: Shawn Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The Broadnose Sevengill Shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations con-ducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, Califor-nia. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill Shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, popula-tion structure and relatedness. Diversity within N. cepedianus was found to be low to moder-ate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent popula-tion bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of Sharks sampled during 2005–2006. Relatedness within sampled populations was high, with per-cent relatedness among Sharks caught in the same area indicating 42.30 % first-order rela-tive relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator
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Preliminary Observations of Population Genetics and Relatedness of the Broadnose Sevengill Shark, Notorynchus cepedianus, in Two Northeast Pacific Estuaries.
PloS one, 2015Co-Authors: Shawn D. Larson, Debbie Farrer, Dayv Lowry, David A. EbertAbstract:The Broadnose Sevengill Shark, Notorynchus cepedianus, a common coastal species in the eastern North Pacific, was sampled during routine capture and tagging operations conducted from 2005–2012. One hundred and thirty three biopsy samples were taken during these research operations in Willapa Bay, Washington and in San Francisco Bay, California. Genotypic data from seven polymorphic microsatellites (derived from the related sixgill Shark, Hexanchus griseus) were used to describe N. cepedianus genetic diversity, population structure and relatedness. Diversity within N. cepedianus was found to be low to moderate with an average observed heterozygosity of 0.41, expected heterozygosity of 0.53, and an average of 5.1 alleles per microsatellite locus. There was no evidence of a recent population bottleneck based on genetic data. Analyses of genetic differences between the two sampled estuaries suggest two distinct populations with some genetic mixing of Sharks sampled during 2005–2006. Relatedness within sampled populations was high, with percent relatedness among Sharks caught in the same area indicating 42.30% first-order relative relationships (full or half siblings). Estuary-specific familial relationships suggest that management of N. cepedianus on the U.S. West Coast should incorporate stock-specific management goals to conserve this ecologically important predator.
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Incorporating heterogeneity into growth analyses of wild and captive Broadnose Sevengill Sharks Notorynchus cepedianus
Aquatic Biology, 2010Co-Authors: J. Matias Braccini, Adam Barnett, David A. Ebert, V. S. Troynikov, Terence I. Walker, Henry F. Mollet, Nicholas KirbyAbstract:Growth estimates for Shark species are mostly derived from length-at-age data, where age information is commonly obtained from hard structures such as vertebrae and dorsal-fin spines. Unfor- tunately, hard structures cannot be used for estimating the age of many Shark species, particularly those occurring in deep water or belonging to ancient groups. Alternative methods are therefore required for the estimation of growth for these Shark groups. The Broadnose Sevengill Shark Notorynchus cepedianus has very poorly calcified vertebrae that cannot be used for age and growth estimations. Three stochas- tic versions of the von Bertalanffy-Fabens growth model with random parameter k were fitted to length- increment data of captive and of wild tagged and recaptured N. cepedianus from southeastern Australia, California and southern Africa. The model based on a gamma distributed parameter k provided the best fit to the data. Captive females and wild females showed the highest and lowest values of mathematical expectation E(k), whereas wild males and wild females showed the lowest and highest values of mean maximum length L∞, respectively. For a time interval of 1 yr, captive females had the highest length in- crement, whereas wild females had the lowest length increment. Our approach allows accounting for the natural heterogeneity of growth in the estimation of the growth parameters of N. cepedianus, which has not been done previously for captive and wild Sharks. This the first study to provide a representative set of growth parameters for male and female N. cepedianus, which is crucial information for the modelling of the population dynamics of this top predator.
Stewart Frusher - One of the best experts on this subject based on the ideXlab platform.
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seasonal occurrence and population structure of the Broadnose Sevengill Shark notorynchus cepedianus in coastal habitats of south east tasmania
Journal of Fish Biology, 2010Co-Authors: Adam Barnett, John D. Stevens, Stewart Frusher, Jayson M. SemmensAbstract:Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the Broadnose Sevengill Shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (LT) classes (<80 cm) from the catches suggests that N. cepedianus are not using these coastal habitats as nursery areas. Of the 457 individuals tagged, 68 (15%) were recaptured. Time at liberty ranged from 6 days to almost 4 years and all but one of the recaptures were caught in its original tagging location, suggesting site fidelity. The large number of N. cepedianus in these coastal systems over summer indicates that these areas are important habitats for this species and that N. cepedianus may have a significant influence on community dynamics through both direct and indirect predator–prey interactions.
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Seasonal occurrence and population structure of the Broadnose Sevengill Shark Notorynchus cepedianus in coastal habitats of south-east Tasmania
Journal of fish biology, 2010Co-Authors: Adam Barnett, John D. Stevens, Stewart Frusher, Jayson M. SemmensAbstract:Research longline sampling was conducted seasonally from December 2006 to February 2009 to investigate the occurrence and population structure of the Broadnose Sevengill Shark Notorynchus cepedianus in coastal areas of south-east Tasmania. Notorynchus cepedianus showed a consistent temporal trend in seasonal occurrence in Norfolk Bay characterized by high abundances in summer to near absence in winter. This pattern was less pronounced in the Derwent Estuary, where fish were still caught during winter. The absence of smaller total length (LT) classes (
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Predator–prey relationships and foraging ecology of a marine apex predator with a wide temperate distribution
Marine Ecology Progress Series, 2010Co-Authors: Adam Barnett, John D. Stevens, Stewart Frusher, Kátya G. Abrantes, Jonah L. Yick, Jayson M. SemmensAbstract:The diet of the Broadnose Sevengill Shark Notorynchus cepedianus was investigated over 3 years from 2 coastal locations in south-east Tasmania: the Derwent Estuary and Norfolk Bay. In general, individuals from both locations consumed the same broad dietary categories (Sharks, batoids, teleosts and mammals). However, within these categories, species composition differed. Variations in chondrichthyan prey consumed matched estimations of prey abundance: Mustelus antarcticus was the primary prey in Norfolk Bay, where it was also the most abundant prey species; similarly, Squalus acanthias was an important prey and the most abundant in the Derwent Estuary. A decline in the catch rates of N. cepedianus and elasmobranch prey, in particular M. antarcticus over 3 years coincided with declines in dietary occurrence of M. antarcticus. Also, N. cepedianus and M. antarcticus abundances were both higher in Norfolk Bay than the Derwent Estuary. The correla- tion with diet and estimations of predator and prey relative abundance suggests N. cepedianus may move into coastal areas to exploit regular seasonal abundant resources, but they can also be versatile opportunistic predators that exploit a temporarily abundant resource.
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Non-lethal method to obtain stomach samples from a large marine predator and the use of DNA analysis to improve dietary information
Journal of Experimental Marine Biology and Ecology, 2010Co-Authors: Adam Barnett, John D. Stevens, Stewart Frusher, Ks Redd, Jayson M. SemmensAbstract:Dietary information of apex predators is crucial to understanding community dynamics and ecosystem processes. However, as dietary studies traditionally involve lethal sampling, obtaining this essential information can have repercussions on predator populations and the structure and functioning of marine ecosystems. With stronger emphasis being placed on conservation of species that are vulnerable to overexploitation, the need for non-destructive methods of sampling is imperative, as is the requirement to maximize the information obtained from each sample. Stomach flushing (gastric lavage) and DNA analysis of stomach contents methods were tested on the Broadnose Sevengill Shark Notorynchus cepedianus Peron 1807. Acoustic tracking and recaptures of Sharks implied high survivorship post-fishing and stomach flushing. From 85 prey items collected, 36 (43%) could be identified to species level using morphological analysis. After DNA analysis, a further 35 items were identified to species level, doubling the information obtained from these stomachs. The number of N. cepedianus that were confirmed to have eaten gummy Sharks Mustelus antarcticus Gunther 1870 also doubled after DNA analysis. Without DNA analysis (of stomach contents) the importance of M. antarcticus in the diets of N. cepedianus would have been substantially underestimated. In addition, the non-lethal approach provides an opportunity to obtain meaningful information from non-harvested, endangered or rare species or sampling of species within protected areas.
