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Daniel P. Cartamil - One of the best experts on this subject based on the ideXlab platform.
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historical reconstruction of gulf of california Shark Fishery landings and species composition 1939 2014 in a data poor Fishery context
Fisheries Research, 2017Co-Authors: Luz Erandi Saldanaruiz, Oscar Sosanishizaki, Daniel P. CartamilAbstract:Abstract The Gulf of California (GC) is one of the most historically important regions in Mexico for Shark fisheries. However, detailed historical Shark landings are not available, making it difficult to plan adequate management strategies. This study analyses historical trends in GC Shark Fishery landings in a data-poor environment to establish a baseline for future research and assessments. The total Shark landings for the artisanal Fishery from 1939 to 2014, middle-size vessel Fishery landings for the 1988–2014, and species composition from 1960 to 2014 were estimated, and we assessed the uncertainty inherent in the data sources and subsequent analyses. Thirty-eight Shark species were identified in the GC artisanal Fishery, of which Mustelus spp., Sphyrna lewini , Rhizoprionodon longurio, Squatina californica, Carcharhinus falciformis, Sphyrna zygaena, and Carcharhinus limbatus were the taxa with the greatest landings. A noticeable decline in landings was observed for Carcharhinus leucas, Nasolamia velox, Negaprion brevirostris, Sphyrna spp. , Carcharhinus altimus, Carcharhinus obscurus, Galeocerdo cuvier, Carcharhinus porosus, Triakis semifasciata, and Carcharhinus brachyurus . Landings of the pelagic Sharks Prionace glauca, Alopias pelagicus, and Isurus oxyrinchu s increased after 1986, mainly due to the development of the middle-size vessel Fishery. The history of GC Shark fisheries and implications for management of sustainable Shark fisheries are discussed.
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Historical reconstruction of Gulf of California Shark Fishery landings and species composition, 1939–2014, in a data-poor Fishery context
Fisheries Research, 2017Co-Authors: Luz Erandi Saldaña-ruiz, Oscar Sosa-nishizaki, Daniel P. CartamilAbstract:Abstract The Gulf of California (GC) is one of the most historically important regions in Mexico for Shark fisheries. However, detailed historical Shark landings are not available, making it difficult to plan adequate management strategies. This study analyses historical trends in GC Shark Fishery landings in a data-poor environment to establish a baseline for future research and assessments. The total Shark landings for the artisanal Fishery from 1939 to 2014, middle-size vessel Fishery landings for the 1988–2014, and species composition from 1960 to 2014 were estimated, and we assessed the uncertainty inherent in the data sources and subsequent analyses. Thirty-eight Shark species were identified in the GC artisanal Fishery, of which Mustelus spp., Sphyrna lewini , Rhizoprionodon longurio, Squatina californica, Carcharhinus falciformis, Sphyrna zygaena, and Carcharhinus limbatus were the taxa with the greatest landings. A noticeable decline in landings was observed for Carcharhinus leucas, Nasolamia velox, Negaprion brevirostris, Sphyrna spp. , Carcharhinus altimus, Carcharhinus obscurus, Galeocerdo cuvier, Carcharhinus porosus, Triakis semifasciata, and Carcharhinus brachyurus . Landings of the pelagic Sharks Prionace glauca, Alopias pelagicus, and Isurus oxyrinchu s increased after 1986, mainly due to the development of the middle-size vessel Fishery. The history of GC Shark fisheries and implications for management of sustainable Shark fisheries are discussed.
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Diel movement patterns and habitat preferences of the common thresher Shark (Alopias vulpinus) in the Southern California Bight
Marine and Freshwater Research, 2010Co-Authors: Daniel P. Cartamil, Nicholas C. Wegner, S. Aalbers, Chugey A. Sepulveda, A. Baquero, Jeffrey B. GrahamAbstract:The common thresher Shark, Alopias vulpinus, is the basis of the largest commercial Shark Fishery in California waters. We used acoustic telemetry to determine the diel movement patterns and habitat preferences of this species inthe Southern California Bight (SCB),where commercial fishing for the common thresher Sharkis concentrated. Eightcommonthreshers (forklength: 122-203cm) weretaggedwith temperature anddepth-sensingacoustic transmitters and tracked for periods ranging from 22 to 49h. Tracked Sharks preferentially utilized deep offshore waters, and avoided shallower waters over the continental shelf. Mean rate of movement (ROMs.d.) was 2.15 � 0.46kmh � 1 . ROM and angularconcentration(r,ameasureofrelativelinearity)bothshowedastrongdaytimepattern,withhighestvaluesatdawn that decreased throughout the day, whereas nocturnal ROM and r were less variable. Daytime vertical movements consisted of either vertical excursions below the thermocline or relatively level swimming within the upper portion of the thermocline. Nocturnally, all Sharks remained within the mixed layer. These findings suggest that the common thresher Shark is primarily a daytime predator, and have relevance for estimating how the alteration of the set depth of fishing-gear could affect catch rates of this species in the SCB.
Colin A. Simpfendorfer - One of the best experts on this subject based on the ideXlab platform.
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Understanding non-compliance in small-scale fisheries: Shark fishing in Myanmar’s Myeik Archipelago
Ambio, 2020Co-Authors: Tracy Mackeracher, Colin A. Simpfendorfer, Me’ira Mizrahi, Brock Bergseth, Khin May Chit Maung, Zin Lin Khine, Ei Thal Phyu, Amy DiedrichAbstract:Achieving fisheries compliance is challenging in contexts where enforcement capacity is limited and the incentives for rule-breaking are strong. This challenge is exemplified in Myanmar, where an active Shark Fishery exists despite a nationwide ban on targeted Shark fishing. We used the Kipling method (5W1H) to gather a complete story of non-compliance in five small-scale fishing communities in the Myeik Archipelago. Among 144 fishers surveyed, 49% were aware of the nationwide ban. Shark fishers (24%) tended to be younger individuals who did not own a boat and perceived Shark fishing to be prevalent. Compliant fishers were motivated by a fear of Sharks and lack of capacity (equipment, knowledge), whereas food and income were cited as key motivations for non-compliance. The results of our study emphasize that in resource-dependent communities, improving compliance for effective Shark conservation may require addressing broader issues of poverty, food security and the lack of alternatives.
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Assessment of a data-limited, multi-species Shark Fishery in the Great Barrier Reef Marine Park and south-east Queensland
Fisheries Research, 2016Co-Authors: Alastair V. Harry, Jonathan J. Smart, Colin A. Simpfendorfer, Richard J. Saunders, Peter M. Yates, Andrew J. TobinAbstract:Abstract The status of five species of commercially exploited Sharks within the Great Barrier Reef Marine Park (GBRMP) and south-east Queensland was assessed using a data-limited approach. Annual harvest rate, U , estimated empirically from tagging between 2011 and 2013, was compared with an analytically-derived proxy for optimal equilibrium harvest rate, U MSY Lim . Median estimates of U for three principal retained species, Australian blacktip Shark, Carcharhinus tilstoni , spot-tail Shark, Carcharhinus sorrah , and spinner Shark, Carcharhinus brevipinna , were 0.10, 0.06 and 0.07 year −1 , respectively. Median U for two retained, non-target species, pigeye Shark, Carcharhinus amboinensis and Australian sharpnose Shark, Rhizoprionodon taylori , were 0.27 and 0.01 year −1 , respectively. For all species except the Australian blacktip the median ratio of U/U MSY Lim was U MSY Lim was low (0.04–0.07 year −1 ) and that U/U MSY Lim was likely to be >1. Harvest of the Australian blacktip Shark above U MSY could place this species at a greater risk of localised depletion in parts of the GBRMP. Results of the study indicated that much higher catches, and presumably higher U , during the early 2000s were likely unsustainable. The unexpectedly high level of U on the pigeye Shark indicated that output-based management controls may not have been effective in reducing harvest levels on all species, particularly those caught incidentally by other fishing sectors including the recreational sector.
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estimating fishing mortality of major target species and species of conservation interest in the queensland east coast Shark Fishery
2014Co-Authors: Andrew J. Tobin, Jonathan J. Smart, Alastair V. Harry, Richard J. Saunders, Colin A. SimpfendorferAbstract:The rate fishing mortality, F, during 2011 and 2012 was estimated for four species of commercially fished whaler Sharks (genus Carcharhinus) in the Great Barrier Reef Marine Park and southeast Queensland from a five year tagging study. Values of F were then used in a range of demographic models to assess whether fishing by the East Coast Inshore Finfish Fishery (ECIFF) and the recreational sector was likely to be have been sustainable. Tag return rates for the two most commonly caught species, Carcharhinus sorrah and Carcharhinus tilstoni, were estimated at 5.6% and 16.4%, respectively. These values corresponded to maximum value of F of 0.06 and 0.13, respectively, for 2011 and 2012 combined. Demographic analysis indicated that this value of F would lead to a positive rate of population increase, r, for C. sorrah (r = 0.10) and a stable population for C. tilstoni (r ≈ 0). Overall tag return rates for two larger species of whaler Sharks, C. amboinensis, and C. brevipinna, caught only as juveniles, were 35.9% and 11.8%, respectively. These values corresponded to a maximum value of F of 0.40 and 0.07, respectively. All demographic analysis indicated that this level of F was within sustainable bounds (r = 0.04) for C. brevipinna, however three out of four analyses indicated that it was unsustainable for C. amboinensis (r =-0.14). Notably though, a demographic analysis using recent empirical estimates of natural mortality, M, suggested that fishing may still be sustainable (r= 0.03). Our findings broadly suggest that the range of management measures have been undertaken over the past decade has been successful in controlling fishing mortality on target species. The high recapture rates for C. amboinensis, a species not typically targeted, suggests that incidental capture of some long-lived and slow growing Sharks by the ECIFF could still be an issue.
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detection of interspecies hybridisation in chondrichthyes hybrids and hybrid offspring between australian carcharhinus tilstoni and common c limbatus blacktip Shark found in an australian Fishery
Conservation Genetics, 2012Co-Authors: Jess A. T. Morgan, Andrew J. Tobin, Alastair V. Harry, David Welch, Raewyn Street, William G. Macbeth, Pascal T. Geraghty, James R White, Colin A. SimpfendorferAbstract:Interspecies hybridisation in nature is a well-studied phenomenon, but it has not been analysed using genetic markers in the class Chondrichthyes (Sharks, rays and chimeras). Two black-tip whaler Shark species (Australian, Carcharhinus tilstoni; Common, C. limbatus) have overlapping distributions in Australia, distinct mitochondrial DNA sequence (ND4, COI, control region) and distinct morphological features such as length at sexual maturity, length at birth and number of vertebrae. A mismatch was observed between species identification using mtDNA sequence and species identification using morphological characters. To test whether hybridisation between the two species was responsible, a nuclear gene with species-specific mutations was sequenced. Extensive interspecies hybridisation was found to be occurring. Hybrids were found from five locations on the eastern Australian coastline, spanning 2,000 km. If hybrid fitness is low and hybrids are common, then fisheries recruitment may be overestimated and the productivity of the black-tip Shark Fishery may be well below that required to support commercial exploitation. To guard against identification errors, the likelihood of hybridisation and subsequent introgression should be assessed prior to using mtDNA (e.g. barcoding) to identify Shark species. The C. limbatus–C. tilstoni species complex provides a unique opportunity to investigate the ability of Sharks to adapt to environmental change, in particular, the impact of hybridization on species distributions which favour C. tilstoni along the north and C. limbatus along the south eastern Australian coastline.
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evaluating catch and mitigating risk in a multispecies tropical inshore Shark Fishery within the great barrier reef world heritage area
Marine and Freshwater Research, 2011Co-Authors: Alastair V. Harry, Andrew J. Tobin, Colin A. Simpfendorfer, David Welch, James R White, Amos Mapleston, Ashley J Williams, Jason StapleyAbstract:Small-scale and artisanal fisheries for Sharks exist in most inshore, tropical regions of the world. Although often important in terms of food security, their low value and inherent complexity provides an imposing hurdle to sustainable management. An observer survey of a small-scale commercial gill-net Fishery operating within the Great Barrier Reef World Heritage area revealed at least 38 species of elasmobranch were present in the catch. Of the total elasmobranch catch, 95% was 25 species of Carcharhiniformes from the families Carcharhinidae, Hemigaleidae and Sphyrnidae. Individual species were captured in a variety of ways by the Fishery, often with strongly biased sex ratios and in a variety of life stages (e.g. neonates, juveniles, adult). Despite this, the main carcharhiniform taxa captured could be qualitatively categorised into four groups based on similar catch characteristics, body size and similarities in life history: small coastal ( 2000 mm); and hammerheads. Such groupings can potentially be useful for simplifying management of complex multispecies fisheries. The idiosyncrasies of elasmobranch populations and how fisheries interact with them provide a challenge for management but, if properly understood, potentially offer underutilised options for designing management strategies.
Andrew J. Tobin - One of the best experts on this subject based on the ideXlab platform.
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Assessment of a data-limited, multi-species Shark Fishery in the Great Barrier Reef Marine Park and south-east Queensland
Fisheries Research, 2016Co-Authors: Alastair V. Harry, Jonathan J. Smart, Colin A. Simpfendorfer, Richard J. Saunders, Peter M. Yates, Andrew J. TobinAbstract:Abstract The status of five species of commercially exploited Sharks within the Great Barrier Reef Marine Park (GBRMP) and south-east Queensland was assessed using a data-limited approach. Annual harvest rate, U , estimated empirically from tagging between 2011 and 2013, was compared with an analytically-derived proxy for optimal equilibrium harvest rate, U MSY Lim . Median estimates of U for three principal retained species, Australian blacktip Shark, Carcharhinus tilstoni , spot-tail Shark, Carcharhinus sorrah , and spinner Shark, Carcharhinus brevipinna , were 0.10, 0.06 and 0.07 year −1 , respectively. Median U for two retained, non-target species, pigeye Shark, Carcharhinus amboinensis and Australian sharpnose Shark, Rhizoprionodon taylori , were 0.27 and 0.01 year −1 , respectively. For all species except the Australian blacktip the median ratio of U/U MSY Lim was U MSY Lim was low (0.04–0.07 year −1 ) and that U/U MSY Lim was likely to be >1. Harvest of the Australian blacktip Shark above U MSY could place this species at a greater risk of localised depletion in parts of the GBRMP. Results of the study indicated that much higher catches, and presumably higher U , during the early 2000s were likely unsustainable. The unexpectedly high level of U on the pigeye Shark indicated that output-based management controls may not have been effective in reducing harvest levels on all species, particularly those caught incidentally by other fishing sectors including the recreational sector.
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estimating fishing mortality of major target species and species of conservation interest in the queensland east coast Shark Fishery
2014Co-Authors: Andrew J. Tobin, Jonathan J. Smart, Alastair V. Harry, Richard J. Saunders, Colin A. SimpfendorferAbstract:The rate fishing mortality, F, during 2011 and 2012 was estimated for four species of commercially fished whaler Sharks (genus Carcharhinus) in the Great Barrier Reef Marine Park and southeast Queensland from a five year tagging study. Values of F were then used in a range of demographic models to assess whether fishing by the East Coast Inshore Finfish Fishery (ECIFF) and the recreational sector was likely to be have been sustainable. Tag return rates for the two most commonly caught species, Carcharhinus sorrah and Carcharhinus tilstoni, were estimated at 5.6% and 16.4%, respectively. These values corresponded to maximum value of F of 0.06 and 0.13, respectively, for 2011 and 2012 combined. Demographic analysis indicated that this value of F would lead to a positive rate of population increase, r, for C. sorrah (r = 0.10) and a stable population for C. tilstoni (r ≈ 0). Overall tag return rates for two larger species of whaler Sharks, C. amboinensis, and C. brevipinna, caught only as juveniles, were 35.9% and 11.8%, respectively. These values corresponded to a maximum value of F of 0.40 and 0.07, respectively. All demographic analysis indicated that this level of F was within sustainable bounds (r = 0.04) for C. brevipinna, however three out of four analyses indicated that it was unsustainable for C. amboinensis (r =-0.14). Notably though, a demographic analysis using recent empirical estimates of natural mortality, M, suggested that fishing may still be sustainable (r= 0.03). Our findings broadly suggest that the range of management measures have been undertaken over the past decade has been successful in controlling fishing mortality on target species. The high recapture rates for C. amboinensis, a species not typically targeted, suggests that incidental capture of some long-lived and slow growing Sharks by the ECIFF could still be an issue.
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detection of interspecies hybridisation in chondrichthyes hybrids and hybrid offspring between australian carcharhinus tilstoni and common c limbatus blacktip Shark found in an australian Fishery
Conservation Genetics, 2012Co-Authors: Jess A. T. Morgan, Andrew J. Tobin, Alastair V. Harry, David Welch, Raewyn Street, William G. Macbeth, Pascal T. Geraghty, James R White, Colin A. SimpfendorferAbstract:Interspecies hybridisation in nature is a well-studied phenomenon, but it has not been analysed using genetic markers in the class Chondrichthyes (Sharks, rays and chimeras). Two black-tip whaler Shark species (Australian, Carcharhinus tilstoni; Common, C. limbatus) have overlapping distributions in Australia, distinct mitochondrial DNA sequence (ND4, COI, control region) and distinct morphological features such as length at sexual maturity, length at birth and number of vertebrae. A mismatch was observed between species identification using mtDNA sequence and species identification using morphological characters. To test whether hybridisation between the two species was responsible, a nuclear gene with species-specific mutations was sequenced. Extensive interspecies hybridisation was found to be occurring. Hybrids were found from five locations on the eastern Australian coastline, spanning 2,000 km. If hybrid fitness is low and hybrids are common, then fisheries recruitment may be overestimated and the productivity of the black-tip Shark Fishery may be well below that required to support commercial exploitation. To guard against identification errors, the likelihood of hybridisation and subsequent introgression should be assessed prior to using mtDNA (e.g. barcoding) to identify Shark species. The C. limbatus–C. tilstoni species complex provides a unique opportunity to investigate the ability of Sharks to adapt to environmental change, in particular, the impact of hybridization on species distributions which favour C. tilstoni along the north and C. limbatus along the south eastern Australian coastline.
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evaluating catch and mitigating risk in a multispecies tropical inshore Shark Fishery within the great barrier reef world heritage area
Marine and Freshwater Research, 2011Co-Authors: Alastair V. Harry, Andrew J. Tobin, Colin A. Simpfendorfer, David Welch, James R White, Amos Mapleston, Ashley J Williams, Jason StapleyAbstract:Small-scale and artisanal fisheries for Sharks exist in most inshore, tropical regions of the world. Although often important in terms of food security, their low value and inherent complexity provides an imposing hurdle to sustainable management. An observer survey of a small-scale commercial gill-net Fishery operating within the Great Barrier Reef World Heritage area revealed at least 38 species of elasmobranch were present in the catch. Of the total elasmobranch catch, 95% was 25 species of Carcharhiniformes from the families Carcharhinidae, Hemigaleidae and Sphyrnidae. Individual species were captured in a variety of ways by the Fishery, often with strongly biased sex ratios and in a variety of life stages (e.g. neonates, juveniles, adult). Despite this, the main carcharhiniform taxa captured could be qualitatively categorised into four groups based on similar catch characteristics, body size and similarities in life history: small coastal ( 2000 mm); and hammerheads. Such groupings can potentially be useful for simplifying management of complex multispecies fisheries. The idiosyncrasies of elasmobranch populations and how fisheries interact with them provide a challenge for management but, if properly understood, potentially offer underutilised options for designing management strategies.
André E. Punt - One of the best experts on this subject based on the ideXlab platform.
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Among-stock comparisons for improving stock assessments of data-poor stocks: the “Robin Hood” approach
Ices Journal of Marine Science, 2011Co-Authors: André E. Punt, David C Smith, Anthony D. M. SmithAbstract:Punt, A. E., Smith, D. C., and Smith, A. D. M. 2011. Among-stock comparisons for improving stock assessments of data-poor stocks: the “Robin Hood” approach. – ICES Journal of Marine Science, 68: 972–981.An approach is outlined for conducting stock assessments in which parameters are estimated for multiple stocks at the same time. Information from data-rich stock assessments, e.g. trends in fishing mortality, and values for parameters of selectivity functions are provided to data-poor assessments in the form of penalties on the estimated parameters, which leads to stock assessments for the most data-poor stocks being informed by those for the most data-rich stocks. The method is applied for example purposes to data for nine stocks in Australia's southern and eastern scalefish and Shark Fishery. The results of the application confirm that results for data-rich stocks are little impacted by being assessed in conjunction with data-poor stocks and that the results for data-poor stocks can be qualitatively different when information for data-rich stocks is taken into account.
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Development and evaluation of a cpue-based harvest control rule for the southern and eastern scalefish and Shark Fishery of Australia
ICES Journal of Marine Science, 2011Co-Authors: L. Richard Little, Sally E. Wayte, Geoffrey N. Tuck, Anthony D. M. Smith, Neil Klaer, Malcolm Haddon, André E. Punt, Robin B. Thomson, Jemery Day, Mike FullerAbstract:Many Fishery management agencies are adopting harvest control rules (HCRs) to achieve harvest policies and management objectives. HCRs, however, often require data-intensive stock assessments to facilitate the harvest prescription. An HCR based on catch and catch per unit effort (cpue) was developed for the southern and eastern scalefish and Shark Fishery of Australia, for stocks that lack the data needed to conduct a full statistical catch-at-age assessment. The HCR produces a recommended biological catch and is characterized by two parameters, target cpue and target catch, both derived from historical data. Simulation tests showed that the HCR could guide the stock to the desired state from different initial levels of depletion. However, the selection of parameter values for the HCR was critical. Achieving Fishery objectives was difficult when the target catch was a function of recent catch, rather than data from a predefined historical reference period. Problems may also arise when specifying the reference period on which the HCR parameters are determined. The cpue-based HCR is a valuable tool for managing fisheries where monitoring and assessment activities are relatively expensive, or in general, where data are scarce.
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experience in implementing harvest strategies in australia s south eastern fisheries
Fisheries Research, 2008Co-Authors: Anthony D. M. Smith, Geoffrey N. Tuck, Neil Klaer, André E. Punt, David C Smith, Ian Knuckey, J D Prince, Alexander K Morison, Rudy J KloserAbstract:Abstract The Southern and Eastern Scalefish and Shark Fishery (SESSF) is a complex multi-species Fishery, with 34 stock units under quota management, for which a harvest strategy framework was developed in 2005. The framework involves the application of a set of tier-based harvest control rules (HCR) designed to provide a precautionary approach to management. The harvest strategy framework has been applied from 2005 to 2007, resulting in substantial reductions in quotas across the Fishery. The experience in implementing the framework, both positive and negative, is described, and general lessons are drawn. Key lessons include the importance of formally testing such strategies using management strategy evaluation, the impact of external management drivers on implementation of the approach, the need to define strategies for setting “bycatch quotas” in multi-species fisheries, and the need for flexibility and pragmatism in the early stages of implementing such an approach.
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assessing the management related benefits of fixed station Fishery independent surveys in australia s southern Shark Fishery
Fisheries Research, 2002Co-Authors: André E. Punt, Terence I Walker, J D PrinceAbstract:Monte Carlo simulation is used to assess the benefits of different levels of survey intensity for a programme of fixed-station surveys using gill-nets, in terms of the ability to satisfy the management objectives for gummy Shark, Mustelus antarcticus, in Bass Strait, Australia. The simulations consider the entire management process: data collection, data analysis, stock assessment, and setting of total allowable catches (TACs). The use in assessments of survey results rather than future commercial catch rates leads to a marked improvement in the ability to satisfy the legislative management objective for Australian fisheries of Ecological Sustainable Development, especially if future catch rates are not related linearly to abundance or if catchability is density-dependent. The benefits of more than six stations per survey site appear limited, however, because of the possible impact of variability in survey results due to factors unrelated to sampling.
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standardization of catch and effort data in a spatially structured Shark Fishery
Fisheries Research, 2000Co-Authors: André E. Punt, Terence I Walker, Bruce L Taylor, Fred PribacAbstract:Abstract The methods used to develop catch rate based indices of relative abundance for the school Shark Galeorhinus galeus resource off southern Australia are outlined. These methods are based on fitting generalized linear models to catch and effort data for several regions in this Fishery. This is to take account of the multi-gear nature of the Fishery and the spatial structure of the trends in catch rate. The data on whether or not the catch rate is zero and the catch rate given that it is non-zero are analysed separately and then combined to provide indices of abundance. The former analysis is based on assuming the data are Bernoulli random variables. Given the uncertainty about the appropriate error-model to assume when fitting generalized linear models to catch and effort data, four alternative error-models — log-normal, log-gamma, Poisson, and negative binomial — were explored when modelling the non-zero catch rates.
Jess A. T. Morgan - One of the best experts on this subject based on the ideXlab platform.
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detection of interspecies hybridisation in chondrichthyes hybrids and hybrid offspring between australian carcharhinus tilstoni and common c limbatus blacktip Shark found in an australian Fishery
Conservation Genetics, 2012Co-Authors: Jess A. T. Morgan, Andrew J. Tobin, Alastair V. Harry, David Welch, Raewyn Street, William G. Macbeth, Pascal T. Geraghty, James R White, Colin A. SimpfendorferAbstract:Interspecies hybridisation in nature is a well-studied phenomenon, but it has not been analysed using genetic markers in the class Chondrichthyes (Sharks, rays and chimeras). Two black-tip whaler Shark species (Australian, Carcharhinus tilstoni; Common, C. limbatus) have overlapping distributions in Australia, distinct mitochondrial DNA sequence (ND4, COI, control region) and distinct morphological features such as length at sexual maturity, length at birth and number of vertebrae. A mismatch was observed between species identification using mtDNA sequence and species identification using morphological characters. To test whether hybridisation between the two species was responsible, a nuclear gene with species-specific mutations was sequenced. Extensive interspecies hybridisation was found to be occurring. Hybrids were found from five locations on the eastern Australian coastline, spanning 2,000 km. If hybrid fitness is low and hybrids are common, then fisheries recruitment may be overestimated and the productivity of the black-tip Shark Fishery may be well below that required to support commercial exploitation. To guard against identification errors, the likelihood of hybridisation and subsequent introgression should be assessed prior to using mtDNA (e.g. barcoding) to identify Shark species. The C. limbatus–C. tilstoni species complex provides a unique opportunity to investigate the ability of Sharks to adapt to environmental change, in particular, the impact of hybridization on species distributions which favour C. tilstoni along the north and C. limbatus along the south eastern Australian coastline.
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towards better management of australia s Shark Fishery genetic analyses reveal unexpected ratios of cryptic blacktip species carcharhinus tilstoni and c limbatus
Marine and Freshwater Research, 2010Co-Authors: Jennifer R. Ovenden, Jess A. T. Morgan, Tom Kashiwagi, Damien Broderick, J. P. SaliniAbstract:The common blacktip Shark (Carcharhinus limbatus) and the Australian blacktip Shark (C. tilstoni) are morphologically similar species that co-occur in subtropical and tropical Australia. In striking contrast to what has been previously reported, we demonstrate that the common blacktip Shark is not rare in northern Australia but occurs in approximately equal frequencies with the Australian blacktip Shark. Management of Shark resources in northern Australia needs to take account of this new information. Species identification was performed using nucleotide sequences of the control, NADH dehydrogenase subunit 4 (ND4) and cytochrome oxidase I (COI) regions in the mitochondrial genome. The proportion of overall genetic variation (FST) between the two species was small (0.042, P < 0.01) based on allele frequencies at five microsatellite loci. We confirm that a third blacktip species (C. amblyrhynchoides, graceful Shark) is closely related to C. tilstoni and C. limbatus and can be distinguished from them on the basis of mtDNA sequences from two gene regions. The Australian blacktip Shark (C. tilstoni) was not encountered among 20 samples from central Indonesia that were later confirmed to be common blacktip and graceful Sharks. Fisheries regulators urgently need new information on life history, population structure and morphological characters for species identification of blacktip Shark species in Australia.
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Towards better management of Australia’s Shark Fishery: genetic analyses reveal unexpected ratios of cryptic blacktip species Carcharhinus tilstoni and C. limbatus
Marine and Freshwater Research, 2010Co-Authors: Jennifer R. Ovenden, Jess A. T. Morgan, Tom Kashiwagi, Damien Broderick, J. P. SaliniAbstract:The common blacktip Shark (Carcharhinus limbatus) and the Australian blacktip Shark (C. tilstoni) are morphologically similar species that co-occur in subtropical and tropical Australia. In striking contrast to what has been previously reported, we demonstrate that the common blacktip Shark is not rare in northern Australia but occurs in approximately equal frequencies with the Australian blacktip Shark. Management of Shark resources in northern Australia needs to take account of this new information. Species identification was performed using nucleotide sequences of the control, NADH dehydrogenase subunit 4 (ND4) and cytochrome oxidase I (COI) regions in the mitochondrial genome. The proportion of overall genetic variation (FST) between the two species was small (0.042, P < 0.01) based on allele frequencies at five microsatellite loci. We confirm that a third blacktip species (C. amblyrhynchoides, graceful Shark) is closely related to C. tilstoni and C. limbatus and can be distinguished from them on the basis of mtDNA sequences from two gene regions. The Australian blacktip Shark (C. tilstoni) was not encountered among 20 samples from central Indonesia that were later confirmed to be common blacktip and graceful Sharks. Fisheries regulators urgently need new information on life history, population structure and morphological characters for species identification of blacktip Shark species in Australia.