The Experts below are selected from a list of 9072 Experts worldwide ranked by ideXlab platform
Carl J. Walters - One of the best experts on this subject based on the ideXlab platform.
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adaptive management of declining fisheries when is it worth trying to rebuild stocks through fishery regulation
Marine Policy, 2017Co-Authors: A Benhasan, Mohsen Alhusaini, Carl J. WaltersAbstract:Abstract Declining catches are typically taken to be a warning sign of overfishing. But in fact, many such declines have been driven by recruitment changes unrelated to stock size, as evidenced by the failure of stocks to recover after reduction in fishing or recovery despite the failure to reduce fishing. Given a declining pattern, supposedly precautionary decisions to reduce fishing should be treated as experimental management options with a high probability of not resulting in the desired recovery to more productive stock sizes. Simple decision tables can be used to compare such experimental options to “wait and see” options that do not involve fishing reductions. A case example with a grouper fishery in Kuwait demonstrates that experimental effort reduction may not be the best policy from a decision Analysis perspective, at least when there are substantial reasons to expect recruitment changes unrelated to stock size. In this case, Virtual Population Analysis and stock reduction Analysis models indicate either unusually weak recruitment compensation (steepness h
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age structured mark recapture Analysis a Virtual Population Analysis based model for analyzing age structured capture recapture data
North American Journal of Fisheries Management, 2006Co-Authors: Lewis G Coggins, Carl J. Walters, William E Pine, Steven J D MartellAbstract:Abstract We present a new model to estimate capture probabilities, survival, abundance, and recruitment using traditional Jolly–Seber capture–recapture methods within a standard fisheries Virtual Population Analysis framework. This approach compares the numbers of marked and unmarked fish at age captured in each year of sampling with predictions based on estimated vulnerabilities and abundance in a likelihood function. Recruitment to the earliest age at which fish can be tagged is estimated by using a Virtual Population Analysis method to back-calculate the expected numbers of unmarked fish at risk of capture. By using information from both marked and unmarked animals in a standard fisheries age structure framework, this approach is well suited to the sparse data situations common in long-term capture–recapture programs with variable sampling effort.
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placing odds on sustainable catch using Virtual Population Analysis and survey data
Canadian Journal of Fisheries and Aquatic Sciences, 1994Co-Authors: Carl J. Walters, Andre E PuntAbstract:Virtual Population Analysis (VPA) is often used in conjunction with survey data to provide estimates of current stock size and an allowable catch that is sustainable in the sense that it is expected to produce some desired trend (or stability) in stock size. But these estimates are generally very uncertain, and should be accompanied by statements about the odds of sustainability for a range of allowable catch options. The odds can be expressed as an easily understood short-term risk function, but potential cumulative risks associated with the function should be simulated as a long-term guide for management. Bayesian estimates of the odds of sustainability can be calculated using the likelihood function of the survey data for different current stock size and natural mortality rate possibilities, with estimates of expected recruitment and recruitment variability. Prerecruitment year classes in the survey are included in the calculation of expected recruitment and its uncertainty, allowing use of survey data...
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quantitative fisheries stock assessment choice dynamics and uncertainty
1992Co-Authors: Ray Hilborn, Carl J. WaltersAbstract:I Introduction.- 1 Role of Stock Assessment in Fisheries Management.- 2 Objectives of Fisheries Management.- II Behavior of Fisheries.- 3 Behavior of Exploited Populations.- 4 The Dynamics of Fishing Fleets.- III Estimation of Parameters.- 5 Observing Fish Populations.- 6 Relating Models to Data: Parameter Estimation.- 7 Stock and Recruitment.- 8 Biomass Dynamic Models.- 9 Delay Difference Models.- 10 Virtual Population Analysis.- 11 Statistical Catch-at-age Methods.- 12 Depletion Estimates of Population Size and Turnover.- 13 Analysis of Body-size and Growth Data.- 14 Multispecies Analysis.- IV Managing Fisheries.- 15 Harvest Strategies and Tactics.- 16 Optimization.- 17 Designing Adaptive Management Policies.- 18 Making Stock Assessment and Management Work.- Author Index.
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Virtual Population Analysis
1992Co-Authors: Ray Hilborn, Carl J. WaltersAbstract:The most common methods currently used in temperate fisheries stock assessments rely on catch-at-age data. While these methods are often referred to collectively as catch-at-age methods, we like to think of them as divisible into two classes of models. The first, commonly called Virtual Population Analysis (VPA) or cohort Analysis methods are recursive algorithms that calculate stock size based on catches with no underlying statistical assumptions. These methods are covered in this chapter. The second class of catch-at-age methods rely on formal statistical models and we consider these in the next chapter (Chapter 11) entitled “Statistical Catch-at-Age Methods.” Megrey (1989) provides an excellent review of all of these methods
Patricia A. Livingston - One of the best experts on this subject based on the ideXlab platform.
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A multispecies Virtual Population Analysis of the eastern
2014Co-Authors: Bering Sea, Patricia A. Livingston, Jesus Jurado-molinaAbstract:The eastern Bering Sea shelf supports a large biomass of several groundfish Populations, particularly walleye pollock (Theragra chalcogramma). The main trophic interactions between dominant groundfish Populations in this region involve walleye pollock as prey. A multispecies Virtual Population Analysis model (MSVPA) covering the period 1979–1995 has been parameterized for the eastern Bering Sea in order to move closer to providing multispecies management advice for this region. The MSVPA model is based on extensive diet data from 70 predator/prey/year/quarter combinations and currently includes the following species as predators: walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), Greenland turbot (Reinhardtius hippoglossoides), yellowfin sole (Pleuronectes asper), arrowtooth flounder (Atheresthes stomias), and northern fur seal (Callorhinus ursinus). Arrowtooth flounder and northern fur seals are entered as ‘‘other predators’’, which means that Population and mortality estimates are not directly made for these species. Estimates of their consumption rates, diet, and Population abundance are input, however, so that their predation on prey species in the model can be calculated. Prey species are walley
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testing the stability of the suitability coefficients from an eastern bering sea multispecies Virtual Population Analysis
Ices Journal of Marine Science, 2005Co-Authors: Jesus Juradomolina, Patricia A. Livingston, Vincent F GallucciAbstract:Suitability coefficients are important for the estimation of predation mortality in a multispecies Virtual Population Analysis (MSVPA) and subsequent use in the multispecies forecasting model (MSFOR). Testing the assumption of the stability of the suitability coefficients is important in assessing the robustness of the predictions made with MSFOR. We used different statistical methods to partially test this assumption for the eastern Bering Sea MSVPA model with eight species, using stomach content data for the years 1985e1989. Comparison of the estimates from two different sets of stomach content data (set one with all data and set two mainly with data from 1985) suggested that the differences between the two types of estimates were much reduced when the number of predator stomachs sampled increased. In a second approach, we contrasted the residual variances of partial data sets with the results from the fit of the total data set. Results suggested a small increase (w10.8%) in the variation of the suitability coefficients. Comparison of the means of the suitability coefficients associated with each predator species suggests that only 13 of the 50 possible pairwise contrasts were significantly different (aZ 0.05). In general, results suggested that the predator preferences and prey vulnerabilities remained stable over the time period studied. Therefore, MSFOR could be considered as a tool to advise fisheries managers within a multispecies context.
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Sensitivity Analysis of the multispecies Virtual Population Analysis model parameterized for a system of trophically-linked species from the eastern Bering Sea Análisis de sensibilidad del modelo de análisis poblacional Virtual multiespecífico aplicado a un sistema de especies relacionadas tróficamente del Mar de Bering Oriental
2004Co-Authors: Jesus Jurado-molina, Patricia A. LivingstonAbstract:A sensitivity Analysis of a multispecies Virtual Population Analysis (MSVPA) model parameterized for the Bering Sea was carried out using two methods for the Analysis. In the first method, four variables related to the predation mortality M2 and Population size of age-1 walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus) were chosen as response variables. Results suggested that the response variables of walleye pollock were sensitive to the residual mortality M1 of walleye pollock, the stock size of arrowtooth flounder (Atheresthes stomias) and ration of both predator species. Pacific cod response variables were sensitive only to variables related to Pacific cod. These results reinforce the importance of cannibalism in the dynamics of walleye pollock and Pacific cod. Results from the individual perturbation parameter Analysis showed that the changes produced by large positive perturbations in the “other food” parameter were small. The overall results suggest that the MSVPA model can be considered robust. These results help to recognize the potential use of MSVPA as a tool to assist in broadening the management of the fishery resources from the Bering Sea within a multispecies perspective.
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A multispecies Virtual Population Analysis of the eastern Bering Sea
ICES Journal of Marine Science, 2000Co-Authors: Patricia A. Livingston, Jesus Jurado-molinaAbstract:The eastern Bering Sea shelf supports a large biomass of several groundfish Populations, particularly walleye pollock (Theragra chalcogramma). The main trophic interactions between dominant groundfish Populations in this region involve walleye pollock as prey. A multispecies Virtual Population Analysis model (MSVPA) covering the period 1979–1995 has been parameterized for the eastern Bering Sea in order to move closer to providing multispecies management advice for this region. The MSVPA model is based on extensive diet data from 70 predator/prey/year/quarter combinations and currently includes the following species as predators: walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), Greenland turbot (Reinhardtius hippoglossoides), yellowfin sole (Pleuronectes asper), arrowtooth flounder (Atheresthes stomias), and northern fur seal (Callorhinus ursinus). Arrowtooth flounder and northern fur seals are entered as ‘‘other predators’’, which means that Population and mortality estimates are not directly made for these species. Estimates of their consumption rates, diet, and Population abundance are input, however, so that their predation on prey species in the model can be calculated. Prey species are walleye pollock, Pacific cod, Greenland turbot, yellowfin sole, rock sole (Lepidopsetta bilineatus), and Pacific herring (Clupea pallasi). Results show that large numbers of walleye pollock, particularly age-0 and age-1 fish, are consumed and cannibalism by adult pollock constitutes the largest source of predation mortality for age-0 fish. Predation plays an important role in explaining the recruitment dynamics of pollock. Further advances may be made when these estimates are linked to models that examine the effect of climate-related factors influencing larval survival. 2000 International Council for the Exploration of the Sea
Patrice Brehmer - One of the best experts on this subject based on the ideXlab platform.
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Bonga shad (Ethmalosa fimbriata) spawning tactics in an upwelling environment
Fisheries Oceanography, 2019Co-Authors: Bocar Sabaly Balde, Julian Doering, Werner Ekau, Malick Diouf, Patrice BrehmerAbstract:Successful recruitment in small pelagic fish Populations inhabiting upwelling zones is subject to variation in fecundity and is driven by spatial and temporal fluctuations in environmental conditions, that is, mainly sea surface temperature, salinity and food availability. These fluctuations in abiotic factors have stimulated small pelagic fish Populations to exhibit specifically adapted spawning tactics. To better understand to what extent a short-lived exploited fish species such as bonga shad Ethmalosa fimbriata has adapted to an upwelling environment, we have investigated the interrelationship between upwelling intensity as a proxy for productivity and Population fecundity by means of a Virtual Population Analysis. We found that females of intermediate size contributed significantly more eggs to the Population's fecundity than smaller or larger ones. Our model results further indicate that E. fimbriata exhibits a spawning preference at water temperatures of around 25 degrees C and upwelling intensities of around 2.5 m(3) s(-1) m(-1). Hence, we hypothesize that climate change-driven increases in sea temperatures and modifications of upwelling-favourable winds could significantly impact the species' reproductive biology. To understand how climate change might impact fisheries, spawning tactics of small pelagic fishes are important to assess as well as their recruitment success. Such information is particularly relevant in countries where the fishery is critical at socio-economic level, to better implement fisheries management addressing multiple stressors.
Jesus Jurado-molina - One of the best experts on this subject based on the ideXlab platform.
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A multispecies Virtual Population Analysis of the eastern
2014Co-Authors: Bering Sea, Patricia A. Livingston, Jesus Jurado-molinaAbstract:The eastern Bering Sea shelf supports a large biomass of several groundfish Populations, particularly walleye pollock (Theragra chalcogramma). The main trophic interactions between dominant groundfish Populations in this region involve walleye pollock as prey. A multispecies Virtual Population Analysis model (MSVPA) covering the period 1979–1995 has been parameterized for the eastern Bering Sea in order to move closer to providing multispecies management advice for this region. The MSVPA model is based on extensive diet data from 70 predator/prey/year/quarter combinations and currently includes the following species as predators: walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), Greenland turbot (Reinhardtius hippoglossoides), yellowfin sole (Pleuronectes asper), arrowtooth flounder (Atheresthes stomias), and northern fur seal (Callorhinus ursinus). Arrowtooth flounder and northern fur seals are entered as ‘‘other predators’’, which means that Population and mortality estimates are not directly made for these species. Estimates of their consumption rates, diet, and Population abundance are input, however, so that their predation on prey species in the model can be calculated. Prey species are walley
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Sensitivity Analysis of the multispecies Virtual Population Analysis model parameterized for a system of trophically-linked species from the eastern Bering Sea Análisis de sensibilidad del modelo de análisis poblacional Virtual multiespecífico aplicado a un sistema de especies relacionadas tróficamente del Mar de Bering Oriental
2004Co-Authors: Jesus Jurado-molina, Patricia A. LivingstonAbstract:A sensitivity Analysis of a multispecies Virtual Population Analysis (MSVPA) model parameterized for the Bering Sea was carried out using two methods for the Analysis. In the first method, four variables related to the predation mortality M2 and Population size of age-1 walleye pollock (Theragra chalcogramma) and Pacific cod (Gadus macrocephalus) were chosen as response variables. Results suggested that the response variables of walleye pollock were sensitive to the residual mortality M1 of walleye pollock, the stock size of arrowtooth flounder (Atheresthes stomias) and ration of both predator species. Pacific cod response variables were sensitive only to variables related to Pacific cod. These results reinforce the importance of cannibalism in the dynamics of walleye pollock and Pacific cod. Results from the individual perturbation parameter Analysis showed that the changes produced by large positive perturbations in the “other food” parameter were small. The overall results suggest that the MSVPA model can be considered robust. These results help to recognize the potential use of MSVPA as a tool to assist in broadening the management of the fishery resources from the Bering Sea within a multispecies perspective.
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A multispecies Virtual Population Analysis of the eastern Bering Sea
ICES Journal of Marine Science, 2000Co-Authors: Patricia A. Livingston, Jesus Jurado-molinaAbstract:The eastern Bering Sea shelf supports a large biomass of several groundfish Populations, particularly walleye pollock (Theragra chalcogramma). The main trophic interactions between dominant groundfish Populations in this region involve walleye pollock as prey. A multispecies Virtual Population Analysis model (MSVPA) covering the period 1979–1995 has been parameterized for the eastern Bering Sea in order to move closer to providing multispecies management advice for this region. The MSVPA model is based on extensive diet data from 70 predator/prey/year/quarter combinations and currently includes the following species as predators: walleye pollock (Theragra chalcogramma), Pacific cod (Gadus macrocephalus), Greenland turbot (Reinhardtius hippoglossoides), yellowfin sole (Pleuronectes asper), arrowtooth flounder (Atheresthes stomias), and northern fur seal (Callorhinus ursinus). Arrowtooth flounder and northern fur seals are entered as ‘‘other predators’’, which means that Population and mortality estimates are not directly made for these species. Estimates of their consumption rates, diet, and Population abundance are input, however, so that their predation on prey species in the model can be calculated. Prey species are walleye pollock, Pacific cod, Greenland turbot, yellowfin sole, rock sole (Lepidopsetta bilineatus), and Pacific herring (Clupea pallasi). Results show that large numbers of walleye pollock, particularly age-0 and age-1 fish, are consumed and cannibalism by adult pollock constitutes the largest source of predation mortality for age-0 fish. Predation plays an important role in explaining the recruitment dynamics of pollock. Further advances may be made when these estimates are linked to models that examine the effect of climate-related factors influencing larval survival. 2000 International Council for the Exploration of the Sea
Bocar Sabaly Balde - One of the best experts on this subject based on the ideXlab platform.
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Bonga shad (Ethmalosa fimbriata) spawning tactics in an upwelling environment
Fisheries Oceanography, 2019Co-Authors: Bocar Sabaly Balde, Julian Doering, Werner Ekau, Malick Diouf, Patrice BrehmerAbstract:Successful recruitment in small pelagic fish Populations inhabiting upwelling zones is subject to variation in fecundity and is driven by spatial and temporal fluctuations in environmental conditions, that is, mainly sea surface temperature, salinity and food availability. These fluctuations in abiotic factors have stimulated small pelagic fish Populations to exhibit specifically adapted spawning tactics. To better understand to what extent a short-lived exploited fish species such as bonga shad Ethmalosa fimbriata has adapted to an upwelling environment, we have investigated the interrelationship between upwelling intensity as a proxy for productivity and Population fecundity by means of a Virtual Population Analysis. We found that females of intermediate size contributed significantly more eggs to the Population's fecundity than smaller or larger ones. Our model results further indicate that E. fimbriata exhibits a spawning preference at water temperatures of around 25 degrees C and upwelling intensities of around 2.5 m(3) s(-1) m(-1). Hence, we hypothesize that climate change-driven increases in sea temperatures and modifications of upwelling-favourable winds could significantly impact the species' reproductive biology. To understand how climate change might impact fisheries, spawning tactics of small pelagic fishes are important to assess as well as their recruitment success. Such information is particularly relevant in countries where the fishery is critical at socio-economic level, to better implement fisheries management addressing multiple stressors.
