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Mark N Maunder - One of the best experts on this subject based on the ideXlab platform.
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can Steepness of the stock recruitment relationship be estimated in fishery stock assessment models
Fisheries Research, 2012Co-Authors: Mark N Maunder, Kevin R Piner, Richard D MethotAbstract:Abstract Steepness of the stock–recruitment relationship is one of the most uncertain and critical quantities in fishery stock assessment and management. Steepness is defined as the fraction of recruitment from a virgin population obtained when the spawners are at 20% of the virgin level. Steepness directly relates to productivity and yield and is an important element in the calculation of many management reference points. Stock–recruitment relationships have traditionally been estimated from time series of recruitment and spawning biomass, but recently interest has arisen regarding the ability to estimate Steepness inside fishery stock assessment models. We evaluated the ability to estimate Steepness of the Beverton–Holt stock–recruitment relationship using simulation analyses for twelve US Pacific Coast fish stocks. A high proportion of Steepness estimates from the simulated data and the original data occur at the bounds for Steepness and the proportion decreased as the true Steepness decreased. The simulation results indicate that, in most cases, Steepness was estimated with moderate to low precision and moderate to high bias. The poorly estimated Steepness indicates that often there is little information in the data about this quantity. However, reliable estimation is attainable with a good contrast of spawning stock biomass for relatively unproductive stocks when the model is correctly specified.
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evaluating the stock recruitment relationship and management reference points application to summer flounder paralichthys dentatus in the u s mid atlantic
Fisheries Research, 2012Co-Authors: Mark N MaunderAbstract:Abstract The stock–recruitment relationship is one of the most uncertain processes of fish population dynamics, and is highly influential with respect to fisheries management advice. The stock recruitment relationship has a direct impact on reference points commonly used in contemporary fisheries management. Simulation analysis has shown that the Steepness of the Beverton–Holt stock–recruitment relationship is difficult to estimate for most fish stocks, which has led to the use of proxy reference points. Proxy maximum sustainable yield reference points based on spawning biomass-per-recruit, which are commonly used when the stock–recruitment relationship is uncertain, are a linear function of Steepness. Risk in terms of lost yield is generally lower when Steepness is underestimated compared to when Steepness is overestimated because the yield curve is flat when Steepness is high (close to one: recruitment is independent of stock size), indicating that using a lower value of Steepness might be appropriate. Simulation analysis based on data for summer flounder in the US mid-Atlantic indicates that Steepness can be estimated from the data. Steepness is estimated to be close to one and a high Steepness is supported by estimates for related species and from life history theory. Current target ( F 35% ) and threshold ( F 40% ) spawning biomass-per-recruit reference points used for summer flounder imply Steepness values of 0.73 and 0.66, respectively, for the Beverton–Holt stock–recruitment relationship.
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implications of uncertainty in the spawner recruitment relationship for fisheries management an illustration using bigeye tuna thunnus obesus in the eastern pacific ocean
Fisheries Research, 2012Co-Authors: Mark N Maunder, Yong Chen, Shelton J Harley, Simon D Hoyle, Alexandre AiresdasilvaAbstract:Abstract The impacts of the Steepness parameter of the Beverton–Holt spawner–recruitment curve on fisheries stock assessment and management performance were evaluated, using data for bigeye tuna (Thunnus obesus) in the eastern Pacific Ocean. The analysis was conducted using the Stock Synthesis model. The estimates of maximum sustainable yield (MSY) and related management reference points are sensitive to the value of Steepness (ranging from 0.4 to 1.0) of the Beverton–Holt spawner–recruitment relationship assumed in the assessment model. Steepness also impacts the evaluation of stock status. A lesser value assumed for Steepness leads to a more pessimistic evaluation of the stock status regarding whether the stock is overfished or overfishing is occurring. However, a lesser value does not reduce the estimates of MSY due to the interaction between Steepness and the estimates of other model parameters. When managing the stock under effort limitation using MSY-based fishing mortality, a lower assumption of Steepness yields less expected losses in catch than does a higher assumption. This is due to the flatness of the yield curve when the Steepness is high. A lower assumption of Steepness also maintains a higher level of spawning biomass and recruitment.
Marc Mangel - One of the best experts on this subject based on the ideXlab platform.
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a perspective on Steepness reference points and stock assessment
Canadian Journal of Fisheries and Aquatic Sciences, 2013Co-Authors: Marc Mangel, Alec D Maccall, Jon K T Brodziak, Robyn E Forrest, Roxanna Pourzand, Stephen RalstonAbstract:We provide a perspective on Steepness, reference points for fishery management, and stock assessment. We first review published data and give new results showing that key reference points are fixed when Steepness and other life history parameters are fixed in stock assessments using a Beverton-Holt stock-recruitment relationship. We use both production and age-structured models to explore these patterns. For the production model, we derive explicit relationships for Steepness and life history parameters and then for Steepness and major reference points. For the age-structured model, we are required to generally use numerical computation, and so we provide an example that complements the analytical results of the production model. We discuss what it means to set Steepness equal to 1 and how to construct a prior for Steepness. Ways out of the difficult situation raised by fixing Steepness and life history parameters include not fixing them, using a more complicated stock-recruitment relationship, and being more explicit about the information content of the data and what that means for policy makers. We discuss the strengths and limitations of each approach. Resume : Nous offrons une perspective sur l'inclinaison, les points de reference pour la gestion des peches et l'evaluation des stocks. Nous passons d'abord en revue les resultats publies et presentons de nouveaux resultats qui demontrent que des points de reference cles sont fixes quand l'inclinaison et d'autres parametres du cycle biologique sont fixes dans les evaluations des stocks reposant sur une relation stock-recrutement de type Beverton-Holt. Nous utilisons des modeles de production et structures par âge pour explorer ces situations. En ce qui concerne le modele de production, nous obtenons des relations explicites pour l'inclinaison et les parametres du cycle biologique, puis pour l'inclinaison et les principaux points de reference. Pour le modele structure par âge, nous devons generalement utiliser une approche numerique et presentons un exemple qui complemente les resultats analytiques du modele de production. Nous discutons de ce que signifie le fait de fixer la valeur de l'inclinaison a ` 1 et de la maniere d'etablir un a priori pour l'inclinaison. Parmi les moyens pour contourner la difficulte soulevee par la fixation de l'inclinaison et des parametres du cycle biologique figurent le fait de ne pas fixer ces valeurs, l'utilisation d'une relation stock-recrutement plus complexe et une approche plus explicite en ce qui concerne le contenu en information des donnees et ce que cela signifie pour les responsables de l'elaboration de politiques. Nous abordons les forces et les limites de chacune de ces approches. (Traduit par la Redaction)
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reproductive ecology and scientific inference of Steepness a fundamental metric of population dynamics and strategic fisheries management
Fish and Fisheries, 2010Co-Authors: Marc Mangel, Jon Brodziak, Gerard DinardoAbstract:The relationship between the biomass of reproductively mature individuals (spawning stock) and the resulting offspring added to the population (recruitment), the stock‐recruitment relationship, is a fundamental and challenging problem in all of population biology. The Steepness of this relationship is commonly defined as the fraction of recruitment from an unfished population obtained when the spawning stock biomass is 20% of its unfished level. Since its introduction about 20 years ago, Steepness has become widely used in fishery management, where it is usually treated as a statistical quantity. Here, we investigate the reproductive ecology of Steepness, using both unstructured and age-structured models. We show that if one has sufficient information to construct a density-independent population model (maximum per capita productivity and natural mortality for the unstructured case or maximum per capita productivity, natural mortality and schedules of size and maturity at age for the structured model) then one can construct a point estimate for Steepness. Thus, Steepness cannot be chosen arbitrarily. If one assumes that the survival of recruited individuals fluctuates within populations, it is possible, by considering the early life history, to construct a prior distribution for Steepness from this same demographic information. We develop the ideas for both compensatory (Beverton‐Holt) and over-compensatory (Ricker) stock‐recruitment relationships. We illustrate our ideas with an example concerning bluefin tuna (Thunnus thynnus/ orientalis, Scombridae). We show that assuming that Steepness is unity when recruitment is considered to be environmentally driven is not biologically consistent, is inconsistent with a precautionary approach, and leads to the wrong scientific inference (which also applies for assigning Steepness any other single value).
Takanori Hino - One of the best experts on this subject based on the ideXlab platform.
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rans investigation of influence of wave Steepness on ship motions and added resistance in regular waves
Journal of Marine Science and Technology, 2018Co-Authors: Si Chen, Takanori HinoAbstract:The motions and added resistance of the S175 containership in regular head waves with different wave Steepness under the same wavelength are investigated using a Reynolds-averaged Navier–Stokes solver based on a finite-volume method. A level set method is used to capture the free surface and dynamic grids are adopted to simulate ship motions. The variation of heave and pitch motions and added resistance with the wave Steepness agrees with the experiment. The higher harmonic components of surge force obtained by the Fourier analysis increase dramatically as the wave Steepness increases, while the higher harmonics of heave and pitch are quite small compared to the first harmonics even under large wave Steepness. The transient pressure distributions are studied to explain the non-harmonic oscillations of the time history of resistance coefficient. The zeroth, first, and second harmonic amplitudes of pressure are plotted on the hull and the major part of resistance increase in steeper waves is found to be induced at the bow.
Richard D Methot - One of the best experts on this subject based on the ideXlab platform.
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can Steepness of the stock recruitment relationship be estimated in fishery stock assessment models
Fisheries Research, 2012Co-Authors: Mark N Maunder, Kevin R Piner, Richard D MethotAbstract:Abstract Steepness of the stock–recruitment relationship is one of the most uncertain and critical quantities in fishery stock assessment and management. Steepness is defined as the fraction of recruitment from a virgin population obtained when the spawners are at 20% of the virgin level. Steepness directly relates to productivity and yield and is an important element in the calculation of many management reference points. Stock–recruitment relationships have traditionally been estimated from time series of recruitment and spawning biomass, but recently interest has arisen regarding the ability to estimate Steepness inside fishery stock assessment models. We evaluated the ability to estimate Steepness of the Beverton–Holt stock–recruitment relationship using simulation analyses for twelve US Pacific Coast fish stocks. A high proportion of Steepness estimates from the simulated data and the original data occur at the bounds for Steepness and the proportion decreased as the true Steepness decreased. The simulation results indicate that, in most cases, Steepness was estimated with moderate to low precision and moderate to high bias. The poorly estimated Steepness indicates that often there is little information in the data about this quantity. However, reliable estimation is attainable with a good contrast of spawning stock biomass for relatively unproductive stocks when the model is correctly specified.
L Van Heukelem - One of the best experts on this subject based on the ideXlab platform.
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simultaneous variation of temperature and gradient Steepness for reversed phase high performance liquid chromatography method development ii the use of further changes in conditions
Journal of Chromatography A, 1998Co-Authors: J W Dolan, L R Snyder, D L Saunders, L Van HeukelemAbstract:The preceding paper (Part I) suggests that simply optimizing temperature and gradient Steepness will often provide an adequate reversed-phase HPLC separation. In some cases, however, this procedure will prove unsuccessful, and then further method-development experiments (involving change in other separation conditions) will be required. One strategy is to change a variable other than temperature or gradient Steepness, followed by re-optimization of the latter two variables. The present paper examines the application of this approach with the aid of computer simulation to several samples.
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combined use of temperature and solvent strength in reversed phase gradient elution iii selectivity for ionizable samples as a function of sample type and ph
Journal of Chromatography A, 1996Co-Authors: P L Zhu, J W Dolan, L R Snyder, D W Hill, L Van Heukelem, T J WaegheAbstract:The ability of temperature and gradient Steepness to change band spacing has been investigated for several ionizable samples that include 8 substituted benzoic acids, 9 substituted anilines, 22 basic drugs, 9 structurally-related herbicide impurities, 7 chlorophylls and 72 peptides and proteins. Mobile phase pH was also varied to determine the effect of sample ionization on temperature and gradient-Steepness selectivity.
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combined use of temperature and solvent strength in reversed phase gradient elution iv selectivity for neutral non ionized samples as a function of sample type and other separation conditions
Journal of Chromatography A, 1996Co-Authors: P L Zhu, J W Dolan, L R Snyder, D W Hill, N M Djordjevic, Jianntsyh Lin, Lane C Sander, L Van HeukelemAbstract:The separation of nine un-ionized samples was studied as a function of temperature (T) and gradient Steepness (b). Selectivity values Δlog α∗ were obtained for 160 compounds, ranging from nonpolar hydrocarbons to very polar drugs. Selectivity varied markedly with sample type: nonpolar compounds such as aromatic hydrocarbons and fatty acid methyl esters generally showed only modest changes in band spacing as temperature or gradient Steepness was varied. More polar samples exhibited larger changes in α (Δlog α∗) when temperature and/or gradient Steepness wee changed, but the largest values of Δlog α∗ for these non-ionized samples are less than the average value of Δlog α∗ for the ionized samples of Part III [1]. Poly-functional silane (“polymeric”) columns exhibit slightly increased b- and/or T-selectivity for some samples.
