scholarly journals Assessment of offshore shrimp stocks of Bangladesh based on commercial shrimp trawl logbook data

2018 ◽  
Vol 65 (1) ◽  
Author(s):  
Suman Barua ◽  
Arni Magnusson ◽  
Nasiruddin MD Humayun
Keyword(s):  
Confidence Intervals ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Assessment Model ◽  
Catch Per Unit Effort ◽  
Harvest Rate ◽  
Stock Size ◽  
Considerable Uncertainty ◽  
Logbook Data

This study presents the results of analytical assessment of offshore shrimp stock in Bangladesh marine waters. A time series of annual catch per unit effort (CPUE) was derived from commercial logbook data during the period from 1986 to 2016 and used as a turning series for a Schaefer biomass model. The current stock size and annual harvest rate were estimated to be around 20300 t and 20% respectively, with the stock size increasing in the last ten years. The estimated maximum sustainable yield (MSY) reference points with 95% confidence intervals are optimal biomass BMSY = 15800 t (11300-22000 t) and optimal harvest rate uMSY = 30% (21-42%). The average annual catch was 4650 t, close to the estimated MSY of 4710 t (4570-4860 t). Overall, the stock is estimated to be in a good state and the data show that CPUE in recent years is slightly above the long-term average. The assessment results are subject to considerable uncertainty, reflected in wide confidence intervals around the estimated stock status. Moreover, the simple assessment model has restrictive assumptions that may not capture the underlying dynamics of the Bangladesh shrimp fishery, a multispecies tropical fishery with changes in the fleet composition and fishing technology. Nevertheless, the model fits well to the CPUE data and the assessment is a valuable basis for giving short-term and long-term management advice.

scholarly journals An explicit solution for calculating optimum spawning stock size from Ricker’s stock recruitment model

PeerJ ◽  
2016 ◽  
Vol 4 ◽  
pp. e1623 ◽  
Author(s):  
Mark D. Scheuerell
Keyword(s):  
Explicit Solution ◽  
Model Fitting ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Stock Size ◽  
Points Of Interest ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Explicit Formulae ◽  
Recruitment Model

Stock-recruitment models have been used for decades in fisheries management as a means of formalizing the expected number of offspring that recruit to a fishery based on the number of parents. In particular, Ricker’s stock recruitment model is widely used due to its flexibility and ease with which the parameters can be estimated. After model fitting, the spawning stock size that produces the maximum sustainable yield (SMSY) to a fishery, and the harvest corresponding to it (UMSY), are two of the most common biological reference points of interest to fisheries managers. However, to date there has been no explicit solution for either reference point because of the transcendental nature of the equation needed to solve for them. Therefore, numerical or statistical approximations have been used for more than 30 years. Here I provide explicit formulae for calculating bothSMSYandUMSYin terms of the productivity and density-dependent parameters of Ricker’s model.

scholarly journals Objectives and harvest control rules in the management of the fishery of Norwegian spring-spawning herring

2009 ◽  
Vol 66 (8) ◽  
pp. 1793-1799 ◽  
Author(s):  
Sigurd Tjelmeland ◽  
Ingolf Røttingen
Keyword(s):  
Stock Assessment ◽  
Maximum Sustainable Yield ◽  
Assessment Model ◽  
Main Element ◽  
Management Objectives ◽  
Control Rules ◽  
Harvest Control Rule ◽  
Stock Recruitment ◽  
Harvest Control Rules

Abstract Tjelmeland, S., and Røttingen, I. 2009. Objectives and harvest control rules in the management of the fishery of Norwegian spring-spawning herring. – ICES Journal of Marine Science, 66: 1793–1799. The main element in the management of the Norwegian spring-spawning herring, as implemented by the coastal states, is to conduct the fishery based on a maximum fishing mortality (F) of 0.125. As the appropriateness of this rule (given the stated objectives) has not yet been tested thoroughly, we set out to do this by long-term simulations, in which we applied a range of alternative stock–recruitment relationships. These different relationships are estimated from historical replicates of the stock, as calculated by the herring-stock assessment model SeaStar. During prognostic simulations, a recruitment model is selected probabilistically for each historical replicate based on Akaike weights. We evaluate whether the management objectives are met by applying the present harvest control rule. Results are given for the current assessment option of natural mortality (M = 0.5) in the oldest aggregated age group and for the assessment option used in 2005 and earlier (M = 0.15). These show that perceptions of the long-term yield differ considerably and that the current management is somewhat on the conservative side from the perspective of maximum sustainable yield.

scholarly journals Bioeconomic multistock reference points as a tool for overcoming the drawbacks of the landing obligation

2016 ◽  
Vol 74 (2) ◽  
pp. 511-524 ◽  
Author(s):  
Dorleta García ◽  
Raúl Prellezo ◽  
Paz Sampedro ◽  
José María Da-Rocha ◽  
José Castro ◽  
...  
Keyword(s):  
Economic Performance ◽  
Net Present Value ◽  
Policy Reform ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Present Value ◽  
Fisheries Policy ◽  
Fleet Dynamics ◽  
The Impact

The landing obligation policy was one of the major innovations introduced in the last Common Fisheries Policy reform in Europe. It is foreseen that the policy will affect the use of fishing opportunities and hence the economic performance of the fleets. The problem with fishing opportunities could be solved if single-stock total allowable catches (TACs) could be achieved simultaneously for all the stocks. In this study, we evaluate the economic impact of the landing obligation policy on the Spanish demersal fleet operating in the Iberian Sea region. To generate TAC advice, we used two sets of maximum sustainable yield (MSY) reference points, the single-stock MSY reference points defined by ICES and a set of multistock reference points calculated simultaneously using a bioeconomic optimization model. We found that the impact of the landing obligation is time and fleet dependent and highly influenced by assumptions about fleet dynamics. At fishery level, multistock reference points mitigate the decrease in the net present value generated by the implementation of the landing obligation. However at fleet level, the effect depends on the fleet itself and the period. To ensure the optimum use of fishing opportunities, the landing obligation should be accompanied by a management system that guarantees consistency between single-stock TACs. In this regard, multistock reference points represent an improvement over those currently in use. However, further investigation is necessary to enhance performance both at fleet level and in the long term.

scholarly journals Evidence of overfishing of geoduck clam Panopea globosa from a length-based stock assessment approach

PeerJ ◽  
2020 ◽  
Vol 8 ◽  
pp. e9069
Author(s):  
Marlene A. Luquin-Covarrubias ◽  
Enrique Morales-Bojórquez ◽  
Juan A. García-Borbón ◽  
Sergio Amezcua-Castro ◽  
Sergio A. Pérez-Valencia ◽  
...  
Keyword(s):  
Stock Assessment ◽  
Growth Patterns ◽  
Reference Points ◽  
Assessment Model ◽  
Individual Growth ◽  
Biological Traits ◽  
Total Biomass ◽  
Fishing Mortality ◽  
Harvest Rate ◽  
Assessment Approach

Stock assessment of the geoduck clam Panopea globosa in Mexico has been based on data-poor without consideration of the biological traits of the species, promoting a passive management strategy without biological reference points for its harvest and conservation, which results in limited advice regarding the sustainability of the fishery. The stock assessment was supported on an integrated catch-at-size assessment model. The model described the population changes, including recruitment, selectivity, fishing mortality, individual growth patterns and survival over time, providing management quantities for the geoduck clam fishery, such as biomass-at-length (total and vulnerable) and harvest rate-at-length. The results indicated overfishing of the geoduck clam population; the harvest rate exceeded the management tactics established for this fishery, even the individuals smaller than the minimum legal size (130 mm) were harvested. Thus, declines in the total biomass (from 3,262 to 1,130 t) and recruitment (representing an 86% decrease) were observed from 2010 to 2012. Although the results showed a recovery trend in recruitment and total biomass from 2014 to 2016, this trend may have been due to the spatial relocation of fishing mortality.

scholarly journals Viability theory for an ecosystem approach to fisheries

2005 ◽  
Vol 62 (3) ◽  
pp. 577-584 ◽  
Author(s):  
Philippe M. Cury ◽  
Christian Mullon ◽  
Serge M. Garcia ◽  
Lynne J. Shannon
Keyword(s):  
Rural Communities ◽  
Marine Ecosystem ◽  
Optimal Solution ◽  
Ecosystem Approach ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Social Constraints ◽  
Viability Theory ◽  
Viability Kernel

Abstract Maintenance of overall ecosystem complexity is perceived as critical to the sustainability of ecosystem use. The development of an operational basis for an ecosystem approach to fisheries, however, faces many difficulties. On the research side, the challenge is in defining proper long-term, ecosystem-related objectives; determining meaningful reference values and indicators for desirable or undesirable states of the ecosystem; and developing appropriate data collection, analytical tools and models. The “viability” concept developed in economics by Jean-Pierre Aubin can be used to assist in the definition, selection of, and interaction among long-term objectives at an ecosystem level. It recognizes that ecosystems are complex assemblages of interacting and self-organizing natural and human components that cannot be predicted. Viability models define an ensemble of “viable states”, in contrast to undesirable states defined as such by ecological, economic, and/or social constraints. These constraints can be derived from fisheries objectives, conservation principles, scientific results of modelling, or precautionary principles, and correspond to limit reference points to be avoided. Viability theory does not attempt to choose any “optimal solution” according to given criteria, but selects “viable evolutions”. These evolutions are compatible with the constraints in the sense that they satisfy them at each time and can be delineated by the viability kernel. The southern Benguela marine ecosystem is presented as a first attempt for the application of this theory. In defining ecosystem-based objectives (and related issues such as target reference points), it seems more difficult to reach consensus among stakeholders on what is desirable than on what is undesirable (e.g. biological or economic collapse, species extinction, displacement of local rural communities). Expressed in the negative form or as limit reference points, ecosystem-based constraints can be considered simultaneously with current target reference points, such as maximum sustainable yield, using viability models. The viability approach can help to progressively integrate ecosystem considerations, such as conservation, into fisheries management.

scholarly journals An explicit solution for calculating optimum spawning stock size from Ricker's stock recruitment curve

2015 ◽  
Author(s):  
Mark D. Scheuerell
Keyword(s):  
Explicit Solution ◽  
Model Fitting ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Stock Size ◽  
Points Of Interest ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Explicit Formulae ◽  
Recruitment Model

Ricker’s stock recruitment model is widely used to describe the spawner-offspring relationship for fishes. After model fitting, the spawning stock size that produces the maximum sustainable yield (SMSY), and the harvest corresponding to it (UMSY), are two of the most common biological reference points of interest to fisheries managers. However, to date there has been no explicit solution for either reference point because of the transcendental nature of the equation needed to solve for them. Therefore, numerical or statistical approximations have been used for more than 30 years. Here I provide explicit formulae for calculating both SMSY and UMSY in terms of the productivity and density-dependent parameters from Ricker’s model.

scholarly journals Measuring fisheries management performance

2020 ◽  
Author(s):  
Ray Hilborn
Keyword(s):  
Fisheries Management ◽  
The United States ◽  
Maximum Sustainable Yield ◽  
Equal Weight ◽  
Sustainable Yield ◽  
Potential Yield ◽  
Stock Size ◽  
Regional Performance ◽  
Equal Weighting

Abstract How do we assess the performance of national and international fisheries management organizations? Many organizations produce measures of the extent of overfishing, typically classifying individual stocks as overfished if they are below some biomass threshold. Most agencies then report their overall status (i.e. percentage overfished, fully exploited, etc.) by giving equal weight to all stocks, regardless of stock size or potential yield. We review the range of indices used to assess overfishing levels and apply them to the data from US fisheries to show how they depict very different performance of fisheries. Given that overfishing is a concept imbedded in the maximization of long-term harvest, we evaluate how well these indices reflect the extent to which fisheries have maximized sustainable yield. Indices that are weighted by the potential yield of the stock much better reflect the regional performance of fisheries but are still limited by the arbitrary use of a threshold abundance. For the United States, weighting by maximum sustainable yield or value suggests that the losses from overfishing are less than existing methods using equal weighting and that underfishing is much more common than overfishing.

Evaluation of a management decision rule for a New Zealand rock lobster substock

1997 ◽  
Vol 48 (8) ◽  
pp. 1093 ◽  
Author(s):  
Paul J. Starr ◽  
Paul A. Breen ◽  
Ray H. Hilborn ◽  
Terese H. Kendrick
Keyword(s):  
New Zealand ◽  
Decision Rule ◽  
Maximum Sustainable Yield ◽  
Assessment Model ◽  
Management Decision ◽  
Catch Per Unit Effort ◽  
Rock Lobster ◽  
Management Actions ◽  
Age Structured ◽  
The Impact

The performance of a proposed management ‘decision rule’–an algorithm that specifies management actions when specified criteria are met–was evaluated by exploring the impact of different choices for three decision-rule parameters on the ability of the rule to achieve management objectives. To do this, forward simulations from an age-structured assessment model for the substock of red rock lobster (Jasus edwardsii) off southern New Zealand were used. The size of this substock is currently estimated to be about one-third of BMSY (the level of vulnerable biomass that would produce maximum sustainable yield), and the management goal is to rebuild it to BMSY. A target rebuilding trajectory to BMSY was generated by allowing the model population to rebuild under the current catch regime with constant recruitment. The decision rule is based on comparison of observed catch per unit effort (CPUE) to predicted CPUE. Process and observation errors, each with a coefficient of variation of 20%, were introduced, and five values were used for each of the three parameters of the rule. The decision rule was effective in removing all instances of failure to rebuild and all excessively slow rebuilding trajectories. The decision rule was also applied to an arbitrarily depressed starting substock size, and the conclusions were the same.

scholarly journals Fitting a non-parametric stock–recruitment model in R that is useful for deriving MSY reference points and accounting for model uncertainty

2012 ◽  
Vol 70 (1) ◽  
pp. 56-67 ◽  
Author(s):  
Noel G. Cadigan
Keyword(s):  
Confidence Intervals ◽  
Model Uncertainty ◽  
Fishery Management ◽  
Reference Points ◽  
Parametric Models ◽  
Parametric Approach ◽  
Stock Size ◽  
Stock Recruitment ◽  
Recruitment Model ◽  
Non Parametric

Abstract Cadigan, N. G. 2013. Fitting a non-parametric stock–recruitment model in R that is useful for deriving MSY reference points and accounting for model uncertainty. – ICES Journal of Marine Science, 70:56–67. Modelling the relationship between parental stock size and subsequent recruitment of fish to a fishery is often required when deriving reference points, which are a fundamental component of fishery management. A non-parametric approach to estimate stock–recruitment relationships is illustrated using a simulated example and nine case studies. The approach preserves compensatory density dependence in which the recruitment rate monotonically decreases as stock size increases, which is a basic assumption of commonly used parametric stock–recruitment models. The implications of the non-parametric estimates on maximum sustainable yield (MSY) reference points are illustrated. The approach is used to provide non-parametric bootstrapped confidence intervals for reference points. The efficacy of the approach is investigated using simulations. The results demonstrate that the non-parametric approach can provide a more realistic estimation of the stock–recruitment relationship when informative data are available compared with common parametric models. Also, bootstrap confidence intervals for MSY reference points based on different parametric stock–recruitment models often do not overlap. The confidence intervals based on the non-parametric approach tend to be much wider, and reflect better uncertainty due to stock–recruit model choice.

scholarly journals An explicit solution for calculating optimum spawning stock size from Ricker's stock recruitment curve

2015 ◽  
Author(s):  
Mark D. Scheuerell
Keyword(s):  
Explicit Solution ◽  
Model Fitting ◽  
Maximum Sustainable Yield ◽  
Reference Points ◽  
Stock Size ◽  
Points Of Interest ◽  
Spawning Stock ◽  
Stock Recruitment ◽  
Explicit Formulae ◽  
Recruitment Model

Ricker’s stock recruitment model is widely used to describe the spawner-offspring relationship for fishes. After model fitting, the spawning stock size that produces the maximum sustainable yield (SMSY), and the harvest corresponding to it (UMSY), are two of the most common biological reference points of interest to fisheries managers. However, to date there has been no explicit solution for either reference point because of the transcendental nature of the equation needed to solve for them. Therefore, numerical or statistical approximations have been used for more than 30 years. Here I provide explicit formulae for calculating both SMSY and UMSY in terms of the productivity and density-dependent parameters from Ricker’s model.

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