A discrete approach to continuum economies

We consider a perfectly competitive economy in which only a finite number of different agents' characteristics can be distinguished. We associate this economy with an n-agents' economy with an ordered Banach commodity space, and we prove that the continuum and the discrete approach to the equilibrium problem can be considered equivalent

A discrete approach to continuum economies.

We consider a perfectly competitive economy in which only a finite number of different agents' characteristics can be distinguished. We associate this economy with an n-agents' economy with an ordered Banach commodity space, and we prove that the continuum and the discrete approach to the equilibrium problem can be considered equivalent.Continuum economies; core; Walrasian equilibrium;

A note on representation of references.

We consider a class of relations which includes irreflexive preference relations and interdependent preferences. For this class, we obtain necessary and sufficient conditions for representation of the relation by two numerical functions in the sense of aPreference; Continuous representation; Pseudotransitivity; Biorders;

A note on representation of references

We consider a class of relations which includes irreflexive preference relations and interdependent preferences. For this class, we obtain necessary and sufficient conditions for representation of the relation by two numerical functions in the sense of a < x if and only if u(a) < v(x)

Endogenous Fishing Mortalities: a State-Space Bioeconomic Model

A methodology that endogenously determines catchability functions that link fi shing mortality with contemporaneous stock abundance is presented. We consider a stochastic age-structured model for a fishery composed by a number of fi shing units (fleets, vessels or métiers) that optimally select the level of fishing effort to be applied considering total mortalities as given. The introduction of a balance constrain which guarantees that total mortality is equal to the sum of individual fi shing mortalities optimally selected, enables total fishing mortality to be determined as a combination of contemporaneous abundance and stochastic processes affecting the fishery. In this way, future abundance can be projected as a dynamic system that depends on contemporaneous abundance. The model is generic and can be applied to several issues of fisheries management. In particular, we illustrate how to apply the methodology to assess the floating band target management regime for controlling fishing mortalities which is inspired in the new multi-annual plans. Our results support this management regime for the Mediterranean demersal fishery in Northern Spain.This work was funded by the European Commission as part of the MINOUW project (H2020-SFS-2014-2, number 634495) and the Spanish Ministry of Economy, Industry and Competitiveness (ECO2016-78819-R, AEI/FEDER, UE

Mitigación de las capturas no deseadas en la pesquería de la merluza del caladero sur ibérico: Mejora de la tecnología pesquera vs políticas de control de mercado

Unwanted catches can be reduced by improving fishing effectiveness in targeting species and sizes and by banning their sale for human consumption. The landing obligation introduced by the European Union can be seen as a combination of these two measures, and the aim of this paper is to analyse its effects on the Southern Iberian Hake Stock fishery. To this end, reference points for a mixed fishery are computed under the two measures as the steady-state solution of a dynamic optimal management problem. Our results show that measures that improve selectivity obtain better results than sales ban strategies in terms of increasing yields and stocks and reducing discards. In particular, we find that reducing the selectivity parameters by 90% for the three early ages leads to an almost six-fold increase in the hake yield and lowers the discard rate by more than 20 percentage points. Banning the sale of the two youngest ages also increases hake yield by 21% and the discard rate by 7 percentage points.Las capturas no deseadas pueden reducirse mejorando la efectividad a la hora de seleccionar las especies y los tamaños elegidos, así como prohibiendo su venta para el consumo humano. La obligación de desembarco impulsada por la Unión Europea (UE) puede entenderse como una combinación de ambos tipos de medidas. El objetivo de este artículo es analizar los efectos de estos dos tipos de políticas aplicados a la pesquería de la Merluza del Caladero Sur Ibérico. Con este objetivo, se computaron los puntos de referencia asociados a una pesquería mixta para las dos políticas como la solución del estado estacionario de un problema de gestión dinámica óptima. Nuestros resultados muestran que las medidas que mejoran la selectividad pesquera generan mejores resultados que las que prohíben la venta, incrementando la producción y el stock y reduciendo los descartes. En concreto, encontramos que reducir los parámetros de selectividad un 90% para las tres edades más jóvenes multiplica la producción de merluza por casi 6, a la vez que reduce la tasa de descartes en más de 20 puntos porcentuales. A su vez, nuestros resultados también muestran que prohibir la venta de las dos edades más jóvenes aumenta la producción de merluza un 21% incrementando también la tasa de descartes en 7 puntos porcentuales

Reconciling yield stability with international fisheries agencies precautionary preferences : The role of non constant discount factors in age structured models

International fisheries agencies recommend exploitation paths that satisfy two features. First, for precautionary reasons exploitation paths should avoid high fishing mortality in those fisheries where the biomass is depleted to a degree that jeopardise the stock's capacity to produce the Maximum Sustainable Yield (MSY). Second, for economic and social reasons, captures should be as stable (smooth) as possible over time. In this article we show that a conflict between these two interests may occur when seeking for optimal exploitation paths using age structured bioeconomic approach. Our results show that this conflict be overtaken by using non constant discount factors that value future stocks considering their relative intertemporal scarcity

Reconciling yield stability with international fisheries agencies precautionary preferences: the role of non constant discount factors in age structured models

International fisheries agencies recommend exploitation paths that satisfy two features. First, for precautionary reasons exploitation paths should avoid high fishing mortality in those fisheries where the biomass is depleted to a degree that jeopardise the stock's capacity to produce the Maximum Sustainable Yield (MSY). Second, for economic and social reasons, captures should be as stable (smooth) as possible over time. In this article we show that a conflict between these two interests may occur when seeking for optimal exploitation paths using age structured bioeconomic approach. Our results show that this conflict be overtaken by using non constant discount factors that value future stocks considering their relative intertemporal scarcity.European Commission (MINOW H2020-SFS-2014-2, number 634495, MYFISH, FP7-KBBE-2011-5, number 289257) and the Spanish Ministry of Economy Competitiveness (ECO2012-39098-C06-01, ECO2012-39098-C06-05 and ECO2012-35820

A bayesian estimation of the economic effects of the Common Fisheries Policy on the Galician Fleet: a dynamic stochastic general equilibrium approach

What would have happened if a relatively looser fisheries policy had been implemented in the European Union (EU)? Using Bayesian methods a Dynamic Stochastic General Equilibrium (DSGE) model is estimated to assess the impact of the European Common Fisheries Policy (CFP) on the economic performance of a Galician (north- west of Spain) fleet highly dependant on the EU Atlantic southern stock of hake. Our counterfactual analysis shows that if a less effective CFP had been implemented during the period 1986–2012, fishing opportunities would have increased, leading to an increase in labour hours of 4.87%. However, this increase in fishing activity would have worsened the profitability of the fleet, dropping wages and rental price of capital by 6.79% and 0.88%, respectively. Welfare would also be negatively affected since, in addition to the increase in hours worked, consumption would have reduced by 0.59%.Da-Rocha, García-Cutrín and Gutiérrez acknowledge financial support from the European Commission (MINOUW, project H2020-SFS-2014-2, number 634495) and the Spanish Ministry of the Economy, Industry and Competitiveness (ECO2016-78819-R, AEI/FEDER, UE). Prellezo acknowledges financial support from the Basque Government (Department of Economic Development and Infrastructures of the Basque Government). Da-Rocha and García-Cutrín also acknowledge financial support from Xunta de Galicia (GRC 2015/014 and ECOBAS). Gutiérrez also acknowledges financial support from the Basque Government (MacLab IT-793-13). This publication reflects the views of the authors only and none of the funding parties may be held liable for any use which may be made of the information contained therein

To shape or to be shaped : engaging stakeholders in fishery management advice

The purpose of this paper is to assess the effectiveness of the collaboration between stakeholders and scientists in the construction of a bio-economic model to simulate management strategies for the fisheries in Iberian Atlantic waters. For three years, different stakeholders were involved in a model development study, participating in meetings, surveys and workshops. Participatory modelling involved the definition of objectives and priorities of stakeholders, a qualitative evaluation and validation of the model for use by decision-makers, and an iterative process with the fishing sector to interpret results and introduce new scenarios for numerical simulation. The results showed that the objectives of the participating stakeholders differed. Incorporating objectives into the design of the model and prioritising them was a challenging task. We showed that the parameterization of the model and the analysis of the scenarios results could be improved by the fishers’ input: e.g. ray and skate stocks were explicitly included in the model; and the behaviour of fleet dynamics proved much more complex than assumed in any traditional modelling approach. Overall, this study demonstrated that stakeholder engagement through dialogue and many interactions was beneficial for both, scientists and the fishing industry. The researchers obtained a final refined model and the fishing industry benefited for participating in a process, which enables them to influence decisions that may affect them directly (to shape) whereas non-participatory processes lead to management strategies being imposed on stakeholders (to be shaped)