Reference Points and Optimal Management in Stochastic Age-Structured Fisheries Models

The purpose of this article is to characterize dynamic optimal harvesting trajectories that maximize discounted utility assuming an age-structured population model, in the same line as Tahvonen (2009). The main novelty of our study is that uses as an age-structured population model the standard stochastic cohort framework applied in Virtual Population Analysis for fish stock assessment. This allows us to compare optimal harvesting in a discounted economic context with standard reference points used by fisheries agencies for long term management plans (e.g. Fmsy). Our main findings are the following. First, optimal steady state is characterized and sufficient conditions that guarantees its existence and uniqueness for the general case of n cohorts are shown. It is also proved that the optimal steady state coincides with the traditional target Fmsy when the utility function to be maximized is the yield and the discount rate is zero. Second, an algorithm to calculate the optimal path that easily drives the resource to the steady state is developed. And third, the algorithm is applied to the Northern Stock of hake. Results show that management plans based exclusively on traditional reference targets as Fmsy may drive fishery economic results far from the optimal.

Reference Points Based on Dynamic Optimisation: A Versatil Algorithm for Mixed Fishery Management with Bio-economic Agestructured Models

Single-species management objectives may not be consistent within mixed fisheries. They may lead species to unsafe situations, promote discarding of over-quota and/or misreporting of catches. We provide an algorithm for characterising bio-economic reference points for a mixed fishery as the steady-state solution of a dynamic optimal management problem. The optimisation problem takes into account: i) that species are fishing simultaneously in unselective fishing operations and ii)intertemporal discounting and fleet costs to relate reference points to discounted economic profits along optimal trajectories. We illustrate how the algorithm can be implemented by applying it to the European Northern Stock of Hake (Merluccius merluccius), where fleets also capture Northern megrim (Lepidorhombus whiffiagonis) and Northern anglerfish (Lophius piscatorius and Lophius budegassa). We find that optimal mixed management leads to a target reference point that is quite similar to the 2/3 of the Fmsy single-species (hake) target. Mixed management is superior to singlespecies management because it leads the fishery to higher discounted profits with higher long-term SSB for all species. We calculate that the losses due to the use of the Fmsy single-species (hake) target in this mixed fishery account for 11.4% of total discounted profits.

Lessons from the northern hake long-term management plan: Could the economic assessment have accepted it?

An economic expert working group (STECF/SGBRE-07-05) was convened in 2007 for evaluating the potential economic consequences of a Long-Term Management Plan for the northern hake. Analyzing all the scenarios proposed by biological assessment, they found that keeping the F in the status quo level was the best policy in terms of net present values for both yield and profits. This result is counter intuitive because it may indicate that effort costs do no affect the economic reference points. However, it is well accepted that the inclusion of costs affects negatively the economic reference points. In this paper, applying a dynamic agestructured model to the northern hake, we show that the optimal fishing mortality that maximizes the net present value of profits is lower than Fmax.

On the Benefits of Including Age-structure in Harvest Control Rules

This paper explores the benefits of including age-structure in the control rule (HCR) when decision makers regard their (age-structured) models as approximations. We find that introducing age structure into the HCR reduces both the volatility of the spawning biomass and the yield. Although at a fairly imprecise level the benefits are lower, there are still major advantages for actual assessment precision of the case study. Moreover, we find that when age-structure is included in the HCR the relative ranking of different policies in terms of variance in biomass and yield does not differ. These results are shown both theoretically and numerically by applying the model to the Southern Hake fishery.

Modelos de empresa multinacional democrática o cooperativa

[ES] En este trabajo analizamos las posibles vías de desarrollar otro modelo de empresa multinacional desde tres puntos de vista. En primer lugar, analizaremos el papel que pueden desempeñar los códigos de conducta como instrumentos complementarios para diseñar una política social internacional. En segundo lugar, realizamos una breve reflexión sobre la cooperativa multinacional, o la cooperativa global, como alternativa cooperativa al modelo de empresa multinacional imperante. Por último, en tercer lugar, desde un punto de vista más amplio, nos referimos a las posibilidades de desarrollar un modelo de empresa multinacional más democrática. En este sentido, estudiamos algunos condicionantes que afectan al funcionamiento y a los procesos de decisión de las empresas multinacionales, en concreto nos referimos a los mecanismos de coordinación entre las diferentes unidades de la estructura multinacional y a las características de las filiales, en cuanto a su fortaleza o calidad.

Ahalmen espaziala hezkuntza matematikoan

[EUS] Matematikaren irakaskuntzaren helburuenetako bat hezkuntza maila guztietan ikasleen ahalmen intelektualen garapena da. Ahalmen espazialaren trataera eskolan urria izan da, bereziki zenbakizko ahalmenak edota arrazonamenduzko ahalmenak izan duten trataerarekin konparatzen badugu. Hezkuntza Matematikoan egindako berrikusketek ahalmen espazialaren azterketaren garrantzia azpimarratzen dute nahiz eta erreferentzi marko baten ezak sakabanatzen eta zailtzen dituen emaitzen lorpena, behin betikoak izateko erreplikagarriak izan behar dutela jakinik. Ondoren proposatzen den ikerketa-lerroak ahalmen espaziala alderdi hirukoitz batetik abiaturik aztertu nahi du: egitura, garapena eta hobetze-proposamenak kontutan harturik. Hiru arlo horietan proposaturiko ereduek bermatuko dute diagnostiko zuzen bat, ikasleen ahalmen espaziala hobetuko duena.

Fixed and Best Proximity Points of Cyclic Jointly Accretive and Contractive Self-Mappings

p(>= 2)-cyclic and contractive self-mappings on a set of subsets of a metric space which are simultaneously accretive on the whole metric space are investigated. The joint fulfilment of the p-cyclic contractiveness and accretive properties is formulated as well as potential relationships with cyclic self-mappings in order to be Kannan self-mappings. The existence and uniqueness of best proximity points and fixed points is also investigated as well as some related properties of composed self-mappings from the union of any two adjacent subsets, belonging to the initial set of subsets, to themselves.

Fixed Points of Closed and Compact Composite Sequences of Operators and Projectors in a Class of Banach Spaces

Some results on fixed points related to the contractive compositions of bounded operators in a class of complete metric spaces which can be also considered as Banach's spaces are discussed through the paper. The class of composite operators under study can include, in particular, sequences of projection operators under, in general, oblique projective operators. In this paper we are concerned with composite operators which include sequences of pairs of contractive operators involving, in general, oblique projection operators. The results are generalized to sequences of, in general, nonconstant bounded closed operators which can have bounded, closed, and compact limit operators, such that the relevant composite sequences are also compact operators. It is proven that in both cases, Banach contraction principle guarantees the existence of unique fixed points under contractive conditions.

Some Results on Fixed and Best Proximity Points of Multivalued

This paper is devoted to investigate the fixed points and best proximity points of multivalued cyclic self-mappings on a set of subsets of complete metric spaces endowed with a partial order under a generalized contractive condition involving a Hausdorff distance. The existence and uniqueness of fixed points of both the cyclic self-mapping and its associate composite self-mappings on each of the subsets are investigated, if the subsets in the cyclic disposal are nonempty, bounded and of nonempty convex intersection. The obtained results are extended to the existence of unique best proximity points in uniformly convex Banach spaces.

Some Results on Fixed and Best Proximity Points of Precyclic Self-Mappings

12 p.

Best Proximity Points of Generalized Semicyclic Impulsive Self-Mappings: Applications to Impulsive Differential and Difference Equations

This paper is devoted to the study of convergence properties of distances between points and the existence and uniqueness of best proximity and fixed points of the so-called semicyclic impulsive self-mappings on the union of a number of nonempty subsets in metric spaces. The convergences of distances between consecutive iterated points are studied in metric spaces, while those associated with convergence to best proximity points are set in uniformly convex Banach spaces which are simultaneously complete metric spaces. The concept of semicyclic self-mappings generalizes the well-known one of cyclic ones in the sense that the iterated sequences built through such mappings are allowed to have images located in the same subset as their pre-image. The self-mappings under study might be in the most general case impulsive in the sense that they are composite mappings consisting of two self-mappings, and one of them is eventually discontinuous. Thus, the developed formalism can be applied to the study of stability of a class of impulsive differential equations and that of their discrete counterparts. Some application examples to impulsive differential equations are also given.

Determinants of self-reported smoking and misclassification during pregnancy, and analysis of optimal cut-off points for urinary cotinine: a cross-sectional study

10 p.

ENEKuS – a key model for managing the transformation of the normalisation of the Basque language in the workplace

The aim of this study is to develop a reference model for intervention in the language processes applied to the transformation of language normalisation within organisations of a socio-economic nature. It is based on the case study of an experience carried out over10 years within a trades’ union confederation, and has pursued a strategy of a basically qualitative research carried out in three stages: 1) undertaking field work through application of action-research methodology, 2) reconstructing experiences following processes of systematisation and conceptualisation of the systematised data, applying methodologies for the Systematisation of Experiences and Grounded Theory, and 3) formulating a model for intervention, applying the Systems Approach methodology. Finally, we identified nine key ideas that make up the conceptual framework for the ENEKuS reference model, which is structured in nine ‘action points', each having an operating sub-model applicable in practice.

New climate scenario framework implementation in the GCAM integrated assessment model

48 p.

Common Fixed Points of Generalized Rational Type Cocyclic Mappings in Multiplicative Metric Spaces

The aim of this paper is to present fixed point result of mappings satisfying a generalized rational contractive condition in the setup of multiplicative metric spaces. As an application, we obtain a common fixed point of a pair of weakly compatible mappings. Some common fixed point results of pair of rational contractive types mappings involved in cocyclic representation of a nonempty subset of a multiplicative metric space are also obtained. Some examples are presented to support the results proved herein. Our results generalize and extend various results in the existing literature.