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ABSTRACTThis study aims to examine the interannual variation in fish biomass and to estimate the maximum sustainable yield (MSY) for the marine fisheries of Kerala, India. Although the productivity of a fishery is known to be dependent on species diversity, this relationship is not widely documented. This paper uses an extended Gordon–Schaefer model that is modified to incorporate species diversity to estimate the MSY levels of catch and the corresponding fishing effort. Species diversity is expressed as both biological and bioeconomic diversity using the Simpson index. The model reports that the actual fishing effort has exceeded the maximum level necessary to support sustainable yield, while the maximum level of catch for maintaining sustainable yield is not known. A comparison of fish landings and effort data across different fishing techniques indicates that there is a potential to decrease the current level of fishing effort without experiencing a significant decline in fish catch.

Ten European fish stocks recognised by the European Union as "outside safe biological limits" are considered in light of widespread reforms to fisheries legislation in 2013, particularly the legal responsibility to exploit these resources sustainably. Given that some of these stocks are – as of 2013 – fished at over 150% the recommended intensity and many have been outside of these limits for the entirety of their assessment history, the utilisation of traditional fisheries management measures of sustainability are questioned and tougher approaches such as "zero-catch" and long-term, expansive spatial closure scenarios are considered. Finally, the pervasive issue of data-deficiency (the status of 54% of European stocks) is briefly considered, with specific reference to the understudied West of Scotland and North Sea stock of European seabass (Dicentrarchus labrax)

We investigate the use of a machine learning (ML) algorithm to identify fraudulent non-existent firms that are used for tax evasion. Using a rich dataset of tax returns in an Indian state over several years, we train an ML-based model to predict fraudulent firms. We then use the model predictions to carry out field inspections of firms identified as suspicious by the ML tool. We find that the ML model is accurate in both simulated and field settings in identifying non-existent firms. Withholding a randomly selected group of firms from inspection, we estimate the causal impact of ML driven inspections. Despite the strong predictive performance, our model driven inspections do not yield a significant increase in enforcement as evidenced by the cancellation of fraudulent firm registrations and tax recovery. We provide two explanations for this discrepancy based on a close analysis of the tax department's operating protocols: overfitting to proxy-labels, and institutional friction in integrating the model into existing administrative systems. Our study serves as a cautionary tale for the application of machine learning in public policy contexts and of relying solely on test set performance as an effectiveness indicator. Field evaluations are critical in assessing the real-world impact of predictive models.

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 ...

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

Based on fisheries landings data I propose the size-base index (community level) Mean Size of the Landing Catch (MSL). The MSL index was estimated based on high taxonomic resolution data available from auctions (species level) and demographic data acquired during the auction, namely species landed by "size-box" categories, which is assessed mandatorily in all EU members state for fisheries quality and statistic proposes. The MSL was calculated from the average inferred size-box categories of a species weighted by their annual catch. The use of MSL allows determining inter-annual changes in the size of the catch when weighted data is available from the fishery. Using the Portuguese fisheries landing data as an example, the MSL revealed that the landing yield of large fish linearly declined over time while the catch of small fishes increased (i.e., survivors to old age was reduced by fishing). The MSL can be easily used to assess trends in marine exploited commercial communities (community rather than population level) and is fully applicable with any species-size data source (e.g., scientific surveys, visual census data). The MSL can also be applied as a key indicator within the new ecosystem-based Marine Policy Framework Strategy (ecosystem approach to fisheries), which required the use of size-based indicators for the assessment of fisheries trends in exploited marine communities. ; CLIMFISH project A framework for assess vulnerability of coastal fisheries to climate change in Portuguese coast - Portugal 2020 n2/SAICT/2017 - SAICT ; info:eu-repo/semantics/publishedVersion

AbstractThis paper aims at explaining the recent rise in profits in the French Guiana shrimp fishery (FGSF) despite the overall fall in activity observed between 1990 and 2009. We develop a stochastic search‐matching version of the usual Cobb–Douglas bioeconomic fishery model. In this version catch per unit effort becomes endogenous, decreasing in the ratio of empty vessels to escaped fish, which we call "anthropic pressure" and which is determined by standard profit maximization. We first estimate the stochastic harvest function, which exhibits nearly constant returns to scale. We then show that a decrease in equilibrium anthropic pressure and congestion between vessels may be more than compensated by the consecutive rise in catch per unit effort. This leads to a fall in average harvesting costs and thus, to a rise in profits. In addition, we identify the condition under which a search‐matching fishery, working under open access, could reach a maximum economic yield equilibrium, which corresponds to a very particular case. Finally, the model makes it possible to evaluate the actual catch per unit effort and explain how the FGSF changed over the period considered with the help of the open access and maximum economic yield frameworks.

45 Pags.- 3 Tabls.- 10 Figs. The definitive version is available at: http://www.sciencedirect.com/science/journal/03783774 ; Water application depth of a center-pivot (CP) irrigation system is not uniformly distributed across a field due to emitter package design, tower dynamics, and meteorological variability. The objective of this research was to measure and model the effect of the intra-irrigation meteorological variabilities on CP seasonal water distribution pattern and corn yield. The 2013 irrigation season of a commercial CP cropped with corn was analyzed. From 60 irrigation events applied to the corn, 10 were evaluated using radial catch cans. The mechanical movement of CP towers for the sixty irrigation events was characterized using Global Navigation Satellite System-Real Time Kinematic (GNSS-RTK) monitoring. Meteorological variables at 1 s frequency were measured with an automatic weather station installed in the farm. The ballistic model calibrated and validated for rotating spray plate sprinklers under different nozzle sizes and wind conditions was mounted on the CP lateral, following the correspondent sprinkler package. The CP lateral was moved following the measured or simulated tower dynamic, and the current or averaged meteorological conditions of each irrigation event were applied to the corn. Crop yield was simulated by coupling the water distribution pattern simulated under the different cases with the Ador-crop model. Differences were observed for simulated seasonal water distribution pattern of the CP under homogeneous wind conditions (averaged for each irrigation event) or under variable of time wind conditions (measures). Simulated yield considering discontinuous tower dynamics and intra-irrigation meteorological variability has the largest correlation coefficient with the measured corn yield. Other factors were not considered in the yield simulation as variability in nutrient availability, emergence problems, and diseases and soil variability could explain the differences between the simulated and measured corn yield. The intra-irrigation meteorological variability has an important effect on the water distribution pattern of windy irrigation events of CP systems. Depending on the wind speed along the crop season, the intra-irrigation variability will have a major or minor effect on seasonal water distribution pattern and crop yield variability. ; This research was funded by the Ministry of Economy and Competitiveness of the Spanish Government through the grants AGL2010-21681-C03-01 and AGL2013-48728-C2-1-R. ; Peer reviewed

Diffusion du document : INRA Station d'Economie et Sociologie Rurales Unité Environnement et Ressources Naturelles 65 rue de Saint-Brieuc 35042 RENNES CEDEX (FRA) ; L'évolution des rendements céréaliers a été analysé dans cette étude, en parcourant les diverses situations possibles d'efficacité micro-économique, depuis l'inefficacité technique jusqu'à l'efficacité-prix. Le niveau d'efficacité conditionnera vraisemblablement l'efficience de la régulation de l'offre céréalière. Cette méthodologie est appliquée à un échantillon d'exploitations céréalières françaises pour les années 1987 à 1990.

Cette étude tente de justifier, au sein du secteur agricole, l'hypothèse suivant laquelle le niveau d'efficacité micro-économique conditionne largement le degré d'efficience des politiques de régulation des marchés. L'illustration porte sur la toute récente réforme de la Politique Agricole Commune qui s'est donnée comme catalyseur une baisse notable du prix des céréales. Un cadre méthodologique non paramétrique permet de révéler les inefficacités proprement techniques de même que les inefficacités allocatives, c'est-à-dire relatives au système de prix. Cette approche est appliquée à l'examen d'échantillons d'exploitations céréalières du RICA, pour les années 1987 à 1990. Les inefficacités techniques observées s'interprètent comme des gains potentiels de productivité traduits ici sous forme d'accroissement des rendements céréaliers à l'hectare. Pour l'année 1990, l'inefficacité technique serait en moyenne d'environ 10% sur l'échantillon considéré. La résorption de cette seule inefficacité technique pourrait conduire à une augmentation de 11,2% des rendements céréaliers. L'effet escompté du gel de 15% des terres sur l'offre céréalière sera donc vraisemblablement amorti. Ce résultat global se différencie suivant les régions et la taille des exploitations.