Suchergebnisse

Under the 2013 Reform of the European Union's Common Fisheries Policy (CFP), fisheries management aims to ensure that, within a reasonable time frame, the exploitation of marine biological resources restores and maintains populations of harvested stocks above levels that can produce the maximum sustainable yield (MSY). The CFP also calls for the implementation of an ecosystem-based approach to fisheries management (EBFM). In this paper, we present the concept of maximum sustainable dead biomass (MSDB) and its associated management reference points for fishing mortality and spawning-stock biomass as alternatives to those associated with MSY. The concept of MSDB is illustrated by a dynamic pool production model of a virtual fish stock which takes into account variations in natural mortality (M), fishing mortality (F), and exploitation pattern. Our approach implies a compensatory mechanism whereby survivors may benefit from compensatory density dependence and is implemented through progressive substitution ofMwith F for varying rates of total mortality (Z). We demonstrate that the reference points for fishing mortality and spawning-stock biomass associated with MSDB are less sensitive to increasing compensation ofMwith F than those associated with MSY and more sensitive to changes in selection pattern. MSDB-based reference points, which are consistent with maximum stock productivity, are also associated with lower fishing mortality rates and higher stock biomasses than their MSY-based counterparts. Given that selection pattern can be influenced through fishery input measures (e.g. technical gear measures, decisions on areas, and/or times of fishing), whereas variations of Min response to F are not controllable (indeed poorly understood), that the results of many fish stock assessments are imprecise, that maximum stock productivity corresponds to MSDB and that MSY-based reference points may best be considered as limits, we propose that MSDB-based reference points provide a more appropriate basis for management under an EBFM.

Here we present a case study toward producing quantitative scientific advice on the application of the EU Common Fisheries Policy (CFP) in the Black Sea. We provide estimates of fishing mortality rates at levels which will lead to rebuilding and maintaining stocks above biomass levels that could produce maximum sustainable yield (MSY) under the IPCC RCP4.5 future climate scenario together with the business as usual (BAU) river discharge scenario. In this study, we have implemented a coupled, basin-scale circulation-biogeochemical model and used its output to feed a food web model to test near-future changes that may be observed in the Black Sea ecosystem under the influence of contemporary fisheries exploitation conditions. In order to test model response to changes in climate and related drivers, the future climate scenario (2015–2020) simulation was compared to the present day (2000–2014) simulation. Likewise, to test the sensitivity of the higher trophic level food web model to changes in fishing pressure, a future estimate of fishing pressure was projected based on its respective contemporary value and applied to each fish stock. Using these models, fishing mortality rates that could produce the maximum sustainable yield (FMSY) in future years 2015–2020 and ensure the long-term recovery of the predatory fish stocks of the Black Sea are predicted. Future projections suggest that all fish stock will decrease in all the regions of the Black Sea except for sprat. Anchovy is expected to show the highest decrease in biomass. Analyses on FMSY estimates show that a significant reduction in fisheries exploitation is required for the sustainable management of the Black Sea ecosystems and the related services. This study, for the first time, presents future stock size, FMSY, and MSY estimates for the Black Sea for 11 fish species. FMSY values are generally lower than estimates of the scientific, technical, and economic committee for fisheries (STECF), mainly because of the explicit food web interactions that the modeling system allows to be considered.

The theoretical determinants of maximum sustainable government debt are investigated using Diamond's overlapping generations model. A level of debt is defined to be 'sustainable' if a steady state with non‐degenerate values of economic variables exists. We show that a maximum sustainable level of debt almost always exists, and it normally occurs where variables such as capital are in the interiors, rather than at the limits, of their economically feasible ranges. This leads to a situation where, when debt is at its maximum, a further infinitesimal increase in debt causes a 'catastrophe', i.e. the economy embarks on a path of unchecked capital decumulation.

ABSTRACTThe overlapping‐generations model of Blanchard, based on a constant probability of death, is used to study the maximum level of government debt consistent with the existence of a steady state equilibrium. In both a small open and a closed economy it is shown that maximum sustainable debt robustly occurs where the consumption of individual households reaches zero, the limit of its feasible range. Taxation absorbs all of the household's labour income here. In a closed economy, at this point the real interest rate also hits a 'ceiling' given by a simple combination of preference parameters and the death probability.

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.

This paper presents the economic optimization of the shrimps fishing industry in the south coast of Central Java and adjacent waters. The physical yield function of the shrimps fishery is incorporated in an economic model to analyze the relationship between the level of fishing effort and the economic efficiency of the fishery. The open access fishery and the controlled fishery at maximum sustainable yield level causes inefficient allocation of resources. Only through control the effort at the level where marginal oost of production equal price resources can be allocated efficiently. The government intervention is necessary to restrict fishing effort to a level that would be economically optimum

This paper presents the economic optimization of the shrimps fishing industry in the south coast of Central Java and adjacent waters. The physical yield function of the shrimps fishery is incorporated in an economic model to analyze the relationship between the level of fishing effort and the economic efficiency of the fishery. The open access fishery and the controlled fishery at maximum sustainable yield level causes inefficient allocation of resources. Only through control the effort at the level where marginal oost of production equal price resources can be allocated efficiently. The government intervention is necessary to restrict fishing effort to a level that would be economically optimum