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MEFISTO: Modelo Bio-económico para la Pesca del Mediterráneo

Table of contents

• Participants
• Introduction
• Conceptual Model 
• Software Requirements
• Examples
• Downloads

   

Participants

Introduction

We present a software package implementing a bioeconomic model for the Mediterranean fisheries. The first objective of the model is to reproduce the bio-economic conditions in which the fisheries occur. The model is, perforce, multispecific and multigear. The main management procedure is effort limitation. The model also incorporates the usual fishermen strategy of increasing efficiency, in order to increase fishing mortality, while maintaining the nominal effort. This is modeled by means of a function relating the efficiency (or technological progress) with the capital invested in the fishery, and time. A second objective is to simulate alternative management strategies. The model allows operating with technical and economic management measures and in the presence of different kind of events.

The objectives of managing the simulated fishery can be diverse. They could be to maximize fishing production or revenues, to minimize catch fluctuations, to avoid the risk of collapse of the resource, etc. The manager has two kinds of tools available: technical (such as effort limitation) or economic (such as subsidies and taxes). The effectiveness of each of these tools in achieving the manager's purpose varies. In a complex system, as fisheries can be, it is not always evident what will be the response from the system to a certain management measure. Thus MEFISTO is designed as a tool to study the outcome of different management measures on a simulated, but realistic, Mediterranean fishery.

The final users of the product are three: the scientist, the decision-maker, and the fisherman. For the scientist the present model constitutes a research tool that should lead to an improved understanding of the mechanisms by which the fisheries system operates. It can also be an advisory tool, as the model acts as a test bench for analysing different management options, decision risks, sensibility of the parameters, etc. For the administrators and decision-makers, the model offers a way to assess the economic and biological effects of particular management measures (technical, economic or both) in the short and mid term. This could be very useful in the design of policies for mid-term objectives and for exploring the different ways to attain them. It is also important that the administrators realize the extent to which the fishery depends on the dynamics of a biological resource and not only on economic decisions.

The model offers fishermen a new perspective on the behaviour of the system, including its temporal scale. The model should contribute to increased comprehension of the usefulness or uselessness of certain management measures, and establish the difference between short and mid term regarding earnings and losses.

Conceptual Model

The objective of the model is to reproduce the fishing conditions characteristic of the Mediterranean, including several aspects that differentiate it from the models elaborated for the Atlantic fisheries. The most important particularities are: 

• The model should necessarily be bioeconomic to accommodate at the same time the dynamic nature of living resources, and the economic relationships that govern Mediterranean fisheries.
• Management is mainly based on effort control, although other technical and economic measures exist.
• The management system is non-adaptive. No regular assessments are done and hence no adaptive management policy is implemented. TACs do not exist and the economic administrative tools acquire as much importance (or more) than the technical tools.
• Increasing "catchability" (in effect, efficiency) is the mechanism of increasing fishing mortality by the fishermen: they cannot increase fishing effort, as it is defined by law in the Mediterranean area. Therefore they will always try to maximize fishing mortality. The only mechanism that they have to increase catch without increasing effort is to increase their catchability by means of investment in technology. An essential point of the model is the exploration of the dependence of catchability as a function of the installed capital and time. In accordance with this hypothesis, a bioeconomic model, rather than a biological one, is the more appropriate to simulate the Mediterranean fishery, since it is in certain measure self-managed by the fishermen through economic mechanisms.
• It is multispecific, multigear, and multifleet.

The model has been built in a modular way on a system of "boxes." A total of three boxes are defined:

• The stock box. This simulates the dynamics of a particular stock. The input is the fishing effort and the catchability (these coming from the fisherman's box) whose product constitutes the fishing mortality applied to the stock. The output is the catch that goes into the market box. The stock box can have diverse simultaneous boxes (multispecificity). There are species of two kinds: the main species, whose dynamics are completely explicit, and the secondary species, whose dynamics are not known but whose yields are computed as a function of those of the main species.
• The market box. This converts the catch into money with some price functions. One has to consider the base (or "shadow") price, importance of the size of the individual fish, and importance of the size of the fish offer.
• The fisherman box. This simulates the fisherman's economic behaviour. Its input is the money coming from the market box; its output is the effort (limited by legislation) and the catchability, over which the fisherman has certain control by way of function of his capital. The parameters of the fisherman's box are contained at different levels: country, fleet, and vessel. The level country contains the most general economic parameters that embrace diverse fleets (such as cost of fuel). The level fleet contains the technical and economic parameters characteristic of each fleet (catchability and fishing mortality initial vectors, GT price, etc.). Finally, the last level, vessel, allows particularisation of the characteristics of each boat. 

The simulations in time are conducted by carrying a complete cycle in each time unit.

Software Requirements

IBM PC and compatibles with 32-bit CPU.
With 16 Mb de RAM
HD 10 Mb for the Software
Operation System Windows 95 / 98 / NT / 2000 / Me

Examples

The software installation includes three example accessible through the from the MEFISTO menu File->Open. The examples are described in the following documents:

Downloads

• Software documentation
• Software