Résumé :
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The vit program was designed to analyse exploited marine populations based on catch data, structured by age or size and by type of gear. the main assumption is that of a steady state because the program works with pseudocohorts and therefore is not suitable for historics series. from the catch data, using some auxiliary parameters and virtual population analysis (vpa), the program rebuilds the population and mortality vectors. after this first step, several analysis tools and reporting options are available to the user : comprehensive vpa results, yield-per-recruit analyses based on the fishing mortality (f) vector, analyses of sensitivity to parameter inputs and transition analyses -outside equilibrium regarding results of changes in exploitation or recruitment patterns. all these analyses are applicable to studies of competition between different kinds of gear. vit also incorporates several interactive options allowing partial results to be visualized, parameters changed and primary data converted from a size to age structure. outputs of the analyses are contained in an ascii file ready to be enterred on a worksheet. this manual provides a complete description of the vit program, including its utilities and limitations and instructions and examples for the operator. it also features a chapter on theorical fundamentals for each of the analyses. the source code has been written in fortran for execution under ms-dos.
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