VIT: software for fishery analysis. User's manual
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The program VIT was designed to analyse exploited marine populations based on catch data, structured by ages or sizes, from one or several gears. The main assumption is that of steady state because the program works with pseudo-cohorts, therefore it is not suitable for historic series. From the catch data with some auxiliary parameters and using Virtual Population Analysis (VPA) the program rebuilds the population and mortality vectors. After this first step the user has several analysis tools a nd reporting options available: obtaining comprehensive VPA results, Yield-per-Recruit analyses based on the fishing mortality (F) vector, analyses of sensitivity to parameter inputs, and transition analyses - outside the equilibrium - due to changes in the pattern of exploitation or recruitment. All these analyses are applicable to studies of competition between different kinds of gears. The program also includes several interactive options in the sense that partial results can be visualised , parameters may be changed and primary data can be converted from size to age structure. The outputs of the analyses are included in an ASCII file ready to be entered onto a worksheet. The present paper includes a complete description of the program, its utilities and limitations, with a complete operator's manual and examples. It also includes a chapter on theoretical fundamentals of each one of the analyses. The source code has been written in FORTRAN and the executables under MS-DOS Operatin g System.