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SKEBUB can thus be run in two modes. In the first instance, input variables 

 are modified and the output data at equilibrium compared. This provides 

 information on the sensitivity of the simulation to changes (or error) in the 

 input data and demonstrates the interactive effects of the model. This mode 

 is used to investigate the relative importance of parameters or species groups 

 to the overall biomass and to the biomasses of other species groups. The 

 second mode starts when the equilibrium forcing constraints are replaced with 

 density dependence and is primarily of use in studying the interactions of the 

 species groups following a perturbation (e.g. increased fishing effort on one 

 species). The time scale of these interactions is strongly dependent on the 

 form of the density dependent formulae. 



As is the case with all simplified ecosystem models it is the repeated 

 running and hypothesis testing that provides the most information, rather than 

 the actual output data from any one simulation. For this reason the code of 

 the model has been kept simple to facilitate users in developing a clear 

 understanding of the component processes. Processing time for a 70 year 

 simulation with 13 species groups is under 30 sees, on a Burroughs B7800 

 mainframe computer, and has a core requirement of less than 8000 words. The 

 FORTRAN code for SKEBUB is available as printed output or on 5 W^ inch 

 soft-sectored disl<ettes written on an Osborne I micro-computer, 



