Some Interactions between North Sea Fish According to a Computer Model
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A problem with the management of the fishing industry is determining how many fish there are available in a population to manage. As a step toward solving this problem, a two-part computer model of multispecies virtual population analysis was developed that (1) estimated current and past populations of nine North Sea fish species, and (2) forecasted estimations of these fish populations. The present set of experiments (computer runs) was done with the first part of the model to examine the interactions between 32 of the input parameters. The parameters chosen to be examined were the following: seven technical parameters (used as a test of the model); the amount that a predator eats (its rations), and the natural mortalities (Ml) of each species but dividing haddock into age classes. The values of the parameter were varied +/- 10% of their original value. Biomass of each species (1974), total biomass (1974-1985) and total amount eaten (1974-1985) were the examined responses. A fractional factorial design was done to find the smallest number of experiments that could be done involving all main interactions (at worst third degree). Multiple regression was applied to the experimental results. It was found that each species' Ml value significantly affected its own biomass. Saithe and mackerel yields were only affected by their own Ml. Haddock mortalities and rations had little effect on any of the yields. These interactions show useful information that can be used when proposing fisheries management schemes.