Browsing by Author "Mertens, Robert George Stephen"

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    A computer simulation of the population dynamics of the Cape hakes (Merluccius capensis and M. paradoxus)
    (1978) Mertens, Robert George Stephen; Field, John G; Newman , G G
    Catch and effort statistics for the Cape hakes (Merluccius capensis and M. paradoxus) have indicated a substantial decrease in the stock size over the period 1955-74; consequently, a catch projection model was designed to investigate the hake population. Where appropriate, available data have been included in the model; however, some further research was required: 1. The monthly pattern of availability for 1974-76 was examined using South African data; it was found to be similar to that reported for earlier years, and the later figures were used. 2. Assuming that selection curves for different mesh sizes are identical except for their position on the X-axis, a method to calculate selection values for combinations of mesh size and fish length has been outlined, and used with data presented by Bohl et al. (1971). 3. An investigation was made of two methods of estimating natural mortality (M), utilizing the results of Virtual Population Analysis (V.P.A.). In both cases the criteria used to judge M were found to be insensitive, and therefore neither can be used. 4. The stock estimates obtained using V.P.A. were applied to two stock/recruit curves. The goodness of fit in both cases was poor, and nearly identical.