Browsing by Author "Botha, Jakobus Stephanus"

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    Modelling dominance shifts of anchovy and sardine with a frame-based approach : sensitivity to the underlying sardine population dynamics
    (2012) Botha, Jakobus Stephanus; Jarre, Astrid
    It has been shown that sardine and anchovy populations in the southern Benguela have alternated dominance during the past 50 years, and a frame based model that explores the usefulness of frames within a marine ecosystem by modelling sardine/anchovy dominance shifts in the southern Benguela has been developed in a previous study. The existing model contains a sardine population sub-model without age structure and the inclusion of age-structure allows age-related dynamics to be incorporated in the model design. In this mini-dissertation, an age-structured sardine population is implemented in the frame based model by using the sardine assessment model from the joint sardine/anchovy Operational Management Procedure, OMP-02. Methods for incorporating biological processes - such as the hypothesised school trap phenomena - that were present in the existing frame based model into the OMP-02 equations are developed, critically analysed and tested.