A quantitative bio-economic investigation of inshore fisheries

[摘要] ENGLISH ABSTRACT:The efficient management of renewable resources may ensure sustainable income tocommunities and countries. In the past the mathematical modelling used in the managementdecisions, in South Africa, was based on biological considerations only. In thisthesis we include economic factors in the models and aim to determine steady stateharvesting levels such that a maximum present value of all future revenues may bereached. A bio-economical approach is followed throughout the study and applied tothe South African Cape Rock Lobster (Jasus lalandii) resource. We first address theproblem using the simplest surplus production models. The model is applied to theCape Rock Lobster, finding that the economical factors do indeed influence the steadystate results, emphasising that they should be incorporated in the modelling process.A more descriptive two-sex-delay-difference model is then applied, which includes delaytimes for juveniles to reach sexual maturity and distinguishes between sexes. Yetfurther involved stage-class models are also studied and we propose a solution to thenon-linear programming problem reached. These models may assist decision makersin future as knowledge on, for example, the growth of the two sexes, proper size limitsand the influence of price differences are gained. Finally, we propose a harvestingstrategy where catch is taken from alternative spatial lanes and apply here resultsfrom reaction diffusion theory. This theoretical approach might provide guidelines tonew and underdeveloped fisheries in future, but also influence current inshore fisheriestowards new management strategies.

[发布机构] Stellenbosch University