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A quantitative bio-economic investigation of inshore fisheriesDu Toit, Elmari 11 1900 (has links)
Dissertation (PhD)--University of Stellenbosch, 2001. / ENGLISH ABSTRACT: The efficient management of renewable resources may ensure sustainable income to
communities and countries. In the past the mathematical modelling used in the management
decisions, in South Africa, was based on biological considerations only. In this
thesis we include economic factors in the models and aim to determine steady state
harvesting levels such that a maximum present value of all future revenues may be
reached. A bio-economical approach is followed throughout the study and applied to
the South African Cape Rock Lobster (Jasus lalandii) resource. We first address the
problem using the simplest surplus production models. The model is applied to the
Cape Rock Lobster, finding that the economical factors do indeed influence the steady
state results, emphasising that they should be incorporated in the modelling process.
A more descriptive two-sex-delay-difference model is then applied, which includes delay
times for juveniles to reach sexual maturity and distinguishes between sexes. Yet
further involved stage-class models are also studied and we propose a solution to the
non-linear programming problem reached. These models may assist decision makers
in future as knowledge on, for example, the growth of the two sexes, proper size limits
and the influence of price differences are gained. Finally, we propose a harvesting
strategy where catch is taken from alternative spatial lanes and apply here results
from reaction diffusion theory. This theoretical approach might provide guidelines to
new and underdeveloped fisheries in future, but also influence current inshore fisheries
towards new management strategies. / AFRIKAANSE OPSOMMING: Die doeltreffende bestuur van hernubare hulpbronne kan 'n volhoubare ekonomiese opbrengs
aan gemeenskappe en lande verseker. In die verlede is die wiskundige
modelle wat in die besluitnemingsproses gebruik is, in Suid Afrika, gebaseer op biologiese
oorwegings alleen. In hierdie studie word ook ekonomiese faktore in die modelle
ingesluit en word ewewigstoestande bepaal vir vangste, sodanig dat 'n maksimum
huidige waarde van toekomstige inkomste uit 'n vissery bereik word. 'n Bio-ekonomiese
benadering word deurgaans gevolg en modelle word toegepas op die Suid-Afrikaanse
Weskus Kreefbron (Jasus lalandii). Die studie begin deur basiese surplus produksie
modelle te gebruik. Die resultate van die toepassing op die Weskus Kreefbron toon dat
die ekonomiese faktore 'n groot invloed op die voorgestelde ewewigstoestand van die
populasie het. Dit benadruk dus die feit dat hierdie faktore in die modelleringsproses
ingesluit behoort te word. Meer beskrywende twee-geslag-vertragings-verskil modelle
word daarna toegepas, en sluit in 'n vertragings periode vir vis om 'n volwasse stadium
te bereik. Hierdie tydfaktor verskil dikwels vir mannetjies en wyfies en daarom
word hier 'n twee-geslag model gebruik. Meer gevorderde klasse modelle word ook
bespreek. Ons stel 'n oplossing vir hierdie nie-lineêre programmeringsprobleem voor.
Hierdie gevorderde modelle mag in die toekoms handige hulpmiddels wees wanneer
inligting rakende 'n spesie gesoek word. Sulke inligting mag insluit die groeitempos
van mannetjies en wyfies, geskikte grootte beperkings vir vangste en die invloed van
prysverskille vir verskillende groottes vis. 'n Nuwe vangste strategie word ook voorgestel
waar vangste slegs geneem word uit alternatiewe ruimtelike bane en pas ons hier
resultate uit die reaksie-diffusie teorie toe. Hierdie teoretiese oplossings mag riglyne
bied wanneer nuwe visserye in die toekoms ontgin word, maar ook huidige visserye
beïnvloed in die rigting van 'n nuwe bestuur strategie.
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Modelling the South African fresh fruit export supply chainOrtmann, Frank Gerald 12 1900 (has links)
Thesis (MSc (Applied Mathematics))--University of Stellenbosch, 2005. / The process of modelling the fruit export infrastructure capacity of South Africa formed part of
a larger project called the \Fruit Logistics Infrastructure Capacity Optimisation Study," which
was coordinated by the Transportek division of the CSIR in Stellenbosch during the period
August 2002 to March 2004. The aim of this project was to create efficiencies for, and enhance
the competitiveness of, the South African fruit industry by improved usage of, and investment
in, shared logistics infrastructure.
After putting the size of the fruit industry into perspective, numerous aspects of the export
process are considered in this thesis so as to be able to perform a comprehensive cost analysis
of the export of fruit, including the cost of handling, cooling and transportation. The capacities
of packhouses, cold stores and terminals are found and presented. This information, combined
with fruit export volumes of 2003, then allow an estimation of the current utilisation of the
South African ports with respect to fruit export.
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