Bibliography: pages 85-95. / Procedures for measuring phytoplankton production in the southern Benguela upwelling region were investigated. A 125 ml incubation bottle is recommended for routine primary production measurements. Exposure of production samples to high light intensities during manipulations on deck was found to inhibit rates of production near the bottom of the euphotic zone particularly below a thermocline. Simulated in situ rates of oxygen production were only slightly higher than in situ rates. When ships time is limited, the simulated in situ method can safely be used in local waters. Definite diel periodicity in rates of production at the sea surface was demonstrated and appears to be linked to light levels and nutrient concentrations, as well as to the ratios of light to dark hours. Since diel variation probably decreases with depth, its effect on integrated daily production is reduced. Nevertheless, the time of incubation should be chosen to minimize the effect of periodicity on daily production estimates. The period spanning noon is recommended for local use. Changes in phytoplankton production and biomass are linked with physical and chemical changes in the upwelling system off the Cape Peninsula. Extremely active upwelling was found to limit primary production and from these measurements the annual net primary production in the Cape Peninsula upwelling region is estimated for the first time to be approximately 1.13 kgC.m⁻ ³.y⁻¹.

Bibliography: pages 113-129. / Inter-basin water transfer (IBT) is defined as the transfer of water from one geographically isolated river catchment, sub-catchment or river reach, to another. Thus, one river becomes a donor, and another the recipient. They are joined by a range of possible transfer routes. In many cases either or both the donor and recipient rivers are impounded. The volumes of water transferred and the operational criteria for IBT schemes vary considerably. This study produced a review of the literature dealing with the ecological (physical, chemical and biological) effects of IBTs. The review highlighted the fact that much of the information available is conceptual, and provides few data collected from systems affected by transfer schemes. The main objective of this study was, therefore, to collect data from a donor and recipient river of a small IBT scheme in the Western Cape, the Riviersonderend-Berg-Eerste River Government Water Scheme (RBEGS). The donor river, the Riviersonderend, is impounded by the Theewaterskloof Dam. Water from this reservoir is transferred through a tunnel to the upper reaches of the Berg River, and then on to the Cape Metropolitan Area (CMA). Approximately 38-45% of the water utilised in the CMA is transferred from Theewaterskloof. The release of water into the upper Berg is f, for irrigation in the upper catchment, and for use by a rainbow trout farm downstream of the outlet.

Bibliography: leaves 93-100. / The primary focus of this thesis was to investigate the movement patterns of the South African West Coast rock lobster, Jasus lalandii, using a diverse range of techniques. These were (1) an examination of long-term data from an ongoing tag-recapture program, (2) observations on rock lobsters in a mesocosm aquarium, (3) surveys that monitored the seasonal fluxes in activities and abundance of rock lobsters in the field, (4) video recordings of movement behaviour in small aquaria and (5) acoustically tracking the movements of four individual rock lobsters.

Includes abstract. / Includes bibliographical references (leaves 59-64). / Exploitation of J. lalandii in South Africa and Namibia is currently limited to harvesting adults from the wild. On growing (farming) of postlarval lobsters to a marketable size could increase production, and potentially relieve fishing pressure and enhance natural populations through reseeding areas with cultured lobsters. Postlarval lobsters are, however, not yet available in sufficient quantities through culture from egg to puerulus, so postlarvae for ongrowing need to be harvested from the wild. Finding a good source of wild postlarvae has hindered the development of lobster farming in South Africa. My study was designed to locate a site of high postlarval settlement and to (1) investigate numbers available for collection (standing-stock), temporal patterns of settlement and their relationships with environmental conditions, postlarval size-distributions and growth, (2) test the relative efficacy of various collector designs for effective collection of postlarvae, and (3) make recommendations for postlarval collection in the future. An oyster farm in Saldanha Bay was chosen as the study site.

Bibliography: leaves 98-111. / A detailed description of the design of an apparatus suitable for investigations into the respiratory physiology of small nektonic organisms at various swimming speeds is presented. Juvenile rainbow trout (Oncorhynchus mykiss) were used to evaluate the performance of the apparatus. Twenty-four hour experiments indicated no detectable diurnal variation in the respiration rates of juvenile rainbow trout. Experiments investigating aerobic energy expenditure at sustained swimming speeds, through measurements of oxygen consumption rates, are described. Oxygen consumption was found to increase exponentially with increasing swimming speed. The influence of body size on this relationship was examined. The contribution of anaerobic metabolism at sustained swimming speeds was investigated.

Includes bibliographical references. / Sustainable diversification and the biological viability of selected aquaculture species are now viewed as being crucial factors that must be assessed in order to introduce the candidate species into commercial production. The biological feasibility of white stumpnose, Rhabdosargus globiceps,as a potential aquaculture candidate, was assessed by examining the ability of the broodstock to be manipulated to spawn in captivity and the viability of the larvae from 0 days post hatch (DPH) to 30 DPH under varied conditions. These factors are recognised as the most significant bottlenecks of development for a potential aquaculture candidate. A compressed photothermal cycle successfully brought about the reproductive maturation of both male and female broodstock. The natural, seasonal reproduction cycle, of the population of Rhabdosargus globiceps in Langebaan Lagoon, and manipulated cycles were comparable with regard to oocyte maturation. Under the compressed cycle an increase in the plasma estradiol 17ß concentration correlated with the increase in oocyte diameter and the presence of late vitellogenic and hydrated oocytes. Reproductively mature broodstock were injected twice with LH-RHa on a 24 hour interval, which successfully induced spawning over four consecutive 24 hour periods. This method of manipulation and induction of spawning was successful twice and the resultant eggs and larvae were used to examine the ontogeny and the optimal rearing temperature of Rhabdosargus globiceps. In the first larval rearing experiment the stages of development from egg to 30 DPH larvae were recorded at 20°C and showed similar developmental stages as other sea bream aquaculture species. The developmental stages were noted as being highly influenced by the available food sources with elevated mortalities recorded during the transitional phase between endogenous food reserves and exogenous feeding. The growth pattern showed the same reduced growth present for other successfully cultured sea bream larvae, suggesting that first feeding and swimbladder inflation was relatively successful. At 30 DPH the larvae reached a mean total length of 11.14 ± 0.44 mm. To determine the optimal rearing temperature and the effect of temperature on embryonic development eggs were placed at three different incubation temperatures (25°C, 20°C and 15°C) and the timing to the developmental stages was recorded from 0 DPH to 30 DPH. Measurements indicated that the larvae reached and exceeded their thermal tolerance at 25°C, with larvae only surviving to 6 DPH at this temperature, while at 20°C the larvae had better growth, and significantly earlier indications and higher percentages of feeding, swimbladder inflation and notochord flexion than at 15°C. The results suggest that the highest quality larvae are achieved at a rearing temperature of 20°C. This thesis describes the induction of spawning and larval rearing of Rhabdosargus globiceps. The ontogeny of the larvae as well as the critical stages of first feeding, swimbladder inflation and notochord flexion are discussed and described in detail. Overall, the life cycle from adult to juvenile was successfully closed and the experiments showed very positive results regarding Rhabdosargus globiceps’ biological capacity and feasibility to become a potential aquaculture candidate in South Africa.

Bibliography: leaves 126-134. / Thalassinidean prawns in the genus Callianassa have been singled out as important bioturbators because of their size and activity, and because they often occur at high densities and burrow deep into the sediments. The ecological effects of bioturbation by Callianassa kraussi on the eelgrass Zostera capensis, and its indirect effects on the sedentary mudprawn Upogebia africana and the biota of an intertidal sandflat were assessed at Langebaan Lagoon, South Africa, through comparative surveys, observations and field experiments. I hypothesised that C. kraussi and Z. capensis have mutually detrimental effects on each other, with bioturbation by C. kraussi leading to smothering of Z. capensis, and stabilising of sediments by Z. capensis impeding burrowing of C. kraussi. I also hypothesised that C. kraussi would be negatively correlated with U. africana because the latter relies on semi-permanent U-tubes to filter-feed, and bioturbation is likely to disrupt these.

Study of the Indian Ocean has lagged behind that of the Atlantic and Pacific, with large knowledge gaps remaining in our understanding of regional or basin-scale controls on productivity and higher trophic levels. A lack of in situ data, especially for mid and upper trophic-level organisms, has commonly limited to small spatiotemporal scales, investigations into environmental control of biological systems. These data gaps are increasingly being filled by coupled bio-physical ocean models. Throughout this thesis, outputs from such a coupled ocean model (NEMO-PISCES) were employed to provide hindcast (1961-2001) records of three-dimensional environmental fields in the Indian Ocean.

Includes abstract. / Includes bibliographical references (leaves 112-121). / An Ecosystem Approach to Fisheries (EAF) is the new management paradigm considered for ecosystems worldwide. Its aim is to balance a multitude of objectives, including those of conservation and exploitation.Ecosystem modelling is recognised as a tool that may be used towards achieving an EAF. Trophic models are explicitly based on the interactions between ecosystem components and therefore allow stakeholders to view how pressures (environmental or anthropogenic) impact upon the ecosystem, as well as its individual components. An updated trophic model representing the 2004-2008 period within the southern Benguela ecosystem was constructed.This current model complements historic 1900s, 1960s and 1980s trophic models previously published. Examinations of the model outputs signify a change in the food web structure of the southern Benguela ecosystem.

Includes bibliography at end of thesis. / In Part I of this study, the social organisation and cormnunicative behaviour of the striped field-mouse Rhabdomys pumilio was studied in a large outdoor cage. It was found that the social organisation was based on a male dominance hierarchy, with the development of territory in the dominant male and breeding females. The level of testosterone in males was found to be a reliable index of social status. Analysis of spatial relationships and behavioural interactions among individuals showed these factors to be closely related to social status. Rhabdomys was found to have a well-developed repertoire of visual displays, to use ultrasonic calls in social interactions, and to be dependent, to a certain extent, on chemical communication. In Part II, an attempt was made to confirm these findings in the field. Home ranges on the Cape Flats were determined by tracking; testosterone was used as an index of. social statua. Similarly structured hierarchies were found, as well as indications of territoriality. Home range sizes, distribution and spatial relationships of individuals were determined. Rhabdomys was found to prefer habitats of good ground cover.