Targeting marine diamondiferous deposits along the south-western Namibian coastline has involved the construction of seawall berms to advance the coastline and permit mining in previously subtidal areas. Large areas are mined out to bedrock level by the removal of overburden (sand and gravel), and after mining is complete, areas behind the seawalls fill with seawater, creating a series of coastal marine ponds that have the potential to function as saline wetlands corresponding to closed estuaries. The study site lies north of the Orange River mouth, within the Tsau//Khaeb (Sperrgebiet) National Park, to which the public has restricted access due to diamond mining in the area. Consequently, there is a focus on biodiversity conservation and the overall objective of this thesis was to determine the ecological value of the mining ponds by investigating whether they harbour sufficient biodiversity to qualify as a viable alternative ecological habitat, rather than restoring them to their original state as backfilled, revegetated dune areas. The study area, approximately 75 kilometres in length, was divided into north, middle and south sections, according to the age and status of mining activities, and I first assessed whether ponds in these three areas differed in their physical properties (Chapter 1). To determine whether the ponds serve as a useful ecological role worth preserving, I then investigated the diversity and amount of saltmarsh vegetation (Chapter 2), bird species (Chapter 3) and fish (Chapter 4) currently benefiting from these mining ponds. Ponds in the north are older and hypersaline whereas the south and middle ponds are younger and closely approach physical conditions in the sea. Diurnal fluctuations in oxygen concentration took place, but oxygen levels never dropped below 80% and were thus not limiting. After about 15 years, ponds developed salinities in excess of 80‰, which is likely to set limits on their ecological viability. Most ponds supported saltmarshes, but only a single species, Salicornia natalensis, grew around them. Its abundance was greatest around old ponds, but its health decreased with salinity. Wind emerged as a likely means of dispersal among ponds. The ponds supported a rich avifauna, averaging 11028 birds per count for all ponds combined; 36 species were recorded, ten being endemics, and five being listed in Namibia's Red Data Book. Numbers were highest for ponds that were being ‘dewatered' to remove water prior to mining, as this exposed a rich benthic epifaunal source of food. Blacknecked Grebe, Cape Cormorant, Greater and Lesser Flamingos, Kelp Gull and Common Tern were the most abundant birds. Salinity did not limit bird numbers or diversity, so the northern high-salinity ponds may continue to serve as bird habitat for periods of time much greater than the 15 years after which they become hypersaline. In comparison with nine other wetlands in the region, the ponds had great numbers, diversity, densities, and numbers of threatened species than about half of these wetlands, many of which are considered Important Bird Areas (IBAs). In many cases, they also supported more species that had numbers in excess of 1% of the southern African population than these IBAs. Only two species of fish commonly occurred in the ponds, the west coast steenbras Lithognathus auratus and the southern mullet Chelon richardsonii, although small numbers of two other marine species were recorded. The diversity of marine fish was thus low, even by the impoverished standards of west-coast estuaries. Unexpectedly, there were no significant differences between the ichthyofauna of ponds in the north, middle and south, nor was there any relationship between total fish numbers and salinity. Body condition of steenbras was lowest in the hypersaline north ponds, and their stomach contents contained a low diversity of food items there. The presence of recruits and the range of gonadal states suggested that both species bred in the ponds. Steenbras proved to be protandrous, with females dominating larger size classes. Growth rates of both species were faster in the ponds than in the adjacent sea, and mullet achieved substantially greater sizes in ponds. Thus, the ponds do serve as viable ecosystems, albeit with a limited range of saltmarsh and fish species, and support an impressively diverse avifauna. Their long-term viability will, however, become limited by rising salinity as their age increases.

The total fatty acid content of an estuarine Flexibacter trip and the relative proportion of the constituent fatty acids were affected by growth temperature, aeration and salinity. The proportion of Cl6:lw5 the main fatty acid, did not change with temperature, but was produced in higher concentrations in xhe aiMOu*t o{ shaking cultures. In contrast, the amount of both linoleic and linolenic acids varied with temperature and aeration. The concentration of Cl6:lw5 per mg of protein changed with temperature, whereas the concentrations of both polyunsaturates were relatively constant. Both the proportion and concentration of the polyunsaturates were markedly stimulated by increases in salinity, although total fatty acid per mg protein decreased with it. The highest concentration of fatty acid per mg of protein did not coincide with the highest percentage of polyunsaturated fatty acids (PUFAs), when Inp was grown in different carbon sources. Inp growing in glucose had the highest concentration of PUFAs per mg of protein. Radio labelled acetate and palmitate were differentially incorporated into the fatty acids of Inp2 a variant of Inp. Addition of cAMP inhibited the incorporation of radioactive precursors into PUFAs. In contrast the antibiotic cerulenin inhibited the incorporation of radio labelled substrate acetate and variant into C16:1. This strongly suggests that lnp2 posseses both the anaerobic and aerobic pathway for UFAs synthesis. Whilst PUFAs were absent when another variant lnp3 was grown in media with an osmotic strength close to that of seawater, PUFAs were produced when Inp3 was grown in a high osmotic strength medium. Addition of cAMP to the high osmotic strength medium prevented PUFAs synthesis. Artemia salina was grown to adulthood on diets consisting of bacteria, bacteria plus algae and algae only. Generally, there were no differences in survival between the diets. However, different diets reflected differences in the total dry weight. Addition of algae to the Inp3 diet increased PUFAs concentration per animal dry weight. It is suggested that Inp3 may be able to provide both PUFAs and exoenzymes, which assist in the digestion of algae.

Includes bibliographical references. / The extent of parasitism by macroscopic parasites was assessed and the relationships between the parasites and their fish hosts in terms of sex, size and the condition factor of the fish were investigated.

Includes bibliographical references. / This study explores inter-annual rainfall variability over the East African coast region (Kenya and Tanzania) for the period 1980-2010 and focuses on dry and wet spell characteristics during the two rainy seasons. The atmospheric and ocean conditions associated with the rainfall variability are also considered. Extreme occurrences of rainfall variable can result in droughts and floods which in turn may lead to socioeconomic disruptions. East Africa is highly dependent and vulnerable to the amounts and timing of rainfall.

Includes abstract. / Includes bibliographical references. / In response to an increase in shark attacks in the Western Cape over the last decade, a shark warning system called Shark Spotters that records white sharks (Carcharodon carcharias) in the surf zone was implemented in 2004 in Cape Town, South Africa.

Inlcudes bibliographical references / Micronekton fauna was investigated as part of a multi-disciplinary research project carried out in two different bioregions of the South West Indian Ocean: the East African Coastal Province (EAFR) and the Indian South Subtropical Gyre (ISSG). Food web structure was addressed using stable isotopes. Since particulate organic matter had high δ 15 N values in the ISSG province, copepods were chosen as baseline in trophic level estimations. Feeding regime and size were shown to influence the trophic position of micronekon. In the ISSG, carnivores (fishes and squids) and omnivores (crustaceans) had higher δ 15 N values and trophic positions than filter feeder s (gelatinous organisms such as salps and pyrosomes) and detritivores (leptocephali larvae). Fishes and squids encompassed a wide range of overlapping isotopic niches suggesting that organisms across different trophic levels feed on the same resources. Estimated trophic levels ranged from 1.67 to 4.73, showing that micronekton in the ISSG can be tertiary consumers. An average enrichment value of 6.7 ‰ was recorded between the sampled micronekton specimens and swordfish Xiphias gladius in the ISSG. Trawls, being selective in nature, were shown to sa mple smaller - sized micronekton with a lower trophic position than the micronekton being eaten by swordfish. In the EAFR, mean δ 15 N values of micronekton were higher than in the ISSG, exhibiting slightly higher trophic levels. Mesoscale dynamics in the EAFR provide mechanisms that enrich surface layers in nutrients and chlorophyll - a, therefore contributing to a higher abundance and micronekton species richness. In the ISSG, the large - scale wind - driven anticyclonic gyre pushes the nitracline, thermocline and deep chlorophyll maximum deeper in the water column , influencing the diel migration patterns of micronekton , with a significant proportion of micronekton staying in deep layers or slightly above the thermocline at dusk . Regardless of the differences in the ISSG and EAFR in δ 15 N values and trophic positions of micronekton, larger - sized swordfish sampled from these two provinces had similar mean δ 15 N values since swordfish are highly migratory and forage in different p arts of the Indian Ocean. However, smaller - sized swordfish specimens had lower mean δ 15 N values. With a combination of trawl surveys, stable isotope estimates, stomach content and acoustic analyses, this study shed new light on trophic interactions in the oligotrophic ISSG province.

Bibliography: leaves 36-43. / The dusky kob Argyrosomus japonicus is an important commercial and recreational linefish species in South Africa. It has a wide distribution range from Cape Agulhas to the Mozambique border. Juveniles A. japonicus <1070 mm) occur inshore and in estuaries where surf-zone and estuarine anglers target them. Adult A. japonicus (> 1070 mm) are caught beyond the surf zone by line fishermen. In this study, 380 juvenile dusky kob were caught by hook and line from the Breede River, Fish River, and Keiskamma River estuaries. Age of juvenile A. japonicus in these three South African estuaries was estimated by counting growth rings in sectioned sagittal otoliths read under a dissecting microscope using reflected light. The reproducibility of otoliths readings was described by the average percentage error (APE) index and was found to be 0.44% (Breede), 2.78% (Fish), 0.25% (Keiskamma) for an experienced reader and 0.5% (Breede), 4.37% (Fish), 0.53% (Keiskamma) for an inexperienced reader. Comparisons of A. japonicus otoliths by an experienced and an inexperienced reader indicated a reasonable between-reader consistency, however, the otoliths from the Fish River estuary were more difficult to read than from the other two estuaries. The Schnute growth model was used to determine which sub-model would best describe the growth of juvenile A. japonicus. Linear regression lines were fitted to the age-at-length growth curves of juvenile A. japonicus for each estuary to determine whether there were significant differences in growth rate. It was found that growth was the highest in the Breede River estuary (113.7 mm/yr), followed by the Keiskamma River estuary (92.1 mm/yr) and the Fish River estuary (83.9 mm/yr). Variable growth rates of juvenile A. japonicus in the three estuaries may be related to food availability and prey item types and to a lesser extent to water temperature in the estuaries. The comparisons of estuarine diets of A. japonicus indicate that juvenile dusky kob in different estuaries have different dominant prey species. There were one or two taxa dominant in each estuary with Galeichthys feliceps (61.9%), and the mysids (71.8%) being the most important prey items in the Breede River and the Great Fish River estuaries respectively, while teleost Pomadasys commersonnii (73.8%) were the most important prey species in the Keiskamma River estuary.

Includes bibliographical references. / Cultured fish are commonly afflicted by disease caused by monogenean flukes, resulting in significant production losses. In vitro trials were conducted to identify an effective treatment against the monogenean flukes Calceostoma sp. and Diplectanum sp. infecting the silver kob Argyrosomus inodorus. Treatments included praziquantel, formalin, freshwater. hydrogen peroxide and copper sulphate. Freshwater was found to be 100% effective on both species of flukes, whereas praziquantel was more effective at a higher concentration. The other treatments were not effective against the flukes and are not recommended for use.

Includes bibliographical references (p. 77-84). / The World Summit on Sustainable Development (WSSD) Plan of Implementation encourages the implementation of an Ecosystem Approach to Fisheries (EAF) management by 2010. Signatory countries, which include Namibia, have adopted this as being necessary for the sustainable use of their marine resources. However, there has been little progress made towards developing simple structured guidelines for implementing an EAF within fisheries management organisations. As part of an EAF project implemented by the BCLME (Benguela Current Large Marine Ecosystem) programme, a series of Ecological Risk Assessments (ERA) were conducted for selected fisheries, which focussed on identifying all major issues related to EAF that are not adequately addressed by present management strategies. This methodology was repeated for the Namibian Rock Lobster fishery. Highly prioritised issues from the workshop were used to construct causal maps and value trees, for which indicators were suggested in consultation with stakeholders. The results of the ERA confirmed that there is a severe lack of transparency and shared understanding among stakeholders in the Namibian Rock Lobster Fishery, which is causing high tension and user conflict within the fishery. However, the importance and strength of the ERA process was found to lie in the discussion that it facilitates amongst stakeholders. Causal maps proved very useful in placing perspective on the perceived problems associated with the current management of the Rock Lobster fishery and the hierarchical structuring of value trees proved extremely useful in facilitating the transparency of the process. A list of specific objectives and suggested indicators is presented here, but there remains paucity in the data that are needed to inform some of these suggested indicators. Thresholds for these suggested indicators are defined here and are needed for evaluating the indicators for combination into an overall evaluation of the implementation of an EAF in this fishery. Expert systems are suggested here as a good tool to do so through synthesizing information from a large number of indicators for the decision-making process and to readily incorporate updated information. The tentative set of indicators presented here needs further work. However, the results of the present thesis can be used in designing such a system, to the benefit of the Namibian Rock Lobster fishery and the ecosystem this fishery depends on.

Summary in English. / Bibliography: p. [199]-210. / The primary aim of the study was to assess the status and productivity of chokka squid. Main hypotheses examined are the following: that the sharp decline in the trawl fishery catch per unit effort (CPUE) data in the early 1980s, reflects a real decline in the trawlers catch rate; that the decline in the trawl CPUE index is caused by the jig fishery removing the biomass that otherwise would be available to the trawl fishery; that the jig fishery "disturbs" the spawning process and causes a decline in subsequent recruitment. Catch and effort data from the two fisheries, as well as biomass estimates from spring and autumn research surveys, were used. The two main fisheries and the catch and effort data are described. General Linear Modelling (GLM) was performed on the CPUE data from the trawl fishery in order to obtain annual indices of abundance. Further, results from a GLM analysis on two years of monthly jig CPUE data are presented. The dynamics of the stock biomass on the spawning grounds were modelled in order to assess the effects of current levels of effort and the existing closed season on the resource. The dynamics of the stock and the fishery were captured by a simple biomass-based model. Two dynamic methods were used to estimate model parameters: 1. a process-error estimator; 2. an observation-error estimator. All model parameter were estimated by maximum likelihood, and the corresponding confidence intervals were estimated by bootstrapping.