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.

Includes bibliographical references (leaves 69-74). / Includes abstract. / Long-term ecosystem changes, such as regime shifts, have occurred in several marine ecosystems worldwide. Multivariate statistical methods have been used to detect such changes, but they have to date not been applied to the southern Benguela ecosystem. A weakness of many of the methods is that they require long time series data and do not provide robust results at the end of time series. A new method known as the sequential t-test algorithm for analysing regime shifts (STARS) is applied to a set of biological state variables and environmental and anthropogenic forcing variables in the southern Benguela.

Includes bibliographical references (leaves 64-70) / This study focuses on general features and variations of sea level at Zanzibar, and the relation of these to climate variability over the tropical western Indian Ocean during the 1997-1998 EI Niño and the 2000-2001 la Niña periods. The sea level data used in this study has been collected over a period of nine years from 1996 to 2004. Analyses have shown that the predominant type of tides at Zanzibar are semidiurnal with two high and two low water levels in each tidal day. Over the monthly cycle, two spring and two neap tides with different tidal ranges are observed. The tidal range may vary depending on the season of the year.

Includes bibliographical references (leaves 35-40) / An experimental trap fishery for the deep-water lobster spiny lobster Palinurus delagoae commenced in 2004, and was run until 2006. Data collected by on-board scientific observers were used to explore fishing effort, catches and catch per unit effort. The recent data were compared with those for a previous experiment conducted in 1994-1997, which apparently contributed to the collapse of the stock, to determine whether the stock had recovered and could sustain a trap fishery. There was a demonstrable recovery of the P. delagoae stock after the previous stock collapse, according to the catch rates and the size composition of catches between 2004-2006. However, catches of P. delagoae declined between 2004-2006. This was related to decreases in effort and in catch per unit effort over the three years. This, and a simultaneous decline in the by-catch of P. delagoae in the prawn trawl fishery off KwaZulu-Natal, suggests that the P. delagoae stock is extremely vulnerable to concomitant trawl and trap fishing. It is recommended that trap fishing should either be permitted at low levels of effort and catch only, or once more be suspended to allow the resource to recover.