Includes bibliographical references (leaves 43-44). / In an attempt to improve the quality of preserving seawater nutrients for delayed analyses, a sample of unfiltered and aged nutrient-depleted seawater was obtained from Marine and Coastal Management (M&CM) and spiked with small different volumes of standard nutrient solutions. These were prepared into 100 mL glass bottles to constitute the lowest, intermediate and highest levels of dissolved inorganic phosphate (0.5, 1.5, 3.0 μM), nitrate (5, 15 and 30 μM) and ammonium (0.5, 1.5, 2.5 μM) that are found in the southern Benguela region. After spiking, the samples were analysed to determine their "true" initial concentrations and immediately quick frozen using liquid nitrogen. A time series analysis (up to seven weeks) was performed by first fast-thawing the samples using a microwave oven and fixing up the nutrients within 20 minutes. Variations in nutrient concentrations did not exceed 7% for phosphate, 4.0% for nitrate at all levels and 8% for ammonium at the intermediate and highest levels, but varied by 19.2% at the lowest level. Statistical tests for significance of the means were made at a = 0.05 level and no difference was found at any level for the nitrate, and the lowest level phosphate. The higher levels of phosphate, and all ammonium were found to be significantly different. Hence, the experimental conditions employed in this paper would not be recommended for the all ammonium and the higher levels of phosphate concentrations. These variations were however not large or regular in pattern but erratic, which suggested that they were not due to microorganisms and optimizing those conditions may well to yield improved results.

Advances in remote sensing and tagging technology have made it possible to investigate the relationship between oceanographic dynamics and the distribution of certain marine species. For this study, surface chlorophyII-a concentration was used as a proxy for underlying related productivity, rather than as a direct indicator of prey density. Post-breeding, adult female southern elephant seals from Marion Island were tagged with conductivity, temperature and depth satellite-relayed data loggers (CTD-SRDL's) and their foraging behaviour was examined in relation to different chlorophyII-a concentrations. Optimal foraging and area restricted search theories predict that travelling speed and turning frequency would be quantifiably affected by prey density, which is in turn affected by the underlying richness of primary producers.

The St Helena Bay Monitoring Line (SHBML) stretches 197 nautical miles off Elands Bay on the west coast of South Africa. It is an extensive long term project on environmental monitoring, running from 2000 till 2012 on an almost monthly basis but currently running on a quarterly basis. It extends through the nursery grounds and part of the transport zone for hydrology and productivity in areas that are significant to early life history of small pelagic fish. Environmental, acoustic and zooplankton data have been collected along the SHBML to obtain information on ocean environment, pelagic fish abundance and also zooplankton abundance. This study used an interdisciplinary approach, analysing historical data collected during biannual surveys of small pelagic fish, to investigate seasonal and spatial variability of pelagic fishes in relation to environmental variability in St Helena Bay. Surface values from 2000 to 2010 of temperature, salinity, oxygen and chlorophyll were analysed in relation to zooplankton and fish densities. The results show partial / weak seasonality of SST in offshore and also in coastal stations. Zooplankton, chlorophyll and oxygen show limited seasonality only in nearshore stations. Strong cross-shelf patterns of SST, chlorophyll, salinity, oxygen, zooplankton biomass and fish abundance were noted. These were expected results from a coastal upwelling system where primary productivity during summer is increased in the nearshore zone. There was a positive relationship between salinity and SST (r = 0.821, p< 0.0001) and a negative relationship between chlorophyll and SST (r = -0.549, p< 0.001), as would be expected in a coastal upwelling environment. When other variables were examined (also in pairs), there were no relationships between SST and oxygen, fish and zooplankton, fish and chlorophyll, fish and SST, fish and oxygen, and chlorophyll and zooplankton. A GLM was fitted to the data to investigate the relationship of pelagic fish density with zooplankton biovolume, chlorophyll, SST and oxygen; the GLM results showed a negative relationship between zooplankton abundance and pelagic fish (t=-1.980, p=0.049). Based on these results, it appears that the SHBML data were not able to pick up seasonal signals but have shown interannual variability and also some inshore-offshore differences.

Includes bibliographical references (leaves 24-26). / Copepod abundance data were collected during the annual pelagic fish spawner and recruit stock assessment surveys, in summer and winter from 1988 to 2000. These data were used to examine temporal and spatial variability in abundance and community structure of copepods in the southern Benguela, by estimating changes in abundance (No. mol) of individual species and size-classes. The relative abundance of Calanus agulhensis, Calanoides carinatus, Centropages brachiatus, Metridia lucens. Oithona spp., On cae a spp., copepod nauplii and other small copepods show that these taxa were important in driving total copepod abundance changes in the region. A general linear model (GLM) was used to help control for different factors that might affect interannual variability in copepod abundance: season, area, chlorophyll concentrations and sea surface temperature. The southern Benguela was divided into six sub-areas. Results of the GLMs show the largest abundances of copepods on the northern and central West Coast, fewer copepods on the central and eastern Agulhas Bank and fewest copepods on the south West Coast and western Agulhas Bank. Relative abundance time-series of four cope pod size-classes (cyclopoid copepods «900 μm total length (TL )), small calanoid copepods (900-1000 μm TL), medium calanoid copepods (1000-2000 μm TL) and large calanoid copepods (2000-5000 μm TL)) show that there was a possible change in control mechanism of copepods in 1996 from bottom-up to top-down. Moreover, in winter 1999 there was a unique event during which the abundance of various species showed a marked decline, but returned to normal levels in 2000. The time series of relative abundance showed reduced numbers of all four size-classes in 1992 1994. These findings indicate that factors affecting interannual variability of copepods are complex, but that, similar to previous findings, the southern Benguela system has not undergone a major change over the past two to three decades in terms of total copepod abundance in the different sub-areas.

Includes bibliographical references (leaves 25-32). / GPS telemetry in conjunction with a recent diet time series and historical dietary informationwas used in this study to obtain novel insight into the dietary trends and feeding ecology of Cape gannets Morus capensis on the Namibian islands. particularly Ichaboe and Mercury. The gannet diet has changed substantially since the 1950s. refiecting spatio-temporal changes in the availability of commercially important pelagic prey species. The more recent diet time series for Ichaboe Island (Nov 1995 to Feb 2004) showed that trawler scavenged hakes Merluccius spp and naturally foraged saury Scomberesox saw'us dominated the diet by both contribution to mass (35 and 34 %, respectively) and frequency of occurrence (34 and 25 %, respectively). In a significant contrast, juvenile horse mackerel Trachurus trachurus capensis (40 % mass, 26 % frequency) and juvenile snoek Thyrsites atun (20 % mass, 20 % frequency) were the two main prey species at Mercury Island during Oct 1996 to Feb 2004. Multivariate analysis of data showed significant time and site effects in diet composition between Ichaboe and Mercury for the period Nov 1996 to Mar 1999. Twenty-five and 15 GPS field deployments were made on birds at Ichaboe and Mercury, respectively, during the 2003/4 breeding season. Birds from both locations showed significant differences in their foraging patterns. Birds from Ichaboe had shorter foraging trips (24.3 hrs vs 29.4 hrs),traveled shorter distances away from their island (130 km vs 197 km) and had shorter foraging path lengths (422 km vs 673 km). Birds from Ichaboe foraged in two dominant directions: west. to obtain mainly scavenged fish offal, and north to obtain forage fish. Mercury birds foraged only north, overlapping their foraging zone with birds from Ichaboe in a northerly direction, between 25.8° Sand 24.4° S. Birds at all colonies - especially in the south - appear to be constrained by lower quality food and generally poor feeding conditions which seem to be a limiting factor.

Includes abstract. / Includes bibliographical references. / The potential of phytoplankton particle spectra to be used as the basis for an indicator of the suitability of feeding habitat for fish recruits in the Southern Benguela was investigated. Phytoplankton samples collected on regular cruises on the St Helena Bay Monitoring Line (SHBML) off Elands Bay on the west coast of South Africa had been analysed with the Coulter Counter and formed the basis of this study. Chlorophyll a content of phytoplankton samples was also measured on monthly cruises and with total particle concentration (determined by the Coulter Counter) showed that overall phytoplankton cells represented a significant portion (76%) of samples collected. Surface particle spectra were constructed for the 12 stations on the SHBML for each of 15 monthly cruises between September 2000 and February 2007.

This study investigates the hydrographic and dynamic properties of the continental shelf region between Cape Juby (28.5 °N) and Agadir (30.4 °N) within the Moroccan Sub-region of the North West African Upwelling System. Data came from two cruises conducted in June (beginning of summer) and November (end of autumn) 2013. Coastal upwelling was obvious in both cruises in the in-situ temperature and salinity data as well as in remotely sensed sea surface temperature maps. ADCP data showed the presence of a strong jet like current associated with enhanced upwelling off Cape Juby. This strong quasi-permanent upwelling center was observed during both cruises. It results from the orientation of this portion of coast which is aligned with the dominant wind direction, as well as a wind intensification near the cape. The presence of a secondary upwelling front was also observed near the shelf break. It was accompanied by an intense baroclinic jet. The EK60 data showed evidence of internal waves as well as small and mesoscale turbulence that were probably strongly interacting with the mean upwelling circulation and made a straightforward interpretation of the data quite challenging. However, this study revealed the main physical processes of this poorly studied region, as well as their seasonal variability.

Sharks are vulnerable to exploitation as a result of their biological characteristics. Markrecapture models were applied to conventional tag recapture data and acoustic telemetry data to estimate abundance, apparent survival, recapture probability and temporary emigration for the pyjama shark, Poroderma africanum in Mossel Bay, South Africa over a five-year period. This study applied Pollock's robust design (with the conventional tag data) and Cormack-Jolly-Seber (CJS) models (with the acoustic tag data) to analyze the mark-recapture data. In addition, a von Bertalanffy model was fit to the data to estimate individual growth. The best-fit robust design model showed the population as having no temporary emigration, survival probability that is dependent on the length at first capture, and time-constant capture probabilities. The best-fit CJS model showed the population also having time-constant survival, but sex dependent capture probabilities. Robust design abundance estimates (with 95% C.I.) in Mossel Bay varied from 279 (102-787) sharks to 733 (320-1777) sharks, although confidence intervals were quite large. CJS apparent annual survival (95% C.I.; CJS) was estimated to be 0.271 year⁻¹ (0.04 to 0.56) and annual recapture probability (95% C.I.) was estimated to be 0.008 year⁻¹ (0.003-0.20), indicating that survival and recaptures for this endemic species are relatively low. Annual somatic growth rate (k) was estimated to be 0.213 year⁻¹, indicating that this population is slow growing, a characteristic common in most shark species. Overall, the results in this study provide baseline knowledge on this population in Mossel Bay and can be used to implement proper management techniques. This knowledge can be further expanded upon to give a more in-depth understanding of all size and age classes in the population and the role that the environment and anthropogenic activities play in the population structure.

Includes bibliographical references (p. 51-59) / A retrospective statistical analysis of catch and effort data for sharks captured in protective gill nets along the KwaZulu-Natal coastline was carried out with the objective to establish if the frequency of shark catches is related to different phases of the moon and secondly to season.

This thesis assesses the relationships between the El Niño-Southern Oscillation (ENSO), rainfall and South African commercial winter wheat yields from 1974 - 2000. The analysis is through a combination of the Pearson's product moment correlation coefficient and an assessment of the magnitude and consistency of rainfall and wheat anomalies in the year of, and the year following warm (El Niño) and cold (La Niña) ENSO events. The ENSO - rainfall relationship is analysed on timescales from 1 - 24 months and this study finds that there are more unusually dry and unusually wet months during El Niño events than during La Niña episodes (where dry and wet months are <75°/o and over 25~·'0 more than the 1921 - 2000 mean, respectively) and these conditions are consistently found in some rainfall areas during each El Niño or La Niño event; there is marked inter - El Niño and inter La Niña variation in late summer and annual rainfall; and that there has been a significant shift in the timings of maximum rainfall anomalies during El Niño episodes from an earlier investigation. The effects of rainfall on the wheat yield vary spatially, but are most apparent in the Free State where severe droughts have resulted in reduced yields. In the Northern Cape and Western Cape anomalously wet conditions, especially in late summer, coincide with reduced wheat yields. The ENSO - wheat yield relationship is not a simple linear one, and despite yields in the Northern Cape and Western Cape tracking Pacific sea surface temperatures by nearly a year, El Niño and La Niña years are not synonymous With increased or decreased yields in any province. ln fact, maximum and minimum yields in the Free State and Northern Cape are found in the year of, or year following a La Niño event, and consequently the present predictability of wheat yields by ENSO is limited. The relationships between ENSO, rainfall and wheat yield in South Africa is not readily apparent, which may be due to the short (<30 years) data set or mediating factors outside this study such as farm - management strategies or hemispheric variation in the evolution of El Niño and La Niña events.