Includes bibliographical references (leaves 48-54). / Ancient intertidal stonewall fish traps are found world-wide and those along the SouthAfrican south coast are the focus of my thesis. These fish traps, known locally as 'vywers', have recently enjoyed much media attention as interest increases in both South Africa's cultural heritage and its diminishing fish stocks. Two pioneering studies, by Goodwin (1946) and Avery (1975), provided the only documented knowledge of these vywers. My study aimed to locate, survey and document the main concentrations of vywers within a 300-km stretch along the south coast. A total of 43 sets of vywers was located by aerial surveys, 30 of which are only accessible through private land. This affords them some measure of protection, together with five located off reserves, but diminishes their educational and tourism value. Four sets of vywers were mapped in detail using aerial photogrammetry, a method that provided a rapid, extensive, accurate survey record in the form of geo-rectified ortho-images of these sites. The vywers are built in both exposed and sheltered environments, constructed from in situ rock material built into walls with either angular or curved shapes. These walls may occur singularly or in complexes of up to 25 traps. Vywers are prone to decimation by wave action and storm damage and so require maintenance to retain their characteristic form and associated cultural information. Tensions have, however, arisen between those who maintain and fish the vywers, and fisheries managers. Data from a questionnaire survey compared with records from the literature showed that species composition has not changed significantly in the last five decades. The fish are caught most frequently during new-moon spring-tides, especially in the winter months. The vywer fishery, currently active at only two sets of vywers, targets primarily mullet species (mostly Liza richardsonii) but infrequently enjoys 'bonanza' catches of over-exploited linefish stocks such as galjoen Dichistius capensis. It is these latter catches that concern managers, in addition to the noncompliance of fishers in terms of catch composition and size, permits and gear.

Bibliography: leaves 54-57. / The economy of Eritrea depends on rain-fed agriculture, which is highly sensitive to seasonal and inter-annual variations of rainfall. Adequate amount of rainfall is required every year for adequate agricultural production and drinking water. Therefore, the distribution of seasonal rainfall in space and time is critical to the country's economy. Drought has great influence on the socio-economic aspect and livelihood of the rural population. Drought occurs in Eritrea due to anomalous regional atmospheric circulation. This study focuses on the summer rainy season of June, July and August (JJA). It examines atmospheric and oceanographic mechanism patterns associated to summer rainfall anomalies. The investigation mainly concentrates on wet and dry spells that occurred over Eritrea during the rainy seasons (June to August) of 1950's-1990's. Rainfall data was available from the Climatic Research Unit (CRU) Hulme dataset for a period of 1950 -1996 and this together with rainfall data from the Africa Data Dissemination Service was used to determine the characteristics of wet and dry spells. Finally, NCEP-NCAR reanalysis climate data was used to analyse the atmospheric circulation associated with wet and dry years. It has been found that the pattern of the SST along the eastern Pacific and the Indian oceans seem to influence the occurrence of the anomaly rainfall years. Correlation analysis shows that Eritrean summer rainfall is more strongly correlated with the eastern Pacific and Indian Oceans SST. Thus, the drought records in Eritrea are mainly associated with EI Nino events.

The South African midwater trawl fishery targets adult horse mackerel (Trachurus capensis) on the Agulhas Bank. The bulk of the catch is taken by a single midwater trawler. The bycatch of this fishery is investigated by analysing observer records from 2004 to 2014 to report on bycatch composition, volumes and temporal and spatial patterns. Small fauna were analysed by extrapolation of sample weights and large fauna were counted. The midwater trawl fishery was estimated to have caught 25 415 t annually, with a bycatch rate of 6.9% of the total catch, by weight. Bycatch species with the highest average annual catches were chub mackerel (Scomber japonicus), redeye roundherring (Etrumeus whiteheadi), ribbonfish (Lepidopus caudatus) and hake (Merluccius spp.). Large fauna bycatch species included Cape fur seals (Arctocephalus pusillus), sharks (15 species), sunfish (Mola mola) and cetaceans (two species). Temporal analysis revealed significant differences between day-time and night-time CPUE for nine species, and significant differences in seasonal CPUE for 17 species. Spatial analysis of small fauna species composition and of large fauna species composition identified three groups in each. The 100% observer coverage is high compared to other South African fisheries, and, although the average sampling rate of 1.56% is low, an increase in the sampling rate might not be feasible owing to the size of catches. The bycatch rate in this fishery is low compared to other South African trawl fisheries but similar to global midwater trawl bycatch rates. There are species overlaps with various fisheries, namely the demersal trawl, small pelagic, linefishery, shark longline and squid fisheries, yet the total catch estimates from this fishery are generally small relative to catches taken in the target fisheries.

Includes bibliographical references (leaves 94-104). / Rainfall over Tanzania is highly variable. In recent decades the country has been devastated by floods and droughts. The Tanzanian population relies heavily on seasonal rainfall. Over the northern part of the country, the rainy season occurs in two phases, the short rains (October-December) and the long rains (March - May). Over the southern and the western areas, the rainy season occurs during November - May. This study aims at identifying factors that may playa role in the rainfall variability over the southern region of Tanzania. This study indicates that over the Indian Ocean, the sea surface temperatures (SSTs) over the northeast of Madagascar have a strong relationship with the rainfall in southern Tanzania during the OND rainfall, while the SSTs over the southeast Atlantic have a strong relationship during the JFM rainfall. It has also been revealed that the El Niño/ Southern Oscillation (ENSO) have influence on rainfall variability over the region. The warm/cold ENSO events would impact both a wet or dry year. Such contradiction has imposed a challenge to the forecasters of seasonal rainfall over southern Tanzania.

Includes abstract. / Includes bibliographical references (leaves 55-61). / An Age Structured Model (ASM) was develop in which dynamic and density-dependent cannibalism was included as a top-down control on a modeled population of M. paradoxus which used spawner biomass and maternal based recruitment. The ASM was used to evaluate the effects cannibalism had on age structure, recruitment and spawner biomass of the modeled population. The development of the model was described and evaluated with special emphasis on incorporating cannibalism and maternal based recruitment.

This study assessed a man-made salt-water pond (saltwater pond 1 SP1) as a potential site for the development of an oyster hatchery in Velddrif, South Africa. Over the study period it was observed that the site was not suitable for oyster larvae culture due to the following factors: temperature spikes during the summer months, low dissolved oxygen levels, high salinity levels, and the proliferation of the filamentous green algae (FGA), mainly the sp. Rhizoclonium implexum. Widespread patches of R. implexum were observed within SP1 and increased in biomass over the study period. Biomass patterns were not measured within this study, however microcosm experiments directed at nutrient depletion rates caused by FGA proliferation assessed the effect of the FGA on the system. Within microcosm experiments with and without FGA, nitrite within the system was significantly lower in the FGA inclusion treatment. Pond nutrient dynamics within the system indicated that widespread nutrient depletion occurred between the incoming water and the rest of the pond, and it was clear that the inflow station had significantly higher nutrient concentrations than all the other stations within SP1. Phytoplankton concentrations were extremely low and could be attributed to the FGA dominated state within SP1. Taken together with the fact the water levels within SP1 were not stable, the data suggested that SP1 was not an optimal source of seawater for either algal or larval oyster culture, and an alternative oyster hatchery site should be assessed.

Bibliography: leaves 73-78. / In this study Quality Index Method (QIM) schemes for raw headed and gutted (H&G) fish and skinless fillets as well as cooked fillets of kingklip (Genypterus capensis) were developed in a shelf life study. The QIM schemes for raw H&G and skinless fillets are based on six and seven quality attributes respectively, with a scoring system from 1 to 6, where a score of six is best quality (perfect). For the case of cooked fillets the scheme is based on six attributes, with a scoring system from I to 5, where a score of five is best quality. Sensory analysis of cooked fillets was carried out parallel to sensory analysis of raw H&G and skinless fillets as well as microbial count study until 18 days of storage. These were used to decide the maximum storage time in ice and to observe how the different quality attributes of cooked fish, especially odour and flavour, deteriorated with storage time in ice, as they are the best symptoms of fish spoilage. However, the microbial count study alone was continued until 22 days in ice in order to follow the bacterial spoilage pattern with storage time.

Includes bibliographical references. / Photography has always had a record-keeping purpose, whether to document famous people, or other news-worthy events, such as wars (Webb et al . 2010). Prior to photography becoming a practical tool, researchers in biology relied on drawings and precise descriptions to pass on what they observed during field work (George 1980). In truth, there are very few fields in science which have not made use of photography in some form (George 1980). Taxonomy has been a benefactor, since colour images taken in the field can be used to record distinctive characteristics of organisms that may later lose their pigmentation during preservation (George 1980). Of more relevance to this paper are the many uses of photography in marine ecology which George (1980) suggests are “...to aid site and habitat description, to record the relationship of plants and animals to the environment and to one another, to measure population numbers and the size of individual organisms, and to record the changes in community structure that take place with time.” This list does not take into account the advantages of video to document behavioural studies. As the old adage explains, “a picture is worth a thousand words” and photographs taken at the shore are often far more valuable than lengthy written descriptions used to “set the scene” (George 1980). As with all methods of sampling, however, there is a trade-off between the advantages and disadvantages involved. The disadvantages are similar to those shared with most disciplines interested in sea-shore studies. For example, time is a limiting constraint, as most photographs need to be taken at low tide and indeed the most effective photographic sampling is carried out during spring low tides , when the greatest area of intertidal habitat is exposed. Capturing images during these brief windows often complicates large-scale spatial studies, especially with limited resources (Murray et al . 2006). Furthermore, issues may arise with the detail that can occur due to the resolution of the photograph, as well as identifying taxa of a similar appearance, and problems with analysis may arise where the organisms are in high concentrations and/or stratified (Murray et al . 2006). There are, however, many advantages to the correctly applied photographic method: the greatest perhaps being that the images may be stored and used for further analysis at a later date. These stored images can also be kept on record and used to analyse changes that may have occurred over time. Photographs also have another advantage, in that they are more easily interpreted by people without scientific backgrounds that may not easily understand graphs or complicated figures (Murray et al . 2006). Further examples of the application of photographic techniques in marine biology include photographic surveys and photographic tagging, which has for many years been used in identifying whales, dolphins or seals (McConkey 1999). Photography has also proved useful as a tool for conducting population counts, such as on the West Coast, where seal populations are photographed from the air to determine breeding success (Griffiths et al . 2004). Aerial photography has also been used in conjunction with infra-red photographic techniques to determine the extent of kelp populations along the South African coast (Bolton and Anderson 1990)... This chapter uses repeat photography to illustrate changes that have occurred on rocky shores in the Western Cape over the past hundred years. Changes are documented under four categories; changes in range, climate change, intertidal invasion and direct anthropogenic effects. Images were sourced from books, members of the public and subject specialists and were selected based on their suitability. The sites of the images were identified and repeat photographs captured. The images depict the slow but progressive easterly spread of the kelp Ecklonia maxima and the range contraction of the warmer-water mussel Perna perna. Evidence suggests that a changing climate is the major driver of both of these changes. No change in zonation due to changing sea levels was observed. However, the range contraction of P. perna is complicated by the introduction of an alien mussel, Mytilus galloprovincialis. Repeat photography shows the changes that M. galloprovincialis has caused on the intertidal community in Saldanha Bay. Another invasive organism, Balanus glandula, is shown to have greatly altered the community structure of the Blouberg intertidal zone. Also of interest is the degree of building development that has taken place along the shore. Repeat photography proved a useful tool for documenting changes that are separated by large amounts of time, and is recommended as a useful technique for the surveillance and monitoring of rocky shores.

The two introduced beachfleas Orchestia gammarellus and Platorchestia platensis reported from South Africa have complicated histories, filled with misidentification and inaccurate documentation of distribution records. At the outset of this study, records of Orchestia gammarellus were restricted to - Langebaan Lagoon, Knysna and Milnerton Lagoon; while Platorchestia platensis had been recorded from Knysna and '34°S/19°E' (Gansbaai area). To verify this information, historical records were re-examined and 16 estuaries and lagoons in the Western Cape and two in the Eastern Cape Province were searched in order to determine the correct historical and current distributions of both species. It was found that historically and still today O. gammarellus occurs in Langebaan Lagoon. Its other current known distribution is the Berg River Estuary, Milnerton Lagoon and the Bushman's River; it never occurred in Knysna and records from that site were misidentifications of P. platensis. Historic records could only confirm P. platensis in Knysna and one other unknown location (specimen apparently mislabelled). Current searches conversely found P. platensis to be wide-spread, its range extending from Langebaan Lagoon to Algoa Bay (regions east of Bushman's River were not searched). Both species were described morphologically in detail taking their growth patterns into account and highlighting their differences, allowing for easier identification.

Includes abstract. / Includes bibliographical references (p. 72-81). / Meristic counts and morphometric measurements were made on previously frozen sardine Sardinops sagax to determine whether there is a difference in the shape of sardine from different areas around southern Africa. Because freezing influences body size, eight different freezing periods were examined to determine the effects of freezing duration on the caudal length, weight and 21 morphometric measurements of sardine collected from commercial catches at Gans Bay and Saldanha Bay, South Africa. The relative weight loss of sardine ranged between 0.86 and 2.49% and the relative loss in caudal length ranged between 1.57 and 2.54%. Most of the morphometric measurements showed small changes with increasing freezing period and, if they decreased, the decrease was gradual. Samples for the morphometric study were frozen between 12 and 17 weeks before analysis. Independent sample t-tests between these freezing periods confirmed that there was no change in the morphometric measurements over this five week period. In total, 35 samples were collected from three main regions: Namibia, the South African west coast and the South African south and east coast.