The principal aim of this study was to establish the biological and environmental parameters governing the successful and sustainable cultivation of mussels in Saldanha Bay. The environmental study investigated seston, chlorophyll-a and particulate organic matter (POM) levels, water temperature dissolved oxygen and salinity levels in the bay and water flow in and around the rafts. The biological part of the study investigated the efficiency of food extraction, growth rates, mussel condition, fouling and production and yield on a rope, raft and farm scale. Saldanha Bay is well suited for the culture of mussels, particularly Mytilus galloprovincialis and Choromytilus meridionalis. Water temperature and salinity in Saldanha Bay were found to be near optimal for mussel culture. POM and chlorophyll-a levels were found to be high due to primary production resulting from the nutrient rich upwelled water outside Saldanha Bay. The mean levels of chlorophyll-a (8,6μg/l) represent 6%, by mass, of the total POM. On a bay scale the POM remained above the mussels maximum requirements (pseudofaeces threshold) during the study period. Mussels showed a preference for the phytoplankton portion of the POM. Approximately 40% of the chlorophyll-a was extracted from the water by the mussel farm. The efficiency of food extraction increased with mussel age. Rafts with seed mussels younger than 2 months, 3 to 4 months, 5 to 6 months and older than 6 months extracted 32%, 55%, 85% and 92% of the available chlorophyll-a respectively. An increase of rope spacing on the rafts resulted in 37% more chlorophyll-a and 30% more particle volume reaching the lee of the raft. Ambient water currents in the bay show flow rates of up to 22cm per second. However, on entering a raft with a rope spacing of 60cm, the water flow is attenuated by 90%. Increasing the rope spacing to 90cm resulted in a water flow attenuation of 72%. The increase in rope spacing ensures that the mussels in the centre of the raft are feeding on food levels close to, or above, the pseudofaeces level. Mussel growth rate at a rope spacing of 90cm is significantly improved as a result of the increased food delivery. There are other factors, however that effect mussel growth. Growth rates were found to be better in summer than in winter. The reduced winter growth rate is possibly due to competition with the maturing fouling organisms which settle in mid to late summer. Fouling by mussel spat and Ciona intestinalis is seasonal, occurring from December to May. C.intestinalis is prevalent in the centre of the farm and rafts as low energy waters are preferred by this species. Mussel spat settles mainly on the periphery of the farm and the rafts. Competition with fouling organisms reduces growth and increases mortality of the cultured mussels. Results indicate that the present spacing of rafts, (1 raft per hectare) is adequate under existing conditions. Any new farms should maintain batches of 50 rafts with channels between them to ensure water current penetration into the furthest reaches of the farm. Rope spacing on the rafts should be increased to between 60cm and 90cm. Mussel density should be regulated according to mussel size and fouling should be controlled to maintain yields.

Thesis (MScAgric)--Stellenbosch University, 2005. / ENGLISH ABSTRACT: This study examines the role of contracting in reducing transaction costs in smalIscale mussel farming in Saldanha Bay. Masiza Mussel Growers (Masiza), an initiative by the public and private sector to address the imbalances of the past through entrepreneurial development, are used as a case study hence a case study approach is followed. Two transactions were considered, one between Masiza and Blue Bay Aqua Farm (Blue Bay) and another between La Vie Sea Food Products (La Vie) and Masiza. These transactions form the basis for analysis. Market risks, uncertainties, environmental risks, information incompleteness, illiteracy, limited technical knowledge of farming, lack of appropriate infrastructure and lack of transport facilities are identified and examined as possible sources of transaction costs that constrain the existing supply chain relationship. The study shows that asset specificity, time specificity, and site specificity playa positive role in the supply chain as they result in relative dependency amongst parties. Opportunistic behavior within the existing supply chain is neutral, but appears to be relatively high on the spot or fresh live market. Characteristics of market transactions for mussels and associated transaction costs suggest that fresh-live spot market trading for Masiza is difficult to attain. This therefore motivates parties (Masiza) to contract or vertically integrate, as it is costly and risky to rely on spot live markets. Interviewees (Masiza) pointed out that the benefits associated with contract farming outweigh the transaction costs associated with this governance structure. Hence a market specification contract with the La Vie (a processing company), and a production management and resource provision contract with Blue Bay (a larger producer) were designed. They reduce transaction costs associated with fresh-live markets and ensure a more stable and reliable market for growers. / AFRIKAANSE OPSOMMING: Die studie ondersoek die rol van kontraktering in die vermindering van transaksie koste vir klein skaal mossel produsente in Saldanha baai. Die Masiza Mussel Growers (Masiza) word as gevallestudie gebruik. Twee transaksies met o.a. Blue bay Aqua Farm (Blue Bay) en La Vie Sea Food Products (La Vie) was ter sprake en laasgenoemde het as basis vir die analise gedien. Mark risiko, onsekerheid, omgewings risiko, gebrekkige informasie, ongeletterdheid, beperkte tegniese kennis, beperkte infrastruktuur en beperkte verroer fasiliteite is geidentifiseer en ondersoek as moontlike oorsake van hoë transaksie koste wat die huidige aanbod ketting strem. Die studie toon aan dat interafhanklikheid tussen die betrokke partye deur bate, tyd en area spesifisiteite bevorder word en dus 'n positiewe rol in die aanbod ketting speel. Opportunistiese gedrag binne die bestaande aanbod ketting is neutraal, maar blyk hoog te wees in die vars mark. Transaksie kostes en eienskappe blyk beduidende beperkinge te wees vir kleinskaal mossel produsente om aktief deel te neem in die mark. Die opstel van kontrakte (of vertikale integrasie) blyk dus 'n uitkoms te wees. Respondente het aangetoon dat kontrak boerdery voordelig blyk te wees. Laasgoemde het tot die ontwikkeling van mark kontrakte met die La Vie ('n verwerkings maatskappy) asook produksie bestuur en hulpbron voorsiennings kontrakte met Blue Bay ('n groot kommersiële produsent) gelei. Die kontrakte beperk transaksie koste vir die vars mark en verseker 'n stabiele en betroubare mark vir produsente. 'n Transaksie koste analiese word gebruik om transaksie kostes te ondersoek en te verifieer binne die industrie.

Mussels are important ecological engineers on intertidal rocks where they create habitat that contributes substantially to overall biodiversity. They provide secondary substratum for other free-living, infaunal or epifaunal organisms, and increase the surface area for settlement by densely packing together into complex multilayered beds. The introduction of the alien invasive mussel Mytilus galloprovincialis has extended the upper limit of mussels on the south coast of South Africa, potentially increasing habitat for associated fauna. The aim of this study was to describe the structure of mussel beds, the general biodiversity associated with multi- and monolayered mussel beds of indigenous Perna perna and alien M. galloprovincialis, and to determine the relationship between mussels and epibiotic barnacles. This was done to determine the community structure of associated macrofauna and the role of mussels as biological facilitators. Samples were collected in Plettenberg Bay, South Africa, where M. galloprovincialis dominates the high mussel zone and P. perna the low zone. Three 15 X 15 cm quadrats were scraped off the rock in the high and low zones, and in the mid zone where the two mussel species co-exist. The samples were collected on 3 occasions. In the laboratory mussel-size was measured and sediment trapped within the samples was separated through 75 μm, 1 mm and 5 mm mesh. The macrofauna was sorted from the 1 mm and 5 mm sieves and identified to species level where possible. The epibiotic relationship between mussels and barnacles was assessed by measuring the prevalence and intensity of barnacle infestation and the condition index of infested mussels. Multivariate analysis was used on the mean abundance data of the species for each treatment (Hierarchical clustering, multidimensional scaling, analysis of similarity and similarity of percentages) and ANOVA was used for most of the statistical analyses. Overall, the results showed that tidal height influences the species composition and abundance of associated fauna. While mussel bed layering influenced the accumulation of sediments; it had no significant effect on the associated fauna. Time of collection also had a strong effect. While there was an overlap of species among samples from January, May and March, the principal species contributing to similarity among the March samples were not found in the other two months. The outcomes of this study showed that low shore mussel beds not only supported a higher abundance and diversity of species, but were also the most structurally complex. Although the condition index of mussels did not correlate to the percentage cover of barnacle epibionts, it was also evident that low shore mussels had the highest prevalence. The levels of barnacle infestation (intensity) for each mussel species were highest where it was common and lowest where it was least abundant. This is viewed as a natural artefact of the distribution patterns of P. perna and M. galloprovincialis across the shore. Mussels are more efficient as facilitators on the low mussel zone than the high mussel zone possibly because they provide habitats that are more effective in protecting the associated macrofauna from the effects of competition and predation, than they are at eliminating the effects of physical stress on the high shore. Although mussels create less stressful habitats and protect organisms from the physical stress of the high shore, there are clear limitations in their ability to provide ideal habitats. The biological associations in an ecosystem can be made weak or strong depending on the external abiotic factors and the adaptability of the affected organisms.