Johannes Angala Iitembu

Giant kelp ( Macrocystis pyrifera ) is a vital primary producer in marine ecosystems due to its high net primary production (NPP) and carbon sequestration potential. This study investigated the NPP and carbon dynamics of farmed giant kelp at a farm site in Shearwater Bay, Lüderitz, Namibia, from May 2023 to April 2024. The study assessed giant kelp biomass, canopy area, seawater temperature, nitrate concentrations, dissolved organic carbon levels and carbon sources at the farm. The farmed kelp exhibited a total NPP of 7.570 kg C·m⁻²·year⁻¹, with a peak NPP of 0.855 kg C·m⁻² in June 2023 (winter), and reached a low of 0.342 kg C⋅m⁻² in August 2023 (winter), where it averaged 0.635 kg C·m⁻²·month⁻¹ with greater variability than in summer, where it averaged 0.627 kg C·m⁻²·month⁻¹. Correlation analyses showed no significant relationship between canopy area and NPP. Kelp biomass exhibited a weak positive correlation with NPP, but this association was not statistically significant. Temperature was also weakly positively correlated with NPP, while nitrate concentrations showed a moderate positive correlation with NPP at the farm. The DOC concentrations ranged from 2.94 to 5.12 ppm, with no significant depth variation. Isotopic analysis showed distinct carbon 13 isotopic signatures (δ¹³C) for seawater DOC (-26.63‰ to -14.61‰) and for the giant kelp (-13.69‰ to -12.32‰), indicating mixed sources like terrestrial inputs, in situ production, shifts and c. The study findings showed that nutrient availability was a key driver of NPP at the giant kelp farm, with implications for optimizing kelp farming management and assessing the impacts of kelp farming in coastal areas. The study supports the development of non-destructive monitoring indicators and calls for further research into nutrient cycling, carbon cycling, ecosystem productivity and blue carbon strategies associated with kelp farming to inform sustainable coastal ecosystem management.

Bottom trawling is not selective fishing method, resulting in the capture of many bycatch species. This study aimed to examine the distribution of bycatch species in the hake-directed bottom fishery and to determine their potential for bycatch management and mitigation. Observer data from a hake-directed bottom trawl fishery in Namibia from 1997 to 2014 was analysed. About 23 bycatch species, weighing 9,031,480 tonnes, were recorded. Trachurus capensis, Trachipterus trachypterus, Helicolenus dactylopterus, Lophius vomerinus, and Genypterus capensis were the dominant species, comprising 63.09% of the total catch by weight. Analysis of Similarities (ANOSIM) (R = 0.88, P< 0.05) revealed significant differences in catch composition based on sampling site. The Similarity Percentage (SIMPER) showed that three bycatch species contributed the most to the dissimilarity in groups for spatial distribution. Widespread distribution of bycatch species, with high densities in the central and southern regions, suggests that hake-directed bottom trawling could have negative effects on these species. Species with a higher proportion of their population removed as bycatch, are considered the most vulnerable and may be nearly exterminated. To avoid the risk of species extinction, the fishery must be managed through spatial exclusion and fishing seasons.

In the face of an increasing world population and a subsequent need for an increase in sustainable and healthy food production, low trophic species, such as oysters, emerge as a promising alternative. However, regional variations in oyster production techniques, market dynamics, and consumption patterns create challenges for both the global and local industry’s growth. In this study, a descriptive qualitative analysis of oyster markets across seven Atlantic regions was carried out. The Pacific oyster (Crassostrea gigas) was found to be farmed in most Atlantic regions except the US but is classified as invasive in Sweden and potentially invasive in South Africa. Other farmed and/or harvested species include native species (C. gasar and C. rhizophorae) in Brazil, the American cupped oyster (C. virginica) in the US, and the European flat oyster (Ostrea edulis) in France, Sweden, and the US. In Irish farms, Pacific oysters are primarily for export to European markets. The marine aquaculture sectors of Sweden, South Africa, and Namibia, as well as Brazil’s farming for C. gasar, were found to be underdeveloped. This study also observed a variation in licensing, property rights, and regulatory frameworks. Financial challenges for small businesses, ecological implications of seed production techniques, biosecurity risks, and public health considerations are emphasized as critical areas for attention. This study offers valuable insights into the selected markets and can serve as a useful resource for policymakers, aquaculture practitioners, and stakeholders in optimizing global shellfish industry strategies.

Southern mullet Chelon richardsonii is one of the important fish species found in the Walvis Bay lagoon (WBL) that is commercially exploited for local consumption. The southern mullet is, however, ...