Development of tilapia cage culture on Lake Victoria, Uganda

Abstract

Lake Victoria is the largest freshwater lake in Africa with significant social, ecological, and economic importance. In the face of declining fisheries, Tilapia cage culture was sought to bridge the demand gap and create employment opportunities. However, in a eutrophic lake with a large population dependent on it, fish farming should be supported by evidence-based decision-making. While used in systems elsewhere, existing tools will need adaption to address freshwater, context-specific challenges. This research aims to contribute towards evidence-based decision support for the planning and management of Tilapia cage culture in Lake Victoria. To set the context, farm production practices, existing regulatory frameworks and stakeholders' views were explored. Spatial planning and prioritization tools for efficient and equitable resource use were investigated. Considering the complex dynamics in the lake ecosystem, monitoring techniques for two objectives; rapid farm impact assessment or on-farm licensing were evaluated. The research investigates different aspects of cage farming in Lake Victoria. However, the findings will be applicable to several other tropical lakes. Results show that Tilapia cage culture is growing rapidly, dominated by large farms. Use of trash feed among smallholders poses a significant environmental risk and hence, strategies targeting them will be required. Using the Q methodology, stakeholders’ views on the growth of cage farming on Lake Victoria revealed optimism for economic growth but concerns around institutional gaps and aquaculture negative externalities. A review of the regulatory framework revealed EIA as a major management tool, but in its guidelines, cumulative organic loading from cages was overlooked. To contribute to protocols for environmental management, benthic macroinvertebrate assessment coupled with nutrient balance modelling were identified as robust tools for on-farm licensing of cage farming in eutrophic freshwater lakes. Other techniques like regression statistical modelling generated simple models that farmers could use to rapidly assess environmental performance. Site hydrodynamics were key in model performance. Using spatial planning, only 9.7% and 3% of the study area was found moderately to highly suitable for Tilapia farming in medium-large cages and small cages respectively. Current production is concentrated in eutrophic, shallow enclosed bays, in which other ecosystem services happen as well. In a spatial optimization scenario of cage culture growth, there were minimal trade-offs between ecosystem services that could occur in deeper waters. By contrast, the greatest compromises were made between recreation services and fishing nurseries. As technology advances, deeper parts of the lake will need exploration for aquaculture expansion.