Managing aquaculture in multi-use freshwater bodies: the case of Jatiluhur reservoir

The pressure on scarce freshwater resources from intensifying human activity is rising across the globe. This study presents the case of Jatiluhur - Indonesia's largest reservoir, where unregulated aquaculture expansion has contributed to environmental degradation and associated conflicts with other water-users. Aiming to identify a strategy to improve the sustainability of cage aquaculture within Jatilihur reservoir and other freshwater bodies facing similar challenges, this study consisted of an initial analysis of time bound satellite images of the reservoir and a systematic survey of 112 aquaculture farms. The results revealed that, with more than 45,000 production units in 2020, more than half of which are placed outside government-approved aquaculture zones, the carrying capacity of the reservoir is exceeded. An analysis of the farm-level production practices, pertinent to environmental regulation, indicated the existence of three main production strategies, with significant differences in eutrophication potential among them that would lead to better articulated policy actions. A feed manufacturer-focused policy to reduce total phosphorus levels in formulated diets by more than half, but still within the optimal level for fish performance, would have the most impact. Enforcement of registration and removal of illegal production units supported by satellite-based monitoring of compliance are key recommendations to support intensive cage culture remaining an important economic activity