A biomass-based trophic indicator approach for assessing fisheries sustainability: a case study of Jatigede reservoir, Indonesia

Sustainability assessment of fisheries as freshwater provisioning services requires indicators that reflect trophic structure and ecosystem function. This Study applies a biomass-based trophic indicator approach to evaluate the sustainability of fisheries in the Jatigede Reservoir, Indonesia. Data were collected from seven sampling stations during 2022–2023, including fish sampling, water quality measurements, and stakeholder interviews. The framework integrates fish diversity, productivity, condition factor, and predator biomass into a composite sustainability index. All indicators were standardized and combined into a composite assessment framework. The ecological status remained moderate (index = 2.0) in both years. Fish diversity increased slightly, whereas productivity declined. Predator biomass remained relatively high (45.7%), suggesting a possible trophic imbalance within the reservoir ecosystem. Compared with the abundance-based indicator, the biomass-based approach may provide an alternative perspective for evaluating trophic dominance and ecosystem structure. Sensitivity analysis using a one-at-a-time (OAT) approach showed that the sustainability classification remained unchanged across most weighting scenarios (Wp = 0.10–0.60), with no category shift observed in approximately 85% of cases. These results suggest that the index classification was relatively stable under the tested weighting assumptions, although broader validation is still required. The main contribution of this study lies in applying biomass-based trophic dominance as a diagnostic indicator within a case-study-based sustainability framework. However, the findings should be interpreted with caution due to limited temporal coverage, expert-derived threshold assumptions, and the absence of external validation. Overall, although the system remained in a moderate condition, the observed decline in productivity and persistent trophic imbalance may indicate early signs of ecological stress, highlighting the need for adaptive management and further validation across different reservoir systems.