Assessment of Fishing Pressure on the Ole Fish Population in the Customary Area of Tomia–Wakatobi National Park Using the FISAT II Approach

The ikan ole population in Tomia Island’s customary fishing grounds is subject to high exploitation from intensive fishing pressure. This study applied the FiSAT II framework to assess stock status by analyzing growth, mortality, recruitment, yield-per-recruit (Y/R) and biomass-per-recruit (B/R) using the Knife-Edge Selection method. Length-frequency data were collected from artisanal fishers between January and March 2023 and were analyzed to estimate von Bertalanffy growth parameters (L∞ and K), mortality rates (Z, M, F), exploitation rate (E), recruitment patterns, and cohort structure through the modal progression analysis. The estimated growth parameters were L∞ = 12.39 cm and K = 1.20 year⁻¹, assuming t₀ = 0. Total mortality (Z) was 6.36 year⁻¹, with natural mortality M = 2.57 year⁻¹ and fishing mortality F = 3.79 year⁻¹, yielding an exploitation rate E ≈ 0.60. Recruitment occurred year-round, with a pronounced peak in June–July that accounted for about 41% of annual recruitment. Cohort analysis indicated that mid-sized individuals (9–10.5cm) at the start of the year progressed into older cohorts (10.8– 11.6cm) by March, while individuals under 9cm were rarely observed, suggesting intense fishing pressure on juveniles. Y/R and B/R analysis showed that E₅₀ ≈ 0.28, at which biomass declined to 50% of its unexploited level with Y/R ≈ 0.045, and Emax ≈ 0.42, which maximized Y/R (≈ 0.060) but reduced biomass to 28% of the original level. The current exploitation rate (E ≈ 0.60) exceeds both thresholds, indicating overfishing. Although growth and recruitment remain stable, high juvenile capture rates and excessive exploitation threaten long-term stock sustainability. Management action is urgently required, including the establishment of a minimum catch size of at least 9.5– 10cm, an increase in mesh size to at least 9mm to reduce juvenile capture, the implementation of a seasonal closure from May to July to protect peak recruitment, and the reduction of fishing effort to align E with sustainable levels. Regular length-frequency monitoring is essential to evaluate the effectiveness of these management measures and to prevent further overfishing of ikan ole stocks in Tomia’s customary fishing grounds.