Linking Hydrodynamic Simulation with Sardinella Lemuru Distribution in the Coastal Water of Trenggalek

Abstract

Sardinella lemuru is a key small pelagic fish in Trenggalek waters, yet its stock is increasingly threatened by overexploitation. Limited understanding of larval dispersal has hindered effective management, particularly in defining critical nursery areas. This study presents the first spatially explicit simulation of S. lemuru larval transport in Prigi Bay, explicitly linking hydrodynamic forcing with early life stage ecology. A coupled MIKE 21 Flexible Mesh (FM) hydrodynamic and Particle Tracking model was applied, integrating bathymetry, tides, wind fields, and temperature. The dispersal of 1000 virtual larvae was simulated over 30 days during four seasonal peaks. Results show that strong Indian Ocean currents (>0.15 m/s) dissipate upon entering the bay, generating complex circulation and eddies that enhance larval retention. A persistent upwelling zone in the southeastern bay supplied high nutrient concentrations and coincided with larval aggregation, indicating a vital nursery habitat. These findings reveal that larval survival depends not only on seasonal current transport but also on local retention processes and food availability from upwelling. By identifying key retention and nursery zones, this study provides novel insights that can guide spatial management, such as the establishment of protection areas and the regulation of fishing seasons, to ensure the sustainability of S. lemuru fisheries in southern Indonesia.