A hydrodynamic and particle-tracking model reveals ENSO-driven dispersal patterns of round scad ichthyoplankton in the Sulu Sea, Philippines

Ichthyoplankton dispersal influences recruitment and sustainability of economically important fish populations. Illegal, unreported, and unregulated fishing has driven recruitment overfishing in the municipal waters of the Sulu Sea. To support stock replenishment, this study developed a high-resolution hydrodynamic model (Delft3D-FLOW) quantitatively validated in Panay Strait and idealized, passive particle-tracking setup (Delft3D-PART) to simulate round scad dispersal under varying El Niño-Southern Oscillation phases: 2010–11 La Niña, 2013–14 neutral, and 2015–16 El Niño. Palawan and the closed season area retained most of the particles across all ENSO phases. During La Niña, the Mindoro and Panay straits functioned as dispersal corridors and transported particles toward Panay. Under neutral conditions, Cuyo was a source and self-seeding zone. El Niño weakened the East Asian Winter Monsoon, leading to surface current reversal and increased particle losses, which may reduce stock replenishment potential. Marine protected areas inside municipal waters are identified as candidate sites that could complement the closed season area by safeguarding key sink and source zones. Because larval behavior and mortality were not included, simulated dispersal patterns represent physically plausible but conservative estimates of connectivity. Accordingly, management implications are intended as science-based preliminary guidance to support conservation and fisheries planning in data-limited regions.