Climate-driven ocean circulation shapes larval migration success and habitat connectivity in the European eel

Whether climate-driven ocean circulation alters larval migration success and habitat connectivity remains a key question in understanding recruitment dynamics of migratory fishes. Using the critically endangered European eel (Anguilla anguilla) as a model species, we combined particle-tracking simulations with synthetic otolith oxygen isotope predictions to examine how contrasting North Atlantic Oscillation (NAO) conditions influence larval migration across the North Atlantic. Simulations compared contrasting multi-year NAO+ (1989–1991) and NAO− (2008–2010) conditions, with migration success defined as simulated larvae crossing eastward of 20°W. Migration success was lower under NAO+ than NAO− conditions (0.00069% vs. 0.0012%), while simulated larvae required nearly 400 days to enter the Gulf Stream under NAO+ conditions compared with approximately 300 days under NAO− conditions. Larval outcomes also varied among release locations and depths, with the highest migration success occurring for May releases at 200 m, highlighting the importance of initial dispersal conditions in shaping transport pathways. Temperature and salinity experienced along simulated trajectories were used to predict synthetic otolith δ¹⁸O signatures. These isotope predictions differed between successful and unsuccessful trajectories and among contrasting migration scenarios, providing a complementary model output for evaluating whether alternative migration histories could generate distinguishable otolith isotope signatures. Overall, our results indicate that large-scale variability in North Atlantic circulation can substantially alter simulated larval migration duration and connectivity in European eels. Integrating particle-tracking models with synthetic otolith geochemistry provides a framework for generating empirically testable migration hypotheses, which could ultimately be evaluated against measured otolith isotope records to improve our understanding of climate-sensitive connectivity in long-distance migratory fishes.