Identifying the critical life stage of a recruitment-driven decline in an exploited marine fish stock: The Bay of Biscay common sole

• Recruitment trends exhibited no spatial consistency across NE Atlantic sole stocks. • In the Bay of Biscay, sole recruitment declined since 2009 despite less fishing. • SSB decreased following the recruitment decrease. • Sole juvenile abundance declined from age 0 in four out of the six BoB nurseries. • Results suggest that pelagic-stage mortality drives BoB-scale recruitment. In the Bay of Biscay (BoB), the common sole (Solea solea) population supports a major commercial fishery. However, a decline in recruitment has been observed since the late 2000 s, despite management measures that have lowered fishing mortality. This study investigates the decline in sole juvenile abundance in the BoB coastal and estuarine nursery grounds and compares recruitment trends among sole stocks across the Northeast Atlantic. The analysis of stock assessment products revealed that recruitment decline preceded and drove the subsequent decrease in the coming spawning stock biomass, with a two-year lag. Time series of juvenile abundance, estimated using habitat suitability models based on young fish survey data, showed a decreasing trend since the 2000 s in four of the six main BoB nursery grounds, for juveniles at ages 0 and 1 year, in both spring and autumn. This decline in sole juvenile abundance shortly after metamorphosis indicates reduced settlement success in nursery habitats. Because this decline was observed across several nursery grounds from early juvenile stage, it suggests that changes in pelagic conditions may have impaired sole larval survival. Across the Northeast Atlantic, recruitment trends among sole stocks displayed no consistent latitudinal or spatial pattern, indicating population-specific responses to local factors.