Population structure of the European seabass (Dicentrarchus labrax) in the Atlantic Iberian Peninsula waters inferred from otolith elemental signatures

The European seabass (Dicentrarchus labrax) is a key coastal species in the northeast Atlantic, supporting valuable commercial and recreational fisheries. However, within the Iberian divisions 8c–9a, as defined by the International Council for the Exploration of the Sea (ICES), information on stock structure remains scarce. To address this gap, otolith elemental composition (element:Ca ratios) was analysed in 75 pre-selected three-year-old individuals (25 per location) collected between January and March 2025 from three sites along the Atlantic coast of the Iberian Peninsula: Avilés, Peniche, and Lagos. Elemental signatures from sagittal otoliths were obtained using solution-based and laser ablation inductively coupled plasma mass spectrometry (SB-ICP-MS and LA-ICP-MS) for bulk, core, and edge analyses, respectively. Six informative trace elements (Sr, Ba, Mg, Mn, Cu, and Li) were quantified, and spatial variation was assessed using univariate and multivariate statistics. Results revealed moderate spatial variability in otolith chemistry, with low to medium overall reclassification success (52% for bulk, 41% for core, and 56% for edge). Distinct elemental patterns were observed across locations, including elevated Mn:Ca ratios in Avilés, likely linked to local Mn pollution, and higher Li:Ca and Ba:Ca ratios in Peniche and Lagos, probably reflecting upwelling influence. Despite some regional heterogeneity, the overall overlap in otolith chemical signatures supports the ICES definition of a single, though not entirely homogeneous, seabass stock in the Iberian divisions (8c–9a). These results highlight a balance between connectivity and regional differentiation in D. labrax populations. Integrating complementary tools such as genetics, tagging, isotopic, and parasite assemblage analyses is recommended to further clarify connectivity and stock dynamics, supporting science-based management and conservation of seabass fisheries.