Spatial and Temporal Variability of Elemental Fingerprints of European Sardine (Sardina pilchardus) Scales: Implications for the Traceability of Geographic Origin and for Fisheries Management

The European sardine Sardina pilchardus, a key marine resource in Portugal and Spain, experienced severe population declines in the 2000s. To support its recovery, confirming the geographic origin of European sardine is essential. This study examines the spatial and temporal variability of elemental fingerprints (EF), using Inductively Coupled Plasma Mass Spectrometry (ICP-MS), of S. pilchardus scales. Specimens were collected from seven (in 2018) and five (in 2019) fishing harbors in Galicia (Spain) and mainland Portugal to confirm their location and time of capture, as well as evaluate how temporal variability influences the location predictive models when samples from different years are used for model development and testing. Thirteen elements (Ba, Ca, Co, Cr, K, Mg, Mn, Na, Ni, P, Sr, V, and Zn) were used in the models developed. Random Forest models using samples from 2018 and 2019 correctly classified over 95% of the specimens by location, within each year. Capture time classification achieved 95.3% accuracy. However, applying the 2018 model to samples from 2019 reduced accuracy to only 24.4%. Despite this constraint, the EF of fish scales provide a practical and reliable method to confirm capture time and geographic origin, allowing a more sustainable management of S. pilchardus stocks.