Spatio-temporal variation of elemental fingerprints of Ruditapes philippinarum shells and its influence on the confirmation of harvesting location and time

Abstract

Mislabeling and illegal, unreported, and unregulated (IUU) fishing of Ruditapes philippinarum has been previously revealed using the elemental fingerprints (EF) of shells to confirm their geographic origin. However, temporal variation in EF may compromise model accuracy, requiring frequent sampling and model updates. This study determined the EF of R. philippinarum shells sampled over three different times (summer of 2018, summer of 2019, and winter of 2020) from several locations along the Iberian Peninsula to: i) evaluate their suitability to confirm geographic origin and evaluate whether temporal variations in these EF influence the accuracy to confirm geographic origin by using samples collected at different times for model development and testing; and ii) determine if this EF based-tool can accurately confirm sampling time. Canonical analysis of principal coordinates (CAP) models accurately allocated samples of summer of 2018, summer of 2019, and winter of 2020 to their original locations (with 86.5 %, 92.2 %, and 97.7 % accuracy). Using the CAP developed with samples from the summer of 2018 and 2019 being used as reference models, samples collected 6, 12, and 18 months later were correctly allocated to their original location with 85.6 %, 63.3 %, and 64.4 % accuracy, respectively. Moreover, a different CAP model successfully allocated 68.3 % of samples to their correct sampling time. The results demonstrated the potential to confirm the sampling location of six-month-old samples, as well as to confirm sampling time. However, it is paramount to determine and continuously update, at least every six-months, a chemical reference library of EF to allow the reliable use of predictive models.