Spatio-temporal variability of elemental fingerprints of goose Barnacles (Pollicipes pollicipes) capitula and its relevance to fight poaching through traceability

The goose barnacle (Pollicipes pollicipes) is one of the most important economic resources in the rocky shores of Portugal and Spain, supporting professional and recreational fisheries. Despite diverse management efforts, poaching remains a widespread problem, often violating spatial and temporal closures. Traceability tools based on biogeochemical signatures of P. pollicipes tissues provide a science-based solution to confirm provenance. This study examines the spatio-temporal variability of elemental fingerprints (EF) in P. pollicipes capitula collected at three different times from two to eight locations per time along the NW and W Iberian coast and assesses the potential of these biogeochemical signatures to confirm location and time of harvesting. Furthermore, to enhance the cost-efficiency of these tools, it also evaluates whether temporal variability affects the accuracy of predictive models by inferring harvesting locations when using samples collected at different times. A marked spatio-temporal variability in EF was observed, with all assessed elements (Al, Ba, K, Mg, Na, P, and Sr) playing key roles in all predictive models. The three Random Forest models assembled, each corresponding to a different sampling time, revealed high accuracy when assigning samples to their original location summer 2018 = 73.3–100 % of correct assignment, mean value 90.8 %; summer 2019 = 80–100 %, mean value 93.3 %. The model developed to confirm the sampling time achieved an accuracy between 86.7 and 100 %, mean value 93.3 %. However, when models were built and tested with samples from different sampling times, location accuracy dropped considerably (ranging from 0 to 83.3 %, mean value 5–31.4 %). Despite this limitation, these findings support fishery management by showcasing the possibility to confirm the geographic origin of P. pollicipes and determine whether they were illegally sourced from no take zones and periods.