Assessing the use of surrogate species for a more cost-effective traceability of geographic origin using elemental fingerprints of bivalve shells

Abstract

Illegal, unreported and unregulated (IUU) fishing is a major threat to marine ecosystems and their living resources. IUU fishing promotes fraudulent mislabeling of seafood, which can pose serious risks to consumers’ health if specimens being traded originate from contaminated areas. The development and optimization of reliable tools to confirm the geographic origin of seafood is therefore of utmost importance under these scenarios. These tools are usually based in reference models of a given species that allows to trace the geographic origin of conspecifics. However, to date, the accuracy of such reference models requires the sampling of specimens of the species being surveyed, an issue that may impair the generalized use of this approach by authorities under real-case scenarios. A potential way to overcome this constraint is to apply a model built for a given species (working as surrogate) to trace the geographic origin of another one. The present study evaluated the effect of species-specific and spatial variability associated with the elemental fingerprints (EF) of shells of three commercially important bivalve species (Cerastoderma edule, Ruditapes decussatus and R. philippinarum) from five different locations over the northwestern and western Iberian coast and tested if a reference model based on one of this species could be used to reliably trace the geographic origin of specimens from the two other species. The EF of shells of the three species were significantly different within each location, as well as among different locations within each species. The reference models of the three species presented high cross-validation accuracy (ranging from 95.3% to 99.3%). The tests to infer if these models could reliably trace the geographic origin of samples from another species presented an overall accuracy ranging between 50% and 82.3%. Based on these results, and other requirements that a surrogate species must fulfil, it is possible to conclude that the three species hold the potential to be used as surrogates of each other, although C. edule is the one that better fulfills the requirements of a surrogate species. The optimization proposed in this study improves the cost-efficiency of using EF of bivalve shells as a tool to trace and confirm the geographic origin of bivalves, while also allowing to deliver a prompter reply to authorities.