Otoliths imprinting of sole ( Solea solea) from the Bay of Biscay: a tool to discriminate individuals from nursery origins?

Sole nurseries are located in the main bays and estuaries of the Bay of Biscay, where juveniles from the same stock concentrate and constitute temporarily isolated groups. This context being favourable for elemental analyses of juvenile otoliths, this study has been initiated with the aim of obtaining environmental imprints of the main nurseries of origin of juveniles recruiting to the adult stock, and of evaluating the relative contribution of these nurseries to the stock. The objectives were to compare (i) the otolith elemental imprints obtained by sampling juveniles in the Loire and the Gironde nurseries, and (ii) two multi-elemental analysis techniques: laser ablation inductively coupled plasma mass spectrometry (LA-ICPMS) and solution-based ICPMS (SB-ICPMS) adapted to small volumes. Depending on the fish origin, differences in Sr and Rb concentrations were shown using LA-ICPMS. Comparisons between the antero-dorsal and postero-ventral sites from where otolith material was ablated also suggested a spatial heterogeneity in otolith composition at least for some metals. From linear discriminant analyses, 73 % and 79 % of individuals (bootstrap estimations) were correctly classified with respect to their origin from the composition of the antero-dorsal and postero-ventral areas, respectively. The SB-ICPMS analysis was more powerful, which resulted in an 89 % rate of correct classification from a 2-variable model (Mg and Cd), whereas a 5-variable model (Li, Mg, Rb, Cd, Th) resulted in a 91 % rate of correct classification (bootstrap estimations). These results confirm that sole juveniles from the main estuaries of the French Atlantic coast could be discriminated by the elemental fingerprints of their otoliths. © 2000 Ifremer/CNRS/IRD/Éditions scientifiques et médicales Elsevier SAS otolith / trace elements / ICPMS / estuarine nursery / juvenile / recruitment Empreintes élémentaires des otolithes de la sole ( Solea solea ) : un outil pour discriminer les nourriceries du golfe de Gascogne ? Les nourriceries de la sole sont localisées dans les principales baies et estuaires du golfe de Gascogne où les juvéniles se concentrent et constituent des groupes du même stock, temporairement autonomes, caractérisés par leurs traits démographiques. L'isolement des juvéniles dans des zones sous diverses influences continentales offre un contexte propice à l'analyse élémentaire de leurs otolithes. Cette méthode permet de rechercher les éléments traces susceptibles de repré