Discrimination of

The pout, Trisopterus luscus, is one of the most important gadoid fish captured by northern Portuguese traditional fisheries. In spite of a substantial decrease in fish catches, little data are available either on the population structure or on the management of the species. In this study, chemical analysis with inductively coupled plasma mass spectrometry of whole otoliths of 90 pouts (age group 2, total length: 17.9–25.0 cm) provided location-specific elemental signatures. Sampling took place in shallow waters along the coastline in three fishing grounds off the Portuguese north coast (Viana do Castelo, Matosinhos and Aveiro) between February and March 2010. Otolith fingerprint analysis detected the presence of several informative trace elements. Molar concentrations for each site were analysed through uni- and multivariate statistical tests. Strontium, barium, magnesium and lithium (Sr, Ba, Mg and Li) differed significantly among locations, while no significant differences were found for manganese (Mn) and nickel (Ni). Canonical analysis allowed us to discriminate the tested individuals with respect to their sampling origin with a mean classification accuracy of 69%. The observed site-specific elemental differences in pout otoliths suggest a high level of site-fidelity in relation to their growing/feeding areas. Pouts from these locations can be regarded as a single, although not necessary homogenous, stock. Furthermore, this study also suggests that the populations of juvenile fish mix partially and, therefore, cannot be assumed to be separate units for fisheries management purposes