Stock discrimination of Diplodus vulgaris through otolith elemental fingerprinting at SW portuguese coast

Tese mest. , Biologia Marinha, 2008, Universidade do AlgarveThe common two-banded sea bream (Diplodus vulgaris) is an important fish of the marine ecosystems of the NW Atlantic and Mediterranean. In south of Portugal is an major fishery resource being captured mainly by the artisanal fleets. Although there is some knowledge about the age, growth and reproductive biology of the species, the information about its population structure is scarce. In this study the otolith elemental fingerprint of a sample of 90 fishes of age group 2+ captured in Sesimbra, Sagres and Ria Formosa have been analyzed by inductively coupled plasma mass spectrometry (ICPMS). Two different methodologies have been applied: study of the entire lifetime of the fish (whole dissolved otoliths, ICPMS-SB) and of the larval stage (otoliths core, ICPMS-LA). Our goal was to detect a natural chemical marker, which could permit to distinguish between different stocks, nursery grounds and also tracks the migration of individuals. ICPMS-SB analysis detected informative concentrations of Ca, Li, Mn, Ni, Sr and Ba in whole dissolved otoliths. ICPMS-LA, sectioned and polished of otolith core, provide information based in concentrations of Ca, Mg, Mn, Sr and Ba. Results of both techniques were analysed by univariate and multivariate statistical analyses. The data showed significant elemental differences among sites to whole otolith and core otolith analyses. Classification accuracy rate are determined by linear discriminant function analyses (LDFA). The data show a high classification rates to all sites (Ria Formosa 93%, Sagres 90% and 80% to Sesimbra) for ICPMS-SB. However LDFA for ICPMS-LA only accurately classify a unique nursery for fishes caught in Sagres (87%). The data suggests that probably exist one only spawning area, which contributes mainly for the SW stock, and that the fishes are relatively sedentary during the juvenile phase, showing high fidelity to the growing zones