Seasonal and ontogenic migrations of meagre (Argyrosomus regius) determined by otolith geochemical signatures

Argyrosomus regius uses different water masses during its life history, being associated with estuaries for reproduction. In order to study the life history and migration patterns, variations in otolith Na, Sr and Ba were measured by laser ablation-ICPMS along transects running from the first year of life to the otolith edge, comprising up to 12 years of age. Visual and statistical modelling approaches were used to analyse both individual- and population-level patterns. Ontogenetic trends in Sr:Ca and Ba:Ca followed a sigmoidal increase over the life span, with an inflection point in Sr:Ca occurring at 5 years of age in males and 6.6 in females, suggesting respective age at maturity. Using reared young-of-year (YOY) meagre for validation, the habitat use of wild fish was characterized and our data suggest that most fish spend the first 2–4 years in offshore waters, and begin moving between water masses after age 6. Population-level analyses indicated significant seasonal variations, with a larger proportion of fish with high otolith Sr:Ca in the spring and summer. Although Sr:Ca would normally be expected to be lower after movement into estuaries, in this case the increase could mark gonad maturation and spawning activity. Alternatively, since the Sr:Ca maxima correspond to higher otolith Ba:Ca in the summer, fish would have moved into the estuarine area, especially since the Guadalquivir river drains metal-rich areas with heavy mining activities leading to elevated Sr concentrations compared to adjacent coastal waters.