Sr:Ca and Ba:Ca ratios in water from the Adour estuary show a clear relationship with the salinity of the surrounding water for salinities <20, while ratios are almost constant above this level of salinity. A Positive relationship was observed for the Sr:Ca ratio, whereas it was inverse for the Ba Ca ratio. These two elemental ratios were measured in the otoliths of the European eels (Anguilla anguilla L) using femtosecond laser ablation linked to an ICP-MS (fs-LA ICP-MS) There was a direct relationship between the elemental ratios recorded in eel otoliths and those found in water from fresh and marine areas, suggesting that Sr Ca and Ba:Ca ratios in eel otoliths can be used as markers of habitat in this estuary Continuous profiling allowed the determination of three behaviour patterns in terms of habitat freshwater, estuary and migratory individuals Finally, the above results support the simultaneous use of both ratios for a better understanding of the migratory contingents and also as a relevant method to avoid a misidentification of environmental migratory history due to the presence of vaterite crystal in the otolith matrix. (C) 2010 Elsevier Ltd. All rights reserved