Since autumn 2007 a European restoration plan on the European Sturgeon has been adopted under the aegis of the Bern convention. This species is critically endangered and the last population is located in the Gironde Dordogne Garonne system (South west of France). Thanks to recent successful assisted reproductions, larvae were stocked in this system. In this context field experiment were initiated in 2008 to document their spatial behaviour and habitat use. An acoustic telemetry experiment was carried out between July and December 2008 with 46 juveniles released at 14 months old in the Dordogne River. Original data were expected because nothing is known about this age class behaviour in the wild. The objective of this first experiment was to assess their spatial behaviour and to test the feasibility of acoustic tracking of small fish in this large and turbid estuary. Passive tracking (fixed hydrophones) and active tracking were deployed. In freshwater, both techniques were successful but in brackish water passive tracking was much more profitable. Thanks to passive tracking, summer and autumn movement patterns of those fish were analysed. Further studies, coupling different techniques, were planned to assess their habitat and their diet.