The main purpose of this study is to know how a rehabilitated harbour seal (Phoca vitulina) reintegrates his natural habitat. CHENE is a rehabilitated center for all wildlife. Each year, we take care of harbors, useally young ones, coming from beach in the north of France (from Baie du Mont-Saint-Michel to Dunkerque). Generally these youngs arrive because of the separation from the mother just before weaning or because they cannot find sufficient food for their energy requierements just after it weaning. Others arrive because of injuries or deseases. It is important to know what happens to these animals after release. This study provides us information about their movement patterns and their behaviour. The tag gives us different kind of data : dive depths, dive durations and haultout.