Ten harbour seals (Phoca vitulina) were captured in the Baie de Somme, Picardie (France) in October 2008 and fitted with Fastloc GPS/GSM tags (Sea Mammal Research Unit - SMRU, UK). The project was funded by the Région Poitou-Charentes. The study was conducted by Cecile Vincent at the University of La Rochelle (France) in collaboration with SMRU, Picardie Nature, PELAGIS (CNRS/La Rochelle University) and the Office national de la chasse de la faune sauvage (ONCFS). Seals were caught under licenses delivered by the French ministry of the environment.