Specimens of Aulacomya atra covering the entire size range present in the population were tagged at different sites in fjord Comau in February 2011. Mechanical and chemical (Calcein) marks were introduced to the shell to tag the initial length. Individuals were recaptured in February 2012. Tagging and recapture were performed in situ by Scientific SCUBA divers. Mussels were tagged in the shallow subtidal zone, 0 to 20 m below Mean Sea Level (MSL).This dataset was generated in the frame of the co-operation between the Huinay Scientific Field Station (http://www.huinay.cl) and the Alfred Wegener Institute, Helmholtz Center for Polar and Marine Research (http://www.awi.de).