This dataset contains observations of mussel (Mytilus edulis) trajectories in an experimental setting. We were interested by one particular behavioral trait of this species, which have the capacity to crawl with the foot to avoid disturbance and choose a better fixation place. Mussels were placed in a 32 x 42 cm box, immersed in a bigger 700 liters tank equipped with a small underwater pump, for water recirculation. Mussels were young individuals collected in the wild, in Normandy (France). A small action camera was placed over the tank to make a movie of the mussel tracks, taking photos at a frequency of one image per minute. We tested 3 mussel densities (25, 50 or 75 individuals per experiment), each with three replicates. The runs lasted from 4 to 6 hours. We corrected the photos to straighten up for fish-eye effect and reframe them. We then pointed the different individuals with an image treatment open-source software to measure length, and determine x and y mussel position every minute. The dataset contains 137913 observations and 5 columns. First column is the individual id-code, second column contains individual length in centimeters, third column bears the time-information, and last x and y columns present the x and y positioning in cm, of the individual at time t.