Data were acquired to study the natural daily gaping activity of the large scallop (Pecten maximus). Autonomous valvometers (Valve-Trek; Technosmart Europe srl, www.technosmart.eu) were used to measure the valve opening (maximum distance between two valves) activity of the great scallops. Including Hall effect sensors, the valvometers were attached (glued with epoxy resin) to the left valve of the scallops to record magnetic field variations of magnets placed (glued with epoxy resin) on the right valve. The sampling frequency of the sensors was set to 2 Hz to record low-frequency movements of the bivalves (variation in their opening status). This sampling rate (0.5 s) also allowed for the recording of punctual behaviors produced by faster movements of their valves (e.g., jumps, partial closures). The sensors and magnets were positioned uniformly on all individuals with the valvometer fixed at the ventral edge on the antero-posterior axis of the scallops. The size of these sensors (length: 22 mm; width: 13 mm; height: 8 mm; weight: 3.5 g) was consistent with potential epibionts of scallops such as the slipper-limpet (Crepidula fornicata). In January 2021, ten great scallops (adult; size: 96.14mm ± 2.80, antero-posterior axis) were harvested by scuba diving at the Auberlach cove site (48.333N, -4.415W; Bay of Brest, France) and transferred to Tinduff Hatchery (48.33852N, -4.37703W; Plougastel-Daoulas, Brittany, France). Individuals were first placed in a supply tank for seven days of acclimatization, during which they were equipped with valvometers. The scallops were then distributed in individual tanks (one scallop per tank) for 16 days (23 Jan to 7 Feb 2021). All tanks used had a surface area of 0.78 m² (length: 130 cm; width: 60 cm; depth: 40 cm), a sandy bottom and had continuous water renewal (completely renewed in 24 hours) by filtered water, pumped from the Bay of Brest. Additional food intakes were added to the supply tank during acclimatization and to the individual tanks during the first ten days of the experiment to ensure that scallops had sufficient food resources for the study period. Photoperiod was fully controlled using an LED spotlight bar (NICREW Classic LED G2 120-150 cm, 40 W, white light mode) placed 1 m above each tank and emitting white light (410-730 nm) to simulate the natural light cycle at the time of the experiment. The light cycle was set with a complete darkness period from 5:30pm to 8:30am, a gradual light increase from 8:30am until 9:00am, and a light decrease from 5:00pm until 5:30pm. Light levels were adjusted according to the advice of the hatchery staff. Salinity, pH, oxygen, and temperature were monitored and controlled to guarantee a stable environment. During the experiment, the water was maintained fully oxygenated (100 % O2 saturated) and at a constant temperature of 12°C (continuous monitoring). Salinity and pH were also constant with values of 31.2 psu and 8.2 respectively (one punctual measurement per day using a pH 3310 probe, WTW™). Because of the water source irrigating the tanks (directly pumped from the bay), these latter parameters are similar to those of the seawater adjacent to the hatchery. Once the scallops were retrieved after 18 days, all recorded time series were calibrated to convert magnetic field intensity variations emitted by magnets (mV) into accurate valve opening distances (mm). Following a standard procedure, this calibration step was performed after the deployment by computing individual calibration curves linking recorded valvometer values to a set of known inter-valve distance (0, 5, 10, 15, 20, 25, 30, 35 mm). This procedure was repeated for each individual separately. We first severed their adductor muscle. Then, the Hall voltages corresponding to the different calibration distances were measured, by inserting a series of calibrated wedges between their valves. The data were then converted to angle (degree) by considering the size of the scallops.