There is little information on the effect of dredging on the vitality of discarded scallops. We aimed to determine the effect of simulated dredging on stress in scallops using the adenylic energetic charge (AEC) of the adductor muscle and the righting and recessing behaviour of individuals as stress indices. The effect of tow speed and tow length on stress, together with the effect of multiple dredge events were tested using a laboratory based dredge simulator. Tow speed had an important impact on both AEC and behaviour. The AEC level decreased from 0.85 to 0.70 and 0.56 after 15 min dredge simulation at low and high speeds, respectively. In addition, the behavioural score declined in dredged animals only at the high tow speed. We compared two different tow lengths (15 and 30 min) and found no difference in the AEC level or behavioural score of the scallops from these two treatments. Recovery was also monitored and was rapid and scallops from the low speed treatments had AEC levels of >0.8 after 2 h, whereas the AEC returned to this level after 6 h in the scallops from the higher speed treatments. Repeated dredging (after 24 h) of scallops at a slower speed had a significant cumulative effect on the AEC level of the animals but no further decrease was evident after repeated dredging at 48 h. Each application of an additional dredge disturbance at a higher speed did not have a significant cumulative effect on the AEC level or behavioural activity of the scallops. The period between disturbances was long enough for the scallops to significantly recover from the previous stress. However, it is not known whether a cumulative stress effect might have occurred in the test scallops if the recovery period was shorter. (C) 2002 Elsevier Science B.V. All rights reserved.