Effects of dredging on undersized scallops

There is little information on the effect of dredging on the physiology and behaviour of discarded scallops. The overall objective of this study was to use changes in adenylic energetic charge (AEC) and righting and recessing behaviour as indicators of stress caused by the act of dredging on scallops. Two field experiments using a commercial dredge and four laboratory experiments using a dredge simulator were carried out. AEC levels decreased in the striated muscle from 0.9 to approximately 0.5 after dredging, however, no difference was found between different lengths of tow or length of time in the dredge simulator (15, 30 or 45 min). The AEC levels of dredged scallops returned to normal after 3 days in optimal conditions. Dredged smaller scallops (<65 mm shell height) had a higher AEC level (0.54–0.58) and were more active than dredged larger animals (>70 mm shell height, AEC level: 0.41–0.46). Dredging followed by emersion had a deleterious effect on AEC levels and on the righting and recessing speed of scallops. Physical movement of the scallops within the dredge bag combined with anaerobic respiration during valve closure has an added stress effect during dredging. Overall, AEC levels were not reduced enough to cause mortality, but the righting and recessing speed of scallops was greatly reduced after dredging. Therefore, these undersized discarded animals may be less able to escape from predators, and may have reduced chances of survival in the open sea.