Damage caused to mussels (Mytilus edulis L.) by dredging and mechanized sorting

Up to 13% of mussels which had passed through a rotary sorting machine experienced shell damage and many apparently suffered some internal damage which impaired their long-term survival out of water. These injuries were superimposed upon others when harvesting was done with large dredges. Sublittoral mussels had a significantly higher shell-damage rate than intertidal mussels of comparable age; they also survived less well out of water. Relaying sublittoral stock into the low intertidal zone, for at least 6 months, increased resistance to sorting damage and to lengthy exposure in air. At least 90% of sorted mussels survived for 8 days out of water in winter in North Wales, and survival for at least 36 days was recorded with a few unsorted individuals.