Harvesting, depuration and marketing
Harvesting mussels grown on rafts is relatively easy. The ropes are hauled out of the water, often using mechanical winches. The mussels can be shaken off the ropes and sorted according to size.
Harvesting from bouchet poles and sticks is normally performed by hand from small boats and the mussels are removed, washed and sorted. The bigger ones (5–7 cm shell length) are sent for depuration or directly to markets. The big mussels are reserved for canning in areas where mussel canning is undertaken. Small mussels are reattached to ropes and transferred to the park for further growing. In bottom culture, harvesting is carried out using dredges from special boats.
Harvested mussels are handled the same way as those from suspended culture, except that the dredged mussels are likely to contain some sand and silt in the shell cavity. The mussels are cleansed in special diked cleansing plots, well protected from winds. They are spread evenly in clean sea water of uniform salinity and high oxygen concentration. Within about 24 hours the mussels are free from sand, but they are kept in the cleansing plots for three to eight days. In areas where the mussels are consumed raw, it is essential to ensure that they are free from any pathogenic organisms. So harvests from areas exposed to contamination have to be depurated, as in the case of oysters. Besides live mussels, mussel meat is also marketed in the frozen (individually or block frozen), canned, smoked or pickled form. The presence of pearls in the mantle epithelium is a problem in the utilization of mussels in certain areas, especially on the north-eastern coast of the USA. Although the exact cause and circumstances of pearl formation are still not fully understood, it is known to be associated with infection by a parasitic trematode, probably of the genus Gymnophallus (Dubois, 1901; Lutz, 1978). There is also some evidence to show that the incidence of pearls is related to the age of the mussels. Raft-cultured mussels which have been in water for less than five years usually provide a high-quality product (Lutz, 1985).