Farming Blue Mussels

Growth

The growth rate of mussels on long lines varies according to the density of the mussels on the line, the depth, an the availability of phytoplankton. Decreased growth is experienced at high stocking densities, greater depths and lower phytoplankton levels. Wild mussels live in dense beds on the bottom or in crowded conditions on jetty pylons. As cultured mussels are kept at relatively low densities on long lines, they generally have a faster growth rate than wild mussels.

In Cockburn Sound, cultured mussels reach about 40-46 mm in six months and 65-85 mm, which is the preferred market size, in 12-14 months.

Harvesting

Harvesting of blue mussels for market requires that the product be removed from the long lines and the shells cleaned of external fouling before sale. This process is usually automated and involves a washer-tumbler machine in which the mussels are rotated and rub against each other to dislodge small mussels and barnacles and other fouling organisms. The mussels are then cleaned, graded and bagged for sale.

Diet

Like most bivalves (molluscs with two shells), mussels are filter feeders. This means they feed by pumping water through a set of gill filaments which filter out small particles such as phytoplankton, zooplankton and other organic material. Sediment is discharged while food is retained and passed into the stomach where it is digested.

Mussels are able to obtain all of their nutritional requirements from the environment. As a result of this feeding mechanism, farmed mussels do not require additional feeding and as an aquaculture operation, are considered to be relatively environmentally benign, with any effects being very localised (see Jeffs et al. 1999).