Farming Blue Mussels

The Culture of Mussels

Culture Techniques:

Several culture techniques for growing mussels have been used worldwide. A selection of these are described below:

Long lines

In Western Australia, all mussels are currently produced by long line culture. A rope is stretched horizontally near the water surface and maintained 1-2 m from the surface with buoys. Mussels are grown on vertical ropes known as ‘droppers' which hang from the horizontal rope for a length of 4m. The droppers are placed a minimum of 0.5 m apart and have at least 4 m of free space from the bottom. In deeper waters the gap between the bottom of the line and the sea floor is greater. Mooring lines extend from each end of the horizontal rope to anchors buried in the mud of the bottom. As the ropes are kept taut, there is no movement around the anchor to disturb the bottom as occurs when boats are anchored.

Small mussels stripped from the collection ropes are inserted into a continuous sock-like cotton tube, which is approximately 17.5 cm in width. This cotton sock is then wound around the dropper. The mussels grow and attach to the ropes using their byssal threads and the cotton sock slowly disintegrates and falls away.

The density at which mussels can be cultured on long lines could be about 300 per metre, but depends on the food availability, which varies from site to site. Mussels grown on longlines can become smothered by naturally settling juvenile mussels and other fouling organisms. For this reason, most farmers prefer to position their farms away from heavy spat settlement areas to avoid layers of spat attaching to larger mussels.

Raft Culture

Raft culture utilises similar principles to long line culture in that the mussels are suspended on droppers but these are suspended from the raft instead of the long lines. The raft itself is anchored to the seabed removing the need for several anchoring systems. Long line culture is usually preferred to raft culture in Western Australia as it creates less of a visual impact, and the droppers can be spaced farther apart to maximise the use of the available phytoplankton. Raft culture is more suited to areas of dense phytoplankton and to smaller operations, as there is less scope for mechanical harvesting. This method of culture is used in Saldahna Bay in South Africa but has been abandoned by the New Zealand industry in favour of long lines.

Intertidal Pole Culture

Intertidal pole culture, also known as the bouchot technique is utilised in France. In this method, ropes with spat attached are wound around large vertical poles (bouchots) in the intertidal zone. A mesh netting is used to cover the mussels to prevent them being detached and lost. A barrier is placed at the bottom of the pole to prevent predators such as crabs from reaching the mussels. This method of culture requires large tidal ranges, in order to supply the densely packed mussels with food. This method is not practiced in Western Australia as the tidal range in the mussel growing region is not sufficient.

Other farming procedures are described in Gosling (1992), Jamieson (1989), and Mackenzie et al. (1997).