A variety of systems are used for mussel grow-out but most of them fall under either raft or longline systems. One grower in BC uses salmon net pens to contain the culture and has installed barrel and timber floats inside the perimeter to hang the mussel socks. The net pen provides a barrier to duck predation. The principle concerns for growout systems are predation control and ensuring calm conditions prevail around the mussels. Too much agitation caused by rough water conditions can result in mussel detachment and significant stock losses.
Long lines are the most common system in use on the Atlantic coast.
On the Pacific Coast, both longlines and raft systems are used. Where conditions are reasobly calm and protected, rafts may be the most suitable system. In the Puget Sound area, rafts are used more frequently than longlines. Raft culture System at Penn Cove Mussels. Rafts have the advantage of offering the potential for very high stock densities, but there will be limitations depending on water flow and food availability.