Each longline spans 600 feet and is anchored at each end to the sea floor by two-ton granite blocks. Two clusters of submersible floats raise the line to form the corners of a horizontal backbone from which loops of mussel grow-out ropes are suspended. Additional floats along the backbone help maintain the line at the desired depth as the mussels gain weight during growout. On the surface, all that is visible are three buoys, one tethered to each granite anchor to mark the location of the longline, and one attached to the center point of the backbone for raising the line to the surface.