Hydrodynamic Forcing of Long-Line Mussel Farms: Observations

Abstract

The first detailed observations of the motion and loading of a mussel (shellfish) aquaculture long-line are described in order to identify the dominant modes of flow-structure interaction and provide a baseline for prediction of future structures. A long-line is typically a 120m long sequence of surface floats beneath which is looped rope bearing the mussel crop. Accelerometer and load cell data from sensors mounted on the structure along with remote radar data are examined in the context of wave and current measurements. The mussels comprise the largest mass and drag element of the structure, and the tidally affected pretensioning of the mooring lines dominates the background load. However, waves and currents increase the maximum load by potentially 100% over this value. The floats at each end of the long-line follow the wave orbital motion reasonably well, more so than the floats in the middle of the backbone. The mussel-laden loops of rope (droppers) clearly respond differently to the floats, implying flexibility in the vertical dimension. This suggests that flow around the droppers, which influences mussel feeding ability and hence production, is complex and highly three-dimensional.