Understanding the effect of design parameters on the filtration efficiency of trawls intended for commercial harvesting of zooplankton

A major challenge for the aquaculture sector is access to sustainable and cost-effective raw materials for feed. Copepods (Calanus spp.) have potential to meet this need for large volumes of marine raw materials to enable sustainable growth of aquaculture production worldwide. However, the lack of an energy- and catch-efficient trawl technology has limited the development of this fishery in the Northeast Atlantic. Therefore, the goal of this study was to develop a next generation trawl for harvesting zooplankton that was less energy demanding and more catch efficient than current trawl designs. We assessed the filtration efficiency of low porosity nets with different solidities and studied the effects of design parameters (mesh opening, twine thickness, porosity, taper angle) at various flow velocities in a flume tank. We found that the filtration efficiency for a square meshed net increased with increasing velocity and decreasing solidity and taper angle. A large open area ratio (the ratio between the open netting area and the net's mouth area) improved the filtration efficiency at towing velocities below 0.5 ms(-1). These results provided an indication of the initial filtration efficiency of the net designs (i.e., before any clogging occurs) but not of the sustained filtration efficiency.