Effects of material and structure types on drifting speed of fish aggregation devices (FADs) in tuna purse seine fishery.

The drifting speed and trajectory of fish aggregation devices (FADs) influence tuna aggregation behavior. Based on expertise, fishermen modify FAD structures to slow down drifting speed, but few studies quantify material and structure effects on this speed. To address this, 14 different types of FAD models were tested under 5 different current velocities in a flume tank and compared drifting using pairwise Wilcoxon tests. Results indicate that 1) FAD models covered with netting exhibited higher drifting speeds than the others. 2) It is feasible that replacing the netting bundle with the cotton rope of the same diameter for constructing submerged structure effectively slows down the drifting speeds of FADs. 3) Additionally, FAD models with a floating structure aspect ratio close to 1 exhibited slower drifting speeds compared to other designs when the submerged structure is the same.