Reducing the catch of sensitive nontarget species is a top priority for all organizations interested in improving the environmental sustainability of tuna purse seine fishing, including ISSF. Here, we briefly outline a few simple things that can be done by the crew to reduce bycatch.
Improved FAD construction. As discussed in an earlier chapter, non-entangling FADs will reduce the incidental capture of turtles and sharks. The “ghost fishing” of certain FAD types seems to be a significant contributor to shark mortality in some regions—that is, even when the purse seiner is nowhere in sight, the FAD could continue to entangle and kill. By ensuring that the FAD is composed of non-entangling materials, this ghost fishing can be minimized or completely eliminated. Additionally, the vessel should consider altering the shape of the FADs’ rafts so that turtles cannot climb them on to rest (i.e., swapping a flat surface for a curved one).
Avoiding small sets. A recent study of bycatch amounts compared to total FAD set sizes (Dagorn et al., 2012) found that small sets had a higher percentage of bycatch than larger sets. For very small sets (less than 10 tons), the effect is most pronounced—in other words, small sets make the least significant contribution to tuna catch, but the most significant contribution to bycatch totals. Averaged globally, sets under 10 tons comprise 3 to10 percent of total catch, but 23 to 43 percent of all bycatch. If a skipper avoids making small sets, he can dramatically reduce his bycatch “footprint” with only a minimal impact on his tuna catch.
Future work. While there are several strategies currently being tested, there are no proven techniques for completely avoiding the bycatch of sharks in purse seine fishing. However, ISSF continues to sponsor bycatch research cruises to study the most promising strategies, including the use of chum to lure sharks away from the tuna aggregation. Further developments in this field will be included in future versions of this training.