SCIENTIFIC COMMITTEE THIRD REGULAR SESSION 13-24 August 2007 Honolulu, United States of America LARGE-SCALE EXPERIMENT SHOWS THAT BANNING WIRE LEADERS HELPS PELAGIC SHARKS AND LONGLINE FISHERS

We assess the performance of wire leaders, which some jurisdictions have banned to reduce shark mortality from pelagic longline fishing. Experiments were conducted on commercial vessels that deployed equal numbers of wire and nylon monofilament leaders randomly along their longlines. Catch rates of several species, including sharks, were significantly lower on nylon than on wire leaders, probably because those animals often escape by severing the nylon leaders. High biteoff rates indicate that as many animals escape from nylon leaders as are caught on nylon leaders. The fate of escaped animals is not known, although large sharks are more likely to survive than are small animals. By contrast, catch rates of valuable bigeye tuna (Thunnus obesus) were higher on nylon than on wire leaders. Bigeye tuna are probably able to see wire leaders and avoid those hooks. The financial benefits of increased bigeye tuna catches outweigh the costs associated with banning wire leaders, such as increased rates of gear loss. Thus, banning wire leaders is an effective way of reducing shark catches that fishers should be keen to adopt.