Factors Influencing Successful Fishing of Tuna Free-Swimming Schools in the Equatorial Western Pacific Ocean

The fishing strategies of tuna purse seine fleets in the equatorial western Pacific Ocean have been characterized by a reversion to pursuing free-swimming schools of skipjack (Katsuwonus pelamis) and yellowfin tuna (Thunnus albacares) in recent years. This has prompted industry to evaluate how to improve their fishing success on unassociated sets. In this study, we determined which potential factors had a significant impact on the fishing result using data collected by observers in the equatorial western Pacific Ocean. The results showed that fishing success was significantly influenced by the average sinking speed of the gear, daylight conditions, and current speed in deep layer. Fast sinking speed will reduce the chance of escape for schools under the sinking net, improving the success ratio. Success rates were higher during the periods of low light intensity, such as dusk. The net sinking speeds were affected by current speed in deep layer, which often were associated with low success rates. The influential factors and their relative influence were listed, which will help fishermen to more effectively transfer their efforts from associated sets towards unassociated sets, contributing to the sustainable use and conservation of tuna stocks in the equatorial western Pacific Ocean.