Loop Lines (Traplines): A New Emerging Terminal Device in Pelagic Longline Swordfish Fisheries

Loop lines (also known as traplines) represent a recent innovation in pelagic longline fisheries, particularly targeting swordfish (Xiphias gladius). Originating in Japanese fisheries during the mid-2000s, their use has expanded across the Pacific, Atlantic, and Mediterranean, yet remains poorly documented in fishing gear classifications and scientific literature. Loop lines consist of concentric monofilament loops attached to the branch line, replacing the conventional hook-and-bait terminal component. Available evidence suggests that this device may enhance swordfish catch rates while exhibiting high selectivity and reduced bycatch of non-target species such as seabirds and turtles. Preliminary observations also indicate size selectivity towards medium-sized individuals. Despite these potential advantages, concerns remain regarding fish welfare, meat quality, operational efficiency, and the risk of increased plastic pollution through gear loss. Given their growing adoption and possible implications for stock assessment, ecosystem impacts, and fisheries management, systematic data collection and observer-based studies are urgently needed to properly characterize their performance and environmental effects.