Developing tori lines for New Zealand’s small-vessel longline fisheries
Tori lines are a well-tested seabird bycatch reduction device with proven efficacy in longline fisheries. However, because they were originally designed for larger vessel fisheries, the application of tori lines to small-vessel longline fisheries can be challenging. This report documents a New Zealand project developing tori lines specifically optimised for safe and effective use on small longline vessels. We worked with the operators of four vessels less than 28 m in overall length to develop and test tori lines and to document tori line performance. Setting speed when fishing and vessel design characteristics (specifically in terms of tori line attachment options) were used to categorise small-vessel fishing fleets for the application of tori line designs. In addition, different tori line designs were required for bottom and surface longliners based on the latter setting gear that remains in proximity of the surface for significantly greater distances astern (thereby increasing the risk of fishing gear tangling with the tori line rig). New construction materials were tested during the project, including deployment poles, streamer materials and terminal sections used for the creation of drag. Further, weak links were designed and incorporated into tori line designs for safety, should tangling with the fishing gear occur. Tori line performance was characterised primarily in terms of the aerial extent each design achieved, streamer behaviour, tracking efficacy, and the amount of water disturbance created at the end of the line. Designs were categorised with reference to a specific deployment height, drag section design, and streamer configuration. The best performing designs emerging from the project are described in this report. While the design and construction of tori lines were the foci of this project, next steps include assessing the performance of the new tori line designs in deterring seabirds from the setting area astern small longline vessels.