Optimizing tori line designs for pelagic tuna longline fisheries

Melvin EF, Walker N (2008) Optimizing tori line designs for pelagic tuna longline fisheries. Report of work under New Zealand Ministry of Fisheries Special Permit 355:1–18

Observations of seabird interactions with pelagic longlines were carried out aboard one of four Japanese vessels participating in the joint venture fishery for southern bluefin tuna in the New Zealand EEZ off the Fiordland coast from 23 April to 2 May 2008. The purpose of the project was to establish protocols to monitor seabird behavior in response to tori lines (also called streamer lines), and to begin to establish essential design elements for effective tori lines. This project was a collaboration of the New Zealand Japan Tuna Company, Ltd, the New Zealand Ministry of Fisheries, and Washington Sea Grant. Ed Melvin was the scientist aboard and made observations reported here.

Pelagic fisheries managed by international agreements (Regional Fishery Management Organizations or RFMOs) constitute one of the greatest conservation threats to Southern and Pacific Ocean seabirds. Although tori lines are the most widely prescribed seabird mitigation tool in longline fisheries, controlled studies demonstrating their effectiveness in pelagic fisheries in the context of production fishing have not been undertaken. Unlike demersal fisheries where all fishing gear sinks below the surface within 50 m of the stern, pelagic longlines are suspended between floats at the surface. This surface fishing gear makes tori lines more challenging to use in pelagic fisheries. Often fishers deploy tori lines to the leeward side of the gear where they are least effective, or do not deploy them at all for fear of hanging up on buoys at the surface jeopardizing the fishing operation. Further, the design and materials of tori lines have not been optimized via research for either demersal or pelagic longline fisheries.

In 2007 the Western and Central Pacific Fisheries Commission Scientific Committee debated the efficacy of different tori line designs used by various longline nations. The underlying science on competing designs was found lacking, frustrating progress toward required seabird mitigation in the fishery. The USA, Australia and New Zealand expressed keen interest in coordinating a series of trials to test various tori line designs in 2008.

This project was the initial critical step in the process of determining the optimal design of tori lines for pelagic longline fisheries. Establishing protocols to monitor seabird behavior in response to tori lines will enable subsequent definitive comparison of tori line designs. The study was also intended to allow for initial comparisons of the effectiveness of different tori line configurations.