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Longline Gear Innovation

Experimental "weak" hooks at various stages of bending
Photo Credit: NOAA


Large Bluefin Tuna on deck
Photo Credit: NOAA


A Leatherback sea turtle swims at sea
Photo Credit: NOAA

NOAA Fisheries works closely with pelagic longline fishers and organizations to develop, test, and implement fishing techniques and gear modifications to improve the selectivity and sustainability of pelagic longline fisheries and increase post-release survival of bycaught animals. This approach is an alternative to other management strategies that reduce available fishing grounds, such as time-area closures.

Sea Turtle Bycatch Mitigation

NOAA researchers participated in cooperative research with the U.S. pelagic longline fishing industry to evaluate the feasibility of alterations to gear and fishing practices to reduce the incidental capture of sea turtles by longline fishing gears. Changes in hook design and bait type were investigated as measures to reduce the bycatch of sea turtles on pelagic longlines in the western North Atlantic Ocean.

Specifically, the effectiveness of 18/0 circle hooks and mackerel bait was evaluated with respect to reducing sea turtle interactions and maintaining swordfish and tuna catch rates. Individually, circle hooks and mackerel bait significantly reduced both loggerhead and leatherback sea turtle bycatch. Circle hooks also significantly reduced the rate of hook ingestion by the loggerheads, potentially reducing postrelease mortality.

The combination of circle hooks and mackerel bait was even more effective for loggerhead turtles and had no negative effect on swordfish catch. These modifications in fishing methods, in conjunction with tools developed to remove hooks and line from the turtles, significantly reduced the capture rate of sea turtles and potentially the post-hooking mortality of those that were caught and did not negatively impact the primary target species catch rate. These results led to the required use of circle hooks by all commercial longline boats operating in both the Atlantic and Pacific Oceans.

See videos of Sea Turtles and Longline Gear Interactions.

Bluefin Tuna Bycatch Mitigation

Bluefin tuna is managed internationally by the International Commission for the Conservation of Atlantic Tunas (ICCAT). Since 1998, an ICCAT rebuilding plan, which was domestically implemented in the NOAA Fisheries Consolidated HMS FMP, has been in place with the goal of rebuilding the western BFT stock by the year 2019.

While directed bluefin tuna pelagic longline fishing is prohibited in the Gulf of Mexico, the incidental catch of bluefin has become an area of heightened concern due to the status of the stock and mortality of incidentally caught spawning bluefin in the yellowfin tuna directed fishery. In response to this critical fishery problem, biologists from Pascagoula's Harvesting Systems Unit worked with the fishing industry and hook manufacturers to develop a prototype hook designed to quickly release incidentally caught bluefin while retaining the target catch. Termed the weak hook, the 16/0 circle hook design meets NOAA Fisheries' current size and offset restrictions and is constructed of round wire stock that is thinner-gauge (i.e., no larger than 3.65 mm in diameter) than the circle hooks currently used in the pelagic longline fishery. This hook design was shown to reduce bluefin bycatch by 56.5% with no statistically significant reduction in the capture of yellowfin tuna.

More Information

• Weak Hook Fact Sheet
• NMFS Highly Migratory Species Division