Effect of circle hooks and feasibility of de-hooking devices to reduce incidental mortality of sea turtles in the Japanese longline fishery. Report to the Western and Central Pacific Fisheries Commission, Kolonia, Federated States of Micronesia

Effects of circle hooks on catch rates of target species and sea turtles were investigated through scientific fishing surveys in the western North Pacific from May to September 2005. There was no difference in hooking rates of loggerhead turtles (Caretta caretta) between tuna and small-sized circle hooks, but large-sized circle hooks had potential to reduce the hooking rates of loggerheads. The ingestion of circle hooks, especially the large-sized hooks, occurred less frequently than that of tuna hooks, which means circle hooks have the potential to improve post-hooking survival of sea turtles. Use of circle hooks had little effects on the catch rates of tuna, but large-sized circle hooks showed negative impacts on billfish catch. Analysis of the resultant data indicated that the effect was variable among the types of circle hooks associated with hook morphology. We are exploring better shape and size of circle hooks in reducing incidental mortality of sea turtles through fishing and captive experiments. To improve post-hooking survival of sea turtles, simple and practical de-hooking devices were developed and distributed to some fishermen for on-site performance tests.