Initiation of sustainable trap cage fisheries improved by observation of behaviors of North Pacific giant octopus

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North Pacific giant octopus is caught by the trap cage for octopus in the coast water of northern Japan. However, the catch is gradually decreasing after 2000. The causes were estimated by the bycatch of small octopus under 3kg BW and cannibalism between octopuses in cage.The aim of this study is to develop improved trap cage for escaping the small octopus. We observed some behaviors of giant octopus in captivity, such as entering into cage, positioning in cage, aggressive behavior and cannibalism between octopuses in cage. After that, we attached the several size of circular ring in the side net of cage. We found that small octopus under 3 kg can escape through the ring of 55 mm in diameter in the side net from cage. We also examined octopus behavior around the setting trap cages by biologging methods. Then, we confirmed that 3 kg octopus was not caught by the improved trap cage. This new trap cage will be more useful for the local octopus fisheries management in the northern Japan.