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University researchers create fishing net designed to stop bluefin tuna extinction

Bluefin tuna are lined up at Sakai Port in Tottori Prefecture, on June 12, 2017. (Mainichi)

A research group has announced that it has created a fixed fishing net that releases young bluefin tuna in response to fears the fish might go extinct.

    "The device can be expected to prevent excessive fishing, and also help protect resources and allow fishing operations to continue," said Tokyo University of Marine Science and Technology associate professor Seiji Akiyama, one of the group's members who made the announcement on March 7. The team's fixed net allows bluefin tuna weighing less than 30 kilograms to escape.

    If a country catches small bluefin tuna in excess of the quotas stipulated under international agreement, there is a risk that it could be prohibited from subsequent fishing with fixed nets, even when fishing operators are targeting other fish.

    The group kicked off their research in the Sea of Japan, off the coast of Fukaura, Aomori Prefecture, in fiscal 2014. They discovered that bluefin tuna tended to gravitate toward the center of fixed fishing nets, prompting the team to place a second net with a bigger mesh in the center of a more finely meshed fixed net.

    As a result, the group was able to catch large fish and also allow smaller fish to escape through a hole at the back of the finely meshed net that opens and closes.

    The research group also found out that yellowtail fish, which are in season at the same time as small bluefin tuna, tended to swim toward the edge of fishing nets, prompting the team to add an adjacent safe-like net to catch the yellowtail, which proved effective. The device can be produced at a low cost, according to the team.

    In order to protect resources, quotas on small bluefin tuna have been implemented since 2015. However, Japan exceeded the quota for the period between July 2016 and June 2017.

    With about six months left in the present season, the quota of roughly 3,400 tons had almost been reached as of January, prompting the Fisheries Agency to ask coastal fishing operators across Japan to exercise restraint concerning the use of fixed fishing nets.

    Fishing operators had been troubled by how to deal with bluefin tuna inadvertently caught in fixed nets, because they die easily even when released by hand.

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