定置網によるウミガメ混獲防止策の開発

摘要

To reduce incidental death of sea turtles by set net fisheries, we examined net designs with a new turtle releasing device (TRD) to release turtles spontaneously from the bag net. We examined a square vent with a flap at the upper part of the bag net. The flap was hinged to the hole to open outside when the turtle pushed the flap to go out from the bag net and the flap closed automatically after the turtle went through the vent, by using the bounce of the netting materials at the hinge. Using the TRD, most of green, loggerhead and hawksbill turtles could escape from the small cone-shaped bag net. In order to apply such a TRD to a large set net with a huge box-shaped bag net, we examined to slope the upper panel of the bag net for guiding sea turtle to the TRD. Because the turtle moved to the shallower space in the net as it was pushing its head continuously up against the upper panel, it approached the top corner of the bag net where the TRD would be installed. In addition, flexible plastic net was provided around the vent to supply consistent tension for the flap to close automatically. With these modifications, preliminary study shows that the new turtle releasing system for the huge box-shaped fish bag worked well as in the small scale fish bag.