Development of sea turtle releasing system for large scale set net/pound net fisheries 2 - practical study to release sea turtle from an experimental bag net

Abstract

We developed a new releasing system to allow turtles to escape spontaneously from underwater bag net of set nets. This system consists of a turtle releasing device (TRD) which is a square vent (1m x 1m) with a flap and a 20 degrees sloping upper panel of the bag net. In this study, we examined the behavior of sea turtles in the experimental bag net and escaping capability through the TRD. The experimental bag net was composed of quadratic-prism shaped upper panels of 20 degrees angle on a box-shaped net (8m x 8m, 1.8m high in total) and the TRD attached on the top of the upper panel. Eleven captive loggerhead, six wild green, and twelve captive hawksbill turtles were used. All the loggerhead and green turtles and about half the hawksbill turtles successfully escaped out through the TRD. Loggerhead turtles reached the TRD by pushing their heads up continuously, while green and hawksbill turtles swam to the shallowest position directly along the upper panel and reached the TRD. All loggerhead and green turtles pushed up the flap strongly and escaped out successfully, while half of the hawksbill turtles didn’t push the flap strongly enough to open it.