그리드형과 망목형 치어 탈출장치의 선택성 비교

Abstract

This thesis is a basic study on the adaptation of escape devices for reducing the catch of small size of fish in fishing gears. Two types of experimental escape devices were made; first, the grid-type devices with three different slit sizes (15, 20 and 25mm) and second, the mesh-type devices with three different mesh sizes (60.6, 75.7, 120.0mm). Size selectivities on escape devices were examined using two type escape devices with a black rockfish (Sebastes schlegeli) and a sea perch (Lateolabrax maculatusi) in the experimental tanks. The size selectivity curve was fitted with a logistic function and the parameters of selectivity curve were estimated with a maximum likelihood method. The results are summarized as follows : 1. 50% selection ranges of the grid-type escape devices with three different slit sizes were 13.30cm, 19.22cm and 22.06cm for a black rockfish, and were 17.64cm, 20.91cm and 22.78cm for a sea perch, respectively. Consequently, it was estimated that the 50% selection range of a black rockfish was wider than that of a sea perch by 1.1~1.3 times. 2. 50% selection ranges for the mesh-type escape devices with three different mesh sizes were 18.99cm and 21.96cm for a black rockfish, and were 22.02cm and 24.46cm for a sea perch, respectively. However, the device of mesh size 120.0mm was not able to estimate a size selectivity as all experimental individuals were escaped from the devices. Consequently, it showed that the 50% selection range of a sea perch was wider than that of a black rockfish by 1.1~1.3 times. 3. The survival rates of escaped individuals after a seven-day lapse were 44.4% for the grid-type device and 18% for the mesh-type device. Therefore, it was estimated that survival rates of escaped individuals in the grid-type device were higher than those in the mesh-type device by 2.5 times. 4. It is thought that the possibility of application of the grid-type would be higher than that of the mesh-type as an escape device for reducing the catch of small size of fish in fishing gears.