망지 특성에 따른 방추형 어류의 크기 선택성에 대한 실험적 연구

Abstract

This study quantitatively evaluated size selectivity for three netting shapes (T0; regular, T45, T90), three mesh sizes (mesh opening 42 mm, 66 mm, 84 mm), and two hanging ratio (35%, 70%) used for trawl codend. The size selectivity experiment was performed in a tank using a cube experimental model with a length of 50 cm on one side and 389 experimental individuals, jack mackerel (Trachurus japonicus). In the selectivity analysis, a selectivity curve was created based on the selection ratio using a logistic function, and the 25%, 50%, and 70% selection length and selection range(SR) were obtained. 1. The T0 netting, T45 netting, and T90 netting with 35% and 70% hanging ratio increased the 50% of selection length as the mesh size increased, and the 50% of selection length increased when the hanging ratio was 70% rather than the 35% hanging ratio. The selection range of the hanging ratio 35% of T0 netting was the widest in 66mm mesh, and the selection range of the hanging ratio 70% was the widest in 84mm mesh. 2. The 50% selection length and selection range of the T45 netting were relatively larger than the T0 netting. In addition, the 50% of selection length and selection range of the T90 netting were relatively larger than that of the T0 netting, similar to the T45 netting. This is believed that there was no difference in selectivity since the difference of two nettings were only the direction for the same mesh size. 3. There was a significant difference in the correlation between the circumference of the inner circle of the mesh by the shape of the netting and the body girth of the experimental individual(Pearson test, r=0.86,p<0.05). For 66 mm mesh, the selection ratio by the T0 netting, T45 netting, and T90 netting with 70% hanging ratio did not show a significant correlation(one-way ANOVA, p>0.05). In this study, it was found that maintaining the hanging ratio of the T0 netting, which maximizes the area of the regular netting, diamond shape, at 70%, selectivity such as T45 netting and T90 netting, and it is believed that the effect of bycatch reducion of immature individuals can be expected.