Effects on Bycatch Reduction in a Shaking Codend Generated By Canvas in a Bottom Trawl

An active stimulating device, such as a fluttering of a codend generating a shaking motion, could help to encourage the escape of juvenile fish. Field fishing trials using a bottom trawl were carried out to examine the effect on the reduction of juvenile fish as discard catch by generating a shaking movement of the codend using round canvas. Bycatch in each haul was measured and analyzed for weight and body size in steady and shaking codend collecting by cover net method. The period of the shaking motion with the round canvas was ranged  10~15 s, and the amplitude as depth change of the codend 0.3~0.7 m by peak event analysis and the global wavelet method. The mean bycatch rate in the steady codend (as codend bycatch by total bycatch including cover net) was decreased significantly from 83% to 70% using a shaking cod end in the bottom trawl, while the marketing catch or total juvenile was similar between steady and shaking codends. There was no difference in the girth size of 50% selective curves between the steady and shaking codend. Above results demonstrate an alternative method for bycatch reduction using an active stimulating device, although more detailed studies are needed.