Effects on Bycatch Reduction in Shaken Codend Generating By Canvas in a Shrimp Beam Trawl

The vertical shaking of the codend as new method for bycatch reduction was generated as an oscillating motion by a variable lifting force of canvas. The downward or upward movement of the net panel during the shaking of the codend may evoke an erratic movement of the fish. Then fish attempted to pass through the mesh rather than being herded by being swept into the middle of the codend from the tank observations. The fishing operation was carried out generating shaking motion of the end of codend by forming a biased cap-like canvas with shaking amplitude as a radius of the codend and period 5s around. The bycatch of the shaking codend was significantly decreased in flat fishes and debris than non-shaking codend of the traditional codend while shrimp catch was no difference between shaking and non-shaking codend. The tension of the tow line when shaking codend was slightly increased than non-shaking codend, and then towing speed was also was slightly decreased in shaking codend. However shaking codend was not deterred towing operation or shrimp catch in commercial fishing. The shaking codend might be considered as a new attempt to reduce bycatch in addition to other BRD.