Estimation of the fishing efficiency of a mid-water trawl for Pacific saury Cololabis saira using a high-frequency side-scan sonar

In order to improve the accuracy of abundance estimations of Pacific saury Cololabis saira, it is important to raise the fishing efficiency precision of a mid-water trawl (type NST-99, the sampling gear used for stock assessment) for saury. Using a 500 kHz side-scan sonar (SSS), we ensonified surface waters and measured the fish number using image processing methods. Simultaneously, we tried to catch saury in the same waters with the mid-water trawl. We estimated the fishing efficiency of the mid-water trawl as 0.179 (current value used is 0.144) by comparing the number of saury caught by the trawl net per swept-area with the number of saury per swath-area estimated from analysis of SSS records.