It is well known that there is bias using sampling gear, such as a framed midwater trawl (FMT), when measuring the density and length distribution of target species. This limit is characterized by the catch efficiency of the gear. To improve the accuracy of abundance estimates from catch, it is necessary to determine the catch efficiency of the sampling gear. Acoustic monitoring can be used to determine the catch efficiency of the gear, as its non-invasive, wide-range sweeps provide more reliable estimates of absolute abundance of the target species. In this study, we proposed a method to estimate the catch efficiency of FMT using acoustic data for juvenile walleye pollock (Gadus chalcogrammus). Experimental hauls using FMT with black netting were conducted 17 times in nighttime, as a result, juveniles of fork length ranged from 10 to 70 mm was caught. The estimated efficiency by each haul decreased with the fork length increases with sampling periods. Additionally, the efficiency was estimated by the fork length class of 10 mm intervals using multiple regression, then its variation with length showed same tendency with the result mentioned above.
