Application of NaLA, a fishing net configuration and loading analysis system, to drift gill nets

We have developed a system called net shape and loading analysis system (NaLA) for determining fishing net configuration and load analysis, and have used it to estimate the dynamic behaviour of actual fishing gear, such as gill nets and aquaculture fish farm nets. In this study, we have refined the NaLA calculation model for application to drift gill nets by introducing additional gear components besides netting and by considering environmental factors, such as waves. The primary objective of this paper was to evaluate the utility of the refined system and examine how accurately it simulates the actual behaviour of a drift gill net by comparing the predictions with measured data. Ten observations to obtain in situ data were recorded between May and June 2003 while assessing salmonid and other pelagic fish stocks in the northwest Pacific. During these operations, the horizontal and vertical displacements of the net were measured using mobile GPS and depth sensors over 10 h soak times. Then, the simulated results of the shape and motion of the gear were compared with the measured horizontal and vertical displacements. There was close agreement between the simulated and measured behaviour of the gear, and we proved that the refined NaLA method can simulate the shape and motion of an actual drift gill net with good accuracy, if the field conditions are accurately input to the calculation.