Measurement Techniques of Fish in Set Net by Use of the Acoustic Camera

Abstract

Laboratory experiments and field surveys in a set net were conducted by use of the acoustic camera, DIDSON, as a device to observe behaviours of various fish species without an influence on them. As a result of laboratory experiments, it was shown that a frame rate of images taken by DIDSON peaked out when an observation distance was shorter than 5m, while the resolution of subject improved in proportion to a shortening of an observation distance and a frame rate improved in inverse proportion to it when a distance was longer than 5m. This may cause an image deformation of the moving subject at a shorter observation distance because DIDSON draws it by the interlace scan. As a result of observations in the set net under the optimized setting of DIDSON taking above results into consideration, it was possible to discriminate images of bluefin tuna from other species.