Abstract
This paper presents results of experiments on the practical use of the horizontal fish finder in the salmon fishing grounds in the North Pacific Ocean. The tests were made in July, 1968. On the ship we mounted two fish finders, each of which had a transducer with a 50 KHz supersonic. We kept these transducers 1 meter deep. The dip angles of the transducers were changed with the state of the sea. These echo patterns were made on the occasion of the voyage of the research ship “WAKASHIO MARU” (153 tons) for fishery investigations. Recordings by the fish finder were made as long as possible while the ship was floating by the set-nets. One of the characteristics of the echo patterns of the horizontal fish finder was that the echo of sawtooth recorded on the paper was cleared away almost completely. Because of the use of T. V. G circuit a relation was found between wind direction and the transducers. The echo patterns of the horizontal fish finder given showed salmon echoes quite clearly. We set salmon gillnets of 55 tans and hauled the nets the next morning. Considering the catches of salmon, we found that the catch of salmon was in proportion to the numbers of echo traces of salmon on the patterns.
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