Abstract
A compact sized split-beam echo sounding system was developed and used in Sagami Bay, Japan, to validate echo trace analysis (ETA) that can observe the length and the behavior of an individual fish. Fishing by hook and line was conducted to confirm the fish species and its length distribution. The echo sounding system was tethered from an anchored ship. Electric power was provided through a cable. This system consists of a split-beam transducer (70 kHz, 118 mm), a transmitting and receiving unit, a data-recording unit, and a control unit and the total weight of the echo sounding system is about 30 kg. Recorded data are up linked to the computer on the ship through a LAN cable. The fish length and fish swimming speed were estimated using ETA. From the fishing results, 79l (Scomber japonicus) or horse mackerel (Trachurus japonicus) had an average fork length (FL) of 27.9 cm. The estimated fish length distribution coincides with that obtained from a fishing well. The estimated swimming speed was 0–1.2 m/s and corresponds to 0–4.3 (FL). These results show the validity of ETA.
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