1Graduate School of Informatics, Kyoto University, Kyoto, Kyoto 606-8501, 2Chateau Marine Survey Co., Ltd., Osaka, Osaka 534-0025, 3Department of Fisheries, Faculty of Agriculture, Kinki University, Nara, Nara 631-8505, 4Department of Environment, Agriculture, Forestry and Fisheries, Osaka Prefecture, Osaka, Osaka 540-8570, Japan
Japanese sea bass Lateprabrax japonicus, captured in the western shore protection region of Kansai International Airport in Osaka Bay, were released near the place of capture with coded ultrasonic transmitters attached (9 individuals in August 2001 and 11 individuals in November 2001). The behaviors of these fish were monitored with 10 ultrasonic receivers, set along the western seawall (8 receivers) and off-shore (2 receivers). As a result, half of the fish provided continuous signals, whereas the others ceased to send signals immediately after the release. The signals of fish which sent continuous signals also broke off for over one day, suggesting that the sea bass occasionally went beyond the range of the receivers ( ca. 350 m). Fish often failed to send signals during the neap tide until the spawning season and drning a cold spell or after an atmospheric depression in the spawning season. We suggest that their off-shore migration is related to tidal and atmospheric changes.