Abstract
A total of 21 specimens of Siganus fuscescens and Kyphosus bigibbus were released on November 16, 2004 off Nomozaki, where a relatively high-density seaweed patch remained, and were tracked for more than 4 months using a biotelemetry system. During the survey, signals from the S. fuscescens were recorded with high frequency in the daytime and with low frequency at night. These was a similar trend of signals from K. bigibbus, but nove was recorded at night. The total signals per day decreased when the water temperature fell to 20°C for S. fuscescens and to 16-17°C for K. bigibbus. The movement patterns of S. fuscescens and K. bigibbus may change with water temperature, however, they still stayed around the seaweed patch off Nomozaki during the winter and never migrated. There is a possibility of causing serious damage to seaweed during autumn and winter, because the activity of fish extended over a long period of time as a consequence of the recent rise of water temperature.
