1Kyoto Institute of Oceanic and Fishery Science, Miyazu, Kyoto 626-0052, Japan
This paper describes the diurnal differences of catch trends and behavioral patterns of willowy flounder Tanakius kitaharai. A beam-trawl net equipped with an underwater video camera was used to investigate these changes in the T. kitaharai population off Tango Peninsula. The catch was smaller in the daytime than at night. The video footage revealed that approximately 80% of observed individuals swam at night and approximately 90% were at rest during the day. These results suggest that individuals of this species are rarely caught when they are settled on the sea bed. Therefore, the T. kitaharai catch in a beam-trawl net carried out during the day and catch efficiency during the night would underestimate the actual resources of this species.