Daily Changes in the Catch of Parapristipoma trilineatum at the Hook and Line Fishing Ground of Toshima Fisherman's Union with the Special Reference to Water Conditions of Uwa Sea, Japan

Daily catches of threeline grunt Parapristipoma trilineatum (CP) at the Toshima hook and line fishing ground was studied during April 1988 and March 1989. Total catch (TC) and CP had seasonal changes; many fish were caught in summer and few in winter, and the PC/TC ratio exceeded 30% between May and September. Daily changes of CP were closely related to the daily changes in the number of fishing boats that caught P. trilineatum (NFP) during June and September. Daily changes of CP and the fluctuation of tide level in a day (FTL) were positively corretated during June and September except for August, and the same relation was found between NFP and FTL. Sudden poor CP was caused by poor NFP and/or great changes of water temperature (CWT). Sudden poor NFP was caused by heavy rain, high wind, public holiday and so on. The daily changes of CP at the Toshima hook and line fishing ground were thus influenced by the tidal cycle and the rapid changes of CWT, which were caused by Kyucho.