Development of an age-determination method using otolith-thin sections and the relationship between age and body length of pointhead flounder in the Pacific Ocean off western Hokkaido Island, Japan

An age-determination method using otolith-thin sections and the relationship between age and body length of pointhead flounder Cleisthenes pinetorum, an important fisheries resource, were investigated in the Pacific Ocean off southern Hokkaido Island, Japan. In otolith-surface observation, the age determined by three readers varied even for young fish and the coincidence rate of two determinations by the same reader was only 58%. In contrast, in thin-section observation, the coincidence rate was 93%, and the surface method tended to result in overestimation compared with the thin-section method. The von Bertalanffy growth formulae were estimated for males and females as Lt＝232×(1−e(−0.57×(t−0.26))) and Lt＝299×(1−e(−0.43×(t−0.29))), respectively. Estimated growth was faster than that in the same area with the surface method and than that of Ishikari Bay, off the western coast of Hokkaido Island. This study proposed an accurate age-determination method for pointhead flounder and the results are fundamental for understanding ecology and for precise stock assessment.