中部北太平洋におけるサンマ Cololabis saira の耳石日周輪に基づく年齢と成長の推定

The age, growth, and hatch dates of the Pacific saury Cololabis saira in the central North Pacific Ocean were estimated by analysing the microstructure of otoliths. Saury samples were collected by drift nets of several mesh sizes from July to August 1989. Growth increments of otoliths were counted under a scanning electron microscope. The sauries were divided into an almost tri-modal size distribution: a small-sized group ( ?? : 210mm in knob length, range 200-240mm), a medium-sized group ( ?? : 260mm, 240-295mm), and a large-sized group ( ?? : 315mm, more than 295mm). Ages in days of sauries of the large-and medium-sized groups were estimated at 560-690 days and 310-450 days, respectively. Birthdate analyses of the sauries showed that the large- and medium-sized groups were estimated to have hatched from November 1987 to January 1988 and from May to August 1988, respectively. It is estimated that the life span of the saury in the central North Pacific area is about 2 years