Catch, weight, and maturity at age of the chub mackerel of Japan

Stock assessment of chub mackerel in the Northwest Pacific has long been conducted by tuned virtual population analysis (VPA) in Japan. For nearly half a century, the length and age data of chub mackerel are collected based on the catch from the Pacific coast of Japan. Catch data are collected by month, prefecture, and gear type. Measurement of length data is obtained from the major landing port and roughly 60000 individual length data are obtained annually. Length data are sorted and reported by month, prefecture, location, and gear type. Length frequency of the catch data is expanded from the length measurement data and developed by month, prefecture, and gear type basis. Age data are obtained from the subsample of mackerels which fork length are measured and annulus of scale or annual increments of otolith are counted. The age data are subdivided into the northeastern and southwestern part of Pacific coastal prefectures of Japan to construct age-length key using “forward age-length key” method. Age-length key is applied to the catch at size to calculate catch at age for VPA analysis. Weight at age is estimated using the estimated catch at age in weight and catch at age in number of fish. Maturity at age for different stock levels are used for the domestic stock assessment according to the previous study.