The estimation method and data on catch, weight, and maturity at age of the chub mackerel caught by Japan up to CY2026/Q2

Stock assessment of chub mackerel (CM) in the Northwest Pacific has long been conducted 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 to develop catch at length from each prefectures on quarterly 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 Eastern and Western part of Pacific coastal prefectures of Japan to construct age-length key and catch at age is calculated for each quarter. In the present paper, updated data used to construct catch at age through CY2026/Q2 are presented. Catch numbers remained low in recent fishing years, while CY2025 showed a slight increase in total catch number and a relatively large contribution of age-0 fish. These updated data are proposed for use in the forthcoming stock assessment of CMs in NPFC.