Age and growth from Oita and Miyagi Prefectures of Japanese jack mackerel Trachurus japonicus

Abstract

The age and growth of Japanese jack mackerel Trachurus japonicus from Oita and Miyagi Prefectures were investigated by means of otolith sectioning. Different types of opaque zones were formed in summer and winter, respectively. The age composition and growth formulas were examined and compared for Oita (2007–2008) and Miyagi (2016–2017) Prefectures from individual age data. We determined that the age–length relationships and parameters for the von Bertalanffy growth function from Oita and Miyagi Pref. were, respectively, L∞ = 342 and 305 mm and k = 0.673 and 0.634 year−1. In Oita Pref., most fish with a fork length (FL) of approximately 180–200 mm were 1+ years of age, while older fish (7+) were rare. In Miyagi Pref., many fish were 3–6+ years of age. Older fish (over 7+ years) accounted for approximately one quarter of the total. These differences in the growth curve and age composition may be reflected by discrepancies in the fishing gears, and multiple life cycle patterns of the Pacific stock which has been unknown.