Age, Growth, and Maturity of Chub Mackerel off Korea

Abstract

AbstractThe age, growth, and maturity of chub mackerel Scomber japonicus were determined by otolith analysis and gonad observation. Fish were subsampled monthly from Korean offshore commercial catches between September 1994 and August 1995. Gonad observations suggest that chub mackerel spawned mainly in May. The size at 50% maturity was calculated to be 28.8 cm fork length at an age of 1.01 years. Annuli in otoliths can be distinguished from false annuli because the true annuli were formed continuously all around the sagittal plane as distinct dark marks. They were mainly formed in May, coinciding with the main spawning season. Chub mackerel grew to over 20 cm by December and attained up to 28 cm in 1 year. Thereafter, the growth rate slowed down. The age composition was 40.2, 42.5, 15.4, 1.7, and 0.1% for age‐groups 0–4, respectively. Using three different approaches, the von Bertalanffy growth parameter was estimated to be between 1.51 and 2.19 and the maximum length between 34.1 and 34.6 cm. The growth coefficient was higher than that in previous studies because of differences in aging technique and the inclusion of juvenile data in one of the approaches. Over 40% of the immature fish of age 0 were included in the current harvest owing to the catch of juveniles in summer and strong fishing intensity in autumn. We recommend regulating catch size during the fast‐growing stage to allow the juveniles to grow and reducing the fishing efforts during autumn to conserve the spawning biomass.