Age, growth and aspects of reproduction of the mackerel Scomber Japonicus in South African waters (Pisces: Scombridae)

Abstract

The age and growth of the mackerel were determined from 1742 otoliths collected from commercial catches. The time of annulus formation was established from otolith edge examinations. Two zones. one opaque and one hyaline, are laid down during a year. The distance of each annulus from the nucleus of the otolith was measured. Mean measurements were substituted in a linear regression equation which describes the relationship between otolith radius and fish length to obtain back-calculated length at age values. Growth in length and in mass are expressed by the von Bertalanffy growth equation. Length and age at first maturity were established by macroscopic examination of mackerel gonads. All mackerel were found to mature during their fourth year of life, at 42 cm standard body length. Spawning takes place during the period June to September.