Age determination of black bream, Acanthopagrus butcheri (Sparidae), from the Gippsland Lakes of south-eastern Australia indicates slow growth and episodic recruitment

Abstract

The age of black bream (Acanthopagrus butcheri) in the Gippsland Lakes of south-eastern Australia was estimated with high precision from sectioned otoliths of fish sampled from 1993 to 1996. Ageing techniques were validated by following the progression of age classes over 4 years. Correct identification of the first increment was aided by reference to the position of the subcupular meshwork fibre zone, and age assignment was confirmed by linear regression analyses of otolith weight against fish age. The growth of black bream was found to be slower, and their natural life span longer, than previously estimated from length–frequency distributions and scale readings. The maximum age recorded was 29 years, with most black bream 4–9 years old and few fish more than 10 years old. There were significant differences between the growth rates of males and females. The von Bertalanffy growth parameters were: L_∞ 54.5 cm FL, t₀ –5.21 years, K 0.042 year^-1 for females and L_∞ 38.2 cm FL, t₀ –3.70 years, K 0.077 year^-1 for males. The current age structure suggests that recruitment has been episodic since 1981 and low for three recent years in succession.