Growth, production and consumption of the thalassinid prawn Upogebia africana (Ortmann) in the Swartkops estuary

Abstract

Populations of large and stunted Upogebia africana were regularly and quantitatively sampled in the Swartkops estuary. The growth of these prawns, determined by cohort analyses, was described by von Bertalanffy equations: Lt = 24,4 (1 – e^{−0,0583 (t + 1,8446)} and Lt– 19,0 (1 – e^{−0,0454 (t + 4,0726)} respectively, where Lt – carapace length (in mm) at age t (in months). Eggs were apparently laid after moulting, which occurred primarily during spring and summer. First sexual maturity was attained after 1,5 years, while the estimated life span was 4 years. The annual somatic production and Pg/B ratios of the populations sampled were 1864 and 1093 kJ.m^-2 and 0,79 and 0,99 respectively. Somatic production of the entire estuarine population was approximately 1077 x 10⁶ kJ.y⁻¹. An estimated 13, 5 and 2% of this was ‘consumed’ by birds, fish and man respectively, while the remainder apparently entered the scavenger and detrital food webs.