Determinations of the reproductive output of populations of a thalassinid prawn Upogebia africana (Ortmann) in the Swartkops estuary

Abstract

Populations of large and ‘stunted’ (adult carapace lengths = 17,0–24,0 and 12,0–19,0 mm respectively) Upogebia africana were regularly and quantitatively sampled in the Swartkops estuary. At the site with ‘stunted’ prawns a well-defined spring (July to October) and summer (December to March) breeding cycle was recorded. The ‘stunted’ female prawns produced two broods of eggs per annum and the brood size ranged from about 305 to 2282 eggs depending on the size of the female. At the site with large prawns the spring and summer breeding cycles tended to merge, forming a longer breeding season, with the adult females apparently producing three broods of eggs per annum. The brood size of these females ranged from about 1304 to 4819 eggs. The calculated reproductive output (Pr) and reproductive biomass ratio (Pr/B) of the latter population were much greater than those of the ‘stunted’ prawns (1331 kJ m⁻² y⁻¹ and 0,53 v. 332 kJ m⁻² y⁻¹and 0,26).