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

ENGLISH 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 Bertalantty equations: Lt = 24,4 (1 - e-O·0583 (I + 1,8446)) and Lt .. 19,0 (1 _ e-O·0454 (I + 4.0726)) respectively, where Lt - carapace length (in mm) at age t (in months). Eggs were apparently laid after moulting, which ocamed primarily during spring and summer. First sexual maturity was attained after 1,5 years, while the estimated life span was 41ears. The annual somatic production and PglB ratios of the populatio!,!s sampled were 1864 and 1093 kJ.m- 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. ******* AFRIKAANSE OPSOMMING: Kwantitatiewe monsters van normale en verdwergde U. africana is met gereelde tussenposes in die Swartkopsgetyrivier geneem. Die groei van hierdie garnale, soos bepaal deur kohort-analise, is deur von Bertalantty groeivergelykings soos volg beskryf: Lt = 24,4 (1 - e-O·0583 (I + 1.8446)) en Lt = 19,0 (1 _ e-O·0454 (I + 4.0726)) waar Lt karapakslengte (in mm) op ouderdom t (in maande). Eiers is blykbaar na vervelling, wat hoofsaaklik gedurende lente en somer plaasgevind het, gele. Geslagsrypheid is na 1,5 jaar bereik, terwyl die berekende lewensduur 4 jaar is. Die jaarlikse somatiese produksie en PglB verhouding van die gemonsterde bevolkings is onderskeidelik 1864 en 1093 kJ.m-2 en 0,79 en 0,99. Somatiese produksie van die hele getyrivier 59 bevolking is naastenby 1077 x 1 cj kJ.J1. 'n Geskatte 13, 5 en 2% hiervan is onderskeidelik deur voels, visse en mense verbruik, terwyl die res waarskynlik die aasvreter- en detritus-voedselwebbinnegedring het.