Acanthopagrus berda is an estuarine-dependent fish species which is widespread in the tropical Indo-Pacific. In South Africa, it is particularly abundant in the three large northern KwaZulu-Natal estuarine systems, namely Kosi Bay, St Lucia and Richards Bay. In these systems, A. berda is harvested by a variety of methods, including traditional fish traps, gillnets and hook and line. The importance of A. berda to the different fisheries was evaluated by analysing all the available monitoring data specific to catches in these three systems. A. berda was found to be one of the five most important species taken in both the gill net and recreational fisheries at Kosi Bay and St Lucia. It was less important in the marine-dominated Richards Bay system. Catches were generally seasonal, with trends in catch per unit effort (cpue) for A. berda related to annual spawning migrations. The long-term trend in cpue for this species in the Kosi recreational fishery showed a disturbing downward trend. Ages of A. berda specimens caught in northern KwaZulu-Natal estuaries were determined by examining whole otoliths. Age estimates were validated by marginal zone analysis and oxytetracycline labelling, which indicated that opaque deposition occurs primarily from September to November each year. The reproducibility of age estimates was described by a coefficient of variation of 10%. The special von Bertalanffy growth curve was found to best describe the growth of A. berda. The parameters of the von Bertalanffy growth curve indicated that A. berda in northern KwaZulu-Natal is slow growing, attaining at least 16 years of age. The age and growth parameters and mortality estimates from catch curves were used to complete a per-recruit stock assessment of the species. The results of the spawning biomass per-recruit model using different ages of first capture indicate that A. berda is at 47% to 55% of its unfished level. Although these results may indicate that A. berda in northern KwaZulu-Natal is not at present overexploited, longevity coupled with late maturation, sex change, estuarine dependency, increasing catches of A. berda and poor monitoring give cause for concern for the continued sustainable use of this species in northern KwaZulu-Natal. / Thesis (M.Sc.)-University of Natal, Durban, 2001.

This study investigated aspects of the biology of Sarpa salpa, such as reproduction, age and growth, and mortality, which are necessary for an assessment of the status of this species off the KwaZulu-Natal (KZN) Coast. The importance of S. salpa to the shore-based fishery in KZN was evaluated using Natal Parks Board shore patrol data. These data were validated by analysing preliminary results of an independent shore-angling survey along the KZN Coast. Despite differences in the catch composition and catch rates between the two analyses, both data sources highlighted the importance of S. salpa to the shore-based fishery in KZN. Shore-based catches were markedly seasonal coinciding with the breeding season of the species. The species in KZN is targeted primarily to provide a supplementary source of animal protein. An investigation of the reproductive biology of S. salpa indicated a protracted spawning period for the species. Size at 50 percent maturity for combined sexes was attained at 145 mm fork length. The sex ratio in shore-based catches was 1:1.6 in favour of males. A frequency distribution by size indicated that males dominated the smaller size classes while females dominated the larger size classes. Detailed histological examination of gonadal development showed that S. salpa has the potential for protandrous sex change. An age and growth study based on the examination of whole otoliths indicated that S. salpa was relatively fast-growing and a maximum age of six years was recorded for the species. One opaque band was laid down per year. This was validated by marginal increment analysis and by an oxytetracycline labelling experiment using captive fish. Growth in S. salpa was described by a Von Bertalanffy growth function: Lage (mm FL) = 224mm(1 -e-o.55 year-1(age+o.51years)) The natural mortality rate (M = 0.6 year-1) was derived using Pauly's equation and the current fishing mortality (F) rate was estimated at 0.8 year-1. The current status of S. salpa in the shore-based fishery was assessed by determining the effects of F and age-at-capture on the yield- and spawner biomass-per-recruit. Current levels of fishing pressure on S. salpa appeared to be appropriate for utilisation of the stock off the KZN South Coast. In terms of management, S. salpa appears to be in no need of any restrictive measures at present. / Thesis (M.Sc.)-University of Natal, Durban, 1995.