The biomass and yield of the dominant fish species in Hartbeespoort Dam, South Africa

Abstract

The standing stocks of the three dominant fish species in Hartbeespoort Dam, O. mossambicus, C. gariepinus and C. carpio, were determined by mark and recapture experiments and Leslie's method of fishing success . The biomass of O. mossambicus increased from 279 t in 1982 to 521 t in 1983, following good recruitment to the population after a year's mild winter mortality . Only one reliable estimate of each of the other two species could be made, C. gariepinus (293 t) and C. carpio (581 t) . The fish community was heavily utilised by recreational anglers and the estimated mean annual yields were O. mossambicus (144 t), C. gariepinus (102 t) and C carpio (449 t) . These yields are probably higher than the longer term mean harvest as a result of low water levels during the study period, which increased catchability . The high standing stocks and yields are ascribed to high nutrient concentrations and primary production .

Diversity of cyanobacteria and cyanotoxins in Hartbeespoort Dam, South Africa

“…Hartbeespoort Dam was completed in 1923 and filled with water in 1925 (Cochrane 1987). The reservoir has a surface area of around 20 km 2 and a mean depth of 9.6 m (Ashton et al 1985).…”

“…The reservoir has a surface area of around 20 km 2 and a mean depth of 9.6 m (Ashton et al 1985). Hartbeespoort Dam was originally planned as a water supply for Pretoria and Johannesburg but, after completion, was mainly used for irrigation and recreation (Cochrane 1987;Water Research Commission 2008). The initial oligotrophic conditions in Hartbeespoort Dam changed over the next 25 years to eutrophic because of excessive nutrient loading (Allanson and Gieskes 1961).…”

An assessment of recreational bank angling in the Free State Province, South Africa, using licence sale and tournament data

“…This is anomalous in the African context as fisheries in other countries are generally heavily exploited by small-scale fishers using gears such as gill nets, seine nets and traps (Weyl et al, 2010;Cooke et al, 2013;Weyl and Cowley, 2015). Although inland fisheries in South Africa are generally considered underexploited from a harvest perspective (Weyl et al, 2007;Britz et al, 2015), case studies of angling on the Hartbeespoort Dam (Cochrane, 1987) and the Gariep Dam (Ellender et al, 2009(Ellender et al, , 2010a(Ellender et al, , 2010b suggest that harvests by recreational and subsistence anglers can be considerable. Cochrane (1987), for example, estimated a mean annual harvest of 695 tons of fish from the 2 000 ha eutrophic Hartbeespoort Dam by recreational anglers from the metropolitan settlements in Gauteng.…”

“…Although inland fisheries in South Africa are generally considered underexploited from a harvest perspective (Weyl et al, 2007;Britz et al, 2015), case studies of angling on the Hartbeespoort Dam (Cochrane, 1987) and the Gariep Dam (Ellender et al, 2009(Ellender et al, , 2010a(Ellender et al, , 2010b suggest that harvests by recreational and subsistence anglers can be considerable. Cochrane (1987), for example, estimated a mean annual harvest of 695 tons of fish from the 2 000 ha eutrophic Hartbeespoort Dam by recreational anglers from the metropolitan settlements in Gauteng. In a more rural setting, Ellender et al (2010a) estimated anglers harvested 88 t·y -1 from the Gariep Dam, situated on the provincial boundary between the Eastern Cape and Free State Provinces.…”

“…Cochrane (1987), working on the eutrophic Hartbeespoort Dam, estimated that 65% of the 695 t annual average harvest by recreational anglers was C. carpio. This is supported by tournament data for the Free State Province, where C. carpio contributed 81% of the total weight and 77% of the total numbers of all fish landed (Table 4).…”