Assessing small-scale fisheries potential of Gariep Dam, South Africa's largest impoundment
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Date
2022-07
Authors
Swanepoel, Pieter Johannes
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Publisher
University of the Free State
Abstract
South African inland fisheries are considered poorly developed and fish resources are mainly utilised by recreational and subsistence fishers. The South African government has identified inland fisheries as an opportunity to contribute to food security, job creation and economic development, and has established a mandate to develop this sector. The Gariep Dam is South Africa’s largest freshwater reservoir, and its fish resources can potentially be utilised by the small-scale fisheries sector. The objectives of this study were to assess the fisheries potential of Gariep Dam by determine the viability of small-scale fisheries development by establishing up-to-date utilisation rates, determining fish abundance and catch rates, and assessing the viability of various harvest strategies. To assess resource status, a fisheries-independent multi-method approach was applied using gillnets, fyke nets and longlines to determine relative abundance, population structure and harvest potential. Fisheries-dependent roving creel surveys and angler counts were conducted to assess the recent utilisation of fish resources. To complement previous biological assessments of other species, Clarias gariepinus was studied to understand the biology, ecology, and population dynamics of this species in Gariep Dam. To assess potential development, a fisheries management plan that determined harvest costs, fish prices and financial viability was included. Labeobarbus aeneus dominated gillnet catches, with an average catch per unit effort of 5.7 ± 4.1 kg.net-1.night-1, which comprised 63% of the species composition. The remainder of gillnet catches comprised C. gariepinus (16%), Labeo capensis (10%), Labeobarbus kimberleyensis (10%) and Labeo umbratus (1%). Longlines proved to be successful in harvesting C. gariepinus, with an average catch per unit effort of 35 ± 24 kg.20-hooks-1.night-1, with very low catch rates for fyke nets. The longline catches were dominated by C. gariepinus (99%) with low numbers of L. kimberleyensis (1%). Roving creel surveys revealed that the Covid-19 pandemic had a major effect on the current hook-and-line fishery that was dominated by subsistence anglers, while recreational fishing disappeared during this period. A large proportion of the subsistence fishing sector were found to be out of work with unemployment rates of 70.9% and 34.5% in the two angling areas. Angler catches were dominated by L. aeneus (37.3%), followed by Cyprinus carpio (32.7%), C. gariepinus (13.7%), L. capensis (14.1%) and L. kimberleyensis (1.4%). The angling effort was estimated at an average of 42 ± 1 anglers.day-1 for the Gariep Dam which harvested an estimated 27 tonnes.year-1 during the sampling period.
Clarias gariepinus from the Gariep Dam represents a stable population that matures late (5.2 years for males and 3.3 years for females), is dominated by old fish (Amax = 32 years) and exhibits slow growth (Lt = 1 013.28 (1-e0.092(t+7.78)) and a low natural mortality rate (0.369 year-1). These characteristics point towards a species that is likely to be utilised by inland fishers; however, spawning stock should be protected through special refuge areas. e study has revealed that the existing hook-and-line fishery is very important to the local communities surrounding the Gariep Dam and should be recognised and protected from future inland fisheries development. Results of the study indicate that a sustainable small-scale fishery is possible in the form of a longline fishery harvesting 40 tonnes.year-1 of C. gariepinus and a gillnet fishery using a 100 mm mesh size to harvest L. aeneus if they are separated by area to protect the current fishery. The financial analysis, however, indicated that substantial fishing effort will be required to harvest the projected amount of fish. With the recent price of freshwater fish (ZAR 13.50–16.00), a longline fishery is likely to be feasible, but a gillnet fishery is unlikely to generate sufficient revenue based on catch rates for a small-scale sector. The results of this study have been used to inform specific recommendations to develop inland fisheries for Gariep Dam, which can be used by government for decision-making.
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Keywords
Gariep Dam, Fisheries-independent, Fish resources, Local government, Ecosystem management -- South Africa -- Gariep Basin, Freshwater fishes, Food security -- South Africa -- Free State