African Journal of Aquatic Science ISSN: 1608-5914 (Print) 1727-9364 (Online) Journal homepage: https://www.tandfonline.com/loi/taas20 Rapid biological assessment of the fishery potential of Xonxa Dam, near Queenstown, South Africa TJ Richardson , AJ Booth & OLF Weyl To cite this article: TJ Richardson , AJ Booth & OLF Weyl (2009) Rapid biological assessment of the fishery potential of Xonxa Dam, near Queenstown, South Africa, African Journal of Aquatic Science, 34:1, 87-96, DOI: 10.2989/AJAS.2009.34.1.9.734 To link to this article: https://doi.org/10.2989/AJAS.2009.34.1.9.734 Published online: 07 Jan 2010. Submit your article to this journal Article views: 90 Citing articles: 10 View citing articles Full Terms & Conditions of access and use can be found at https://www.tandfonline.com/action/journalInformation?journalCode=taas20 African Journal of Aquatic Science 2009, 34(1): 87–96 Copyright © NISC (Pty) Ltd Printed in South Africa — All rights reserved AFRICAN JOURNAL OF AQUATIC SCIENCE ISSN 1608–5914 EISSN 1727–9364 doi: 10.2989/AJAS.2009.34.1.9.734 Rapid biological assessment of the fishery potential of Xonxa Dam, near Queenstown, South Africa TJ Richardson, AJ Booth* and OLF Weyl Department of Ichthyology and Fisheries Science, Rhodes University, PO Box 94, Grahamstown 6140, South Africa * Corresponding author, e-mail: [email protected] Received 16 May 2008, accepted 17 November 2008 Rapid biological assessments have been proposed as the most cost-effective approach to identify suitable target species and to set initial catch and fishing effort levels for new fisheries. Xonxa Dam, a turbid irrigation dam situated in the White Kei catchment, rural Eastern Cape, is shown to provide fisheries potential for two alien species — smallmouth yellowfish Labeobarbus aeneus and sharptooth catfish Clarias gariepinus — that had been previously introduced into the catchment. Rapid appraisal of the biology, relative abundance, and population dynamics of the fish was effected during three sampling events in 2007. Using a combination of empirical yield and dynamic pool models, it was shown that two discrete fisheries can be developed. For L. aeneus a 60 mm stretched mesh gill net fishery could harvest 23 t y–1 and for C. gariepinus a longline fishery could yield 4 t y–1. The combined fisheries could be valued at c. R135 000 (USD 18 000) per annum. Periodic monitoring would be necessary; firstly, to ensure that spawner biomass per recruit is not reduced below 40% of current levels and, secondly, to refine the potential harvest available from the resource once harvesting is initiated. Keywords: Clarias gariepinus, Labeobarbus aeneus, rapid biological assessment, reservoir fisheries, spawner biomass per recruit, target reference points, yield per recruit Introduction In Africa, the harvesting of fish from small reservoirs has fishery, viability analyses and resource assessment should been identified as an important food resource for small rural be undertaken. communities, particularly those living close to waterbodies Weyl et al. (2007) suggest a rapid assessment based on a (Kapetsky and Petr 1984, Marshall and Maes 1994, van fishery productivity analysis, species composition, stakeholder der Knaap 1994). Development of fisheries to utilize these consultation, market access and availability, and personal resources has recently been identified by the African Union observations to recommend whether a fishery could be as a priority investment area for poverty alleviation and developed. This rapid assessment would also provide informa- regional economic development (NEPAD 2005). Within tion on the suitability of the fishery’s being a community- a South African context, it is suspected that there will be managed subsistence fishery, a commercial fishery, a increased interest in developing these fisheries to address recreational fishery, or simply for the fishery to remain at its major national policy objectives, which include food security, open-access equilibrium. Each fishery type then requires economic empowerment, optimal economic benefit from exploitation rules, such as quotas, minimum size limits, closed water, and poverty eradication (RSA 1998a, 1998b). seasons, gear limitations and access or effort limits. South Africa, however, presents a somewhat anomalous To ensure that long-term resource and socio-economic situation. The lack of a fishing history in communities, the sustainability is achieved, it is necessary to set initial exploi- lack of species with a high fisheries potential, inadequate tation rules. This is, unfortunately, only possible in the inland fisheries policy and a lack of directed fisheries presence of a fishery. In a fished situation, if catches and development have resulted in low utilisation levels of fish catch-rates are monitored, then the population dynamics of resources in South African reservoirs (Weyl et al. 2007). the harvested resources can be modelled using the most However, there are also positive aspects. For example, appropriate stock-assessment methods. In new fisheries the the large number of reservoirs, particularly those constructed choice of assessment method is constrained by the inherent for irrigation, now support large populations of alien fishes data-limited nature of the fishery. In such situations, fisheries that could be commercially or recreationally harvested. managers in developing countries have focused on the Inland fisheries in rural areas are being touted as a ‘golden application of per-recruit models (Beverton and Holt 1957) as goose’ and a possible solution to poverty alleviation. It is, a cost-effective stock assessment technique (Thompson and however, prudent that, prior to the initiation of any form of Allison 1997, Booth and Weyl 2004, Kanyerere et al. 2005, Published online 07 Jan 2010 88 Richardson, Booth and Weyl Weyl et al. 2005a, 2005b). The application of per recruit or muddy banks, while the southern arm is dominated by models allows for the assessment of biological reference steeper rocky banks. Mean annual water temperature is points (BRPs) to achieve management targets. 16.5 °C (Table 1) and annual changes in water volume did This paper presents a rapid biological assessment of the not exceed 3% during the study period. fish resources of Xonxa Dam that proposes initial exploi- Previous research catches by Schramm (1993) were tation regimes for harvesting two alien, although South dominated by Cyprinus carpio and L. aeneus at 7.4% and African, fish species: smallmouth yellowfish Labeobarbus 92.6%, respectively. Small quantities of banded tilapia aeneus and sharptooth catfish Clarias gariepinus, that Tilapia sparmanii and bluegill sunfish Lepomis macrochirus have invaded the White Kei catchment (Scott et al. 2006). were also caught. Current fishing activity is low, with It is hoped that this research can serve as a case study children and adults using handlines with small hooks baited on the use of this methodology in providing rapid assess- with earthworms to target L. aeneus and C. gariepinus. ments of the biological potential of reservoirs for fisheries The reservoir is situated on communal land with an development. estimated c. 15 000 people living in the surrounding rural settlements (Rouhani 2002). Fishery development on the Material and methods reservoir has previously been suggested (Duncan-Brown 1980, Schramm 1993, Rouhani 2002) but without a prior Study site assessment to estimate initial sustainable harvest levels. Xonxa Dam (31°49′30.40′′ S; 27°10′56.22′′ E; 937 m asl), Although attempts to develop a gillnet fishery have failed situated 27 km from Queenstown (Figure 1), at full capacity (Duncan-Brown 1980) there is renewed interest in fishery is a 1 450 ha impoundment on the White Kei River in the development by the local municipality to provide additional Eastern Cape Province of South Africa. Construction was employment opportunities. completed in 1971 and, at full capacity, the reservoir has a mean depth of 10.87 m (DWAF 1997) and a maximum Sampling methods depth of 36.9 m (Schramm 1993). The western and northern Three sampling trips were conducted in March, May and arms of the dam are dominated by gently sloping, rocky August 2007 when gill nets, longlines, fyke nets and a seine net were used to sample fish. Sampling gear was set in all available habitat types to ensure representative sampling. 27° E 28° E Habitat types included muddy and sandy substrates over both steep and shallow banks. Experimental multifilament gill net fleets, comprising 9 m long × 3 m deep panels of 0 25 50 km netting with 44 mm, 60 mm, 75 mm, 100 mm and 144 mm Xonxa Dam stretched mesh size were set at the surface overnight. Queenstown 32° S Longlines with circle hooks (Mustad sizes 5/0–11/0) spaced at 2–3 m intervals and baited with fish were set overnight. EASTERN CAPE To supplement samples for age and growth, a 15 m seine K ei net with 10 mm mesh size was used to sample shallow habitats and five fyke nets were deployed during the first sampling trip. The soak time of each gear was recorded. AFRICA Environmental data such as water temperature, pH, SOUTH electrical conductivity (EC), total dissolved solids (TDS), South AFRICA INDIAN OCEAN Africa dissolved oxygen (DO) and Secchi depth were recorded at 33° S each sampling site (Table 1). Dam level data were obtained from the Department of Water Affairs and Forestry. Physico- Figure 1: Map showing the location of Xonxa Dam on the Kei River chemical characteristics were found to be similar to those system in the Eastern Cape recorded