Anthropogenic effects on sustainability of fish biodiversity in Tyume River, Eastern Cape, South Africa

Abstract

To determine the anthropogenic effects on the sustainability of fish biodiversity in Tyhume River, a mixture of ecological, economic and institutional parameters were used. To measure ecological parameters, 10 study sites were selected to represent varying intensities of anthropogenic effects on habitat, to represent typical river zones, and to correspond with historical survey sites for trend analysis. In these study sites, habitat characteristics that represent geomorphology (habitat quantity), water quality and ‘alien’ (non–native) fishes were used to determine anthropogenic effects on habitat and fish assemblage. The measured geomorphology characteristics included current velocity, wetted width and depth. The water quality characteristics used were temperature, pH and conductivity. To determine the effects of native and non-native on indigenous fish species in situ, electro fishing was used in riffles, small pools and runs; as well, in situ seine-netting was done in pools. The riches of river fish species was measured, using numbers abundance and longitudinal distribution indices. It was established that only 11percent of the Tyhume River habitat was relatively near natural, while 89percent exhibited anthropogenic habitat modification. Three major sources ofanthropogenic modification on habitat were identified. The major contributor of anthropogenic effects was Binfield Park Dam which accounted for 43percent of modification. The second source of anthropogenic effects on habitat was Alice urban area where storm water runoff accounted for 28percent of modification. Agricultural and livestock grazing, the third anthropogenic effect, accounted for 18percent of modification. The Eastern Cape Rocky, Sandelia bainsii Castelnau, 1861 and Border Barb, Barbus trevelyani Günther, 1868, exhibited reduced distribution. B. trevelyani longitudinal distribution was less than 25 km along the river continuum, with sporadic presence in the sandy foothills. S. bainsii was not found in the Lowland Zone, while previously this species extended from the mountainous zone to the confluence of the Tyhume and Keiskamma Rivers in the Lowland Zone. These indices supported the homogenization theory, as reflected by increased dissimilarity for two indigenous fish species, S. bainsii and B. trevelyani, among study sites. S. bainsii was previously distributed from source to confluence, while B. trevelyani recorded a 50percent decline at the study site below the Binfield Park Dam. To assign economic value to ecosystem services and assess post Rio-institutional parameters two hypothetical scenarios were developed from the ecological survey; one depicting current conditions and another depicting improved ecosystem services. Using a structured interview questionnaire, five ecosystem services in need of restoration were described to respondents. Applying the contingent valuation method respondents were asked a dichotomous choice question on willingness to pay (WTP). Results of the economic study from 209 personal interviews revealed, individuals were willing to pay an additional R 32.00 on their monthly water bill or R 384.00 annually. Generalizing this to 2 829 households living in the Alice and Ntselamanzi urban areas, a total value of R 1 086 336 would be realized annually. This was equivalent to the Nkonkobe Municipality annual budget for storm water management in Alice urban area. Costs/benefits revealed a positive net present value (NPV) = 1, which, in line with economic theory, meant gainers were able to compensate losers The institutional part of the economic survey sought to determine the effects of post Rio Earth Summit institutional measures on sustainable management of Tyhume River fish assemblage. A desk review of Rio Declaration and three South African statutes were used namely; Constitution Act 108 of 1996 (South African Constitution 1996); the National Environmental Management Biodiversity Act No. 10 of 2004 (NEMBA 2004), the National Environmental Management Act (NEMA) No. 107 of 1998 (NEMA 1998), and the National Water Act No. 36 of 1998 (NWA 1998). The Institutional and Analytic Development (IAD) Framework, coupled with requirements for sustainability of Multiple Use Resource Domains were used for the analysis. De Jure, the statutes had internationalization of environmental costs through “polluter pays principle”, while sustainable use was the overarching goal. De facto, the community participation, a requisite of post Rio measures, was low; however 89percent of community respondents were willing to join an environmental conservation group. This, coupled with the fact that 77percent of those interviewed supported the establishment of a Tyhume River Restoration Fund, provided scope for a broad based community participation framework This study contributes to sustainable use of Tyhume River and other lotic systems by generating information on the link between anthropogenic effects on fish biodiversity, economic value of ecosystems services and institutional mechanisms