TSITSIKAMMA RIVERS INVERTEBRATE RESEARCH PROJECT

Background, context and motivation for the study

(Medium-term consultancy)

Preliminary surveys of aquatic macroinvertebrates undertaken between August 2000 and April 2004 in the Salt River (east of Plettenberg Bay in the Southern Cape) revealed the presence of 16 new species and 3 new genera, and the river was found to support the highest known diversity of species in the mayfly family, Teloganodidae, in Africa. This discovery highlighted not only the conservation importance of this river, which is viewed in the Garden Route Initiative as a priority system with the potential of establishing a corridor linking conservation areas upper catchment to Tsitsikamma National Park and the associated Marine Protected Area, but also the potential conservation importance of other less well studied rivers in the region.

This high species diversity can be partly attributed to there having been no major catastrophic event such as glaciation, flooding by epicontinental seas or total aridity since the middle Cretaceous (over 100 million years ago). The cold, acidic waters, characteristic of rivers in the region, house the remnant of the cold-adapted, temperate Gondwanan fauna that was common to the southern land-mass during the Permian to the Jurassic periods, before the splitting of Gondwanaland in the Cretaceous. This has resulted in a high degree of endemism in this region. Several surveys also indicate that there are no freshwater fish found in the Salt River and, it is suggested that the resulting lack of predation on the aquatic insects may have contributed to their current structure and diversity. However, as no comparable surveys have been undertaken in adjacent systems which do support indigenous freshwater fish populations (principally Pseudobarbus afer) it is unclear the extent to which the unique fishless status of the Salt River contributes to the composition and structure of invertebrate communities.

Rivers in the Tsitsikamma region, and the Salt River in particular, are being subjected to increasing development pressures. For example, initial invertebrate surveys in the Salt River were undertaken as part of an environmental impact study for the proposed introduction of alien trout (both rainbow Oncorhynchus mykiss and brown trout Salmo trutta) into the mid and upper reaches to establish a recreational fishing business in areas where the river flows through private property. From 2002 onwards, the rate of development in the Salt River and some adjacent catchments has increased significantly, with in particular polo fields and housing developments posing threats to the health of river systems. For example, currently 480 low-cost houses are in the process of development, while further low cost and high income housing developments for in excess of 1 600 units are proposed in The Crags adjacent to and overlapping the Salt River catchment area.

The Salt River is the main water source for the area, and significant increases in abstraction are proposed to supply developments. An intermediate ecological reserve study on the Salt River is currently being undertaken by consultants appointed and funded by developers of the polo estate. Through the Nature’s Valley Trust lobbying the Department of Water Affairs & Forestry (DWAF), a flow rate gauge has been installed on the Salt River and data from this will feed into the reserve study as well as to DWAF. The information coming out of the reserve study should, in theory, enable Salt River users and authority bodies to make better informed decisions regarding the amount of water which can sustainably be abstracted from the system. The Nature’s Valley Trust attempted, unsuccessfully, to lobby for a comprehensive reserve study to be undertaken on the Salt River in view of the presence of the unique macroinvertebrate biota. The intermediate ecological reserve study being undertaken does not take into account the ‘unknowns’ of the unique biota known to occur in the system. Ecological reserve determinations have not been undertaken for any other comparable rivers in the Tsitsikamma region.

Little research work has been undertaken on rivers of the Tsitsikamma region other than the Salt River. The aquatic macroinvertebrates present in most of these rivers have not previously been comprehensively surveyed or described hence it is not known whether species assemblages are similar to those already described in the Salt River, which is arguably currently the most threatened. Furthermore little is known about the environmental requirements of the macroinvertebrates in this region and hence their potential vulnerability to current or potential man-induced environmental changes. To address this shortfall a three-phased project is proposed. In Phase 1 surveys of aquatic macroinvertebrates will be undertaken in 11 rivers in the Tsitsikamma region (Matjies, Buffels, Salt, Bobbejaans, Groot (West), Bloukrans, Lottering, Elandsbos, Storms, Elands, Groot (East)) enabling spatial comparison of species assemblages to identify and prioritize rivers in terms of regional and national conservation importance. Phase 2 of the project, which will be informed by Phase 1, will focus on the environmental requirements of aquatic macroinvertebrates in selected high conservation priority rivers, with particular emphasis on endemic or rare biota. Phase 3 will utilize information gained in phases 1 and 2 to facilitate effective conservation and wise management of rivers in the Tsitsikamma region by promoting stewardship and private ownership conservation initiatives, with particular emphasis on rivers of high conservation importance by virtue of their aquatic macroinvertebrate assemblages.