chapter 3: choice and description of study area

CHAPTER 3: CHOICE AND DESCRIPTION OF STUDY AREA 3.1. INTRODUCTION Once the priority for a study on the reproduction strategy and breeding behaviour of Labeobarbus

polylepis was identified and motivated by aquatic scientists from Mpumalanga Parks Board internal reports (Engelbrecht, 1997 and Roux, 1997), the search began to find experimental Labeobarbus

polylepis populations that were not impacted by anthropogenic activities. The IUCN fish database and Mpumalanga Parks Board fish database were used to identify appropriate Labeobarbus

polylepis populations within the province that were not subjected to stream regulation and were also minimally impacted by other anthropogenic activities. Consequently two riverine ecosystems containing isolated populations of Labeobarbus polylepis that conform to the requirements of this study were identified on the escarpment near Lydenburg and Bourkes Luck respectively (Fig 3.1). These are the upper reaches of the Spekboom and Blyde rivers. Prior to commencement of the study it was also known from previous observations by anglers and during biomonitoring assessments that Labeobarbus polylepis display spawning activities in these reaches. 3.2. THE BLYDE RIVER The Blyde River rises on the farm Hartbeesvlakte (163KT), east of the town of Sabie, and is joined by the Treur River at the Bourke’s Luck Potholes (Fig 3.2). From here the Blyde River flows north through the Blyde River Canyon (eastern escarpment of the Drakensberg) into the Blydepoort Dam before it enters the Lowveld where it joins the Olifants River (Limpopo River system). At its source the Blyde consists of small tributaries that forms a small mountain stream, which flows through the farms: In de Diepte and Hartbeesvlakte. From the foothills of Mount Anderson the river follows a course through the Escarpment to the base of the Blyde River Canyon at Swadini, through the Lowveld to its confluence at the Olifants River near Gravelotte. The Blyde catchment area is 2842 km2 with a mean annual runoff of 402.6 (106m3). The Blyde River is characterised by an unconfined sinuous channel with a strong bedrock influence. The

Chapter 3 Choice And Description Of Study Area page 3-1

Reproduction Strategy Of Labeobarbus Polylepis (Smallscale yellowfish)


Figure 3.1: Labeobarbus polylepis distribution map.

Labeobarbus polylepis population

NORTH WEST

GAUTENG

Johannesburg

MPUMALANGA

LIMPOPO

KWAZULU NATAL

Blyde River

Lydenburg

Spekboom River

Pongola



Figure 3.2: Study area in the Blyde River



morphology is dominated by rapids/ riffles and pools. The mean annual precipitation for this areas is between 500 – 800 mm (Midgley et.al., 1990).

3.2.1. Geomorphology and Lithography of the Blyde River Catchment The Drakensberg Escarpment probably started developing during the Early or Middle Jurassic and it probably was a noteworthy landmark since the Middle Cretaceous Period. Its appearance can possibly be attributed to the disintegration of Gondwanaland. The Escarpment was formed by erosion, a process that is currently continuing, slowly weathering away in the direction of the Highveld (Bosch, 1991). The Blyde River originates at Mauchsberg in the northeastern Mpumalanga Escarpment, which forms part of the Great Escarpment at the eastern edge of the interior plateau of southern Africa. The Blyde River incised four main geological systems, namely the Chuniespoort- and Pretoria Groups, Blackreef Formation, Wolkberg Group and Achean Granite (Matthews, 1991 and Bosch, 1991). Chuniespoort Group

The head waters of the Blyde River consists mainly of a small mountain stream that cuts through the Timeball Hill Formation and Malmani Dolomite, Chuniespoort Group. This section of the river provides the habitat for the only surviving population of the endemic Labeobarbus treurensis in the Blyde River. The rare Natal Ghost Frog Heleophryne natalensis also occurs in this section (Theron, 2006). Trout were introduced in the river section below Christmas Falls and is probably responsible for the extinction of Labeobarbus treurensis in this part of the river.

Blackreef and Main Quartzite Formations

At Bourke’s Luck the river weathered away the softer rocks right up to the hard quartzite of the Main Quartzite and Blackreef Formations. The river probably caused accelerated erosion along a weak zone such as a seam or fault, resulting in the formation of the deep Blyde River Canyon (Bosch, 1991). The layers at the base of the Potholes are relatively soft and were therefore eroded away at a faster rate. The swirling action of the water in the narrow rapids, together with the grinding action of pebbles and boulders, caused the wearing away of the potholes. Erosion



occurred faster in the Blyde than in the Treur River, with the result that the Blyde River is deeper and lower than the Treur River (Bosch, 1991). The Treur River is an important tributary of the Blyde River and is the type locality of Labeobarbus treurensis, which became extinct in the Treur River after the introduction of Smallmouth Blackbass in the river in 1966.

Wolkberg Group

The Blyde River also incised through the Wolkberg Group which has an estimated age of approximately 2 300+ million years, and is amongst the oldest sedimentary rock found in South Africa. The group consists of six formations namely Sadowa Formation (mudstone and sandstone), Mabin Formation (sandstone), Selati Formation (mudstone, quartzite), Schelem Formation (conglomerate), Abel Erasmus Formation (lava, mudstone, dolomite) and Sekororo Formation (sandstone, conglomerate). The banks of the Blyde Dam, which was build below the confluence of the Blyde and Ohrigstad Rivers, are situated in the Sekororo Formation (Bosch, 1991).

Basinal Rock

Intrusive igneous rock is present at the very base of the Blyde River Canyon and the Escarpment as well as in the Lowveld, and comprises granite from Swazium rock approximately 3000 million years old. Tufa Formation In Tributaries Of The Blyde River

One of the special features of the Blyde River Canyon is the formation of Tufa in two of its tributaries. The word Tufa is derived from Latin tofos meaning porous rock. Tufa is presently deposited in the Kadishi and Klipspruit streams which flows into the Blyde Dam. Tufa formation takes place through a very interesting and very complex chemical process. Calcium carbonate and magnesium carbonate are dissolved from the dolomite in the Malmani Subgroup and these ions are transported in a dissolved state in the Kadishi and Klipspruit streams. Due to a loss of carbon dioxide by turbulence and the possible interaction of moss and algae, calcium bicarbonate is changed to calcium carbonate that then precipitated on the rocks, forming tufa (Marker 1973).



3.2.2. Geomorphology and Riparian vegetation of the Blyde River The riparian vegetation of the Blyde River Canyon and the study site consists mainly of large trees, with sparse grasses and sedges and patches of reeds (Phragmites spp.) The dominant trees are Syzygium cordatum, Breonadia microcephala, Nuxia oppositifolia, Mimusops zeheri, Diospyros

whyteana, Acacia robusta, Celtis africana, Ficus sycomorus, Ficus sur, Albizia versicolor,

Rauvolfia caffra, Trema orientalis, etc.

3.3. THE SPEKBOOM RIVER This river has its source in the foothills of Mount Anderson (2285 m), which is situated between the towns of Lydenburg, Sabie, Graskop and Ohrigstadt. The river flows in a westerly direction from the mountains to the north of Lydenburg (Fig 3.3). The R36 crosses the Spekboom just north of Lydenburg, and approximately from this point the river starts to flow in a north, northwest direction, before it has its confluence with the Steelpoort River to the north west of the town Burgersfort. The Spekboom is approximately 60 km in length. The Spekboom and Steelpoort Rivers eventually drains into the Olifants River. The Spekboom River catchment area is 596km2 with a mean annual runoff of 116.72 (106m3) (DWAF, 2001). The Spekboom River is characterised by an unconfined sinuous channel with a strong bedrock influence. The morphology is dominated by rapids, riffles and pools. The mean annual precipitation for this areas is between 500 – 800 mm (Midgley et.al., 1990). 3.3.1. Geomorphology and Lithography of the Spekboom River Catchment The Spekboom River incise the geological system known as the Transvaal Sequence, subdivision Pretoria Group, which consists of four formations of which the Timeball Hill Formation is of importance (Lurie, 1981). The Pretoria Group is made up essentially of sedimentary rocks and consists mainly of shale and quartzite, which varies from 900 m to 1600 m thicknesses. The important Timeball Hill Formation consists predominantly of sales and mudstones, with zones of quartzite. The quartzite zone being more resistant to weathering, giving rise to the mountain peaks such as Mount Anderson, and ridges of this geological zone (Matthews, 1991). Numerous diabase intrusions are found in the Pretoria Group, called Transvaal Diabase. These intrusions are for the



most part responsible for the forming of riffles in the river streambed, which provide spawning beds and invertebrate food for fish and other biota. 3.3.2. Geomorphology and Riparian vegetation of the Spekboom River The upper reaches of the Spekboom flow through the vegetation type classified by Acocks (1988) as Northeastern mountain sourveld (No.8) and Bankenveld (No. 61). The vegetation types of the middle and lower reaches include mixed bushveld or Sourish mixed bushveld (Acocks no.19) and Mixed bushveld (Acocks no.18). Essentially the riparian zone in the upper reaches comprises mainly of grasses, while in the middle and lower reaches of the river the riparian zone is dominated by woody species. The different riparian zones will contribute (alongside the geomorphology) to the creation of different habitats in the river, for example the presence of overhanging vegetation and root wad biotopes. The different riparian zones also influence the types of vegetation that falls into the stream that provides a food source for different macro-invertebrates. The dominant tree and shrub species of the riparian zone is: Combretum erythrophyllum, Salix

mucronata, Rhus transvaalensis, Mimusops zeyheri, Kiggelaria africana, Gomphostygma sp. The instream vegetation consists mainly of grasses, sedges and reeds, with the dominant reeds being Phragmites australis. The Acocks Veld Types in this area is Tropical bush & Savannah, Pure grassveld, False grassveld and Inland tropical forests.



Figure 3.3: Study area in the Spekboom River

chapter 3: choice and description of study area

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