BLACK BASS (MICROPTERUS SPP.) IN THE OLIFANTS- DOORN RIVER SYSTEM: DISTRIBUTION, DISTRIBUTION BARRIERS, PREDATORY IMPACT AND MANAGEMENT by Johannes Adriaan van der Walt Thesis submitted in partial fulfilment of the requirements for the degree Master of Technology: Nature Conservation in the Faculty of Applied Sciences at the Cape Peninsula University of Technology Supervisor: Dr Frans Radloff Co-supervisor: Dr Olaf Weyl Cape Town November 2014 CPUT copyright information The dissertation/thesis may not be published either in part (in scholarly, scientific or technical journals), or as a whole (as a monograph), unless permission has been obtained from the University DECLARATION I, Johannes Adriaan van der Walt, declare that the contents of this thesis represent my own unaided work, and that the thesis has not previously been submitted for academic examination towards any qualification. Furthermore, it represents my own opinions and not necessarily those of the Cape Peninsula University of Technology. Signed Date ii ABSTRACT In the Cape Floristic Region the Olifants- Doorn River (ODR) system is a known biodiversity hotspot in terms of endemic freshwater fish. Eight of the 10 described native freshwater fish species are endemic to this river system. One of the main threats to these fish is predation by introduced predatory fishes. Three species of alien invasive black bass (Micropterus salmoides, Micropterus dolomieu and Micropterus punctulatus) were introduced into the ODR system during the 1930s but prior to this study, their distribution and impacts had never been quantified on a system-wide basis. This study aimed to clarify the current distribution, distribution barriers, predatory impact and best management options for black bass in the ODR system. This was achieved by conducting a system-wide survey of 578 km of stream covering 41 tributaries in the ODR system. Black bass presence was tracked upstream within each tributary to its uppermost distribution point where physical barriers preventing further spread were identified and described. Fish species composition, abundance and size were recorded directly above and below these barriers to quantify black bass impact on the native fish. This research demonstrated that since introduction, natural and human assisted dispersal has facilitated not only the establishment of black bass in the Olifants and Doring main streams but also facilitated the invasions into 22 tributaries. Based on survey results it was estimated that 81.5 % of the ODR system that was previously occupied by native cyprinids is now invaded by black bass. Assessments of native fish abundance and size distribution above and below black bass invasion barriers demonstrated that in invaded tributaries only adults of larger cyprinids (Labeo seeberi, Labeobarbus capensis and Barbus serra) were able to co-occur with black bass species. Smaller fish such as juvenile L. seeberi, L. capensis and B. serra and native minnows (Barbus calidus, Pseudobarbus phlegethon and Barbus anoplus) were absent from the black bass invaded reaches. The findings of this catchment scale study are consistent with findings from other studies in the region. As a result, most native fishes are now restricted to streams above the natural barriers that limit the upstream invasions of black bass. Black bass eradication from invaded reaches is therefore necessary for habitat iii restoration. Effective eradication will however depend on the presence of barriers to prevent re-invasion from downstream sources. To better understand what constitutes the nature of such barriers, this study characterised the natural barriers that inhibited black bass invasions in 17 tributaries. Natural barriers comprised of 15 waterfalls, two cascades and one chute ranging in height from 0.49 m to 3.5 m with an average vertical drop of 1.21 ± 0.67 m. These findings suggest that black bass have poor jumping abilities and the recommended height of artificial barriers as part of a black bass management program should be between 80 and 100 cm depending on the size of the tributary. As a result, the presence of natural barriers or the construction of artificial barriers to prevent black bass invasions is considered a vital component of native fish conservation projects. Finally, the study assessed the feasibility of black bass eradication from the 22 invaded tributaries in the ODR system based on eight criterion covering aspects of biological, physical, anthropogenic and logistical importance. This assessment showed that effective eradication was most likely only feasible in seven tributaries. Prioritisation of these seven tributaries for black bass eradication based on the threatened status of the resident native species, the land-use in the respective catchments and the tributary length available for rehabilitation indicate that the Breekkrans, Biedouw and Thee Rivers should receive the highest priority. iv ACKNOWLEDGEMENTS I wish to thank: . My supervisors, Dr Frans Radloff and Dr Olaf Weyl for sharing their knowledge, patients and general support during my studies. Dr Daragh Woodford for his assistance with field surveys and data analysis. Craig Garrow for his general support and sharing his knowledge on fish photography. Dr Martine Jordaan, Ben van Staden and Dean Impson from CapeNature for their general support. Tumisho Ngobela and Marius Wheeler for their assistance during field surveys. Wessel Pretorius and Mandy Schumann from DENC for their assistance during field surveys in the Northern Cape. CapeNature field rangers from Knersvlakte Nature Reserve, Cederberg Wilderness Area and Matjies River Nature Reserve for their assistance during field surveys. The financial assistance of the South African Institute for Aquatic Biodiversity (SAIAB) towards this research is acknowledged. Opinions expressed in this thesis and the conclusions arrived at, are those of the author, and are not necessarily to be attributed to SAIAB. v DEDICATION I would like to dedicate this thesis to my wife Marika and our three children, Franzelle, Adriaan and Zani. vi TABLE OF CONTENTS DECLARATION ii ABSTRACT iii ACKNOWLEDGEMENTS v DEDICATION vi TABLE OF CONTENTS vii LIST OF FIGURES ix LIST OF TABLES xiii GLOSSARY xv CHAPTER 1: GENERAL INTRODUCTION 1.1 Introduction and impact of alien invasive freshwater fish 1 1.2 Introduction and spread of black bass 3 1.3 Black bass impacts on native fish abundance in the CFR and ODR 5 1.4 Natural black bass barriers 8 1.5 Artificial barriers as a management tool 9 1.6 Eradication options for black bass in the CFR 10 1.7 Objectives of this thesis 11 1.8 Structure of the thesis 12 1.9 References 14 CHAPTER 2: STUDY AREA 2.1 General introduction 23 2.2 Study sites 25 2.2.1 Olifants River Management Area 25 2.2.2 Knersvlakte Management Area 30 2.2.3 Doring River Management Area 32 2.2.4 Koue Bokkeveld Management Area 35 2.3 Freshwater fish of the ODR system 37 2.3.1 Native fish of the ODR system 40 2.3.2 Black bass of the ODR system 50 2.4 References 54 CHAPTER 3: BLACK BASS (MICROPTERUS SPP.) DISTRIBUTION IN THE HEADWATERS OF THE OLIFANTS- DOORN RIVER SYSTEM AND A DESCRIPTION OF PHYSICAL BARRIERS PREVENTING FURTHER SPREAD 3.1 Introduction 59 3.2 Material and methods 61 3.3 Results 63 3.3.1 Extent of black bass invasion in the ODR system 63 3.3.2 Natural black bass barriers 69 3.3.3 Native cyprinid upper limit 88 3.4 Discussion 88 3.5 Concluding remarks 93 3.6 References 94 vii CHAPTER 4: PREDATORY IMPACT OF INVASIVE ALIEN BLACK BASS (MICROPTERUS SPP.) ON INDIGENOUS FISHES IN THE HEADWATERS OF THE OLIFANTS- DOORN RIVER SYSTEM 4.1 Introduction 99 4.2 Materials and methods 102 4.2.1 Data collection procedures 102 4.2.2 Data analysis 105 4.3 Results 106 4.3.1 Species composition above and below bass barriers 106 4.3.2 Co-occurrence of native species and black bass 108 4.3.3 Presence absence of native species 109 4.3.4 Length structure of native fish populations 110 4.3.5 Length classes of black bass below the black bass barriers 112 4.4 Discussion 113 4.5 Concluding remarks 117 4.6 References 118 CHAPTER 5: THE MANAGEMENT OF INVASIVE ALIEN BLACK BASS (MICROPTERUS SPP.) IN THE HEADWATERS OF THE OLIFANTS- DOORN RIVER SYSTEM 5.1 Introduction to the control and eradication of alien black bass in the ODR system 124 5.2 Assessment of tributaries that are suitable for black bass eradication in the ODR system 129 5.3 Artificial barriers of part of black bass management 135 5.4 Review of available methods for black bass eradication 136 5.5 Choice of piscicide: Rotenone vs Antimycin A 139 5.6 Recommendations 140 5.7 References 141 APPENDICES Appendix A: Olifants- Doorn River tributary descriptions 146 Appendix B: Freshwater fish distributions in the ODR system 164 Appendix C: Example of snorkel survey data collection sheet 165 Appendix D: Full criteria for prioritizing tributaries in the ODR system for black bass eradication 166 viii LIST OF FIGURES Figure 2.1 A map showing the Olifants- Doorn River catchment, the main rivers within this system and the four management areas it has been divided into by the Department of Water Affairs 24 Figure 2.2 A map of the Olifants Management Area with all the tributaries that formed part of this study 27 Figure 2.3 The upper catchment of the Diepkloof River rises in the Koue Bokkeveld Mountains in the background of the photograph 29 . Figure 2.4 A typical pool in the upper Rondegat River, Olifants- Doorn River system 29 Figure 2.5 The Knersvlakte Management Area with its main tributary, the Sout River 30 Figure 2.6 The Sout River