Influence of the invasive fish, Gambusia affinis, on amphibians in the Western Cape R Conradie orcid.org 0000-0002-8653-4702 Dissertation submitted in fulfilment of the requirements for the degree Master of Science in Zoology at the North-West University Supervisor: Prof LH du Preez Co-supervisor: Prof AE Channing Graduation May 2018 23927399 “The whole land is made desolate, but no man lays it to heart.” JEREMIAH 12:11 i DECLARATION I, Roxanne Conradie, declare that this dissertation is my own, unaided work, except where otherwise acknowledged. It is being submitted for the degree of M.Sc. to the North-West University, Potchefstroom. It has not been submitted for any degree or examination at any other university. ____________________ (Roxanne Conradie) ii ACKNOWLEDGEMENTS I would like to express my gratitude to the following persons and organisations, without whose assistance this study would not have been possible: My supervisor Prof. Louis du Preez and co-supervisor Prof. Alan Channing, for guidance, advice, support, and encouragement throughout the duration of this study. Prof Louis, your passion for the biological sciences has been an inspiration to me since undergraduate Zoology classes five years ago. Prof Alan, you were a vital pillar of support for me in the Cape and I am incredibly grateful towards you. Thank you both for all the time and effort you have put into helping me with my work, for all your honest and detailed advice, as well as practical help. It is truly a privilege to have had such outstanding biologists as my mentors. My husband Louis Conradie, for offering up so many weekends in order to help me with fieldwork. Thank you also for allowing me to turn our home into a laboratory for the several months that protests prevented me from working at proper facilities, and showing a keen interest in this study. Your selfless love and care has indirectly contributed to this work in innumerable ways. The National Research Foundation (NRF Freestanding, Innovation and Scarce Skills Masters Scholarship ‒ Grant UID 100217). Their financial assistance towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and not necessarily to be attributed to the NRF. CapeNature for the permission to collect tadpoles and mosquitofish (permit numbers: 0056-AAA008-00049 and 0056-AAA043-0017). AnimCare, Faculty of Health Sciences of the North-West University for the relevant ethical approval of this study (ethical clearance number: NWU-00377-16-A5). The Botany Department of the University of the Western Cape, for allowing me to use their facilities for the mesocosm trials, and to Francois Muëller and Lyle Wilson for their practical help and kindness. Cliff Dorse from the Biodiversity Management branch of the City of Cape Town, for immense help in obtaining landowner permission to sample mosquitofish and tadpoles. iii The conservation managers who granted permission or that helped with surveying for mosquitofish: Sabelo Memami from Kenilworth Racecourse Conservation Area, Lamees Chikte and Vibeke Maass from the Uitkamp Wetlands Nature Reserve, Koos Retief from Table Bay Nature Reserve, and Elton le Roux from Kirstenbosch Botanical Gardens. The landowners that granted permission to collect tadpoles: Lydia Anderson, the body corporate of Burgundy Estate, and the owners of the Twee-en-Twintig Watervalle farm. I thank you so much for your friendliness towards me and your concern for amphibian conservation. Artherton de Villiers and Tania Morkel for their help by collecting tadpoles for experiments, to Roger Bills from SAIAB for mosquitofish collection data, and to John Measey for valuable advice given at the beginning of this study. Thank you all for your willingness to help. Family and friends for their interest, encouragement, love, and prayers, and lending me their ears to talk about this study. No man is an island, and your thoughtfulness and consideration have been invaluable. I especially want to thank my father and mother, Stefan and Althea Viviers, my mother-in-law Erma Conradie, and my dear friends Jennie Boersma, Rozelle Johnson, Janeé Coetzer, Lizzy and Petro Hamman, Laurencia van Deventer, Anne Jacobs and Megan McGee. My greatest thanks are toward my Creator and Saviour, the Lord Jesus Christ, who gives me an immovable reason for living every day of my short life, whether those days are joyful or dreadful, exhilarating or mundane. Lord, I thank you for this privilege to study further, as well as for guidance, wisdom, and perseverance throughout the course of this study. iv ABSTRACT The worldwide dispersal and establishment of invasive fish is partly responsible for the global decline in amphibian species. Unfortunately, this is a significant problem in the Western Cape in South Africa, as the region is both a hotspot for alien freshwater fish and an area of critical conservation concern for endemic and threatened amphibians. Research abroad has shown that one of the invasive fish that occur in the region, the Western mosquitofish (Gambusia affinis), is a threat to the persistence of amphibians. However, there are no South African studies that examine the impact of mosquitofish on local species, and consequently this study arose from this research need. Consequently, the influence of mosquitofish on native amphibian species was examined by determining the extent of mortalities and injuries inflicted on amphibians by way of mesocosm trials. These trials revealed that these alien fish have the potential to completely obliterate amphibians within a micro-habitat. However, mosquitofish predation effects were different between amphibian species, suggesting that certain species are more susceptible to mosquitofish predation than others. This phenomenon was further examined by way of predation experiments, which in combination with the mesocosm trials suggest that local non-bufonid species are at a higher risk of mosquitofish predation than bufonids. Indirect predation effects were also examined during the mesocosm trials, and it was revealed that surviving tadpoles were severely impacted through retarded development, stunted growth, limb and tail injuries, and the manifestation of stress-induced behaviour. The mechanisms of mosquitofish predation were also further explored, and it was found that attack behaviour on tadpoles is socially facilitated, which indicates that predation intensifies as group sizes of mosquitofish increase. Furthermore, the extent of their spread within the Cape Town area was determined by conducting a literature review and preliminary field survey. This information was further used to determine areas where mosquitofish occur in sympatry with threatened amphibians. It was found that mosquitofish are widely distributed throughout this area, and also that numerous endemic amphibians are vulnerable and likely to be negatively impacted by this invasive fish. There is, however, only one endemic species with an IUCN Threatened status that is potentially jeopardised by the mosquitofish. Key terms: Gambusia, Anura, Cape Floristic Region, invasive species, predation, tadpole, conservation. v OPSOMMING Die wêreld-wye verspreiding van indringer visspesies is een van die groot oorsake in die afname van amfibieë. Ongelukkig is hierdie probleem dubbelvoudig in die Wes-Kaap, aangesien daar in die streek ‘n groter aantal indringer visspesies voorkom, en ook omdat dit ‘n sensitiewe bewaringsarea is, wat krities bedreigde en endemiese amfibieë ondersteun. Huidige internasionale navorsing bewys dat een van hierdie indringer visspesies wat in die Wes-Kaap voorkom, die muskietvis (Gambusia affinis), ‘n bedreiging vir amfibieë-spesies is, maar ongelukkig is daar tot dusvêr geen Suid-Afrikaanse studies wat die impak van muskietvisse op amfibieë ondersoek nie. Die doel van hierdie studie was dus om die invloed van die muskietvis op plaaslike amfibieë te bepaal. Deur middel van mesokosm studies, is daar ondersoek tot watter mate muskietvisse beserings en vrektes van paddavissies meebring. Die proewe het bewys dat die muskietvis paddavissies binne ‘n mikro-habitat kan uitwis. Die mate van die impak van die muskietvis op paddavissies het verskil tussen amfibieë-spesies, wat ‘n aanduiding is dat sekere spesies meer kwesbaar as ander is. Dié verskynsel is bevestig deur predasieproewe, waar dit verder openbaar is dat plaaslike nie-‘bufonid’ spesies heel waarskynlik meer kwesbaar is as ‘bufonid’ spesies. Indirekte predasie effekte is ook tydens mesokosm proewe ondersoek. Dit was duidelik sigbaar dat paddavissies wat aanvanklik predasie oorleef het, hewig beïnvloed was deur die vertraging van ontwikkeling en groei, beserings, asook die verandering van gedrag as gevolg van spanning. Daar is ook verder bevind dat die aanvalsgedrag op paddavissies toeneem soos die muskietvisgroep groter raak, met ander woorde dat die visse mekaar beïnvloed om meer intense aanvalle op hul prooi te loots. Ten slotte word daar in hierdie studie verwys na die verspreiding van die muskietvis in die wyer areas rondom Kaapstad, wat bepaal is deur middel van ‘n literatuurstudie asook ‘n praktiese opname. Hierdie ingligting is gebruik om te bepaal waar muskietvisse saam met bedreigde amfibieë-spesies voorkom. Bevindinge bewys dat die muskietvis reeds baie wyd verspreid voorkom, en dat verskeie endemiese spesies kwesbaar is. Daar is egter slegs een IUCN Bedreigde spesie wat moontlik negatief deur die muskietvis beïnvloed kan word. Sleutel terme: Gambusia, Anura, Wes-Kaap, indringerspesie, predasie,