Fish Diversity, Community Structure, Feeding Ecology, and Fisheries of Lower Omo River and the Ethiopian Part of Lake Turkana, East Africa Mulugeta Wakjira Addis Ababa University June 2016 Cover photos: Lower Omo River at Omorate town about 50 km upstream of the delta (upper photo); Lake Turkana from Ethiopian side (lower photo). © Mulugeta Wakjira and Abebe Getahun Fish diversity, Community structure, Feeding ecology, and Fisheries of lower Omo River and the Ethiopian part of Lake Turkana, East Africa Mulugeta Wakjira A Thesis Submitted to the Department of Zoological Sciences, Addis Ababa University, Presented in Partial Fulfillment of the Requirements for the Degree of Doctor of Philosophy in Biology (Fisheries and Aquatic Sciences) June 2016 ADDIS ABABA UNIVERSITY SCHOOL OF GRADUATE PROGRAM This is to certify that the thesis prepared by Mulugeta Wakjira entitled, "Fish Diversity, Community Structure, Feeding Ecology, and Fisheries of lower Omo River and the Ethiopian part of Lake Turkana, East Africa", and submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Biology (Fisheries and Aquatic Science) complies with the regulations of the university and meets the accepted standards with respect to originality and quality. Signed by the Examining Committee Examiner (external): Dr. Leo Nagelkerke Signature ____________ Date_________ Examiner (internal): Dr. Elias Dadebo Signature ____________ Date_________ Advisor: Dr. Abebe Getahun Signature ____________ Date__________ ____________________________________________________________ Chair of Department or Graduate Program Coordinator Abstract Ethiopia has a freshwater system in nine major drainage basins which fall into four ichthyofaunal provinces and one subprovince. Omo-Turkana Basin, spanning considerable geographic area in southwestern Ethiopia and northern Kenya, essentially consists of Omo River (also known as Omo-Gibe) and Lake Turkana. The entire of Omo River and about 1.3% of the lake (ca. 98 km2) lie within Ethiopia. The Ethiopian part of the basin generally lacks comprehensive study and proper scientific documentation on its ichthyofaunal diversity, ecology and fisheries. This study was thus undertaken to address these gaps. Data were obtained using various methods over a period of two years, and analyzed using various computations, univariate tests and multivariate methods. Thirty-one fish species were identified from lower Omo River and the Ethiopian part of Lake Turkana, with some new records, from the present collections. Omo River system was found to be more species rich than Lake Turkana but poorer in abundance. The basin’s extent of ichthyofaunal diversity within the limit of Ethiopia was specifically addressed, for which an artificial identification key was prepared. Annotated checklist for the native species was provided for the entire basin. Composition of the most important species (total index of relative importance, IRI > 94%) was essentially similar for the river and the lake, but differed in the relative importance of each species. Cluster analysis and principal component analysis (PCA) produced distinct habitat-associated species patterns across the riverine and lacustrine environments. The Ethiopian part of Lake Turkana community consisted of 18 fish species, of which two-thirds were species of highest relative importance. The lower Omo River community consisted of 13 species of largely lower IRI. Ionic concentration measured as total dissolved solids (TDS) was found to be the key environmental factor determining fish community structure in lower Omo-Turkana sub-basin. Feeding habits of eight selected fish species from the Ethiopian part of Lake Turkana have been identified and described. Although 11 major prey groups were identified for all species, only 7 prey categories viz. aquatic insects, phytoplankton, macrophytes, fish, zooplankton, detritus and prawn were the most important contributors to the fishes’ dietary variations. Fish, aquatic insects, phytoplankton and zooplankton constituted the most diversified prey categories. The eight species ranged in the generalist-specialist feeding strategy spectrum with Synodontis schall (Bloch & Schneider, 1801) being the most generalist feeder, while Oreochromis niloticus (Linnaeus, 1758) was the most specialist feeder. Each fish species consisted of subpopulations with various dietary niche width contributions to the species’ overall feeding strategy. Ontogenetic and seasonal dietary variations were observed for all the fish species examined except for S. uranoscopus whose diet virtually remained constant across fish size and seasons. The eight examined fish species formed two trophic guilds, with the mainly piscivorous group consisting of Schilbe uranoscopus Rüppell, 1832, Bagrus bajad (Forsskål, 1775) and Lates niloticus (Linnaeus, 1758), and the mainly planktivorous group consisting of i S. schall, Distichodus nefasch (Bonnaterre, 1788), Alestes baremoze (Joannis, 1835), Citharinus citharus (Geoffroy St. Hilaire, 1809) and O. niloticus. The number of guilds and dietary items that defined guild structures did not vary on seasonal and non- seasonal situations; however, a change in guild organization was observed. The computed Horn’s dietary niche overlap indices corroborated categorization of the examined fish species according to their prime dietary resource utilization. The river and the lake supported small-scale gill net fisheries that provided livelihood, income and employment to three major fisher-categories. Fisheries value chain was developed and major issues arising out of the chain components were addressed, fishers’ perceptions about the resource condition and management status were identified and discussed. In order to sustain fisheries socioeconomic contributions to livelihoods of the local people, the government in particular the regional state should take a prime responsibility to address the major socioeconomic issues arising out of the fisheries value chain analysis and issues related to resource management. Particularly, conflict of the Ethiopian fishers with the rival Turkana tribe fishers of Kenya should be properly addressed as it could jeopardize any attempt of resource management effort. Keywords: Annotated checklist, community structure, diversity, Ethiopia, feeding habits, fish, Lake Turkana, Omo River, small-scale fisheries, socioeconomics, total dissolved solids, trophic guild. ii Dedication I dedicate this dissertation to my parents Wakjira Kabeta (dad) and Jalane Gilo (mom) who are the main reasons for who I am today. I also dedicate it to my beloved wife Yetinayet Husien who bore full responsibility of taking care of our son Jonathan Mulugeta and our daughter Hawi Mulugeta while I was away for the study. iii Acknowledgements I am very much grateful to my advisor, Dr. Abebe Getahun, for his boundless support from the inception all the way through the entire process of the research work. Besides his intellectual input, this study would have not been realized had it not been for his generous arrangement of additional funding. I kindly thank the Ethiopian Ministry of Water and Energy and the Dasenech Wereda (District) Administration, southern Ethiopia, for granting me permission to conduct fish sampling and data collection in the study area. In particular, I would like to appreciate Mr. Shumare and Mr. Lotuk, the former and current administrators of the Wereda, respectively, for their positive minds towards the values of scientific studies, and thus for being very considerate. I am also very thankful to the Dasenech Wereda Police Bureau and officers for providing me all the supports I needed. I duly acknowledge Alemayehu Bayissa (vehicle driver) and Yedilfire Hailu (fisher and boat operator) for their kind supports and assistance during the entire fieldworks. I kindly thank Mr. Demeke Dano, Mr. Wendu Dano and Mr. Taye Bekele (RIP), who were all members of the fishing community in the Ethiopian part of Lake Turkana, for their assistance in sampling and especially as local guides thereby ensuring my safety while on field work. I was deeply saddened to come to learn towards the end of my 2-year fieldwork about the death of Mr. Taye Bekele, a very young fisherman and my best local guide and fishing assistant, who reportedly was killed by the Kenyan rival fishers while fishing in the Ethiopian part of Lake Turkana. I have no words to express my appreciation and thanks to Mr. Woldemichael Getaneh, a licensed Ethiopian fish trader on Lake Turkana, for kindly allowing me station at his business camp located at Bubua landing site during fish sampling. I also thank the fish traders: Mr. Sisay Tefera, Mr. Afework Game, Mr. Wondwossen Leselmay, Mr. Antehun Gizaw iv and Mr. Wadu Simon, all residents in Omorate town of Dasenech Wereda for their hospitality and kindness. I thank School of Graduate Studies, Addis Ababa University, Ethiopia for financial support. I also thank Prof. E. Zhang from Chinese Academy of Sciences for covering the field costs of my last trip. I am grateful to Mr. Dereje Denu, Lecturer at Jimma University, for his utmost assistance in developing map of the study sites. I thank Jimma University, my employer, for granting me a study leave to undertake the PhD study. I am also very much grateful to the Royal Museum for Central Africa, Tervuren (Belgium) for the training opportunity on FishBase and Fish taxonomy that greatly supported my thesis write up. My thanks go to Dr. Debebe Habtewold (MoFED) and Dr. Chekol Kidane for proof