Cage aquaculture and environment in Lake Malawi: an assessment of water quality, food web shifts, and development of a decision support tool for sustainable aquaculture A DISSERTATION SUBMITTED TO THE FACULTY OF THE GRADUATE SCHOOL OF THE UNIVERSITY OF MINNESOTA By Messias Alfredo Macuiane IN PARTIAL FULFILMENT OF THE REQUIREMENTS FOR THE DEGREE OF DOCTOR OF PHILOSOPHY Advisors: Professors: Robert E Hecky and Stephanie Guildford April, 2014 © Messias Alfredo Macuiane 2014 i Acknowledgements Special thanks go to Drs: Robert E. Hecky and Stephanie J. Guildford for working with me over the past four and half years as my advisors and sponsors at University of Minnesota Duluth (UMD), without them my journey wouldn’t have been possible. I enjoyed having their support, guidance in all stages of my research project. I thank Drs. Raymond Newman, Jay Austin, and Thomas Hrabik for serving as academic committee members. I sincerely thank the WorldFish Center for providing partial support during my first academic year. Dr. António Hoguane from Eduard Mondlane University/Mozambique played a major role in getting me started at WorldFish Center. I thank Dr. Daniel Jamu, former Regional Director for Southern Africa at WorldFish Center and now Aquaculture Specialist at Maldeco Aquaculture for his support towards my PhD. Professor Randall Hicks from Department of Biology/UMD played an important role in sourcing additions financial support during the period when my professors were retired and away from Duluth. I would like to thank the Department of Fisheries for supporting my Masters and Doctorate research in Malawi and for providing accommodation and laboratory facility at Malawi College of Fisheries. I am grateful to Maldeco Aquaculture Limited for allowing me to conduct field research in their farm. The staff members provided transportation and support during data collection at the farm. Funding was provided by the Office of International Programs-Global Spotlight/University of Minnesota and New Partnership for African Development (NEPAD). I thank Dr Emmanuel Kaunda from University of Malawi and Dr. Sloans Chimatiro from NEPAD for providing additional support for field research activities and travel to Malawi through Funding through the NEPAD Regional Fish Node-SANBio. Many thanks to Ms Kathy Oliver, Yvonne Chan, Sarah Grosshuesch, and all members of Large Lakes Observatory for providing valuable guidance. My colleagues, Geoffrey House, Thomas Pevan, Rozhan Zakaria, Jillian Votava, Hongyu Li, Jilying Li, and Lucas Gloege contributed greatly in many aspects of my career at UMD. I would like to thank Bonnie Anderson from University of Minnesota Twin Cities for guiding me in academic issues during my first two years in Duluth. ii Dedication To my wife Rosita, my daughter Claire Cátia Macuiane and son Messias Alfredo Macuiane Junior, my nephews, my mother Catarina Gilberto Macuiane, my brothers and sisters, thank you for your endless support. iii Abstract The impact of cage aquaculture on the water quality and native fish community was studied between November 2011 and September 2012 in the South East Arm of Lake Malawi. This ancient African Great Lake has the greatest number of fish species of any lake in the world, and the fishery is a major source of animal protein in Malawi. However, the decline of the capture fishery stocks has forced the Government of Malawi to promote cage aquaculture. The Maldeco Aquaculture Limited is the first cage aquaculture operation initiated in 2004 to farm endemic and native fish species in Lake Malawi at commercial scale. Unfortunately there is no legal framework for sustainable cage aquaculture development. The study found that cage aquaculture attracts wild fish populations and also changes their community structure. However, the diversity was not significantly affected by the cage farm despite the increased abundance of fish, especially smaller fish. Water temperature and dissolved oxygen were minimal between April and June, a period that cage aquaculture farms should consider as critical in their operation. Chlorophyll a had a single seasonal peak in April concurrent with the minimum in transparency. There was no significant difference in water quality parameters between the aquaculture site and sites 5 km away. Stable isotope signatures of carbon (δ13C) and nitrogen (δ15N) of the wild fish revealed shifts in small particle feeding planktivorous fish and possibly in zooplanktivorous fish, but not in benthivorous, molluscivorous, and zoobenthivorous fishes which maintained their natural diets even at the farm site. A dissolved oxygen model indicated that the average carrying capacity of the farm is 1,870,000±96, kg. A mean stocking density of 23,000 ±440kg per cage is recommended to allow adequate fish growth rates and attainment of desirable marketable size within a iv short cycle without significant impact on oxygen concentration. Un-regulated expansion of cage aquaculture activities at Maldeco Aquaculture farm or increase in the number of cage farms has the potential of increasing changes in wild fish community structure, modifying food webs, and causing conflicts with local fishermen. v Table of Contents List of Figures ................................................................................................................................. xi Chapter 1 Overview of the fisheries sector in Malawi ..................................................................... 1 1.1 Introduction ............................................................................................................................ 1 1.2 Thesis objectives and hypothesis ........................................................................................... 4 Chapter 2 Changes in fish community structure associated with cage aquaculture in Lake Malawi ......................................................................................................................................................... 6 2.1 Introduction ............................................................................................................................ 8 2.2 Materials and methods ......................................................................................................... 12 2.2.1 Lake Malawi.................................................................................................................. 12 2.2.2 Study area ......................................................................................................................... 13 2.2.3 Sample collection .......................................................................................................... 15 2.2.4 Data analysis ................................................................................................................ 17 2.3 Results .................................................................................................................................. 19 2.3.1 Changes in fish community structure ............................................................................ 27 2.3.2 Fish abundance, biomass, and diversity indices ........................................................... 34 2.3.3 Health status of fishing sites ............................................................................................. 36 2.3.4 Diversity indices ............................................................................................................ 39 2.5 Discussion ............................................................................................................................ 40 2.4.1 Implications to fisheries and aquaculture policy .......................................................... 44 2.5 Conclusion ........................................................................................................................... 46 2.7 Recommendations ................................................................................................................ 48 Chapter 3 Temporal and spatial changes in water quality parameters in Lake Malawi/Niassa, Africa: implications for cage aquaculture management................................................................. 51 3.1 Introduction .......................................................................................................................... 53 3.2 Materials and methods ......................................................................................................... 57 3.2.1 Data collection .............................................................................................................. 57 3.2.2 Statistical methods ........................................................................................................ 60 3.3 Results .................................................................................................................................. 62 3.4 Discussion ............................................................................................................................ 68 3.5 Conclusions .......................................................................................................................... 79 vi Chapter 4 Application of δ13C and δ15N isotopes to trace the use of cage aquaculture wastes by wild fish populations in Lake Malawi, Africa ............................................................................... 81 4.1 Introduction .......................................................................................................................... 83 4.2