LAKE VICTORIA ENVIRONMENT MANAGEMENT PROJECT (LVEMP) SYNTHESIS REPORT ON FISHERIES RESEARCH AND MANAGEMENT TANZANIA Prepared by Prof Y.D. Mgaya National Consultant November , 2005 TABLE OF CONTENTS TABLE OF CONTENTS .................................................................................................. ii ABBREVIATIONS AND ACRONYMS...................................................................... viii ACKNOWLEDGEMENTS .............................................................................................. x EXECUTIVE SUMMARY ............................................................................................... xi CHAPTER ONE ............................................................................................................... 1 INTRODUCTION ............................................................................................................ 1 1.1 Background ........................................................................................................... 1 1.2 History ................................................................................................................... 3 1.2.1 Lake Victoria Environmental Management Project ................................ 3 1.2.2 Fisheries Research and Management and Components of LVEMP ..... 4 1.3 Objectives of LVEMP and Justification of the Present Consultancy ............ 5 CHAPTER TWO ............................................................................................................... 8 HISTORICAL TRENDS IN FISHERIES RESEARCH IN TANZANIA .................... 8 2.1 Introduction .......................................................................................................... 8 2.2 Fish and Fisheries ................................................................................................. 8 2.3 Environmental and Phytoplankton Studies ................................................... 10 2.4 Changes in Primary Production ...................................................................... 12 2.5 Zooplankton ........................................................................................................ 13 2.6 Macroinvertebrates ............................................................................................ 14 2.7 Small Water Bodies ............................................................................................ 14 2.8 Aquaculture ........................................................................................................ 15 2.9 Socio-economics ................................................................................................. 16 2.10 Conclusion .......................................................................................................... 18 CHAPTER THREE ......................................................................................................... 19 ENVIRONMENTAL QUALITY ................................................................................... 19 3.1 Introduction ........................................................................................................ 19 3.1.1 Background Information ........................................................................... 19 3.2 Justification ......................................................................................................... 20 3.3 Results .................................................................................................................. 21 3.3.1 Indicators for Environmental Quality ..................................................... 21 3.3.2 Nutrients Levels/Changes ....................................................................... 21 3.3.3 Total Annual Rainfall ................................................................................ 22 3.3.4 Water Transparency .................................................................................. 24 3.3.5 Dissolved Oxygen ...................................................................................... 25 3.3.6 Temperature................................................................................................ 27 3.3.7 Utilization of Fertilizers ............................................................................ 28 3.4 Discussion ........................................................................................................... 29 3.4.1 Nutrient Dynamics .................................................................................... 29 3.4.2 Spatial and Temporal Distribution of Rainfall ...................................... 29 3.4.3 Water Transparency .................................................................................. 30 3.4.4 Dissolved Oxygen and Thermal Stratification ....................................... 30 ii 3.5 Conclusions ......................................................................................................... 30 3.6 Recommendations .............................................................................................. 31 CHAPTER FOUR ........................................................................................................... 32 LIFE HISTORY INDICATORS ..................................................................................... 32 4.1 Introduction ........................................................................................................ 32 4.2 Lates niloticus ..................................................................................................... 32 4.2.1 Length Frequencies .................................................................................... 33 4.2.2 Reproduction .............................................................................................. 35 4.2.3 Growth ......................................................................................................... 36 4.2.4 Distribution ................................................................................................. 37 4.2.5 Spatial and Temporal Distribution .......................................................... 38 4.2.6 Food and Feeding ...................................................................................... 38 4.3 Rastrineobola argentea ...................................................................................... 39 4.3.1 Introduction ................................................................................................ 39 4.3.2 Distribution ................................................................................................. 40 4.3.3 Absolute Fecundity .................................................................................... 40 4.3.4 Length Frequencies Distributions............................................................ 41 4.4 Oreochromis niloticus ....................................................................................... 42 4.4.1 Introduction ................................................................................................ 42 4.4.2 Food ............................................................................................................. 43 4.4.3 Fecundity ..................................................................................................... 44 4.4.4 Length Frequency Distributions and Size at First Maturity ................ 44 4.5 Conclusions ......................................................................................................... 46 CHAPTER FIVE ............................................................................................................. 47 STOCK ASSESSMENT OF COMMERCIAL FISH SPECIES OF LAKE VICTORIA ........................................................................................................................................... 47 5.1 Introduction ........................................................................................................ 47 5.2 Justification ......................................................................................................... 48 5.3 Results .................................................................................................................. 48 5.3.1 Stock Abundance from Trawl Catches ................................................... 48 5.3.2 Spatial Changes of Abundance ................................................................ 52 5.3.3 Biomass Estimates by Swept Area Method ............................................ 57 5.3.4 Stock Abundance from Hydro-acoustic Survey .................................... 58 5.3.5 Abundance from Gillnet Catches ............................................................ 61 5.4 Discussion ........................................................................................................... 62 5.4.1 Trawl Catches ............................................................................................. 62 5.4.2 Hydro-acoustic Surveys ............................................................................ 63 5.4.3 Spatial and Temporal Variation in the Biomass of R. argentea ........... 65 5.4.4 Changes in the Biomass of Haplochromines ......................................... 65 5.4.5 Temporal Variations .................................................................................. 66 5.4.6 Batho-spatial Variations ............................................................................ 67 5.4.7 Changes in Trophic Interrelationships ................................................... 67 5.4.8 Gillnet Catches ...........................................................................................