The Sea Cucumber Holothuria (Halodeima) atra (Jager, 1833), in South Tarawa Lagoon (Republic of Kiribati): Environmental Variability, Population Biology and Fishing Pressure. Teatim Tamaroa A thesis submitted as partial fulfilment for the degree of Master of Science in Marine Biology 2010 Abstract Holothuria atra or lollyfish is the most common sea cucumber in the Pacific and Indian Oceans. The current status of Holothria atra at 13 sites of South Tarawa lagoon (Republic of Kiribati) was established by using biological surveys and fishers‟ questionnaires. A preliminary investigation was conducted in order to assess how and why environmental variability and fishing pressure have affected the spatial and temporal distribution, mean abundant and mean size of this species at the sites. The 13 sites were selected randomly, and marked with a GPS on the map of South Tarawa. Sedimentary characteristics were determined for each site, and a qualitative assessment of sites health was made. Lollyfish length, biomass and abundance and transect density were calculated for each site. The weight of organic matter content and size of sediment sample were determined. Data were analysed using Kruskal- Walis (KW) and Repeated measures (RM) ANOVA tests. This thesis shows that the environmental variability could not offer reasons as to why the biological data of lollyfish varied from one site to another. However, other factors that were tested may explain the variation in biological data. Fishing pressure is one of those parameters that can regulate the lollyfish distribution and density and responses from local fishers indicate that fishing pressure is high and that the lollyfish resource is under considerable harvest pressure. Dissolved oxygen concentration in the water column and in the sediment may be also involved in the variation in lollyfish distribution and density but this was not tested. The findings of this research lead to a number of recommendations for the sustainable harvest of lollyfish in Tarawa lagoon. These include consideration of gear restrictions, lollyfish size and number limits, and the establishment of marine protected areas under co-management arrangements. i Acknowledgements I‟d like to thank: The New Zealand Government through New Zealand International Development Aid (NZAID) for financing this study. Without such assistance, it would have been impossible for me to complete this research. My only great and admirable supervisor, Jonathan Gardner, for supporting my studies by providing sharp decisive advice and constructive feedback. To you, Jonathan, you are the greatest leader and supervisor! My English tutor, Brie Jessen, who had been requested and appointed by my sponsor NZAID to help me throughout my studies. Without your commitment and time into my writing, this thesis would not come at the end. You are a great English teacher. To Sheree Christian, thank you for proof reading my first draft for chapter one, and suggesting ways for it‟s improvement. Without your wisdom and expertise, chapter one could not be a better chapter. Staff at the Student Learning Support Services; Ema Sanga, Ruth-Davidson- Toumu‟a, Liz O‟Connor, Debora Laurs, Mary Robert and Dennis Dawson, thank you all for your help in correcting my thesis, and encouraging me to write academically. Liz Richardson for allowing me to use the whānau room for 24 hours. I would like to thank all my friends in the Āwhina whanau for their help, especially Alex Richardson, Ali Richardson, Natalie Stewart, and Emma Leigh for their spontaneous responses to my questions. To you all, you have taught me to help others. Vinaka vakalevu. Kabunare‟s family for providing me with a shelter to rest. Thank you, Kabunare and your family for giving me more time to study. I would also like to thank Tebou, for sharing his room with me as a secondary place to sleep and relaxed. Thank you, Tebou, for your kindness. Lastly, I would like to thank my brother-in-law Mautaake Tamoa and cousin Raratu Tebuka in Tarawa, who had tirelessly worked with me like remoras during data collecting. Big thank to you two, for your great assistance for without it, this thesis would not come this far. ii CONTENTS Abstract...................................................................................... i Acknowledgements.................................................................... ii List of Tables.............................................................................. vi List of Figures............................................................................ ix Chapter One – Introduction 1.1 - Lollyfish biology.................................................................................... 1 1.2 - Exploitation............................................................................................ 2 1.3 - Socio – economic and ecological significance ..................................... 5 1.4 - Research rationale .................................................................................. 6 Chapter Two – Material and methods 2.1- Study site ............................................................................................... 8 2.2 -Description of study locations................................................................ 10 2.3- Biological survey.................................................................................... 10 2.4-Environmental survey.............................................................................. 11 Chapter Three – Results 3.1 – Biological and Environmental survey................................................. 16 3.1.1 – Density................................................................................. 16 3.1.1.1 – Non-parametric analysis............................ 16 3.1.1.2 – Parametric analysis..................................... 18 3.1.2 - Individual length.................................................................. 23 3.1.2.1 - Non-parametric analysis............................ 23 3.1.2.2 - Parametric analysis...................................... 25 3.1.2.3 - Length-frequency distribution................... 30 3.1.3 - Total lollyfish weight............................................................ 36 3.1.3.1 – Non-parametric analysis………………... 36 3.1.3.2 – Parametric analysis …………………….. 39 iii 3.1.4 - Transect biomass.................................................................... 43 3.1.4.1 – Non-parametric........................................... 43 3.1.4.2 – Parametric analysis..................................... 46 3.2 – Bottom sediment……............................................................................ 50 3.2.1 – Organic matter.......................................................................... 51 3.2.2 – Sediment grain size................................................................... 52 3.3 – Linking biological and environmental variables..................................... 58 3.4 – Fishermen questionnaires........................................................................ 61 Chapter Four – General discussion and conclusions 4.1 Introduction............................................................................................... 71 4.2 Biological and Environmental Survey..................................................... 73 4.2.1 Density distribution...................................................................... 73 4.2.1.1 Non-parametric and parametric analyses...................... 73 4.2.1.1.1 Actual mean density........................................ 73 4.2.1.1.1.1 Low – mean density.......................... 73 4.2.1.1.1.2 Medium-mean density..................... 74 4.2.1.1.1.3 High-medium density...................... 76 4.2.1.1.1.4 Variability in density....................... 81 4.2.1.2 Parametric Analyses: Repeated Measures ANOVA … 81 4.2.2 Length distribution....................................................................... 82 4.2.2.1 Non – parametric and parametric analyses................... 83 4.2.2.1.1 Actual mean-ranked length.............................. 83 4.2.2.1.1.1 Small-mean ranked length............... 83 4.2.2.1.1.2 Medium-mean ranked length........... 84 4.2.2.1.1.3 Large-mean ranked length................. 84 4.2.2.1.1.4 Variability in length......................... 84 4.2.2.2 Parametric analyses: Repeated Measures ANOVA…. 87 4.2.2.3 Size-frequency distribution.......................................... 87 4.2.3 Weight distribution...................................................................... 87 4.2.3.1 Non – parametric analyses.............................................. 88 iv 4.2.3.1.1 Actual mean-weight........................................ 88 4.2.3.1.1.1 The lighter or (low) – weight........ 88 4.2.3.1.1.2 The medium-weight…………...... 89 4.2.3.1.1.3 Heavy-weight ................................. 90 4.2.3.1.1.4 Variability in weight..................... 91 4.2.3.2 Parametric Analyses……………………………….. 93 4.2.4 Biomass distribution.................................................................. 95 4.2.4.1Non – parametric analyses............................................ 95 4.2.4.1.1 Actual mean biomass.................................... 95 4.2.4.1.1.1 Low-mean biomass....................... 95 4.2.4.1.1.2 Medium-mean biomass................. 96 4.2.4.1.1.3 High-mean biomass....................... 97 4.2.4.1.1.4 Variability in biomass................... 99 4.2.4.2 Parametric Analyses ………………………………. 99 4.3. Environmental survey………………………………………………….. 100 4.3.1 Organic matter contents……………......................................