FISH AND FISHERIES IN THE SEAGRASS BEDS OF THE QUIRIMBA ARCHIPELAGO, NORTHERN MOZAMBIQUE FIONA RACHEL GELL Thesis submitted for the degree of DPhil University of York Tropical Marine Research Unit, Departmentof Biology August1999 0 Pescador Velho Pescador vindo do largo com o teu calgado de algas diz-me o que trazes no barco donde levantas a face a tua face marcada pelo sal de horas choradas da-me o teu peixe pescado bem Iä no fundo do mar -nesta ägua näo tem peixe- pescador da-me um sb peixe nem garoupa nem xareu sG -um peixinho de prata -nesta ägua näo tern peixe fol tudo procurar deus pro lado do Zanzibar. Gloria de Sant'anna, Mozambique ABSTRACT Despite being an important and widespread use of marine resources, tropical seagrass fisheries have been the subject of very few biological studies. The fish communities of tropical seagrass beds have also been little studied in comparison to the fish communities of coral reefs, which have been the subject of extensive research. Seagrass fisheries are of importance to coastal communities in developing countries because they are usually shallow and close to shore, and in many cases are more accessible than coral reefs, especially to the poorest fishers on foot or in small canoes. The importance of seagrass beds as a component of the interacting tropical coastal ecosystem (with coral communities and mangroves) is more widely recognised. Seagrass beds are often acknowledged as important nursery areas for fisheries or for their role in nutrient cycling and this is often incorporated to some extent in their management. However, the direct use value of seagrass beds as habitats for economically important species is largely ignored. The faunal diversity of seagrass systems is also something that has been studied to a limited extent. Whereas coral reefs are described as the "rainforests of the sea", seagrasses are often thought of as monospecific marine grasslands, productive but not particularly diverse. In this thesis a fishery based almost exclusively on seagrass beds is described, the seagrass beds are characterised in terms of plant species diversity, biomass and cover, and the seagrass fish communities which the fishery exploits is described. Experiments to determine the relative fish productivity and diversity in three of the main seagrass species are described, and experiments determine the efficiency of the trap fishing methods used by local fishers in the seagrass beds. Five of the most abundant species in the fishery, Siganus sutor, Leptoscarus vaigiensis, Lethrinus variegatus, Lethrinus lentjan and Gerres oyena are studied in more detail, aspects of their biology and life histories are described and are related to possible management strategies for the seagrass fishery. The seagrass fishery was found to be highly productive, to have a remarkably high species diversity and was the major single source of income to local people. The main species of fish in the fishery were found to have very different life histories and ecology, and this coupled with the high overall species diversity presents the prospective manager with the challenge of sustaining an important fishery whilst conserving habitat 1 integrity and species diversity in what is evidently an ecologically important area. Carefully selected long-term no-take zones, established in close collaboration with fishers and other members of the community, are proposed as the ideal form of management of this multi-species, multi-gear fishery. 6 2 TABLE OF CONTENTS Abstract Table of contents 3 Acknowledgements 5 Declaration 8 Introduction 9 Chapter 1: Characterisation of the fishing sites of the Montepuez Bay Abstract 14 Introduction 14 Study Site 20 Methods 20 Results 23 Discussion 36 Conclusion 46 References 47 Chapter 2: Fishing methods, effort and yiglds of an artisanal seagrass fishery at Quirimba Island, Mozambique Abstract 56 Introduction 56 Study Site 59 Methods 59 Results 62 Discussion 80 References 89 Chapter 3: The catch composition of the net and trap fisheries of the Quirimba seagrass beds Abstract 95 Introduction 95 Methods and Study Site 97 Results 99 Discussion 147 References 164 3 Chapter 4: Observations on the biology and life history of 5 important fishery species: Siganus sutor, Leptoscarus vaigiensis, Lethrinus lentjan, Lethrinus variegatus and Gerres oyena in the Quirimba Island seagrass fishery Abstract 170 Introduction 171 Study Site 172 Methods 173 Results 174 Discussion 196 Conclusion 209 References 212 Chapter 5: A comparison of fish caught in 3 species of seagrass: Enhalus acoroides, Thalassodendron ciliatum and Cymodocea spp. In the Montepuez Bay by experimental trap fishing Abstract 216 Introduction 216 Study Site 217 Methods 217 Results 219 Discussion 231 Conclusion 236 References 237 Chapter 6: The price of fish and the value of seagrass beds: socio- economic aspects of the seagrass fishery on Quirimba Island, Mozambique Abstract 240 Introduction 240 Study Site 242 Methods 244 Results and Discussion 245 Conclusion 282 References 283 Final Discussion 290 4 ACKNOWLEDGEMENTS This thesis is the result of two eventful and often disastrous periods of fieldwork based on Quirimba Island, Mozambique. On my first journey from Tanzania to the Quirimba Archipelago the boat sank and I lost virtually all my DPhil equipment, notes and books and all my personal belongings and the project's boat, radios and some diving gear were also lost. After swimming to shore on Mafia Island I had 2 days in Dar es Salaarn to buy some clothes and send some faxes then I set off again to the Quirimbas. Five weeks after leaving the UK I arrived at the project "base camp" on Quirimba to find that the camp consisted of two bamboo walls surrounded by dense bush so the first task was to build a camp for 20 people from scratch. All the other camp equipment including diving gear and the second project boat were held in customs until three months later. For those months we lived under a tarpaulin (this was still the rainy season), built the camp and huddled round one lamp and a small camp fire every evening while we waited for a the radio, generator, diving equipment and everything else to arrive. On my second fieldtrip I again arrived on Quirimba 5 weeks after having left the UK, this time spending three weeks stranded on the project's new boat in a small southern Tanzanian port waiting for a vital engine part to arrive and then a week's stormy journey down to the Quirimbas. I must thank my supervisor Dr Rupert Ormond for giving me the opportunity to risk life and limb in remote parts of East Africa through his collaborationwith the Darwin/Frontier-Mocambique Quirimba Archipelago Marine Research Programme. Without working with a large concern like the Frontier-Mocambique project I would never have been able to work in such an interesting and remote place and I thank the Society for Environmental Exploration for taking me on board. They have helped in innumerable ways. I'd like to thank the field staff I worked with in Mozambique, particularly project Research Co-ordinator Dr Mark Whittington who acted as my field supervisor and provided valuable advice, logistical support and the time of the project participants to assist in aspects of my work, Counterpart Research Co-ordinator Mario Carvalho (also of MICOA, the Ministry for the Co-ordination of Environmental Affairs, Mozambique) who introduced me to the wonders of seagrass biology and helped greatly with 5 translation and his local knowledge, and Assistant Research Co-ordinator Alex Corrie who was instrumental with Mario in setting up the collaboration with the fishermen that proved so valuable. I am extremely grateful to Mike Myers, Project Co-ordinator, who organised my Mozambican work permits, and also organised all the other bureaucratic aspects of the research and the complex logistics of life on Quirimba. The project would not have happened without him. Pete Gaunt, the project diving officer, gave generously of his time to help me undertake the dive surveys that fell outside the project work programme and provided boat support and back-up on numerous occasions. I would also like to thank other field staff Damon Stanwell-Smith and Mikey Heasman for their support. Thanks also to the Dar es Salaam office staff who kept us in touch with the outside world and helped with supplies, visas and who put me up in Dar, Frontier-Tanzania staff for accommodating me at their camp in Mtwara and London office staff. I am extremely grateful to all the Frontier volunteers and Mozambican project participants who assisted in the fisheries data collection. My biggest thank go to the people of Quirimba, particularly the fishermen of Quiwandala, who were so supportive of my work and so friendly and welcoming. I could not have undertaken this research without the interest and enthusiastic involvement of the fishers. They were generous with their time and their fish, they were patient with me and taught me so much about fish, fishing and their way of life. Special thanks to Mussa and Lamu the net fishermen who taught me a lot when I first started my research and became good friends over the time I was in Quirimba. Anibal Amade, our camp guard by night and trap fisherman by day helped me in many ways. He taught me Portuguese, vital bits of Kimwani, how to make a marema traps and how to fish them, and I couldn't have done the trap fishing experiments or sampled the trap fishery without his untiring and enthusiastic help and advice. Anibal was very interested and involved in my research and collected data from his catches when I was doing other work. I'd like to thank him for his kindness and friendship. Awaje Shale, employed by the project as a cook, was a great friend and taught me everything I know about cooking over temperamental fires and turning weevil-beans, a couple of coconuts and a selection of my study species into a meal.