Is Gear-Based Management of Herbivorous Fish a Viable Tool to Prevent Or Reverse Phase Shifts in Coral Reefs?

Master´s Thesis, 60 credits Ecosystems, Governance and Globalisation Master´s programme 2009/11, 120 credits Is gear-based management of herbivorous fish a viable tool to prevent or reverse phase shifts in coral reefs? Linking resilience theory to practice Quentin Dilasser 1 Is gear-based management of herbivorous fish a viable tool to prevent or reverse phase shifts in coral reefs? Linking resilience theory to practice Quentin Dilasser 2 Is gear-based management of herbivorous fish a viable tool to prevent or reverse phase shifts in coral reefs? Linking resilience theory to practice Master thesis (60 hp) Stockholm Resilience Center, Stockholm University Supervisors: Dr. Magnus Nyström, Stockholm Resilience Center, Stockholm University Dr. Narriman Jiddawi, Inst. Marine Science, University of Dar es Saalam Phd student Matilda Thyresson, Dept of Systems Ecology, Stockholm University Stockholm Resilience Center Stockholm University Kräftriket 2B 10691 Stockholm Sweden 3 Acknowledgment This thesis is dedicated to my parents that always supported me. This master thesis gathers the scientific results of this year-based project but does not capture the full picture of this journey and especially its wonderful human experience. Therefore, I would like to express my grateful to the people with whom I had the chance to work and live with. First of all, I would like to sincerely thank my two supervisors Dr. Magnus Nyström and Matilda Thyresson for giving me the opportunity to work on a project I always dreamed about, that involve oceans and humans. Thank you also for giving me the possibility to work in a creative atmosphere, for sharing your knowledge and time and to believe in me enough to carry out this study. Also thanks to Mickael Tedengren, associate professor at the department of Systems Ecology for his help for the administrative work. I would also like to thank my local supervisor, Dr. Narriman Jiddawi, for all the advises, contacts and sharing of information and also the research team from the Institute of Marine Sciences in Zanzibar for letting me using their materials and buildings as my base for the study. Thank you to my translator Yussuf for being a friend and for its pertinent advices throughout the field study. Special and sincere thanks to the Dugeish family for letting me the privilege to stay with them during my fieldwork and for considering me as a member of their family. Thank you for your moral support, for your contacts, for the fun you gave me and for taking care about me during difficult times. Without you this research would not have been possible to accomplish. Thanks to the fishers communities of Malindi, Mazizini, Buyu and Nyamanzi that let me interview them but also to let me live good moments with them, thank you for your time and your willingness to share the valuable information you have. Thanks to the Swedish International Development Agency (SIDA) that supported this thesis with a scholarship (MFS). 4 Abstract. Herbivorous reef fish are a key functional group for the ecological resilience of coral reefs. As they feed on algae, a major resource competitor of coral polyps, they can prevent and reverse coral-macroalgal phase shifts. The resilience of the reefs against such phase shifts is given by the ability of herbivores to keep the system in a cropped state from filamentous algae or by their capacity to feed on macroalgae. Most of the management plans that aim to protect coral reefs have been focusing on the establishment of marine protected areas or no-take areas where fishing activities are strictly restricted or prohibited. In low-income countries, such managed areas can be difficult to accept from a fisher´s perspective and lack of money also tends to lead to limited surveillance capabilities and lowered compliance. These challenges are important to address when managing small-scale fisheries and where fish are considered as both, a marketable commodity and a subsistence good. A perhaps less contentious strategy for fishers is gear-based management, where the use of fishing gears that are detrimental to coral reef resilience are restricted and at the same time gears that do not compromise resilience are promoted. This study aims to investigate how nine different fishing gears (i.e. different lines, traps, nets and spears) used in the coral reef fisheries of Zanzibar (Tanzania) capture herbivorous reef fish that can prevent (preventers) or reverse (reversers) coral-macroalgal phase shifts. Two interesting findings emerged from the study. First, different fishing gears had different impacts on these two functional groups where lines, large traps and seine nets fisheries had most impacts. Second, there were monsoonal differences in the catch of preventers and reversers. These findings are discussed in relation to i) similar studies conducted in different reef environments and ii) the feasibility of gear-based management in Zanzibar. Key words: Coral reefs, resilience, gear-based management, herbivores, preventers and reversers, phase shifts, fisheries, Zanzibar 5 Table of Contents Acknowledgement……………………………………………………………..........................3 Abstract…………………………………………………………………………………….......4 1. Introduction…………………………………………………………..…………...…...7 1.1 Problem statement……………………………………………...…………7 1.2 Objectives………………………………………………………………....8 1.3 Hypothesis………………………………………………………………...9 1.4 Research question………………………………………………………....9 2. Conceptual framework………………………………………………………….…...10 2.1 Social-ecological systems and coral reefs resilience ……………...……...10 2.2 Coral-macroalgal phase shifts……………………………...……...…........11 2.3 Herbivores: a key functional group in coral reef dynamics………...…......12 2.4 Preventers and Reversers: a functional dichotomy………...…...………....14 2.5 Gear-based management…………………......……………………...….....15 3. Method……………………………………………………………..…………..……...16 3.1 Study area…………………………………….………………...……..…..16 3.1 a) Study site…………………………………………….………........16 3.2 Coral reefs in Zanzibar……………………………………………..……...17 3.2 a) Description of the reefs…………………………………...............17 3.2 b) Multiple uses, multiple ecosystem services……………..…….......17 3.2 c) Threats to Zanzibar coral reefs …………………………..………18 3.3 Coral reef fishery in Zanzibar…..……….………………………..……......18 3.3 a) Generalities……………………………………………………......18 3.3 b) Monsoonal patterns………………………………………………..20 3.3 c) Spatio-temporal variability…………………………………….…..20 3.3 d) The coral reef fish catch composition…………………………….. 21 3.3 e) Signs of overfishing……………………………………………...... 21 3.3 f) Existing protected areas………………………………………….. .22 3.3 h) Fishing gears……………………....................................................22 3.4 Epistemological frame…………………………………………….…..……23 3.5 Field study…………………………………………….………………..…..24 3.5 a) Fishers interviewed (questionnaires).……………….....…….…….24 3.5 b) Procedure of the questionnaires..…………………………….…….25 3.5 c) Categorization into preventers and reversers…………………….. 26 3.5 d) Data preparation and statistical analysis……………….………….27 3.6 Limitations of the methodology…………….…………………………........28 6 4. Results………………………………………………………………………………..30 4.1 Average daily catches (based on annual results)…………...……………...30 4.2 Monsoonal variability………………………………………………….…..33 5. Discussion………………………………………………………………………….…36 5.1 Fishing gears versus functional groups…………………………………….36 5.1 Monsoonal variability………………………………………………………37 5.2 Is gear-based management a real option?......................................................37 6. Conclusion………………………………………………………………………..…..42 Literature cited………………………………………………………………………..……..44 Appendix 1: Fishing vessels in Zanzibar……………………………………………...58 Appendix 2: a) Total catch of fish in Zanzibar. b) Fish catch in the three regions of Zanzibar………………………………………………………………..60 Appendix 3: Coral reef fish composition of the catch and their name in Swahili……..61 Appendix 4: Fishing gears in Zanzibar………………………………………………...62 Appendix 5: The different spatio-temporal drivers affecting the coral reef fisheries in Zanzibar………………………………………………..…....67 Appendix 6: Interview outline…………………………………………………………66 Appendix 7: Species list of herbivorous reef fish used in the study and their functional group affiliations…………………………………………......71 Appendix 8: Average Bray-Cutis dissimilarities (<50%) between gears for the catch of preventers and reversers obtained by the SIMPER test…….…..74 Appendix 9: Average abundances of preventers and reversers caught by each gear and per day………………………………………………………….75 7 1. Introduction 1.1 Problem statement Coral reefs are tropical, biogenic and shallow-clear water biophysical structures. They are primarily composed of scleractinian (stony) coral species that build a calcium carbonate skeleton and occur as colonies of polyps or in solitary form (Achituv & Dubinsky 1990; Richmond 1997). Even though they compose less than 0.1% of the ocean floor (Spalding et al. 2001), these ecosystems are among the most complex and biologically diverse ecosystems (Odum & Odum 1955; Spalding et al. 2001; Green & Bellwood 2009) and are sometimes referred to as underwater tropical rain forests (Reaka-Kugla 1997). Coral reefs provide essential ecosystem services (e.g. food supplies, aesthetic, cultural, recreational, tourism, physical barrier against storm) for millions of people (Costanza et al. 1997; Moberg & Folke 1999; MA 2005). Many coral reefs are located in developing countries (Donner & Portere 2007) and are thus capital ecosystems that generate socio-economic and ecological assets (Hughes et al. 2010). However, coral reefs are

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