Bennett 2007

CORE Metadata, citation and similar papers at core.ac.uk Provided by South East Academic Libraries System (SEALS) OPTIMISATION OF A SAMPLING PROTOCOL FOR LONG-TERM MONITORING OF TEMPERATE REEF FISHES A thesis submitted in fulfilment of the requirements for the degree of MASTER OF SCIENCE of RHODES UNIVERSITY by RHETT HAMILTON BENNETT June 2007 ABSTRACT Marine Protected Areas (MPAs), the Ecosystem Approach to Fisheries management (EAF) and Integrated Coastal Management (ICM) have been identified as possible alternatives to traditional linefish management measures, which have largely failed. Monitoring and assessment of fish communities on a long-term basis is necessary, and will provide a means to evaluate the effectiveness of such management measures. Therefore, standardised protocols and optimal sampling methods for long-term monitoring (LTM) and assessment of coastal fish communities are essential. This study aimed to identify suitable methods and develop a protocol for assessment of inshore reef fish communities. A suitable location for evaluation of proposed methods was identified in the warm temperate biogeographical region of South Africa, encompassing the well-established Tsitsikamma Coastal National Park MPA and an adjacent exploited area. Chrysoblephus laticeps (roman) was identified as an indicator species for the study, as it has been well-studied and is well represented in the area. Underwater visual census (UVC) and controlled fishing were identified as suitable methods. UVC transects were found to be superior to point counts, in terms of sampling efficiency, variability, bias and required sample size. An effort of two angler hours per fishing station was shown to provide low catch variability, while at the same time a representative catch and low overall cost and required time. The methods were incorporated in a proposed sampling protocol, and evaluated. The methods were able to detect known differences between protected and exploited communities. It is i recommended that LTM within protected areas, for detection of natural change, be focused on community-level indicators, while LTM in exploited areas, aimed at detection of anthropogenic change, be focused on species-level indicators. The proposed protocol with standardised methods will allow for comparisons across a network of LTM sites and provide the opportunity for a broad-scale assessment of the effects of environmental variables on reef fish stocks. The protocol developed in this study has application in other biogeographical regions in South Africa, and other parts of the world. Shift in the focus of much marine research, in South Africa and elsewhere, to LTM, highlights the relevance and timeous nature of this study. ii CONTENTS ABSTRACT i ACKNOWLEDGEMENTS iv CHAPTER 1 - GENERAL INTRODUCTION 1.1 FISH STOCKS AND FISHERIES MANAGEMENT 1 1.2 FISHERY ASSESSMENTS AND MONITORING 4 1.3 AIMS AND OBJECTIVES 7 CHAPTER 2 - REVIEW OF REEF FISH MONITORING METHODS 2.1 METHODS FOR MONITORING FISH COMMUNITIES 10 2.2 PROBLEMS WITH REEF FISH MONITORING AND ASSESSMENT 17 CHAPTER 3 - STUDY AREA 3.1 IDENTIFYING A SUITABLE STUDY AREA 21 3.2 DESCRIPTION OF STUDY AREA 24 3.3 SAMPLE SITE SELECTION 25 CHAPTER 4 - COMPARISON OF UNDERWATER VISUAL CENSUS AND CONTROLLED FISHING METHODS 4.1 INTRODUCTION 29 4.2 METHODS AND MATERIALS 35 4.3 RESULTS 41 4.4 DISCUSSION 48 CHAPTER 5 - DEVELOPMENT OF A SAMPLING PROTOCOL 5.1 INTRODUCTION 54 5.2 DEVELOPMENT OF A PROTOCOL 57 5.3 PROPOSED PROTOCOL 76 CHAPTER 6 - IMPLEMENTATION AND EVALUATION OF PROPOSED PROTOCOL 6.1 INTRODUCTION 78 6.2 METHODS AND MATERIALS 78 6.3 RESULTS AND DISCUSSION 86 6.4 CONCLUSIONS 109 CHAPTER 7 - GENERAL DISCUSSION 111 REFERENCES 119 APPENDICES 142 iii ACKNOWLEDGEMENTS Firstly, a project such as this could not have been possible without the many sources of financial support. The financial assistance from the Rhodes University Henderson Postgraduate Scholarship towards this research is hereby acknowledged. Opinions expressed and conclusions arrived at, are those of the author and are not necessarily to be attributed to Rhodes University or the donor. Thanks must also be extended to the office of the Dean of Research, for securing the Henderson Postgraduate Scholarship, and for administrative assistance throughout the project. I would like to thank Tony Lubner and the ORCA Foundation, in Plettenberg Bay, for funding the project, and for financial and logistical assistance during the project. Thanks also to the South African Environmental Observation Network (SAEON) in Grahamstown, for partial funding of the project. To my supervisors, Prof. Warwick Sauer and Dr. Paul Cowley, thank you for the time that was devoted to my project, particularly towards the end where many hours of reading were required. On the same note, many thanks to Dr. Albrecht Götz, who acted like a supervisor, helping with data collection and analysis, structuring of the thesis, and assistance with the numerous computer programs used in the study. I would like to thank John Fairweather for the many hours spent on the beach fixing the research boat and Mr. Terry Longman for the technical assistance in the department. For technical assistance within the Tsitsikamma National Park and securing the permit to undertake research, I would like to thank Nick Hanekom, Rob Milne and Andre Riley. I would like to thank Prof. Colin Buxton, Dr. Burghard Flemming, Dr. Nick Hanekom, Kyle Smith and Kelly King for the data they each provided. I would like to thank Dr. Albrecht Götz and Prof. Tony Booth for much needed help with data analysis, and Dr. Götz and Tanith Grant for assistance with ArcView. iv I would like to thank all the people who helped me in the field, particularly Michael Markovina, Tanith Grant and Konrad Czypionka, as well as Casper J. Kruger (and for the many braais in Nature’s). I would also like to thank the staff at Ocean Blue Adventures for all the help, Charlie, Meyer, Tracy and Velishia, and particularly for all the help on the beach, Madala, Enoch and Zola. Furthermore, thanks to the ladies from Tsitsikamma Divers, for technical assistance and the many dives. I think a special word of thanks is due to Ryan Palmer, who selflessly gave up many days in the field for my project, and who was with me on every sampling day at sea throughout the project. Thanks Farmy, for the almost 200 dives and almost 300 hours of fishing, even though it meant that your work suffered. Then finally, to Mom, Dad and Kelly, for financial and moral support from first year right through my MSc, and to Granny Sue and Tan for being my only family in the country for much of the project, thank you all so very much. v Chapter 1 – General Introduction Chapter 1 General Introduction 1.1 Fish stocks and fisheries management Increases in human population size, dependency on marine resources and technological advancements in fishing gear have resulted in steady increases in fishing pressure over the last century. Consequently, an estimated 52% of world fish stocks are fully exploited and 25% overexploited or depleted (FAO 2006). As world population and the demand for marine resources increase, the problems of declining fish stocks are only going to worsen (Caddy and Griffiths 1995). In South Africa, increases in fishing effort and inefficient regulations have resulted in a steady decline in fish stocks (Sauer et al . 2003) and the collapse of most linefish stocks (many of which are reef-associated), with the commercial extinction of Polysteganus undulosus (seventyfour). Analysis of catch-per-unit-effort (CPUE) data from the linefishery showed that catches are less than 10% of those reported at the beginning of the twentieth century (Griffiths 2000), and in 2000, the linefishery was declared to be in a state of crisis (Sauer et al . 2003). Fishing can affect biomass (Buxton and Smale 1989), stock size structure (Roberts and Polunin 1991, Buxton 1993a), growth rate (Buxton 1987, Russ 1991), genetic diversity and population dynamics, at the species level, and community structure, species composition and biotic diversity at the ecosystem level (Buxton and Smale 1989, Burger 1990). Buxton (1993c) suggests harvesting of such species is analogous to harvesting capital (standing stock), as opposed to harvesting interest (surplus production) as in many of the pelagic fisheries. The effect is greatest on reef species, because of late attainment of sexual maturity, lower natural mortality and greater longevity (Buxton 1993a). As a consequence, they are affected by lower levels of fishing effort, are less resilient to such impact and recovery is slower than in species with more r-selected life histories (Russ 1991). Removal of larger, more predatory species is likely to affect biological interactions, such as predator-prey and competition interactions and may allow entry of smaller, less valuable species 1 Chapter 1 – General Introduction (Hoggarth et al . 2006), referred to as “fishing down the food chain” (Pauly et al . 1998). Although the effects of fishing on fish stocks have been well documented (e.g. Russ 1991, Smith et al . 1991, Buxton 1993a, 1993c, Caddy and Griffiths 1995, Levin and Grimes 2002), monitoring of population dynamics is essential to provide an understanding of the magnitude and implications of these effects (Buxton 1993b). Conventional management strategies, such as closed seasons, daily bag and minimum size limits, are “not practical to enforce” (Attwood and Bennett 1994) and, as a result, have failed to sustain many reef-associated fishes (Kerwath 2005). This failure of traditional management measures has brought about the need for the use of complementary management measures in conjunction with traditional bag and size limits, and the need to manage marine resources from an ecosystem perspective (Cochrane et al . 2004). Having realised that there may be few viable alternatives fisheries managers in numerous countries have turned to marine protected areas and Ecosystem Based Management (EBM) for management and protection of reef fish stocks (Roberts and Polunin 1991, DeMartini 1993, Penney et al .

Load more