The Biology and Fishery of Common Octopus (Octopus Vulgaris
Total Page：16
File Type：pdf, Size：1020Kb
THE BIOLOGY AND FISHERY OF COMMON OCTOPUS (OCTOPUS VULGARIS, CUVIER 1797) IN THE KENYAN SOUTH COAST GIDEON MBITHI KIVENGEA A THESIS SUBMITTED TO THE UNIVERSITY OF NAIROBI IN FULFILMENT OF THE REQUIREMENT FOR THE AWARD OF DEGREE OF DOCTOR OF PHILOSOPHY IN ZOOLOGY SCHOOL OF BIOLOGICAL SCIENCES, UNIVERSITY OF NAIROBI NOVEMBER, 2014 Declaration ii Dedication This work is dedicated to my parents, the late Mr. Wilson Kivengea Nzivo and Mrs. Mary Kivengea iii Acknowledgements Foremost, I would like to express my sincere gratitude to my supervisors Prof. M. J. Ntiba, Dr. D.O. Sigana and Dr. A. W. Muthumbi for the continuous support during my research work, for their patience, motivation, enthusiasm, and immense knowledge. Their guidance was important during research and write up of this thesis. I have been extremely lucky to have supervisors who cared so much about my work, and who responded to my questions promptly. I could not have imagined having better supervisors and mentors for my Ph.D study. I would also like to thank all the staff of University of Nairobi, School of Biological Sciences, for their support in preparation for this work. In particular, I would like to thank Mr. Francis M. Nyaga and Mr. James Samoei Kipyego, the Hydrobiology Laboratory Technicians, for their assistance by providing laboratory equipment and chemicals when I needed them. I am extremely grateful to the Director, Kenya Marine and Fisheries Research Institute (KMFRI), Dr. Johnson Kazungu, for allowing me to do my laboratory work at the Institute. The help of Mr. Boaz Okeyo Orembo and Mr. James Reuben Gonda, the KMFRI Laboratory Technicians is also highly appreciated. Let me thank, in a special way, Mr. Daniel Ocharo and Mr Kenneth Omondi, the KMFRI field officers, for their assistance during my data collection. My sincere thanks also go to the artisanal fishermen and the staff of the State Department of Fisheries at Mombasa, Shimoni and Vanga and all those who helped me in one way or another in my sampling exercises. I also thank Mr. Edwin Oloo for his assistance during data collection on marketing and industrial processing of octopus. iv I am very grateful to Dr. George Ombakho, the Director, Directorate of Research Management and Development, and the entire staff of the Ministry of Education Science and Technology for their encouragement and financial support which enabled me to undertake this study. Last, but not the least, I would like to thank my wife Mrs. Stellah Mueni Mbithi and my two Children, Charity Mutave Mbithi and Angela Nthenya Mbithi; they have been a constant source of emotional and moral support during my study period. v Table of Contents Contents Page Title…………………………………………………………………………………………. i Declaration…………………………………………………………………………………. ii Dedication………………………………………………………………………………….. iii Acknowledgements………………………………………………………………………… iv Table of Contents………………………………………………………………………….. vi List of Tables……………………………………………………………………………..... xi List of Figures………………………………………………………………………………. xii List of Plates……………………………………………………………………………….. xv Acronyms…..………………………………………………………………………………. xvi Abstract……………………………………………………………………………………... xviii CHAPTER 1: GENERAL INTRODUCTION AND LITERATURE REVIEW…………… 1 1.1 Background………………………………………………………………………… 1 1.2 Problem Statement…………………………………………………………………. 3 1.3 Overall objective of the study……………………………………………………… 3 1.3.1 Specific objectives of the study……………………………………………………. 3 1.4 Significance of the study…………………………………………………………... 4 1.5 Scope and limitations of the study…………………………………………………. 4 1.6 Literature Review………………………………………………………………….. 5 1.6.1 Marine fisheries landing trends - a global perspective……………………………. 5 1.6.2 Global landing trends of octopus………………………………………………….. 7 1.6.3 National marine fisheries landing trends………………………………………….. 8 1.6.4 Description and behaviour of common octopus………………………………….. 10 vi 1.6.5 Growth and Temporal distribution of common octopus…………………………. 12 1.6.6 Reproductive biology of common octopus……………………………………….. 15 1.6.7 Food and feeding habits of common octopus…………………………………….. 18 1.6.8 The fishery, processing and marketing of common octopus……………………… 20 1.6.9 Fisheries legal and regulatory framework in Kenya………………………………. 21 CHAPTER 2: STUDY AREA, GENERAL MATERIALS AND METHODS…………….. 23 2.1 Description of the Kenyan coastline……………………………………………….. 23 2.2 Description of the study sites………………………………………………………. 24 2.3 Characteristics of the common octopus……………………………………………. 25 2.4 Study design……………………………………………………………………….. 27 2.5 Common octopus fishing method………………………………………………….. 28 2.6 Treatment of specimens……………………………………………………………. 29 2.7 Preservation of specimens………………………………………………………… 30 CHAPTER 3: GROWTH AND TEMPORAL DISTRIBUTION OF COMMON OCTOPUS…………………………………………………………………………………... 31 3.1 Introduction………………………………………………………………………… 31 3.2 Materials and Methods……………………………………………………………. 32 3.2.1 Assessment of class size distribution of common octopus……………………….. 32 3.2.2 Assessment of relative weight growth of common octopus………………………. 32 3.2.3 Assessment of relative condition factor of common octopus……………………… 33 3.3 Results……………………………………………………………………………… 33 3.3.1 Dorsal mantle length (DML) class size frequency distribution……………………. 33 3.3.2 Monthly mean DML distribution………………………………………………….. 35 3.3.3 The BW class size frequency distribution of common octopus…………………… 37 vii 3.3.4 Monthly mean BW distribution of common octopus……………………………… 39 3.3.5 Length-weight relationship of common octopus at Shimoni………………………. 40 3.3.6 Length-weight relationship of common octopus at Vanga………………………… 42 3.3.7 Condition factor (K) of common octopus at Shimoni and Vanga…………………. 43 3.3.8 Monthly demographic structure of common octopus……………………………… 44 3.4 Discussion………………………………………………………………………….. 44 3.5 Summary and conclusions…………………………………………………………. 48 CHAPTER 4: REPRODUCTIVE BIOLOGY OF THE COMMON OCTOPUS IN KENYAN SOUTH COAST………………………………………………………………… 49 4.1 Introduction………………………………………………………………………… 49 4.2 Materials and Methods……………………………………………………………. 50 4.2.1 Assessment of sex ratio of common octopus………………………………………. 50 4.2.2 Assessment of size at first maturity in common octopus………………………….. 51 4.2.3 Assessment of maturity stages of gonads of common octopus……………………. 52 4.2.4 Assessment of the gonadosomatic index (GSI) of common octopus……………… 52 4.2.5 Assessment of relative fecundity of common octopus……………………………. 52 4.3 Results……………………………………………………………………………… 54 4.3.1 Sex ratio of common octopus……………………………………………………… 54 4.3.2 Size at sexual maturity of common octopus……………………………………….. 55 4.3.3 Maturity stages for female common octopus gonads ……………………………... 58 4.3.4 Maturity stages for male common octopus gonads……………………………….. 65 4.3.5 Gonadosomatic Index (GSI) of common octopus………………………………… 71 4.3.6 Fecundity of common octopus……………………………………………………. 73 4.4 Discussion………………………………………………………………………….. 74 viii 4.5 Summary and conclusions…………………………………………………………. 77 CHAPTER 5: FOOD AND FEEDING HABITS OF THE COMMON OCTOPUS……….. 79 5.1 Introduction………………………………………………………………………… 79 5.2 Materials and Methods…………………………………………………………….. 80 5.2.1 Collection and treatment of specimen……………………………………………... 80 5.2.2 Methods of stomach content analysis……………………………………………… 80 5.3 Results……………………………………………………………………………… 82 5.3.1 The stomach fullness indices of common octopus………………………………… 82 5.3.2 Common octopus stomach fullness analysis by length class………………………. 84 5.3.3 Common octopus frequency of occurrence (FO) analysis………………………… 87 5.3.4 Stomach contents analysis by length class………………………………………… 89 5.4 Discussion…………………………………………………………………………. 91 5.5 Summary and conclusions…………………………………………………………. 94 CHAPTER 6: THE FISHERY, PROCESSING AND MARKETING OF COMMON OCTOPUS………………………………………………………………………………….. 96 6.1 Introduction……………………………………………………………………….. 96 6.2 Materials and Methods…………………………………………………………….. 97 6.2.1 Assessment of the Catch Per Unit Effort (CPUE) of common octopus……………………………………………………………………………... 97 6.2.2 Assessment of common octopus landings…………………………………………. 97 6.2.3 Assessment of industrial and traditional value addition processes by use of a Questionnaire………………………………………………………………………. 98 6.3 Results……………………………………………………………………………… 99 6.3.1 Monthly common octopus landings……………………………………………….. 99 ix 6.3.2 Traditional processing of common octopus……………………………………….. 100 6.3.3 Industrial processing of common octopus…………………………………………. 102 6.3.4 Marketing of common octopus…………………………………………………….. 107 6.4 Discussion………………………………………………………………………….. 109 6.4.1 Common octopus catches………………………………………………………….. 109 6.4.2 Traditional processing of common octopus………………………………………. 110 6.4.3 Industrial processing of common octopus…………………………………………. 112 6.5 Summary and conclusions………………………………………………………… 115 CHAPTER 7: GENERAL DISCUSSION, CONCLUSIONS AND RECOMMENDATIONS…………………………………………………………………… 117 7.1 General discussion………………………………………………………………… 117 7.2 Conclusion………………………………………………………………………… 121 7.3 Recommendations…………………………………………………………………. 123 7.3.1 Future studies……………………………………………………………………… 123 7.3.2 Management and policy actions…………………………………………………… 123 REFERENCES……………………………………………………………………………… 124 x List of Tables Table Page 4.1 Monthly common octopus sex ratio variations at Shimoni 2010-2012…………….. 54 4.2 Monthly common octopus sex ratio variations at Vanga 2010 -2012……………… 55 4.3 The four female’s reproductive stages of common octopus ……………………….. 58 4.4 The four male reproductive stages of common octopus …………………………… 65 6.1 Common octopus logbook data sheet ……………………….……………………….