© University of Cape Coast https://erl.ucc.edu.gh/jspui UNIVERSITY OF CAPE COAST ASPECTS OF THE BIOLOGY AND LENGTH-BASED ASSESSMENT OF THE CHUB MACKEREL SCOMBER COLIAS (SCOMBRIDAE) STOCK OFF THE COAST OF GHANA JEMIMAH ETORNAM KASSAH 2020 i Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui ©Jemimah Etornam Kassah University of Cape Coast ii Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui UNIVERSITY OF CAPE COAST ASPECTS OF THE BIOLOGY AND LENGTH-BASED ASSESSMENT OF THE CHUB MACKEREL SCOMBER COLIAS (SCOMBRIDAE) STOCK OFF THE COAST OF GHANA BY JEMIMAH ETORNAM KASSAH Thesis submitted to the Department of Fisheries and Aquatic Sciences of the School of Biological Sciences, College of Agriculture and Natural Sciences, University of Cape Coast, in partial fulfilment of the requirements for the award of Doctor of Philosophy degree in Fisheries Science JANUARY 2020 iii Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui DECLARATION Candidate’s Declaration I hereby declare that this thesis is the result of my own original research and that no part of it has been presented for another degree in this university or elsewhere. Candidate‟s Signature ………………………… Date ...………… Name: Jemimah Etornam Kassah Supervisors’ Declaration We hereby declare that the preparation and presentation of the thesis were supervised in accordance with the guidelines on supervision of thesis laid down by the University of Cape Coast. Principal Supervisor‟s Signature ……………………… Date ………….. Name: Professor John Blay Co-Supervisor‟s Signature ……………………………… Date ………….. Name: Dr. Najih Lazar ii Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui ABSTRACT The biology and population dynamics of the chub mackerel Scomber colias (Gmelin 1789), one of four small pelagic fish of high economic and nutritional value in Ghana waters, were studied from February 2016 to July 2017 to obtain information for management of its fishery. Total length of the fish in the artisanal landings ranged between 13.7 cm and 40.7 cm with two modal length classes. The von Bertalanffy growth parameters estimated using the ELEFAN method -1 were L∞ = 42.5 cm TL and K = 0.28 yr , and the mortality parameters were M = 0.70 yr-1, F = 0.52 yr-1 and Z = 1.22 yr-1. Monthly analysis of growth marks in the otoliths indicated deposition of an incremental (opaque) zone in August, which happens to be the peak upwelling period in Ghana waters. The species had a maturity size (Lm50) of 25.6 cm TL, maturity age (tm) of 2-3 years, and longevity (tmax) of 10 years. Asynchronous egg development and batch spawning was suggested by the presence of two distinct size groups (0.4 mm and 0.8 mm) of ova in mature ovaries. A mean ( s. e) absolute fecundity of 48,238 ± 2834 eggs and relative fecundity of 240 10 eggs g-1 was estimated for the fish. Spawning was estimated to occur between February and September with peaks in March-April and July-August. Fish were recruited into the stock throughout the year with two peak recruitment periods in April and August. Food of the chub mackerel comprised a wide range of invertebrates with fish, mainly anchovies (Engraulis encrasicolus), as the preferred item. Comparison of the current exploitation rate (Ecurr = 0.43) and optimum exploitation rate (E50 = 0.39) suggests that the chub mackerel stock may be overexploited, as generally assessed for the small pelagic fishery in the country. The status of the chub mackerel in trawl by-catch, and proximate analysis of the fish is also discussed. iii Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui KEY WORDS Ageing Exploitation Growth Mortality Nutrient value Reproduction Scomber colias iv Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui ACKNOWLEDGEMENTS I wish to sincerely thank my supervisors, Professor John Blay and Dr Najih Lazar of the Department of Fisheries and Aquatic Sciences and the Coastal Resource Center, University of Rhode Island respectively for their guidance and effective supervision. I am also indebted to the staff of the Coastal Resources Center at the University of Rhode Island, the age laboratory of the Rhode Island Department of Environmental Management (RIDEM) at Fort Wetherill, the age laboratory of the Northeast Fisheries Science Center (NEFSC) at the Woods Hole Oceanographic Institution in Massachusetts, as well as Professors Jeremy Collie and Kevin Freidland who gave sufficient technical input and practical training in fisheries oceanography and otolith ageing techniques. I would like to thank the USAID/UCC Fisheries and Coastal Management Capacity Building Support Project for the full scholarship granted to me for the duration of my studies. Thanks also go the academic as well as non-teaching staff of the Department of Fisheries and Aquatic Sciences for their support in diverse ways. Of particular mention are Mr Armstrong Apprey, Mr Prosper Dordunu and Mr Thomas Robin Davis. Colleague postgraduate students of the Department of Fisheries and Aquatic Sciences especially Michelle N. K. Clottey, Ernest Obeng Chuku, Delali Gamor, Gabriel Gator and Isaac Kofi Osei also deserve a special mention. I especially thank my husband Francis Kassah, children Setornam and Sedudzi, parents Yvonne and Ralph Avornyo, siblings, other family members and the Clotteys for their invaluable support and contribution during these trying years of study. v Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui DEDICATION To the memory of my maternal grandmother, Elizabeth Adakou Afiwa Lawson. vi Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui TABLE OF CONTENTS Content Page DECLARATION ii ABSTRACT iii KEY WORDS iv ACKNOWLEDGEMENTS v DEDICATION vi TABLE OF CONTENTS vii LIST OF TABLES x LIST OF FIGURES xi CHAPTER ONE: INTRODUCTION Background to the Study 1 Description and distribution of Scomber colias 2 The importance of fish in human society 5 Overview of Ghana‟s marine fishery 6 Challenges facing the marine fishing industry in Ghana 10 Status of small pelagics in Ghana 14 Statement of the Problem 16 Main Objectives 17 Significance of Study 18 Delimitations of the Study 19 Limitations of the Study 19 Organisation of Study 20 Chapter Summary 21 vii Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui CHAPTER TWO: LITERATURE REVIEW Size and Length-Weight Relationships 22 Condition Factor and Visceral Fat Index 23 Reproduction 24 Ageing 27 Growth, Mortality and Exploitation 31 Food and Feeding Habits 33 Proximate Nutrient Composition 36 CHAPTER THREE: MATERIALS AND METHODS Sampling Sites 38 Fish Sampling 40 Data Collection 41 Analysis of Scomber colias Data 51 CHAPTER FOUR: RESULTS Length-Frequency Distributions of S. colias 56 Length-Weight Relationships 58 Monthly Fluctuations in Condition Factor 60 Monthly Fluctuations in Visceral Fat Index 61 Reproductive Biology 62 Food and Feeding Habits 72 Ageing of Fish from Otoliths 77 Growth 83 Mortality Parameters 85 Exploitation Rate 88 Scomber colias Specimens in “Saiko” Samples 89 viii Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui Nutrient Content of Fish Muscle Tissue 91 CHAPTER FIVE: DISCUSSION Size Structure and Length-Weight Relationship 93 Reproductive Biology 95 Food and Feeding Habits 99 Otolith Macrostructure and Age Structure of the Population 101 Growth Characteristics 103 Mortality Parameters and Exploitation Rate 105 Nutrient Content of Fish Muscle 106 Status of Scomber colias in the “Saiko” Fishery 107 CHAPTER SIX: SUMMARY, CONCLUSIONS AND RECOMMENDATIONS Summary of Key Findings 109 Conclusions 111 Recommendations 113 Suggestions for Further Research 114 REFERENCES 116 APPENDICES 141 ix Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui LIST OF TABLES Table Page 1 Description of fish gonads at different developmental stages; adapted from Holden and Raitt (1974) 42 2 Monthly sex ratios of Scomber colias in the coastal waters of Ghana (NS-Not Significant, S- Significant at the 5% level of significance) 63 3 Prey items encountered in Scomber colias stomachs during the study period 72 4 Mean Length-at-Age Key for Scomber colias from the coastal waters of Ghana; number of fish in the sample in parenthesis 82 x Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui LIST OF FIGURES Figure Page 1 Map showing the distribution of resident populations of Scomber colias in the world. Image credit: (Collette et al., 2011). 3 2 Map of Southern Ghana, the study area, showing the locations of the sampling sites for the study. Inset is a map of Ghana in the top left corner. 38 3 Atlantic chub mackerel (Scomber colias) on a measuring board. 41 4 Ovum diameter measurement using a graticule under the microscope. 44 5 Excised stomach of a Scomber colias specimen. 44 6 Dissected head of Scomber colias showing the otoliths (arrowed) in the sacculus. 45 7 Morphological features and axes of measurement of S. colias otolith as seen under a microscope with reflected light. 46 8 Length-frequency distribution of Scomber colias in the coastal waters of Ghana (N = sample size). 57 9 Relationship between total length (TL) and body weight (BW) of (a) all fish, (b) males and (c) female Scomber colias in the coastal waters of Ghana (N = sample size). 59 10 Monthly mean condition factor of Scomber colias in the coastal waters of Ghana. Vertical bars indicate ± 1 s. e. 60 11 Monthly mean visceral fat index in Scomber colias in the coastal waters of Ghana. Vertical bars represent ± 1 s. e. 61 xi Digitized by Sam Jonah Library © University of Cape Coast https://erl.ucc.edu.gh/jspui 12 Cumulative frequency ogives for estimation of length at 50% maturity of (a) male, and (b) female Scomber colias from the coastal waters of Ghana.