Louisiana State University LSU Digital Commons LSU Historical Dissertations and Theses Graduate School 1995 Modelling a Multispecies Schooling Fishery in an Upwelling Environment, Mauritania, West Africa. Sidina Ould dedah Louisiana State University and Agricultural & Mechanical College Follow this and additional works at: https://digitalcommons.lsu.edu/gradschool_disstheses Recommended Citation Ould dedah, Sidina, "Modelling a Multispecies Schooling Fishery in an Upwelling Environment, Mauritania, West Africa." (1995). LSU Historical Dissertations and Theses. 6149. https://digitalcommons.lsu.edu/gradschool_disstheses/6149 This Dissertation is brought to you for free and open access by the Graduate School at LSU Digital Commons. It has been accepted for inclusion in LSU Historical Dissertations and Theses by an authorized administrator of LSU Digital Commons. For more information, please contact [email protected]. INFORMATION TO USERS This manuscript has been reproduced from the microfilm master. UMI films the text directly from the original or copy submitted. Thus, some thesis and dissertation copies are in typewriter face, while others may be from any type of computer printer. The quality of this reproduction is dependent upon the quality of the copy submitted. Broken or indistinct print, colored or poor quality illustrations and photographs, print bleedthrough, substandard margins, and improper alignment can adversely affect reproduction. In the unlikely event that the author did not send UMI a complete manuscript and there are missing pages, these will be noted. Also, if unauthorized copyright material had to be removed, a note will indicate the deletion. Oversize materials (e.g., maps, drawings, charts) are reproduced by sectioning the original, beginning at the upper left-hand comer and continuing from left to right in equal sections with small overlaps. Each original is also photographed in one exposure and is included in reduced form at the back of the book. Photographs included in the original manuscript have been reproduced xerographically in this copy. Higher quality 6” x 9” black and white photographic prints are available for any photographs or illustrations appearing in this copy for an additional charge. Contact UMI directly to order. UMI A Bell & Howell Information Company 300 North Zeeb Road, Ann Aibor MI 48106-1346 USA 313/761-4700 800/521-0600 MODELLING A MULTISPECIES SCHOOLING FISHERY IN AN UPWELLING ENVIRONMENT, MAURITANIA, WEST AFRICA A Dissertation Submitted to the Graduate Faculty of the Louisiana State University and Agricultural and Mechanical College in partial fulfillment of the requirements for the degree of Doctor of Philosophy in The Department of Oceanography and Coastal Sciences by Sidina Ould Dedah B.S. Institut Agronomique et Veterinaire Hassan II, 1989 Master of Applied Statistics, Louisiana State University, 1995 December 1995 UMI Number: 9618339 UMI Microform 9618339 Copyright 1996, by UMI Company. Ail rights reserved. This microform edition is protected against unauthorized copying under Title 17, United States Code. UMI 300 North Zeeb Road Ann Arbor, MI 48103 ACKNOWLEDGMENTS I would like to especially acknowledge Dr. Richard F. Shaw, the chairman of my committee, for his continuous support, advice and assistance throughout my stay at Louisiana State University. I also would like to express my sincere appreciation to all my committee members: Drs. R. Condrey, J. Geaghan, G. Turner and W. Wiseman. Each of them provided me with all the help, guidance, constructive critiques and inputs that I needed. A great deal of appreciation to Dr. R. Labonte for his review of the manuscript. I would like also to thank Drs. L. Escobar, M. Inoue, R. Machiavelii, E. B. Moser and W. Keithly for their patience, many helpful discussions, and insights on the various subjects that dealt directly or indirectly with my dissertation. Many people have their share in the realization of this work. I especially want to thank my colleagues at the Centre National de Recherches Oceanographiques et des Peches in Mauritania for providing fisheries and hydrographic data and for USAID- Mauritanian scholarship support. In addition, I would like to acknowledge the LSU’s Department of Oceanography and Coastal Sciences (DOCS) for graduate teaching assistantship and LSU’s Coastal Fisheries Institute (CFI) for graduate research assistantship funding. Without their support, this work would not have been completed. Also thanks to my fellow graduate students in DOCS. Many thanks go to the staff and faculty of the CFI. I am grateful to Mr. R. Allen and Ms Carol Fleeger and Pam Bloom who facilitated paper work burdens and for their "cheering" during difficult moments. Finally, last but not least, I am indebted to my parents, brothers and sisters. This work is dedicated to all my friends, especially to Hamady Diop, Mohamed Ahmedna, Dah Elva and Wane Ousmane. PREFACE The Mauritanian Exclusive Economic Zone (EEZ) is the site of complex hydrographic and meteorologic processes. Mixing between the cold Sahara Current waters and the warm Mauritania Current surface waters, as well as the wind-induced coastal upweiling process, creates a unique environment favorable for the spawning and survival of many temperate and tropical species on the Mauritanian shelf and in adjacent coastal areas (Banc d'Arguin). As a result, a number of commercially-important neritic species and demersal species are found in this area. The objective of this study is to explore developing a general fisheries modelling framework that takes into consideration species-specific, environmental, regional, fleet behavioral, and economic factors to better represent the Mauritanian pelagic fishery. The first chapter presents a description of the general geologic, physical, chemical and biological characteristics of the Mauritanian upweiling zone as it is presently understood. It also highlights differences between this system and other major upweiling centers in the world (e.g., off Peru and California). The second chapter explores the structure and timing of the seasonal cycles of water temperature and wind in order to describe the hydrographic conditions that prevail in the Mauritanian EEZ. The main focus is to identify any recent changes in the upweiling regime and their potential impact on fish populations. In addition this chapter investigates the applicability of using iv oceanographic data from coastal stations to adequately represent offshore conditions. Chapter three gives a quantitative description of the fishery. It main focus is to identify catch composition, to characterize seasonal (hydrographic) and zonal patterns, and to explore potential differences between fishing vessel types in the yields of the small pelagic fishery. The fourth chapter investigates how these seasonal patterns influence abundance estimates of the individual species. Specifically, it looks at various methods of adequately allocating the nominal fishing effort among species and species groupings. In this regard, various methods of computing catch per unit of effort (CPUE) are compared. Chapter five presents a predictive model for the fishery and discusses the management implications of using raw unpartitioned versus proportionally allocated fishing effort in the model. It also derives a formula that can be used to compute confidence intervals around the Maximum Sustainable Yield of the species in the fishery. Finally, the summary section brings together all the pertinent results, findings and limits of the study. v TABLE OF CONTENTS ACKNOWLEDGMENTS................................................................................................ ii PREFACE.......................................................................................................................iv LIST OF TABLES......................................................................................................... vii LIST OF FIGURES........................................................................................................xi ABSTRACT.................................................................................................................... xv CHAPTER 1 OVERVIEW ON THE PHYSICAL, CHEMICAL AND BIOLOGICAL CHARACTERISTICS OF THE STUDY A REA..................................1 2 SPATIAL AND TEMPORAL TRENDS OF SEA-SURFACE TEMPERATURE AND WIND PATTERNS...................................,.2 4 3 THE SMALL PELAGIC FISHERY........................................................56 4 ESTIMATION OF CATCH PER UNIT OF EFFORT.......................102 5 SURPLUS PRODUCTION MODELLING......................................... 131 SUMMARY...................................................................................................................155 REFERENCES...........................................................................................................159 VITA 178 LIST OF TABLES 2.1. Number of observations for sea surface temperature data on the Mauritanian shelf by the 20' x 20' squares and month (1985-1993). Location of the squares is shown in Figure 2.1.......................................................................26 2.2. Monthly mean wind speed (V;m/s), its standard deviation (STD) and alongshore component (UY;m/s) and Coastal Upweiling Index (CUI; m3.s'1 per 100m of coastline) at Nouadhibou ......................................................... 31 2.3. Percent frequency of observed wind direction at Nouadhibou .............31 2.4. Wind mean speed (V;m/s), its standard deviation (STD)