ISSN 1198-6727 Fisheries Centre Research Reports 2004 Volume 12 Number 7 WEST AFRICAN MARINE ECOSYSTEMS: MODELS AND FISHERIES IMPACTS Fisheries Centre, University of British Columbia, Canada West African Marine Ecosystems: models and fisheries impacts edited by Maria Lourdes D. Palomares and Daniel Pauly Fisheries Centre Research Reports 12(7) 221 pages © published 2004 by The Fisheries Centre, University of British Columbia 2259 Lower Mall Vancouver, B.C., Canada, V6T 1Z4 ISSN 1198-6727 FISHERIES CENTRE RESEARCH REPORTS 12(7) 2004 WEST AFRICAN MARINE ECOSYSTEMS: MODELS AND FISHERIES IMPACTS edited by MARIA LOURDES D. PALOMARES AND DANIEL PAULY CONTENTS Page DIRECTOR’S FOREWORD ........................................................................................................................ 1 INTRODUCTION........................................................................................................................................ 2 Ecosystem-based fisheries management: the role of the SIAP project Daniel Pauly.................................................................................................................................. 2 WEST AFRICAN ECOSYSTEMS................................................................................................................. 4 Modèle écotrophique du Banc d’Arguin (Mauritanie) dans la période 1988 à 1998 Mahfoudh Ould Taleb Ould Sidi and Diop Mika Samba............................................................. 4 Modèle écotrophique de la ZEE mauritanienne: comparaison de deux périodes (1987 et 1998) Mahfoudh Ould Taleb Ould Sidi and Sylvie Guénette ............................................................... 12 Ecopath model of the Cape Verde coastal ecosystem K.A. Stobberup, V.D.M. Ramos and M.L. Coelho ...................................................................... 39 Dynamique du réseau trophique de l’écosystème sénégambien en 1990 Birane Samb et Asberr Natoumbi Mendy.................................................................................. 57 Addendum : L’écosystème sénégambien en 1964 à 1981 (Birane Samb) .................................. 71 Long-term trends in al fishery resources of Ghana in response to fishing pressure Kwame Koranteng and Daniel Pauly ........................................................................................ 75 A trophic model of the Gambian continental shelf system in 1986 Asberr Natoumbi Mendy ............................................................................................................ 81 Addendum: The Gambian continental shelf ecosystem in 1992 and 1995 ................................ 89 Preliminary Ecopath model of the Guinea-Bissau continental shelf ecosystem (NW-Africa) Patrícia Amorim, Gregório Duarte, Miriam Guerra, Telmo Morato, and Kim A. Stobberup ....................................................................................... 95 Modèle trophique du système côtier du plateau continental Guinéen Ibrahima Diallo, Ibrahima Cissé and Amadou Bah................................................................. 113 Addendum: Modèles de la côte guinéenne, 1985 et 1998 (Sylvie Guénette and Ibrahima Diallo).................................................................................... 124 Structure and dynamics of the marine ecosystem off Sierra Leone for three time periods: 1964, 1978 and 1990 Johanna J. Heymans and Jan Michael Vakily........................................................................ 160 Biodiversity of the Namibian Exclusive Economic Zone: a brief review with emphasis on online databases Maria Lourdes D. Palomares and Daniel Pauly ..................................................................... 170 ANALYSES ............................................................................................................................................. 171 Mass balance of Atlantic oceanic systems Marcelo Vasconcellos and Reg Watson.................................................................................... 171 Trends in fish biomass off Northwest Africa, 1960-2000 Villy Christensen, Patricia Amorim, Ibrahim Diallo, Taib Diouf, Sylvie Guénette, Johanna J. Heymans, Asberr Natoumbi Mendy, Mahfoudh Ould Taleb Ould Sidi, Maria Lourdes D. Palomares, Birane Samb, Kim Stobberup, Jan Michael Vakily, Marcelo Vasconcellos, Reg Watson, and Daniel Pauly ........................................................... 215 APPENDICES ......................................................................................................................................... 221 A Research Report from the Fisheries Centre at UBC 221 pages © Fisheries Centre, University of British Columbia, 2004 Fisheries Centre Research Reports are abstracted in the FAO Aquatic Sciences and Fisheries Abstracts (ASFA) ISSN 1198-6727 West African marine ecosystems, M.L.D. Palomares and D. Pauly 1 DIRECTOR’S FOREWORD West African fisheries are under tremendous pressure, some of this due to the increasing local demand for fish, and the growth of locally based industrial and artisanal fisheries. However, the main reason for the much depleted state of West African fisheries resources lies in the presence, along the West African coast, of a huge array of Distant Water fleets from Western and Eastern Europe, and from East Asia. And every few years, new ‘access agreements’ are signed that increase this external pressure, not to mention numerous cases of illegal fishing by a variety of countries. Evaluations of the effects of the resulting fishing effort on West African resources have been rare so far, and widely scattered, as they were mainly dealing with isolated, local stocks. Broad-based studies, on the other hand, have been entirely lacking. This report begins to fill this gap in that it covers much of the West African coast. However, the focus has been on one region (Northwest Africa), for which a synthesis, i.e., a documentation of long-term biomass declines is presented. This report focuses on descriptions of the methods and data used in this synthesis, i.e., in the construction of quantitative food web (‘Ecopath’) models of the ecosystems of the Northwest African subregion (Mauritania, Cape Verde, Senegal, The Gambia, Guinea-Bissau, Guinea and Sierra Leone) for contrasting periods (usually 1960 vs. 2000). Following a training course/workshop given in Dakar, Senegal, on February 9-23, 2001, the bulk of these models were constructed during a workshop held, also in Dakar, on August 10-18, 2001, and attended by participants representing the countries in question, all members of the European Union funded project known as ‘Système d’Information et d’Analyse des Pêches’ (SIAP; ‘Fisheries Information and Analysis System’, or FIAS in English). These models were subsequently refined in extensive collaboration among the editors and the authors, which culminated in a third workshop jointly organized by the Sea Around Us and SIAP projects, held in January 2002 at the Fisheries Centre, University of British Columbia, Vancouver, and attended by three members of the SIAP project, representing Mauritania1, Senegal and The Gambia. The food web models resulting from this process were complemented by models initiated by members of the Sea Around Us project, for Sierra Leone, Guinea and the Central Atlantic. This first-ever coverage of the entire Northwest African subregion with ecosystem models, mostly pairs covering two different periods in the same country, allowed the creation of regional biomass maps for 1960 and 2000, illustrating the massive decline of the abundance of larger fishes along the West African coast. This, we assume, should impact on negotiations about access by Distant Water fleets. The assistance provided in the preparation and actual realization of the workshops by the Director and staff of the Centre de Recherches Océanographiques de Dakar-Thiaroye (CRODT) is gratefully acknowledged, as is the readiness of various research institutions (CNSHB, Guinea; IEO, Spain; and IPIMAR, Portugal) to provide funding from their institutional budget for the participation of additional researchers in the workshops. Moctar Bâ, Director of the Coordination Unit of the SIAP project, is thanked for his untiring efforts to promote the goals and objectives of the SIAP project in the region, thus rallying the necessary support for its successful implementation. Dr. Michael Vakily, Coordinator of the SIAP project, must also be thanked for his untiring support of the work summarized in these pages. The Pew Charitable Trusts, Philadelphia, are also thanked for their support of the Sea Around Us Project. Daniel Pauly December 2004 1 The printed version of this report failed to include a paper describing the Mauritanian ecosystem in 1987 and 1998, included in this online version. 2 Ecosystem based fisheries management : the role of the SIAP project, D. Pauly INTRODUCTION ECOSYSTEM-BASED FISHERIES MANAGEMENT: THE ROLE OF THE SIAP PROJECT2 Daniel Pauly Science Adviser, SIAP project, Fisheries Centre, University of British Columbia 2259 Lower Mall, Vancouver, BC V6T 1Z4 CANADA While pre-industrial fisheries in Africa and elsewhere usually had the capacity to extirpate some freshwater and coastal fish populations, it is only since the advent of industrial fishing, about a century ago, that the sequential depletion of coastal then offshore populations of marine fish has become the standard operating procedure. In the late 19th Century, in the North Sea, where British steam trawlers were first deployed, it took