TTanzania CCoastal MManagement PPartnership THE PRESENT STATE OF KNOWLEDGE OF MARINE SCIENCE IN TANZANIA SYNTHESIS REPORT Edited by: A.S. Ngusaru Tanzania Coastal Management Partnership Support Unit And the Science and Technical Working Group May 2000 Working Document: 5047 TCMP A joint initiative between the National Environment Management Council, the University of Rhode Island/Coastal Resources Center and the United States Agency for International Development ------------------------------ Tanzania Coastal Management Partnership THE PRESENT STATE OF KNOWLEDGE OF MARINE SCIENCE IN TANZANIA: SYNTHESIS REPORT. Edited by: A.S. Ngusaru Tanzania Coastal Management Partnership and the Science and Technical Working Group May 2000 Working Document: 5047 TCMP ____________________________________________________________________ A joint initiative between the National Environmental Management Council, the University of Rhode Island/Coastal Resources Center and the United States Agency for International Development. PREFACE The Tanzania Coastal Management Partnership (TCMP) established Science and Technical Working Group (STWG) in July 1999. TCMP is a joint initiative between the Government of Tanzania, the National Environmental Management Council, the United States Agency for International Development (USAID) and the Coastal Resources Center (CRC) of the University of Rhode Island (URI). The main goal of TCMP is to establish the foundation for effective coastal management in Tanzania. TCMP is committed to working with the existing network of Integrated Coastal Management (ICM) programme and practitioners to facilitate a participatory transparent process to unite the Government and the community, science and management, sectoral and public interests with a primary goal of conservation and development of coastal ecosystems and resource. STWG is intended to provide the primary bridge between coastal managers and the science community studying coastal marine issues at the local and national level. More specifically, STWG provides a clearinghouse mechanism for the integration of science and better coastal management. The Institute of Marine Sciences (IMS) of the University of Dar es Salaam provides the Secretariat to the STWG and the IMS Director is the Chairperson of the Group. This document contains the synthesis reports based on the available marine science literature in six thematic areas: shoreline erosion, water quality and pollution, marine fisheries, coral reefs, mangroves and other marine living resources. These were selected as natural science topics with relevance for coastal management in Tanzania. The syntheses were prepared after careful reviewing of a comprehensive list of literature with the goal of establishing the state of existing scientific knowledge in these themes. Therefore the syntheses exhausted most of the existing literature (publications, reports, grey literature, proceedings, etc.) that were readily available in major libraries and marine research and teaching institutions in Tanzania. The information presented is the summary of the considered papers and followed the same format for all themes.. The literature reviews work started in 1999 and involved the formation of a team of six "Theme Expert Leaders" (TELs), all members were from the University of Dar es Salaam under the coordination of the Science and Technical Working Group. The TELs worked together with their graduate students in expanding the list of scientific references and synthesizing the information. The theme expert leaders and their respective themes were, Dr. Narriman Jiddawi (marine fisheries), Dr. Salim M. Mohammed (water quality and pollution), Dr. Yunus D. Mgaya (other marine living resources), Prof. A.K Semesi (mangroves), Dr. Alfonce M. Dubi (shoreline erosion), and Dr. Greg Wagner (coral reefs). The information from all these themes were later compiled and edited by Dr. A.S Ngusaru of TCMP/University of Dar es Salaam. Dr. Jim Tobey of the Coastal Resources Center, University of Rhose Island provided the scientific advisory during the period of preparation of this document. 2 Science and Technical Working Group Chairperson Julius Francis Institute of Marine Sciences University of Dar es Salaam Members Narriman Jiddawi Institute of Marine Sciences University of Dar es Salaam Salim Mohammed Institute of Marine Sciences University of Dar es Salaam Jude Shunula Institute of Marine Sciences University of Dar es Salaam Yunus Mgaya Zoology and Marine Biology University of Dar es Salaam Greg Wagner Zoology and Marine Biology University of Dar es Salaam Alfonce Dubi Institute of Marine Sciences University of Dar es Salaam Secretariat/Editor Amani Ngusaru Institute of Marine Sciences University of Dar es Salaam Technical Advisor Jim Tobey Coastal Resources Center (University of Rhode Island) 3 TABLE OF CONTENTS Preface……….………………………………………………………2 Acknowledgement…….…………………………………...………...3 Coastal Erosion…...……….………………………………………...5 Water Quality and Pollution……..…...…………………………….43 Marine Fisheries…………………………….……………………...64 Coral Reefs……………………………………….……………….101 Mangroves…………………………………………….……….….138 Other Marine Living Resources…………………………….…….166 4 Chapter 1 COASTAL EROSION A. Dubi University of Dar es Salaam, Institute of Marine Sciences, P.O.Box 668 Zanzibar, TANZANIA 1.0 Background information 1.1 Introduction Communities living in coastal areas are often faced with the problem of coastal erosion. This is a condition whereby the shoreline position changes with time. Such problem of shoreline retreat, commonly known as beach or coastal erosion, often results in the loss of land area and property. The consequence is an immense pressure for the concerned society and coastal managers to undertake protective measures. In the absence of proper knowledge for the design principles of the protective structures and the consequences associated with the adopted measures, any attempt to abate erosion may end up being costly and useless. It is therefore a general recommendation that prior to any design of shoreline protection structures, geological and hydrodynamic conditions should be well studied to prevent unexpected results. Tanzania lies south of the Equator, between latitudes 4-120 S and longitudes 29-400E, covering an area of approximately 945,200 km2, of which 883,500 km2 is land and 61,500 km2. is covered by water. Unguja and Pemba Islands, which constitute Zanzibar, cover an area of 1,500 km2 and 900 km2 respectively. The total population of Tanzania, according to 1988 census, is about 24 million, of which approximately 3.6 million people live within the coastal zone (Bureau of Statistics, 1988). The coastal zone is defined as that area surrounding the interface between land and sea. It typically includes coastal plains, river deltas, wetlands, lagoons, beaches, dunes, mangroves, reefs and other coastal features, as well as the continental shelf. The coastal zone of Tanzania includes a land area of approximately 30,000 km2, three major islands, viz. Unguja, Pemba and Mafia and numerous small but beautiful islands and reefs such as Latham, Tutia, Songosongo, Mbudya, Pangavini, Bongoyo, Inner and Outer Nyakatombe, Kendwa, Inner and Outer Sinda. The Tanzania coastal zone is characterised by coastal forests, thickets, mudflats, seagrass beds, coral reefs and wetlands. Numerous rivers entering the Indian Ocean drain the coastal plain. Some of the major rivers include Pangani Wami, Ruvu, Rufiji, Matandu, Mbwemkuru and Ruvuma. The width of the coastal zone varies between 20-70 Km, while the width of the continental shelf ranges between 4-35 nautical miles with a total area of about 17,500 km2. The total length of the Tanzania coastline is about 800 km extending from the border with Kenya in the north to Ruvuma River in the south on the mainland, 430 km around Unguja and 450 km around Pemba. The East African coastal waters are subjected to the East African Coastal Current (EACC) with two alternating seasons; the southern and northern monsoons (Newell, 1957). The southern monsoons, which begin in April and end in October/November, are usually strong and are predominantly southerly. The northern monsoons, which begin in November and end in March, are lighter and are predominantly northerly (Figures 1a and 1b). Dubi (1998) analysed 25-year wind data collected between 1972-1996 at Tanga, Dar es Salaam, Zanzibar and Mtwara 5 and found the 50-year return wind speeds to be 26 knots for Tanga, 27 knots for Dar es Salaam, 29 knots for Zanzibar and 36 knots for Mtwara. Newell (1957) describes the East African Coastal Current as a current that moves northward throughout the year, but changes speeds during the two monsoons. During the southerly monsoons, it moves with a speed of about 4 knots after being accelerated by the trade winds. The current is pressed in towards the western side of the ocean. During the northerly monsoons, the current is retarded by the northerly winds along the coast. From the equator northwards, it is reversed to flow in the southerly direction. The reversed current meets the much-decelerated EACC at about 10S, where both are deflected out to the sea forming the Equatorial Counter Current (Figures 1a and 1b). About 2/3 of the coastline has fringing reefs, often close to the shoreline and broken only by river outlets like the Rufiji delta. Mangrove forests are found along sheltered parts of the coastline, in bays and estuaries, protecting the shore and coastal low-lying areas from storm surges, thereby giving a natural barrier against eminent erosion.