ISSN: 1683-1489 Mekong River Commission The Stationary Trawl (Dai) Fishery of the Tonle Sap-Great Lake System, Cambodia MRC Technical Paper No. 32 August 2013 . Cambodia Lao PDR Thailand Viet Nam Page 1 For sustainable development Cambodia . Lao PDR . Thailand . Viet Nam For sustainable development Mekong River Commission The Stationary Trawl (Dai) Fishery of the Tonle Sap-Great Lake System, Cambodia MRC Technical Paper No. 32 August 2013 Cambodia . Lao PDR . Thailand . Viet Nam For sustainable development Published in Phnom Penh, Cambodia in August 2013 by the Mekong River Commission Cite this document as: Halls, A.S.; Paxton, B.R.; Hall, N.; Peng Bun, N.; Lieng, S.; Pengby, N.; and So, N (2013). The Stationary Trawl (Dai) Fishery of the Tonle Sap-Great Lake, Cambodia. MRC Technical Paper No. 32, Mekong River Commission, Phnom Penh, Cambodia, 142pp. ISSN: 1683-1489. The opinions and interpretations expressed within are those of the authors and do not necessarily reflect the views of the Mekong River Commission. Cover Photo: J. Garrison Editors: K.G. Hortle, T. Hacker, T.R. Meadley and P. Degen Graphic design and layout: C. Chhut Office of the Secretariat in Phnom Penh (OSP) Office of the Secretariat in Vientiane (OSV) 576 National Road, #2, Chak Angre Krom, Office of the Chief Executive Officer P.O. Box 623, 184 Fa Ngoum Road, P.O. Box 6101, Phnom Penh, Cambodia Vientiane, Lao PDR Tel. (855-23) 425 353 Tel. (856-21) 263 263 Fax. (855-23) 425 363 Fax. (856-21) 263 264 © Mekong River Commission E-mail: [email protected] Website: www.mrcmekong.org Table of contents List of tables .... ...................................................................................................................................... vi List of figures ......................................................................................................................................... ix List of Plates ........................................................................................................................................ xiv Acknowledgements .............................................................................................................................. xv Abbreviation and acronyms ................................................................................................................. xvi Glossary ..............................................................................................................................................xvii Glossary of parameters (from formulas used in the paper) .................................................................. xxi Abstract ........................... ...................................................................................................................xvii 1. Introduction ..................... ...................................................................................................................1 1.1. The Tonle Sap-Great Lake (TS-GL) System ............................................................................1 1.1.1. Location, origins and physiography .............................................................................1 1.1.2. Hydrology and hydrodynamics ....................................................................................3 1.1.3. Ecology of the Tonle Sap .............................................................................................5 Biodiversity and endemism ..........................................................................................5 The flood pulse .............................................................................................................6 1.1.4. Fisheries of the TS-GL System ....................................................................................8 Threats to fishery resources ........................................................................................12 1.2. The Tonle Sap dai fishery ......................................................................................................12 1.3. The purpose and scope of the paper .......................................................................................13 1.4. The structure of the report ......................................................................................................14 2. The Dai Fishery of Tonle Sap-Great Lake (TS-GL) System ...........................................................15 2.1. The Location of the fishery.....................................................................................................15 2.2. Target species .........................................................................................................................18 2.3. Fishing gear and operation .....................................................................................................24 2.4. Fish disposal ...........................................................................................................................30 2.4.1. Prahok ........................................................................................................................30 iii The Stationary Trawl (Dai) Fishery of the Tonle Sap-Great Lake System, Cambodia 2.5. Economics ............................................ ...............................................................................31 2.6. Management ...........................................................................................................................35 2.6.1. Legislation ..................................................................................................................35 2.6.2. Closed season .............................................................................................................35 2.7. Effort control/Licensing .........................................................................................................36 2.8. Gear restrictions......................................................................................................................37 3. Routine monitoring activities and survey methodologies.................................................................39 3.1. Purpose of monitoring ............................................................................................................39 3.2. A history of survey methodologies and sampling regimes .....................................................39 3.3. Spatial and temporal variation in sampling effort ..................................................................43 3.4. Current survey methodology ..................................................................................................49 3.4.1. Sample stratification ...................................................................................................49 3.4.2. Data collectors and data collection process ...............................................................50 3.4.3. Variables enumerated ................................................................................................50 3.5. Catch estimation methodology ...............................................................................................52 3.5.1. Aggregated total catch................................................................................................52 3.5.2. Species-wise CPUE and catch ...................................................................................54 4. The Dai Fishery database: storage and processing ...........................................................................55 4.1. Database evolution .................................................................................................................55 4.2. Description of the current database ........................................................................................58 4.2.1. Data tables ..................................................................................................................58 4.2.2. Lookup Tables ............................................................................................................59 4.2.3. Length Frequency tables ............................................................................................60 4.2.4. Additional tables ........................................................................................................60 4.3. Current Database Query descriptions .....................................................................................60 5. The Ecology of the Fishery ...............................................................................................................61 5.1. Longitudinal (upstream/downstream) variation .....................................................................61 5.1.1. Aggregated catch, effort and CPUE ...........................................................................61 5.1.2. Catch diversity and composition ...............................................................................64 5.1.3. Fish size (weight) .......................................................................................................70 5.2. Variation in catch rates among individual dais .......................................................................71 5.3. Intra-annual variation .............................................................................................................77 5.3.1. Abundance (CPUE) ....................................................................................................77 5.3.2. Species diversity and similarity ................................................................................83