THE MASS-BALANCE ECOPATH MODEL OF THE COASTAL MEKONG DELTA, VIET NAM Can Tho University, Viet Nam: Mai Viet Van Nguyen Thanh Phuong Tran Dac Dinh Toulouse University, France Jacque Moreau

VIET NAM – MEKONG DELTA Introduction The Mekong delta is the most important area of fisheries and aquaculture of Viet Nam. It shares over 80 % of total national culture area and production. The Mekong delta has a 700 km coastline and a sea territory of 360,000 km 2. Where also has an abundant potential in marine resources. Many species have huge reserve and high economic value as shrimp, snapper, mackerel, madras snapper, amphioxus, etc. That is suitable for marine fishing and contributing to the increase of income, the improvement of people's living standard and enriching the country.

In the past decade, the Mekong delta fisheries sector has achieved considerable growth. However, the sector suffers from many problems that need to be resolved to ensure sustainable development. Such problems include over fishing in the coastal area, degradation of the marine environment and coastal resources, underdeveloped infrastructure, and lack of effective resource management.  Problems  The objectives To determine of the mass-balance Ecopath Model of the coastal Mekong Delta. The report presents indicative action programs for improving fisheries management and attaining sustainable development of coastal fisheries in the Mekong Delta of Vietnam.

Methodology Ecopath Model: The modeling approach used in this study is the Ecopath-Ecosim 5.1 software of Christensen and Pauly (2000). In Ecopath model it is assumed that the ecosystem modeled is in steady state for each of the living groups, which implies that input equals, i.e. Q = P + R + U, where Q is consumption, P production, R respiration, and U unassimilated food. The above equation can be structured around a system of linear equations for expressing mass-balance with the simplest form. It can be expressed for an arbitrary time period and for each element i of an ecosystem by the formula: Bi* (P/B)i*EEi = * (Q/B)j*DCij - EXi Where Bj is the biomass of function group i during the period covered (conventionally, a year); (P/B)i production/biomass rate; EEi ecotrophic efficiency, i.e., the fraction of the production that is utilized within the system for predator j to prey i; (Q/B)i, the relative food consumption ratio of i; and DCij is the fraction of prey i in the diet of predator j. The simultaneous linear equations using in Ecopath model states that the production and consumption are balance within an ecosystem.

The Ecopath model of the coastal Mekong Delta is going to construct a quantitative description of trophic structure on the ecosystem. The model can be used to estimate some important biological parameters and the relationship among the different groups in the coastal Mekong delta. The model is based on the monthly data from the bottom trawling of the coastal Mekong delta ecosystem survey project completed during January 2000 to December The mass-balance Ecopath model of the coastal Mekong Delta has 14 function groups based on 58 species from the coastal Mekong delta survey. The definition of function group is very crude because of the limited type of survey data available in the region. The Ecopath Model of the Coastal Areas in the Mekong Delta

Species groupScientific name ShrimpsParapenaeopsis cultrirostris Parapenaeopsis hardwickii Parapenaeopsis hungerfordi Matapenaeus tenuipes Metapenaeus affinis Metapenaeopsis barbata Penaeus merguiensis Penaeus monodon MolluscaSepioteuthis lessoniana Sepia inermis Loligo spp Octopus ocelatus CrabsPortunus pelagicus Callappa pelagicus Portunus sangui Portunus pelagicus, Callappa pelagicus, Portunus sangui Main functional groups in the Coastal Mekong Delta Ecopath model

MackerelScoberomorus guttatus, Scoberomorus commerson Small pelagicHarpodon nehereus Selaroides leptolepis Pampus argenteus Formio niger Decapterus maruadsi Demersal fishSaurida tumbil, Trachynocephalus myops Pristipomoides filamentosus Siniperca chua-tsi Pseudobagrus fulvidraco Ophiocara porocephala Polydactylus plebejus Clupanodon punctatus Argyrosomus argentus, Argyrosomus nibe, Spotted maigre Arius thalassinus Continue

Trash fish Harengula sp, Commersonii anchovy, Rastrelliger brachysoma, Selaroides leptolepis, Cynoglossa lingua Benthic feedersSoleidae Sillago sihama Cociella crocodilus,Hoplichthys sp, Rogadius asper Dasyatis bleekri, Parapercis barbata Upeneus suphureus Predator fishsTrichiurus haumela, Trichiurus lepturus Lates calcarifer Plotosus anguilaris Epinephelus areolatus, E. akaara, E. fasciatus Continue

Species Group Catch (ton/km2)P/B =Z(P/B)/2 = F Biomass B = Catch/F Shrimps Squids Crabs Mackerel Small pelagic Demersal fish Benthic feeders Predator fishes Trash fish Calculating of Species Group Biomass No biomass data for the species in the Microzoobenthos, Zooplankton, Benthic producers, Phytoplankton and Detritus groups so the biomass was estimated by the model using the fixed ecotrophic efficiency (EE=0.95).

Calculating of P/B and Q/B value It is very hard to find the P/B and Q/B value from one species to the whole group because many species are include in one function group in the model. The P/B and Q/B value in the Ecopath model of the coastal Mekong Delta were set based on the one from similar function group in the models of the Brunei Darussalam-South China sea (Silvestre, et al., 1993) and the Georges Bank Ecosystem (Sissenwine, et al., 1984).

Input data for the Ecopath model of the coastal Mekong Delta

Input data for Ecopath Modeling

Diet composition Trophic interations were pooly investigated in the coastal ecosystem of the Mekong Delta. Due to the lack of available information on diet composition of groups considered, data were taken from Fishbase (Froese and Pauly, 2005) and from Mohsin and Ambak (1996).

Results Results of Basic estimates All species groups were arranged into 3 trophic level. The estimated total fish biomass was 5.24 t/km2/year. For several groups, the EE values were hight, meaning that these groups exploited by small mesh for which possible over fishing might be considered.

Flow chart of trophic interactions in the Ecopath model of the coastal Mekong Delta

Mixed trophic impacts for the each groups in the coastal Mekong Delta ecosystem

TitleEffortShrimpsSquidsCrabsMackerel Small pelagic Demersal fish Benthic feeders Predator fishesTrash fish Pool code Type Time series data

Ecosim results of some species in gill-net

Ecosim results of some species in Trawl-net

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