ECOLOGICAL MODEL OF THE MEKONG DELTA, VIET NAM Can Tho University, Viet Nam y, Sept. 25-28, 2007
VIET NAM MEKONG DELTA 27.223 65 VietNam: 3,260 km of coastline; 660,000 ha of tidal areas. 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 the abundant potential in coastal resources which is suitable for fishing and contributing to the increase of income, the improvement of people's living standard and enriching the country. Bac Lieu (BL) and Soc Trang (ST) province: + Coastline: 128 km (Bac Lieu: 56 km; Soc Trang: 72 km). + Fishing ground: 14,045 km 2 + Fishing gears: Single trawl, purse seine, bottom gillnet, trammel net, long line, drift gillnet, squid hand line,
Yield 100000 90000 80000 70000 Bac Lieu Soc Trang Yield, ton 60000 50000 40000 30000 20000 10000 0 95 96 97 98 99 00 01 02 03 04 05
Species Composition in BL & ST Yield, Ton 30000 25000 20000 15000 10000 5000 0 Species Group Bac Lieu Soc Trang Total
Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Demersal Fish 1858.70 1470.70 3329.40 9.0 Croaker (Argyrosomus sp.) CáĐù 1247.30 1283.3 2530.60 6.7 Ray (Dasyatis sp.) CáĐuối 447.90 98.8 546.70 1.6 Shark Cá Nhám 100.60 17.9 118.50 0.3 Snapper (Lutjanidae) Cá Hồng 52.20-52.20 0.2 Lizardfish (Saurida) Cá Mối 8.80 41.6 50.40 0.1 Threadfin bream (Nemipterus sp.) Cá Lượng 1.90 29.1 31.00 0.1
Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Big Pelagic 1828.20 141.10 1969.30 6.2 Mackerel (Scomberomorus sp.) Cá Thu 1822.10 13.4 1835.50 5.9 Big Tuna (Thunnus tonggol) Cá Ngừ 6.10 127.7 133.80 0.3 Small Pelagic 1029.60 3441.70 4471.30 10.7 Pomfret Cá Chim 632.30-632.30 2.0 Pampus nozawae Cá Chim Giang 273.10 2.2 275.30 0.9 Indian mackerel (Rastrelliger kanagurta) Cá Bạc Má 86.80 120.1 206.90 0.6 Priacanthydae sp. Cá Trác 34.00 30.2 64.20 0.2 Scads (Decapterus sp.) Cá Nục 1.20 3104.8 3106.00 6.6 Small Tuna Cá Ngừ Nhỏ 1.40 124.2 125.60 0.3 Yellow stripe travellies (Selaroides lysan) Cá Chỉ Vàng 0.80 60.2 61.00 0.1
Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Shrimps 7206.10 18769.90 25976.00 63.3 Shrimp (Parapenaeopsis sp.) Tôm Sắt 4400.00 1231.6 5631.60 16.7 Spear Shrimp (Metapenaeopsis barbata) Tôm Choán 2171.90 15415.4 17587.30 40.0 Jinga Shrimp (Metapennaeus spp) Tôm Chì 441.60 1126.5 1568.10 3.8 Yellow shrimp (Metapenaeus breviornis) i Tôm Bạc Nghệ 176.80 929.4 1106.20 26 2.6 White prawn (Penaeus spp) Tôm Thẻ 15.80 67.0 82.80 0.2
Group of Species Group of Species (in Vietnam) Bac Lieu Soc Trang Total (Ton) Total (%) Crabs 214.20 1130.30 1344.50 3.1 Crabs (Scylla sp.; Portunus sp.) Cua, ghẹ 214.20 1130.3 1344.50 3.1 Squids 1483.60 4030.30 5513.90 13.4 Cephalopods Mực 1337.30 1959.9 3297.20 8.5 Cuttlefish (Sepiidae sp.) ) Mực Nang 98.9090 919.5 1018.40 23 2.3 Squid (Loliginidae sp.) Mực Ống 47.40 290.1 337.50 0.8 Octopus (Octopiidae sp.) Bạch Tuộc 860.8 860.80 1.8
Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Mixed fish 12548.70 9814.70 22363.40 61.2 Mixed fish, Small Cá xô nhỏ 7669.50 1777.3 9446.80 28.4 Mixed fish, Medium Cá xô vừa 1101.60 628.7 1730.30 4.8 Mixed fish, Big Cá xô lớn 469.80 352.6 822.40 23 2.3 Trash fish Cá tạp 3307.80 7056.1 10363.90 25.7
The Biological Characteristics of Commercial Species 1. Length-Weight Relationship (W = al b ) Species Name Species Name a b R 2 n Psettodes erumei Cá Bơn Vĩ 0.0044 3.233 0.9018 23 Onigocia macrolepis Cá Chai 0.0496 2.2338 0.942 47 Stolephorus commersonii Cá Cơm 0.0035 3.3953 0.9728 113 Argyrosomus argentatus Cá Đù 0.0118 2.9715 0.9531 934 Decapterus maruadsi Cá Nục 0.0358 2.3952 0.941 55 Tihi Trichinrus lepturus Cá Hố 0.0000700007 3.534 0.9792 48 Trypauchen vagina Cá Kèo Đỏ 0.0417 2.0287 0.91 112 Setipinna taty Cá Lẹp 0.0048 3.2257 0.8005 24 Thrissa mystax Cá Lẹp Trắng 0.0108 2.75 0.9107 45 Cynoglosus robustus Cá Lưỡi Trâu 0.017 2.5425 0.8872 266 Upeneus bensasi Cá Phèn 0.0029 3.3141 0.9728 145 Sardinella gibbosa Cá Trích 0.0099 2.915 0.9509 205 Arius thalassinus hl Cá Út 0.0114 2.8762 0.9656 21
Species Name Species Name a b R 2 n In Vietnamese Parapeaeopsis hardwicki Tôm Sắt 0.00860086 2.9616 0.9624 28 Parapenaeopsis cultrirostris Tôm SắtRằn 0.0248 2.5309 0.7454 544 Parapenaeopsis hardwickii Tôm SắtCứng 0.0176 2.6944 0.9459 271 Parapeacopsis tenella Tôm Sắt Láng 0.0269 2.5006 0.8028 21 Metapenaeus tenuipes Tôm Bạc 0.0174 2.596 0.9146 547 Metapenaeus breviornis Tôm BạcNghệ 0.1555 2.6738 0.8783 631 Mt Metapenaeus afficus Tôm Chì 0.01040104 2.836 0.8979 397 Harpiosquilla harpax Tôm Tích 0.0194 2.7512 0.9373 715 Penaeus indicus Tôm Thẻ 0.0068 3.0582 0.9347 158 Parapenaeopsis p gracillima Tôm Giang Bóng 0.0096 2.9174 0.7929 1247 Parapeaeopis hardwickii Tôm Giang Đá 0.0059 3.0891 0.7902 2473 Haliporoides sibogae Tôm LửaChủy Dẹp 0.0223 2.3834 0.8357 534 Hadropenaeus lucasii Tôm LửaVỏ Dầy 0.0548 2.2291 0.8175 17 Metapenaeus ensis Tôm Đất 0.01020102 2.8331 0.8545 94 Metapenaeus stridulans Tôm Gậy 0.0089 2.8898 0.9662 608 Penaeus japonicus Tôm He NhậtBản 0.0181 2.643 0.8811 36
2. Growth Parameters Species Name Species Name L K to Score Argyrosomus argentatus Cá Đù 31.03 0.23-0.32 0.474 Upeneus bensasi Cá Phèn 24.86 0.59-0.06 0.635 Cynoglosus robustus Cá Lưỡi Trâu 37.72 0.19-0.22 0.389 Stolephorus commersonii Cá Cơm 14.98 1.12-0.58 0.999 Metapenaeus breviornis Tôm Bạc Nghệ 10.66 205 2.05-0.06 006 0.777 Metapenaeus tenuipes Tôm Bạc 10.89 2.46-0.62 0.525 Parapeaeopsis hardwicki Tôm Sắt 17.9 1.88-0.19 0.823 Parapenaeopsis p hardwickii Tôm Sắt Cứng 13.16 0.51-0.63 0.727 Parapenaeopsis cultrirostris Tôm Sắt Rằn 16.32 0.84-0.25 0.628 Harpiosquilla harpax Tôm Tích 29.72 0.33-0.66 0.551 Exopalaemon styliferus Tôm Vát Giáo 12.33 0.77-0.69 0.971 Parapenaeopsisgracillima illi Tôm Giang Bóng 10.1717 114 1.14-0.18 018 0.895 Haliporoides sibogae Tôm LữaChủy Dẹp 11.42 0.89-0.04 0.53
Parapenaeopsis cultrirostris Upeneus bensasi
3. In progress: 1. Total mortality (Z) 2. Natural mortality (M) 3. Fishing mortality (F) 4. Exploitation rate (E) 5. Maximum exploitation rate (E max ) 6. Optimum exploitation rate (E opt or E 0.1 )
Calculating of Species Group Biomass Catch Biomass Species Group (ton/km2) P/B =Z (P/B)/2 = F B=Catch/F Shrimps 1.602 2.5 1.250 1.28 Squids 0.616 2.0 1.000 0.62 Crabs 0.183 2.0 1.000 0.18 Mackerel 0.017017 1.991 0.996 0.0202 Small pelagic 0.073 2.0 1.000 0.07 Demersal fish 1.036 10 1.0 0.500 207 2.07 Benthic feeders 0.196 1.0 0.500 0.39 Predator fishes 0.064064 0.5 0.250 0.26 Trash fish 0.585 3.4 1.700 0.34 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).
Input data for the Ecopath model of the coastal Mekong Delta
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 of Basic estimates Results All species groups were arranged into 4 trophic levels. l The estimated total fish biomass was 5.24 t/km 2 /year. For several groups, the EE values were high, meaning that these groups exploited by small mesh for which possible over fishing might be considered.
Results of Consumption
Flow chart of trophic interactions in the Ecopath model of the coastal Mekong Delta The ecosystem was phytoplankton based on 16.94% of the total food consumption come from primary producers and only 14.28% from detritus. Most primary production was consumption by the benthic producer and zooplankton groups.
Mixed trophic impacts for the each groups in the coastal Mekong Delta ecosystem The results suggests that an increase in abundance of any fish group would be impacted on the ecosystem. The whole ecosystem would be more sensitive to abundance of food items such as phytoplankton, zooplankton and benthic. The small size fish populations would be affected.
Time series data for Ecosim running Title Effort Shrimps Squids Crabs Mackerel Small pelagic Demersal fish Benthic feeders Predator fishes Trash fish Pool code 1 1 2 3 4 5 6 7 8 9 Type 3 6 6 6 6 6 6 6 6 6 2000 1568 1.6 0.62 0.18 0.02 0.07 1.04 0.2 0.06 0.58 2001 1663 1.41 0.47 0.13 0.03 0.08 1.29 0.32 0.1 0.49 2002 1518 1.62 0.98 0.41 0.04 0.11 1.53 0.47 0.11 0.29 2003 1492 1.59 0.85 0.44 0.11 0.16 1.2 0.5 0.15 0.3 2004 1914 1.41 0.67 0.44 0.13 0.22 1.46 0.37 0.19 0.4 2005 1913 1.33 0.7 0.38 0.12 0.19 1.31 0.31 0.18 0.38
Ecosim results of Shrimp
Ecosim results of Squids
Ecosim results of Crabs
Ecosim results of Mackerel
Ecosim results of Small pelagic
Ecosim results of Demersal Fishes
Ecosim results of Benthic Feeders
Ecosim results of Shrimp
Ecosim results of Trash Fish
Ecosim results of Microzoobenthos
Ecosim results of Zooplankton
Ecosim results of Benthic producers
Ecosim results of Phytoplankton
Ecosim results of Detritus
Conclusions It was noted that the rapid depletion of the fish resources in the coastal Mekong Delta. There are few possibilities to increase the current exploitation of large pelagic fishery resources. Fishermen e who are currently engaged in coastal small scale gill-net and trawl-net fishery should to use drift gillnet to exploit large pelagic fish; therefore, reduce the fishing pressure on fishery resources.
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