ECOLOGICAL MODEL OF THE MEKONG DELTA, VIET NAM. Can Tho University, Viet Nam Sept , 2007

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1 ECOLOGICAL MODEL OF THE MEKONG DELTA, VIET NAM Can Tho University, Viet Nam y, Sept , 2007

2 VIET NAM MEKONG DELTA 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.

3 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,

4 Yield Bac Lieu Soc Trang Yield, ton

5 Species Composition in BL & ST Yield, Ton Species Group Bac Lieu Soc Trang Total

6 Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Demersal Fish Croaker (Argyrosomus sp.) CáĐù Ray (Dasyatis sp.) CáĐuối Shark Cá Nhám Snapper (Lutjanidae) Cá Hồng Lizardfish (Saurida) Cá Mối Threadfin bream (Nemipterus sp.) Cá Lượng

7 Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Big Pelagic Mackerel (Scomberomorus sp.) Cá Thu Big Tuna (Thunnus tonggol) Cá Ngừ Small Pelagic Pomfret Cá Chim Pampus nozawae Cá Chim Giang Indian mackerel (Rastrelliger kanagurta) Cá Bạc Má Priacanthydae sp. Cá Trác Scads (Decapterus sp.) Cá Nục Small Tuna Cá Ngừ Nhỏ Yellow stripe travellies (Selaroides lysan) Cá Chỉ Vàng

8 Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Shrimps Shrimp (Parapenaeopsis sp.) Tôm Sắt Spear Shrimp (Metapenaeopsis barbata) Tôm Choán Jinga Shrimp (Metapennaeus spp) Tôm Chì Yellow shrimp (Metapenaeus breviornis) i Tôm Bạc Nghệ White prawn (Penaeus spp) Tôm Thẻ

9 Group of Species Group of Species (in Vietnam) Bac Lieu Soc Trang Total (Ton) Total (%) Crabs Crabs (Scylla sp.; Portunus sp.) Cua, ghẹ Squids Cephalopods Mực Cuttlefish (Sepiidae sp.) ) Mực Nang Squid (Loliginidae sp.) Mực Ống Octopus (Octopiidae sp.) Bạch Tuộc

10 Group of Species Group of Species (in Vietnamese) Bac Lieu Soc Trang Total (Ton) Total (%) Mixed fish Mixed fish, Small Cá xô nhỏ Mixed fish, Medium Cá xô vừa Mixed fish, Big Cá xô lớn Trash fish Cá tạp

11 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 Onigocia macrolepis Cá Chai Stolephorus commersonii Cá Cơm Argyrosomus argentatus Cá Đù Decapterus maruadsi Cá Nục Tihi Trichinrus lepturus Cá Hố Trypauchen vagina Cá Kèo Đỏ Setipinna taty Cá Lẹp Thrissa mystax Cá Lẹp Trắng Cynoglosus robustus Cá Lưỡi Trâu Upeneus bensasi Cá Phèn Sardinella gibbosa Cá Trích Arius thalassinus hl Cá Út

12 Species Name Species Name a b R 2 n In Vietnamese Parapeaeopsis hardwicki Tôm Sắt Parapenaeopsis cultrirostris Tôm SắtRằn Parapenaeopsis hardwickii Tôm SắtCứng Parapeacopsis tenella Tôm Sắt Láng Metapenaeus tenuipes Tôm Bạc Metapenaeus breviornis Tôm BạcNghệ Mt Metapenaeus afficus Tôm Chì Harpiosquilla harpax Tôm Tích Penaeus indicus Tôm Thẻ Parapenaeopsis p gracillima Tôm Giang Bóng Parapeaeopis hardwickii Tôm Giang Đá Haliporoides sibogae Tôm LửaChủy Dẹp Hadropenaeus lucasii Tôm LửaVỏ Dầy Metapenaeus ensis Tôm Đất Metapenaeus stridulans Tôm Gậy Penaeus japonicus Tôm He NhậtBản

13 2. Growth Parameters Species Name Species Name L K to Score Argyrosomus argentatus Cá Đù Upeneus bensasi Cá Phèn Cynoglosus robustus Cá Lưỡi Trâu Stolephorus commersonii Cá Cơm Metapenaeus breviornis Tôm Bạc Nghệ Metapenaeus tenuipes Tôm Bạc Parapeaeopsis hardwicki Tôm Sắt Parapenaeopsis p hardwickii Tôm Sắt Cứng Parapenaeopsis cultrirostris Tôm Sắt Rằn Harpiosquilla harpax Tôm Tích Exopalaemon styliferus Tôm Vát Giáo Parapenaeopsisgracillima illi Tôm Giang Bóng Haliporoides sibogae Tôm LữaChủy Dẹp

14 Parapenaeopsis cultrirostris Upeneus bensasi

15 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 )

16 Calculating of Species Group Biomass Catch Biomass Species Group (ton/km2) P/B =Z (P/B)/2 = F B=Catch/F Shrimps Squids Crabs Mackerel Small pelagic Demersal fish Benthic feeders Predator fishes Trash fish 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).

17 Input data for the Ecopath model of the coastal Mekong Delta

18 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).

19 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.

20 Results of Consumption

21 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.

22 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.

23 Time series data for Ecosim running Title Effort Shrimps Squids Crabs Mackerel Small pelagic Demersal fish Benthic feeders Predator fishes Trash fish Pool code Type

24 Ecosim results of Shrimp

25 Ecosim results of Squids

26 Ecosim results of Crabs

27 Ecosim results of Mackerel

28 Ecosim results of Small pelagic

29 Ecosim results of Demersal Fishes

30 Ecosim results of Benthic Feeders

31 Ecosim results of Shrimp

32 Ecosim results of Trash Fish

33 Ecosim results of Microzoobenthos

34 Ecosim results of Zooplankton

35 Ecosim results of Benthic producers

36 Ecosim results of Phytoplankton

37 Ecosim results of Detritus

38 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.

39 Thanks for your attention!