Mekong River Commission REPORT ON MONITORING OF ECOLOGICAL HEALTH OF THE MEKONG RIVER by Lieng Sopha Inland Fisheries Research and Development Institute (IFReDI) Department of Fisheries, Phnom Penh, Cambodia Contract No. PP03-035 Period: March-December 2003 INTRODUCTION Besides rice, fishes are important to mankind as a vital source of protein and cash income for many of the poor in the Mekong River Basin. Fish is a highest trophic level of aquatic animal and main resources in the Mekong River System. In the Mekong, fish are the major protein consumed more than other meats such as poultry, pork, and beef. Fish is a traditional product such as fish paste, and smoked fish are an invaluable source of calcium, vitamin A, and other nutrients. Fish is easier to digest and still comparatively cheap, the poor can afford to buy and can find almost everywhere. Fish is not only a source of vital protein to the population, it also provides employment for the rural people, gaining some of foreign exchange and creating opportunity for recreation such as ornamental and sport fishes. In 2003, the annual catch in the whole Lower Mekong Basin, Cambodia, Lao PDR, Thailand, and Vietnam is estimated 1.5 millions tones, with another 500,000 tons raised in reservoir an other forms of aquaculture. The annual value of the capture fishery is an estimated USD 1,042 million, aquaculture an estimated USD 273 million and the reservoir fishery an estimated USD 163 million, excluding the considerable earnings from trading and processing (MRC report, 2003). The fishery of the Mekong is very important for the 55 million people who live in the Lower Mekong Basin. An estimated 40 million rural dwellers are involved in fishery at part-time or seasonally. In Lao PDR, for instance 71 percent of rural households depend on fishery to varying degrees. In Cambodia, more than 1.2 million of 11 million Cambodian people who live in fishing communes around the Tonle Sap Lake depend almost entirely on fishing for their livelihood. The fishery is vital important for their nutrition, food security and income. Although there is a report that the status of the Mekong River is still relatively healthy, but there is a number of threats to the Mekong fishery. The changes of the volume of flow, timing and duration of the Mekong flood caused by the dams and weirs built for hydropower, erosion and sedimentation, irrigation and flood control are constructed not in the way safe for the health of the river and have increased concern the impact on fish habitat and aquatic resources in the Mekong as whole. Therefore, the monitoring system to investigate the status of the Mekong River must be established as soon as possible, so that measures could be taken on time to maintain the health and the resources of the Mekong River, the vital source of livelihood of the Mekong people. Among the aquatic animal in the basin, fish is the highest trophic level. Monitoring of the status and trend of fish and the fisheries indicate the final consequences from all human activities that people are interested to know. Therefore, the monitoring of fish and fisheries are initiated to be set up as an indication of ecological health of the Mekong River, and the status of fish as food and income of the rural poor. The trial fish survey was conducted at 11 sites from Nam Ou, Lao PDR, down to Ubon Ratchathani, Thailand and to Cambodia from middle of May to early June 2003. The objectives of the survey is to test and formulate a comprehensive fish biological monitoring method, which can be applicable to the whole Mekong River, where there is different water regime, aquatic resource and ecological characteristics at each section of the River. 2 METHODS DATA COLLECTION Fish sample were taken from gillnets of multiple mesh sizes (2.5, 3.5, 4.5, 6.5, 8 and 10 cm) with length of 80 m and 2 meters depth. The gillnets were set along riverbank at both left and right sides according to the condition of riverbanks. Two fishers were hired to set nets at each sampling site. The nets were set in the morning (9-10AM) and taken out in the afternoon (15-16 PM). The nets were soaked in water for about 5-6 hours per day. All relevant information, such as time of setting and taking out the net, size and mesh size of gill nets were filled on species composition data sheets (Appendix I). As soon as the fish catch were released from nets, they were sorted out by species. The fish were identified to species level at the field. All fish catch were identified, weighed individually and entirely, and counted total number of fishes. Fish sample were identified based on Fishes of the Cambodian Mekong guidebook (Rainboth, 1996), the fishes of Laos, and other reference documents available. The information on the species, and weight were recorded on data sheets of species composition. Data for condition factor was also collected for the survey. Species which are abundant such as Hennicorhyncus siamensis, Cyclocheilichthys enoplos and Sikukia sudgeri were measured their total length in milimetres and weighed individually at the precision of 0.001 grams (Appendix II). This data were taken from fishes from fishermen fishing around the sampling sites. All this fish data was sampled from the following sites: Table 1. Sampling Sites and Dates: Sites No Dates Sampling locations Countries Codes 1 24/05/03 Pak Nam Ou Lao PDR LPN 2 25/05/03 Nam Ou Lao PDR LNO 3 23/05/03 Luang Prabang Lao PDR LPB 4 27/05/03 Vientiane Lao PDR LVT 5 29/05/03 Pakse Lao PDR LPS 6 31/05/03 Ubon 1 Thailand TM1 7 01/06/03 Ubon 2 Thailand TM2 8 02/06/03 Ubon 3 Thailand TM3 9 07/06/03 Upper Mekong Cambodia CUP 10 06/06/03 Phnom Penh Port Cambodia CPP 11 05/06/03 Koh Khel, Bassac River Cambodia CBS DATA ANALYSIS The collected was processed using descriptive statistics. The condition factors were analyzed for 5 species: Cyclocheilichthys enoplos, Barbodes gonionotus, Cyclocheilichthys lagleri, Henicorhynchus siamensis and Dangila sp. Cf. cuvieri are studied by using all length and weight data collected in the survey from 19 May to 7 June 2003 at the sampling sites: Luang Prabang, Nam Ou ,Vientiane and Pakse, Lao PDR, Phnom Penh port and Phnom Penh upper Mekong, Cambodia. The condition factor qi is calculated for individual fish of known-length and weight, when the general length-weight equation is determined for each species. The length-weight relationship 3 was established by calculating the least squares fit through the data points of each species using the equation y = qxb , where q and b are constants, y the weight and x the total length. This length-weight equation is given for each species in the chart with the data points (Dirk, 2001). A mean weight-based condition factor (CFw) can be calculated from this: -1 CFw = (mean weight).(predicted mean weight) To define the condition factor, we need to define the relationship between fish length and weight for the selected species. It is universal that the growth of fish or any other animal increases with influence in body length. Length and growth of a species are interrelated (Biswas, 1993). The formula describing the relationship between fish length and weight are: W = a Lb (Huxley 1924). Where W stand for weight, L for length, a is constant and b the exponent. In isometrically growing fish, the exponent in the power equation describing the relation between the length of a fish and its weight is "3". The equation W = aL3 describe the relation between length and the weight. In case of allometry, the exponent b in the more general power of the equation b will be differ from "3". In these equations, a is a constant to be determined empirically. RESULTS SPECIES DIVERSITY There is 59 species encountered the catch monitoring survey (Appendix III). The frequency of species occurrence varied between sites. Ubon Ratchatthani sites TM2 (22 species) and TM3 (12 species) have the most number of fish species and Pakse, Lao PDR 11 species. There is commonly around 5 - 12 species encountered at each site. The number of species is likely to increase downstream, although Ubon Ratchathani site 2 and site 3 got the highest frequency of species occurrence (Fig.1). All 59 species represent 14 families. The family Cyprinidae has the most number of fish species (30 species) and followed by Panagasidae, Mastacembelidae, and Bagridae. Most of the families consists of a few species occur in the survey (Fig. 2). 4 Figure 1. Frequency of Species Occurrence at each Site LPN Upstream LNO LPB N = 94 LVT LPS TM1 TM2 TM3 CUP CPP Downstream CBS 0 5 10 15 20 25 Number of Species Figure 2. Species Occurrence by Family Notopteridae Nandidae Helostomatidae Engraulidae Eleotridae Channidae Chachiridae Siluridae Cobitidae N = 59 Pangasiidae Mastacembelidae Bagridae Cyprinidae 0 5 10 15 20 25 30 35 Number of Species All 59 species were observed occurring in 5 communities based on their frequency of occurrence. Paralaubica riveroi (Par. ri) uniquely occurred separately. It has no association with any other species. The large community consists of 48 species. They are associated in the large community, which is composed of many sub-communities. The other three communities resemble in a group of 2-4 species (Fig. 3). 5 0102030 Par. ri. Pun. gon. sites (Fig.the other from 6). distinct associated with each other. The site at Bassac River and site 3 at Mun River appear ways ofsimilarityspeciesof occurrence.