A. THE AGNO BASIN (THE PHILIPPINES) (contd.)

4. AGNO RIVER BASIN DEVELOPMENT AND FISHERIES

The 270 km long Agno River has never been considered a fishery resource. For apart from its indirect use as a source of water for fish ponds, there is no substantial capture fishery to speak of. Only limited data are available on the fisheries of the river itself, its tributaries, and the other water bodies with which it is interlinked. There is a lack of specific data on the effects of erosion, sedimentation, flooding, and pollutant discharges on water quality, freshwater and marine habitats, and fisheries. Although the BFAR annual statistics show the kinds and volumes of fish caught off the Lingayen Gulf, they do not say how much of it was caught in the areas directly influenced by the Agno River discharge. It is also not possible to assess the extent of decrease in fish yield in the estuarine and coastal waters as a result of pollution and silt load from the Agno.

The following discussion is therefore based on qualitative descriptions.

4.1 The environment of the Agno River: A recapitulation

The most damaging environmental factors relating to Agno River water resource development, including the fisheries component, are excessive soil erosion and soil contamination with heavy metals contained in sediments originating from the watershed. Continued deforestation, shifting cultivation, overgrazing, and forest burning, have all resulted in accelerated soil erosion leading to high sediment build-up in the Binga and Ambuklao dams, which have so far served as efficient traps.

Downstream of Binga reservoir, the clarified Agno River water receives further heavy input of erosion-derived sediments from the deforested watershed and from mines. The river water, recharged with a high sediment load, is diverted by the ARIS irrigation weir into its main intake structure, and into the ARIS canals and laterals, to irrigate some 40,000 hectares of agricultural lands of the Pangasinan plain.

Amongst the major tributaries of the Agno River is the Tarlac River. In lowlands, during flooding and high tides, the Agno connects with the Dagupan-Malabago-Sinocalan river systems which drain the urban areas of Dagupan, Santa Barbara, and Calasiao. The catchments of these rivers are intensively developed for irrigated rice farming, and have poor and largely inadequate waste disposal facilities even in the urban and industrial centres.

The Agno water discharging into the Lingayen Gulf thus carries a pollutant load consisting mostly of toxic metals and sediments from the upper catchment, fertilizer and pesticide residues from agricultural lands (which have been increasing their application rates in an effort to increase crop production), and domestic and industrial wastes from the urban centres.

4.2 Impacts of development on the fisheries

4.2.1 The Agno River:

Development projects in the Agno River have impacted the fishery resources of the basin largely on account of their interference with the quality of the fish habitat and the disruption of fundamental chains in the food web. The impact of the hydroprojects on fisheries by way of habitat transformation (from lotic to lentic) and loss of seasonal inundation appears to be less than impacts of toxic metals, pesticide and fertilizer residues, domestic wastes, and suspended sediments. Changes in feeding, growth, reproductive, and mortality rates of fish are believed to be consequences of the deterioration of the quality of the habitat (UNESCO/UNEP, 1979; NACIAD et al., 1981). Such a situation is apparent in the individual fishery zones along the stretch of the river from its source to its outlet into the sea.

4.2.2 The reservoirs:

The shortage of pre- and post-impoundment data for the Ambuklao and Binga reservoirs makes an accurate evaluation of the impact of their construction on the Agno River fisheries rather difficult. Hydrobiological surveys conducted by the BFAR in 1955 and 1960 when the two reservoirs just filled showed the essential physico-chemical parameters to be within optimum levels for aquatic biological production and noted the presence of gobies and eels. Since then, the BFAR has stocked the reservoirs with fingerlings of tilapias, Therapon sp., milkfish (Chanos chanos), mudfish (Channa striata), blackbass (Micropterus salmoides), blue gill (Lepomis macrochirus), and the giant freshwater prawn (Macrobrachium sp.). No follow-up studies have been conducted subsequent to these introductions which makes evaluation of the success of the stocking programme impossible. The only base for making tentative conclusions on the status of the fisheries of the two reservoirs are the verbal reports of catches of fish by the fishermen in the area. No official fish yield figures are available. As a result of the input of large quantities of nutrient-rich sediments from the watershed, there is an abundance of phytoplankton and zooplankton (Aypa et al., 1983). The reservoirs would therefore appear to have a good fisheries potential.

To supplement natural fish production in the reservoirs, the culture of tilapia in floating cages shall be pilot-tested by the National Power Corporation in cooperation with BFAR. The probability of success of this scheme seems to be high on account of the high primary productivity of the reservoirs, which is essential to fish growth and survival. A land-based tilapia hatchery-nursery complex is also being proposed together with the installation of the fish cages. This will ensure the availability of fish seed for cage culture and for direct stocking in the reservoirs. The BFAR has also proposed to undertake an evaluation of the present fish stocks in the reservoirs, to be used as a basis for appropriate stocking and re-stocking of suitable fish species (Aypa et al., 1983).

4.2.3 Fisheries downstream of Binga Dam:

In mid-1979, hydrobiological surveys were conducted by BFAR personnel along 110 km from the upper portions of the Agno River to its lower reaches near its mouth in the Lingayen Gulf. This survey, conducted by Gracia et al. (1979), concluded that the upper Agno is poor in fish and hardly ever fished except in the rainy season when water level is high. Instead, the people carry out gold-panning.

The scarcity of fish in the upper Agno may be due primarily to the poor water quality as characterized by low dissolved oxygen transparency and pH values with lower values found higher upstream (Table 17). This may be due to the heavier silt load of water closer to their point of origin, in this case, the water discharged by the irrigation systems located nearer the ARIS main intake structure (UNESCO/UNEP, 1979). Natividad and Magsumbol (1979) found that except for the pH of river water in the municipality of Bayambang, the measured physico-chemical parameters improve as the river progresses downstream (Table 18). The lower Agno has a better fishery than the upper reaches. Experimental fishing by the BFAR in the lower Agno revealed the presence of mullet, carp, tilapia, mudfish, and freshwater snails (locally known as “bisokol”) (Natividad and Magsumbol, 1979). The numbers of freshwater fish species, however, are perceived to be lower than in the past (NACIAD et al., 1981). Also, it has been observed that some aquatic plants such as Vallisneria spp., and benthic organisms like whelks, mud crabs, and tubiferous worms have become very scarce in the river system (NACIAD et al., 1981). These changes may result from the increased sedimentation and pollution. The present Agno River system is obviously no more capable of supporting a rich biomass and diversity of aquatic life.

Note:
Average of measurements taken at six sampling stations per municipality.

The municipalities are arranged in the order of increasing proximity to the river's origin, with San Nicolas being the closest to the source.

The impacts of silt, heavy metals, and pesticides on aquatic organisms are well known. The UNESCO/UNEP Report (1979) summarized the effects of siltation on aquatic organisms as follows: “Siltation destroys spawning grounds and eggs of fish, and kills insects that are essential as fish food. It restricts light penetration and reduces growth and photo-synthetic activity of oxygen-producing aquatic plants. Silt suffocates fish and irritates gill membranes, thereby contributing to fish stress and increasing their susceptibility to disease.” Furthermore, the gradually increasing concentration of silt leads to a change in dominant species, with fish feeding visually unable to stay while those using fish sensors for locating food may move in (Petr, 1983). The effects of suspended and sedimentary loads are manifested by increased competitiveness of various species, occurrence of diseases, gradual decline of, or change in, the composition of the population or the whole ecosystem, and the reduction of fish stocks by mass mortalities (UNESCO/UNEP, 1979). To complicate the situation further, toxic metals in the mine tailings discharged into the upper Agno eventually settle into the river, delta, and estuary where they become available to benthic algae and infauna which may accumulate them to concentrations several times over those which occur in the ambient environment (Everett and Associates, 1980).

Note:
Average of measurements taken at five sampling stations per municipality.

The municipalities are arranged in order of increasing proximity to the river origin, with Villasis located farthest upstream.

The Fe⁺⁺ in water from mine drainage may precipitate out as Fe(OH)₃ and be carried as a flocculant in colloidal suspension which has a detrimental effect to fish, as it impairs gill respiration (Everett and Associates, 1980). Mercury at concentrations above 0.30 mg/1 HgC1₂ has been shown to cause a significant inhibition of enzyme activity, act as a vascular poison, cause damage to accessory respiratory organs, decrease oxygen consumption, and cause blindness in Oreochromis mossambicus (Spehar et al., 1981). Cadmium has been reported to inhibit growth of fish while lead has been known to cause ovulation stress, loss of muscular coordination, balance, deformity, and embryo and fry mortality in cichlids (Spehar et al., 1981).

In the Agno River system, the problem of high levels of heavy metals may be further complicated by the presence of pesticide residues or associated polyphosphates present in agro-chemicals, on which the heavy metals may adsorb (NACIAD et al., 1981), and cause pathological conditions in fish, such as disease and/or deformity (Spehar et al., 1981). This situation may actually be more serious than it appears, especially if it is considered that farmers have been applying significantly more fertilizers and pesticides in an effort to increase their yields, which have been severely reduced as a result of the ARIS sedimentation problem (UNESCO/UNEP, 1979).

Pesticide use is also known to have a negative impact on the paddy, canal, pond, and mainstream fish. Tissue samples of fish taken from Pangasinan were found to contain excessive loads of gamma betaheptachlor (4.35 – 27.36 μg/kg of fish) and dieldrin (0.83–32.08 μg/kg of fish) (NACIAD et al., 1981), compounds known to have a particularly toxic effect on fish. At the FAO/WHO recommended acceptable daily intake (ADI) of 10 μg/kg of body weight for gamma betaheptachlor and 0.1 μg/kg body weight for dieldrin, it is the low income families who would be the most affected since fish constitutes their main protein source.

4.2.4 Brackish-estuarine fisheries:

Estuaries, coastal swamps and mangroves are ecologically important areas which serve as spawning, nursery, and feeding grounds for a variety of commercially valuable fish and shellfish. In the Agno River the major areas of impact from the point of view of water resource development are the coastal fringes along Lingayen Gulf near the mouth of the Agno River, and the Dagupan estuary area and the brackishwater fishponds in the coastal municipalities of Pangasinan. The occurrence of heavy metals, is at least partially attributable to contaminants flowing through the river system. Concentrations of Hg, Cd, and Pb above acceptable limits in waters of Lingayen Gulf (Table 5) present threat not only to the lower aquatic organisms but also to man, the ultimate consumer. These heavy metals can be bound by organic detritus and subsequently concentrated in the tissues of detritus-feeders (e.g. oysters, shrimp larvae, mullets) and by plants (e.g. nipa palms) (NACIAD et al., 1981). The input of pesticides and fertilizers via agricultural practices has created unrecognized problems for aquaculture and for the river/marine/coastal wild fish stock.

Mining activities which result in the input of large volumes of mine tailings into the Agno River system also destroy the mangrove ecosystem by siltation and a high turbidity of water, which also negatively affects benthic communities and threatens adjacent coral reefs. Siltation on coral reefs is known to be a major source of their destruction (Soegiarto, 1980).

Compounding these problems of heavy metals and pesticides are the waste disposal problems posed by human activities. In mangroves, which act as a pollutant sink, microbial action under appropriate conditions may deposit heavy metals as insoluble sulfides (NACIAD et al., 1981). Enterobacteria which are known to readily absorb heavy metals, abound in the sewage-polluted waters and local streams of the Dagupan-Calasiao estuary area which is connected with the Agno River during floods. For example, zinc and cadmium are known to reach concentrations in sediments as high as 100,000 ppm and 30,000 ppm, respectively (NACIAD et al., 1981). The probable implication of this on estuarine fish and shellfish production, especially in the Dagupan estuary where oyster culture is being promoted, is evident.

A similar situation may exist in brackishwater fishponds in the lower Agno, which have been shown to contain high dissolved concentrations of heavy metals (0.15 ug/1 lead and 0.1 – 0.27 ug/1 Hg) as a result of the use of the contaminated water from the Agno River (GOPA, 1983). It is then highly possible that fish ponds in the Dagupan-Binmaley-Lingayen area would be subject to long-term heavy metal contamination through biological release and recycling associated with flooding, flushing, and use of the Agno River as a supply source (NACIAD et al., 1981). Furthermore, the possibility also exists for the accumulation of toxic metals by algae grown in these ponds and their subsequent transfer up the food chain.

To conclude, the brackish-estuarine zone of the Agno River Basin is a highly stressed ecosystem, mainly as a result of ecological imbalance due to various development activities in the upper catchment area. The long-term accumulation of mineralized sediments and heavy metals, the chronic application of agrochemicals, and the indiscriminate disposal of domestic and industrial wastes into the Agno River system, have altered the natural habitats for aquatic organisms by their interference with water chemistry and sediment quality and quantity.

4.3 Multi-purpose river basin development and fisheries

The concept of multipurpose development is and shall be always a challenge to planners. For while multiple use may be viewed as a “group of industries, farmers, municipalities, and government agencies, all cooperatively using a single water supply without encroaching on the rights of others, this utopian situation does not now exist anywhere and is not likely to exist … (as) it is virtually impossible to use water for one purpose without interfering with other beneficial uses” (Cairns, 1972). The fact remains that “of several useful services of a typical river system, some are competitive, some neutral, and a few complementary” (Crutchfield, 1972). And as is often the case, among several potential uses of a river, the fisheries sector falls low in the order of priorities for development. Power generation, irrigation, and flood control usually occupy first positions in the hierarchy of planning goals, which, until recently, has neglected the fisheries.

In the Philippines, as in the other developing countries of Asia and Africa, high population growth rates necessitate the proper development and management of drainage basins for domestic, agricultural, and industrial uses. Like in Africa, the fisheries are generally treated as incidental, though not altogether ignored, often receiving little or no attention in the planning and execution of land and water resources development (cf. Awachie, 1981; Litterick, 1981).

Over the past three decades, since the first hydroproject in the country was established in the upper Agno, river basin development has been geared towards the satisfaction of the more economically rewarding goals of hydroelectricity, irrigation, and flood control, without much consideration for the other sectors, especially the fisheries, which are likely to be affected by the development. Rather than think of the possibilities of fish stock depletion and the conservation of endangered fish species, government planners have confined their attention to hydroelectric power production and an irrigation scheme and to secondary benefits like prevention of flood losses. Thus, no pre-impoundment fisheries surveys were conducted before dam construction (Gracia and Magsumbol, 1983). The absence of such data, therefore, makes any evaluation of the impact of these projects on the original fish fauna and fisheries difficult. Lack of statistics on fish yield and fisheries in the reservoirs also hinders fisheries planning and management. The poor state of the Agno River fisheries and the environment is also an indication of administrative weakness and poor management. In 1981, the problems were summarized by NACIAD et al. (1981) as follows: Administrative responsibilities for (the) various components of natural resource managment are segregated and interrelationships and cooperation at the provincial and regional levels among agencies appears to be minimal. Overall responsibilities for environmental policy and investigations and pollution problems lie with the National Environmental Protection Council (NEPC) and the National Pollution Control Commission (NPCC), agencies not yet represented at the regional and provincial office levels. The National Economic Development Authority (NEDA) regional office is the agency which has the capability and responsibility to plan for resource allocation and development but at this stage, environmental and pollution-related problems experienced by the local people can only be dealt with indirectly through representations with selected officials.

What further aggravates the situation is the fact that most of the effects now being felt by the numerous families and communities in the river basin are caused by environmental degradation and policy decisions outside Pangasinan - the origin of the sedimentation problem being poor watershed management and mining practices in Benguet Province. Consequently, the decisions on mitigating measures to alleviate or rectify major environmental problems are beyond the influence of provincial representatives. For example, projects on irrigation works rehabilitation and large-scale reafforestation of the watershed can only be approved and implemented by national agencies.

At the national level, decision-making tends to involve multiple agencies with poorly defined channels of control and weak linkages. Fisheries has been mostly considered only as an afterthought. This explains why fisheries, especially those initiated several years ago, were usually unplanned activities, without much prior thought and preparation. The fish stocking programme in man-made lakes is a case in point. With no benchmark ecological data, no previous biological studies, no stock data and catch statistics, a stocking programme was initiated. In the Ambuklao and Binga reservoirs, fingerling dispersal was a one-time affair. Both the poor policy directives and management on behalf of a number of agencies seemed to be behind this. After the initial effort at fish stocking, there was hardly any subsequent activity to determine its success or failure, thereby rendering futile any attempt to make a thorough evaluation of the merits of the fisheries management programme (Baluyut, 1983).

5. PROSPECTS FOR FUTURE DEVELOPMENT

Inspite of the slow start of the Agno River fisheries, the prospects for change and improvement look promising. Recently, there has been a growing interest and involvement of government agencies and, in particular, of the BFAR in the Agno River. The BFAR has sent out survey teams to the upper and lower Agno River to look into the possibilities of aquaculture in the existing reservoirs and to conduct pre-impoundment surveys as part of the planning activities for the San Roque Project. Aypa et al. (1983) are confident that the floating cage culture project they are establishing in the Ambuklao and Binga reservoirs would succeed on account of the high primary productivity of the water. Fisheries officials and senior level personnel have also become more actively involved in the river basin development planning and management. Unlike before when multipurpose water projects were established without having taken the interest of fisheries into consideration, the pre-impoundment survey conducted recently on the lower Agno River at the San Roque dam site of the existing fishery resources will serve as a basis for future fisheries programmes. The Asian Development Bank-assisted Aquaculture Development Project for implementation by BFAR in selected brackishwater fish ponds in Pangasinan promises to optimize resource utilization through intensification rather than opening up new mangrove areas for extensive fish pond development. Under this project, participating fish pond owners/operators shall be provided with credit assistance for pond renovation and redesign and purchase of inputs needed for intensified prawn and/or milkfish culture, in addition to the provision of various support facilities like hatcheries and ice plants, training and extension, and environmental management.

On a broader planning and administrative level, two large development projects aim to alleviate present problems and difficulties and give the people of Pangasinan something to look forward to. First, the San Roque Multipurpose Project, for immediate implementation by the National Power Corporation with funding assistance from the Japanese Government, promises to provide a much needed boost to the river basin economy by serving as a sediment trap, while at the same time generating power, irrigating farmlands, and controlling floods. The project is deemed of critical importance in reestablishing the viability of the Agno River Basin environment by preventing further accumulation of heavy metal-laden sediments and mineralized clay particles from the watershed. The silt-free water to be released by the dam is expected to exert a scouring action on the thick sediment deposits in the river and its tributaries, the ARIS irrigation canals, and the coastal zone, with the concommitant improvement of the environment and the renewal of the fisheries and aquatic resources.

As a corollary measure, the reafforestation and proper management of the Agno watershed, begun in 1981, shall be undertaken on a continuing basis. The Bureau of Forest Development has already replanted about 8,832 out of a total projected area of 23,250 ha. Jointly with FAO/UNDP, it has prepared the investment portfolio of the Multi-Use Forest Management Project aimed at the comprehensive rehabilitation of the Upper Agno district as a long-term ameliorative measure for the heavy siltation problem. This US $32.4 million project for eventual foreign funding has been prepared using the Integrated Area Development (IAD) approach, following existing political and administrative set-ups, and with the full cooperation and coordination of the local and national agencies. It aims at an accelerated agricultural and fisheries production; intensified forestry, agrarian reform, and cottage industry activities; credit provision and management; water supply and sanitation; nutrition improvement; vocational and technical skills training; infrastructure development; and environmental protection.

All these projects and programmes, which directly or indirectly seek the ultimate rehabilitation of the Agno River Basin, seem to have been predicated on the complementary and interrelated strategies of proper and rational land utilization on the one hand and water resources development and management on the other. Development projects like those proposed to be undertaken by the PIADP and economic activities likely to be stimulated by the establishment of the San Roque Multi-purpose Project and the Aquaculture Development Project, are projected to create new employment opportunities, increase incomes, and generate other spin-off effects, all leading towards greater cultural opportunity, socio-economic uplift and environmental harmony.

6. REFERENCES

Awachie, J.B.E., 1981 Some general consideration on river basins in Africa and their management and development in relation to fisheries. CIFA Tech.Pap./Doc.Tech.CPCA, (8):2–23

Aypa, S.M., 1983 A.M. Galicia, Jr. and R. Magsumbol, Hydrobiological investigation and survey on suitable sites for fish cage project in Ambuklao and Binga dams, Benguet Province. Quezon City, Bureau of fisheries and Aquatic Resources. (mimeo)

Baluyut, E.A., 1983 Fish introductions in lakes and reservoirs in the ASEAN region: a review. FAO Fish.Tech.Pap., (236):82 p.

BFAR (Bureau of Fisheries and Aquatic Resources), 1981 Fisheries statistics of the Philippines. Fish.Stat.Philipp., (31)

Cairns, Jr. J., 1972 Rationalization of multiple use of rivers. In River ecology and man, edited by R.T. Oglesby, C.A. Carlson and J.A. McCann. New York, Academic Press, pp.421–30

Crutchfield, J., 1972 Multiple use of river systems: an economic framework. In River ecology and man, edited by R.T. Oglesby, C.A. Carlson and J.A. McCann. New York, Academic Press, pp.431–40

Dasmann, R.F., J.P. Milton and P.H. Freeman, 1973 Ecological principles for economic development. New York, John Wiley and Sons

ELC (Electroconsult S.p.A.)/EDCOP (Engineering Development Corporation of the Philippines), 1979 San Roque multipurpose project. Feasibility study. Main report. Metro Manila, EDCOP

Everett and Associates, 1980 Estimates of geochemical processes and chemical concentrations in the Fly River drainage that may result from development of the Ok Tedi Project, Western Province, Papua New Guinea. 2 vols. (mimeo)

GOPA Consultnts, 1983 Aquaculture development project technical assistance study. (Draft final report). Bad Homburg, West Germany, GOPA Consultants

Gracia, D.M., n.d. General information on Philippine reservoirs. Quezon City, Bureau of Fisheries and Aquatic Resources. (mimeo)

Gracia, D.M. and J.M. Natividad, 1979 The Agno River: Its fishery resources, hydrobiological parameters, and potential land uses. Survey report. Quezon City, Bureau of Fisheries nd Aquatic Resources (mimeo)

Gracia, D.M. and R.M. Magsumbol, 1983 Report on the pre-impoundment survey of lower Agno River (San Roque Dam). Pangasinan, August 25–30, 1983. Quezon City, Bureau of Fisheries and Aquatic Resources, Fish Propagation Division. (Unpubl.Rep.)

Hanson, .J. and Koesoebiono, 1977 Setting coastal swamplands in Sumatra - a case study for integrated resource management. Environmental Research Training Project. Bogor, Indonesia, Center for Natural Resources Management and Environmental Studies, Bogor Agricultural University

Litterick, M., 1981 River basin management and development in Kenya. CIFA Tech.Pap./Doc.Tech.CPCA, (8):25–33

NACIAD et al., 1981 Pangasinan integrated area development project. Final report. Vols.1–4. Quezon City, National Council on Integrated Area Development

Natividad, J.M. and R.M. Magsumbol, 1979 Inventory survey and hydrobiological investigation on the upper Agno River. Quezon City, Bureau of Fisheries and Aquatic Resources (mimeo)

NEDA (National Economic Development Authority), 1982 Philippine statistical yearbook. Manila, NEDA

NPC (National Power Corporation), 1972 Management of Ambuklao - Binga watershed and sedimentation of Ambuklao reservoir. Paper presented to the Tenth Regional Conference on Water Resources. UN/ECAFE, 18–25 Sept. 1972

NPCC n.d. (National Pollution Control Commission), Water quality criteria and rules and regulations relating to water pollution control. Manila, NPCC

NWRC (National Water Resources Council), 1976 Philippine water resources. First national assessment report, No.(19). Quezon City, NWRC

NWRC (National Water Resources Council), 1983 Agno River basins - Central Luzon. Framework plan. In Regional water resources development strategies. Vol.3. (Draft MS)

Petr, T., 1983 Conflicts arising for fish and fisheries from poor land use and urbanization. FAO Fish. Rep., (288):76–82

Philippines, 1983 National Environmental Protective Council and National Council on Integrated Area Development (NEPC and NACIAD), Ecological profile of Pangasinan. Report. Manila, NEPC/ NACIAD

Soegiarto, A., 1980 Status report on research and monitoring of the impact of pollution on mangrove ecosystems and its productivity in Indonesia. Country paper presented at the SCSP-FAO/UNEP Expert Consultation Meeting on impact of pollution on mangrove ecosystems and its productivity in Southeast Asia. Manila, Philippines. 4–8 Feb. 1980 (mimeo)

Spehar, R.L. et al., 1981 Effects of pollution on freshwater fish. J.Water Pollut.Control Fed., 53(6):1028–76

Tamayo-Zafaralla, M., 1983 Conflicts between fisheries and mining, industrialization and pollution of inland waters in the Philippines. FAO Fish.Rep., (288):83–7

UN, 1970 Integrated river basin development. Report of a Panel of Experts. Revised edition. New York, United Nations

UNESCO/UNEP, 1979 Programme for the Development of Ecological Pilot Projects in Tropical Forest Areas, Integrated approaches to coastal zone management and river basin development through implementation of pilot projects at Puerto Galera and Agno River Basin, Philippines. Final report. December 1979. Vol.1 Paris, Unesco, MAB Secretariat, 247 p.

Anon, 1982 Marcos tells energy officials to hurry. Philipp.Daily Express, 26 October 1982 issue

B. THE NAM PONG BASIN (THAILAND)

by

Thiraphan Bhukaswan
National Inland Fisheries Institute
Department of Fisheries
Bangkok
Thailand

ABSTRACT

The main features of the Nam Pong River Basin Development in Thailand are a hydroelectric dam, and a downstream situated irrigation system. Since the dam closed the river in 1965, fishing has considerably improved the diet and income of a number of farmers. In 1978, there were 5,628 fishermen operating on the Ubolratana reservoir, who captured 1,846 tonnes of fish which is equal to a fish yield of 47 kg/ha/yr. Fisheries management practices have included stocking of 19 species of fish, some of which have become prominent in fish yields: Trichogaster pectoralis dominated the yields between 1969 and 1972. Fish processing involves smoking, salting and fermenting. In 1982, aquaculture in the Nam Pong River Basin was practised in 4,336 fish ponds and other water bodies, with a total surface area of 665 ha, and in 437 ha of paddy fields; the total fish production was 1,134 tonnes. In “other water bodies” stocking has improved annual fish yield from 90 kg/ha to 300 kg/ha. Socio-economic evaluation of fisheries has shown differences in profit in different areas. In one village, 80% of the fish captured were consumed in households, with the rest sold or bartered. In another area, 80% of fish captured were sold, while the rest was consumed.

An irrigation system for 42,287 ha of land downstream from the reservior is almost completed, and cultivation practices are shifting from one rice crop per year to continuous rice production.

A benefit-cost analysis has shown that the river basin development project benefits are negligible, in other words, the project has been a poor financial investment.

Figure 1. The Nam Pong River Basin

1. INTRODUCTION

The Nam Pong River Basin covers an area of about 12,560 km², partly in the provinces of Petchaboon, Loei, Chaiyaphum, Udon Thani and Khon Kaen. Geographically, it lies between 16° and 17°30'N and 101°15" and 102°45" E (Fig. 1). The upper part of the basin is mountainous and covered with different forest types. The lower part consists mainly of paddy fields, and is more heavily populated. Five major rivers, i.e. the Huai Som, Lam Phaniang, Nam Pong (including Nam Mo and Nam Phuai), Huai Bong and Nam Choen (including Nam Phrom), enter the reservoir.

The Nam Pong or Ubolratana Dam impounding the water runoff from the Nam Pong Basin for power generation was completed in 1965. The reservoir at its maximum storage elevation of 182 m above mean-sea level (MSL) has a surface area of 410 km² with an average depth of about 16 m, and the maximum storage of 2,550 million m³. At its minimum water level of 176 m, its surface area is 160 m², and the average depth is about 12 m (Fig. 2). The water discharged from the power house, or spilled, enters the Nong Wai diversion which irrigated 500 km² of land. In 1983, about 90% of this area was already irrigated. The use of water for irrigation determines the quantity and quality of water received by water bodies situated downstream.

2. PROFILE OF THE NAM PONG RIVER SYSTEM

2.1 Topography

The land surface in the watershed is generally undulating and sloping towards the east and southeast. The elevation of the relatively flat area around the reservoir is about 190 m MSL. The western watershed, from which the Nam Pong and the Nam Phrom originate, consists of many mountain ranges with an average elevation of 900 m MSL, and up to 1,300 m MSL at Phu Kradung. To the east of the western boundary, between the Nam Pong and the Nam Phrom, the Nam Choen originates from Phu Tham Porn, the elevation of which is about 260 m MSL. The Nam Pong and Nam Choen flow eastwards directly into the reservoir, while the Nam Phrom merges with the Nam Choen before discharging into the reservoir. In the north are mountains with the elevation of about 540 m MSL. The Lam Phaniang originates from the western region of Phu Phan and flows southwards into the reservoir. The southern watershed boundary at Phu Khieo has an elevation of up to 1,000 m MSL (Fig. 1).

The Ubolratana Reservoir (Fig.2) is relatively shallow with a depth ranging from less than one meter to 20 m. The inundated land was mostly paddy fields interspersed with shrubs and trees. The downstream and the irrigating areas are level to gently undulating. The elevation there ranges from 153 to 200 m MSL.

2.2 Climate

The climate is tropical monsoonal, with clearly defined wet and dry seasons. The hot season is from February to April, when the weather is hot and dry with the temperatures from 20°C at night to over 35°C at mid-afternoon. During the rainy season, covering the period from May to October, the southwest monsoon brings rain from the Indian Ocean. Heavy rainfalls occur in August and September, with a very heavy rainfall caused by typhoons originating in the South China Sea. Because of the rainshadow caused by mountain chains between the central plains and the northeastern plateau, typhoons are the major source of precipitation in Nam Pong River Basin. The average rainfall in this area is approximately 1,200 mm and is heaviest along the high ridges. The temperature during this period is moderate, ranging from 23°C to 32°C. The rainy season is followed by the cold season (November to January), when the northeast monsoon from mainland China dominates the region. The weather is cold and dry, with temperatures ranging from 12°C at night to 30°C in mid-afternoon.

Figure 2. The Ubolratana Reservoir at maximum and minimum water levels

2.3 Soils

Soils of the Nam Pong Basin were developed from parent materials of Pleistocene age and most of the soils are distinctly pale. In general, soils of the high mountains and steep hills in the western part of the basin area are latosols and lithosols and on the rolling hills and high plains in the east, soils are sandy ferruginous latosols. The eastern part of the basin is dominated by low humic grey soils and grey podzolic soils or red-yellow podzolic soils on alluvium. The major parent materials are old alluvium sediment, residum, and slope colluvium of acid rocks and granite. The soils have a thin surface horizon and they normally have a weak horizon development. Surface soils are mostly sandy loam or loamy sand, with a sandy clay or a sandy clay loam in the subsoils. The dry surface layer is generally a light grey colour which changes to brown when moist. Subsoils are yellowish-brown or reddishbrown in colour. The soils have a pH ranging from 4.5 – 5.0 (Wacharakitti et al., 1979).

These authors also described the soil characteristics on steep land in the west and on some hilltops in the eastern part of the basin.

2.4 Hydrology

The water balance study in the Ubolratana reservoir indicates that the average annual rainfall over the catchment area of the reservoir is 1,200 mm, or 14,400 million m³. The average annual runoff collected by the reservoir is 2,340 million m³, of which, around 14% is the result of direct precipitation into the reservoir. It is estimated that, of the annual inflow, approximately 15% is lost by evaporation, 60% is the regulated outflow, 20% is lost by seepage and the rest is being temporarily stored in the reservoir (Sethaputra et al., 1979). They have also reported that the groundwater levels, upstream and downstream of the reservoir, fluctuate in a seasonal cycle. On the average, the water level drops to 5 m in the dry season. Groundwater discharges into the reservoir and the streams throughout the year. The reservoir appears to have only weak interaction with the surrounding aquifers.

Prior to the construction of the Ubolratana Dam on the Nam Pong River, flooding of large tracts in the lower part area used to be a regular hazard. This did not only impede, but made agriculture virtually impossible in the wet season. Completion of the Ubolratana Dam reduced the flood peaks in the Nam Pong River. As a result, flooding occurs less frequently. However, the dam is less effective in flood control aspects as one moves further downstream.

2.5 Water quality

The quality of water in upstream tributaries is subject to watershed characteristics including morphology, geology, soils, plant coverage and land use, climate, hydrology and human related activities. All tributaries in the watershed, except the Nam Choen, have very low dry-season flow. In places, the water in the streams is impounded by earth dykes for dry-season use. The Nam Choen is kept running throughout the dry period by the water released from the Nam Phrom reservoir (Chulabhorn Dam). The runoff on the small tributaries occurs intermittently, while that in larger tributaries is continuous. The peak flood of the year is between late September and mid-October. Suspended particles, chemical components including nutrients, reach the reservoir mostly during the wet season. Heavy rains always result in high erosion, and this increases the amount of suspended particles with their organic and inorganic components in water.

In all tributaries the dissolved concentration of the essential nutrients (N,P,K) is usually low. This is because soils in watersheds of these tributaries are highly eroded with a low fertility. Faecal pollution has been recorded in all the tributaries throughout the year. Concentrations of dissolved solids are normal.

2.6 Groundwater

Groundwater plays a minor role in furnishing village domestic water supplies in the Nam Pong River Basin. The use of groundwater for irrigation has not yet been reported. The interaction of the fluctuating reservoir water level with groundwater is quite complex, both hydrologically and hydraulically. It was observed that the groundwater in Khon Kaen increased significantly in 1966, just after the first reservoir filling, and showed a mild increasing trend throughout the following years (Sethaputra et al., 1979). They believed that the increase in ground water level was probably the result of the impoundment of water in the reservoir. This observation may indicate that the reservoir is probably losing water to the confined aquifers as seepage.

The upstream groundwater levels showed seasonal fluctuations. The level rises during the rainy season particularly in June and July and declines during the dry season. Fluctuations are also due to groundwater movement into or out of the aquifers and evapotranspiration losses. Upstream groundwater movement was found to follow a similar pattern of surface drainage. Groundwater discharges into the Nam Pong River and the Ubolratana reservoir. However, the reservoir appears to have weak interaction with the surrounding water-table aquifers.

Seasonal fluctuations of downstream groundwater levels are similar to those upstream. Evapotranspiration losses and discharge to the Nam Pong River are belived to account for the decline of groundwater level in the dry season. The decline of groundwater levels are correlated resonably well with the estimated evapotranspiration in the irrigation area (Sethaputra et al., 1979).

2.7 Fish and the fisheries in the Nam Pong River system

The Department of Fisheries conducted a fishery biological study in the Nam Pong River system prior to the impoundment of the Ubolratana reservoir (Sidthimunka et al., 1968). They found 76 species of freshwater fish, mostly riverine species (Appendix A). The species composition was dominated by carps (31 species, contributing 59.9% by weight), catfishes (14 species, contributing 20.6% by weight), murrels (4 species, contributing 7.0% by weight) and other species (27 species, contributing 19.50% by weight). The average standing crop of fish caught by rotenone sampling was 117.50 kg/ha.

The subsistence fisheries - the only type prior to damming the Nam Pong River - was carried out by part-time fishermen, mostly farmers. They fished rivers, streams, lakes, canals and paddy fields. Although fish were abundant at certain times of the year, their distribution pattern did not allow intensive fishing. The fishing season in this region more or less coincides with the rainy season, starting in May or June and ending in December or January when the paddy fields, lakes and most of the natural water bodies dry up. During the dry season only a few farmers keep catching fish in the rivers and other remaining natural water bodies.

3. THE NAM PONG RIVER DEVELOPMENT PROJECT

The Nam Pong river project is located at Pong Neeb, about 50 km northwest of Khon Kaen town. It is a multipurpose project, serving the interest of hydropower generation, irrigation, fisheries enhancement, flood control, and recreation. The project consists of the Ubolratana Dam and power plant, a diversion dam at Nong Wai, and irrigation canals to be built on both banks of the Nam Pong River. The Nam Pong Resettlement Scheme, located about 36 km north of Khon Kaen town, and the Non Sang Resettlement Scheme located some 70 km northwest of Khon Kaen town are parts of the project (Fig. 3).

The preliminary investigtion and feasibility studies of the project were completed in 1959. The construction of the Ubolratana Dam was carried out from 1964 to 1965. The power plant was officially inaugurated on 14 March 1966.

3.1 Ubolratana Dam and hydropower plant

The Ubolratana Dam was constructed across the Nam Pong River at Pong Neeb, 50 km northwest of Khon Kaen town. The dam site is at the gorge where rock is dense and massive enough to resist the weight of the dam and the water pressure. Both sides of the river upstream of the dam are encircled with mountains, namely Phu Pan and Phu Pan Kam. The resulting reservoir contains 2,550 million m³ of water, and at full supply level it covers an area of 410 km². The dam type is rockfill with clay core, 800 m long at the crest, 32 m high at the maximum section. The thickness at the maximum section is 120 m at the dam base and 6 m at the crest.

The spillway is located on the right abutment. Each of the four overflows is 14.50 m wide. These overflows are capable of discharging 2,500 m³/sec. The radial gates are 19.5 m wide by 6 m high each.

The power plant is located on the left abutment. It is a semi-outdoor, reinforced, concrete building. Inside this building are 3 Kaplan type turbo-generating units. Each unit has a 8.3 MW generator. The average annual energy production is 65 million kwh.

Three penstocks 4.5 m in diameter are present. The intake water level is at 167.41 m MSL. The possible maximum operating head, or drop from the surface of the reservoir to the river immediately downstream of the power plant is 18.5 m.

The energy generated from the Ubolratana power plant is distributed to 8 provinces in the northeast, namely Khon Kaen, Udon Thani, Nong Khai, Kalasin, Maha Sarakham, Roi-et, Chaiyaphum and Nakhon Ratchasima. The distribution system comprises 115 kv transmission lines interconnecting 6 sub-stations located at Khon Kaen, Udon Thani, Phol, Maha Sarakham, Nakhon Ratchasima and Nong Khai.

Figure 3. The NAm Pong river Development Project showing the dam site, reservoir, re-settlement and irrigation areas

3.2 Nong Wai irrigation system

The Nong Wai irrigation system was designed for 42,287 ha (264,292 rai) of land which was limited to rainfed cropping in the past. Under the irrigation scheme, either additional rice crops or other types of cultivated products are feasible. The construction of Nong Wai diversion dam and other engineering works were completed in 1967. The irrigation system on the right bank of the Nam Pong River was completed in 1982, comprising 47 km of main canal, 80 km of laterals and 61 km of sublaterals, covering an area of 7,340 ha. The left bank was developed in two phases. The first phase was completed in 1979, comprising 40 km of main canals, 55 km of laterals and 60 km of sublaterals, covering an area of 9,860 ha. The second phase comprises of 43 km of main canals, 190 km of laterals and 197 km of sublaterals, covering the area of 22,045 ha. By the end of 1982, the main canal was completed together with 79 km of laterals and 82 km of sublaterals, covering an area of 7,340 ha. The rest is under construction and expected to be completed by the end of 1985.

The Nong Wai irrigation system will provide enough water for agricultural purposes. The cultivation practices in the area would shift from the rainy season single rice crop production to throughout-the-year rice crop production. Also by introducing cultivation of upland crops, which secure a higher earning rate, this plan is envisaged to improve the management of agriculture and to increase the profitability of agricultural production.

3.3 Resettlement

The development of the resettlement areas has been underway since 1964 for the benefit of the farmers who lost their land to the Ubolratana reservoir and to a few farmers who had moved from other places and needed land for farming. The displaced population was of the order of 4,000 families or around 20,000 persons. They have been resettled to Nam Pong and Non Sang, which are 36 km and 70 km distant from Khon Kaen town.

4. UBOLRATANA RESERVOIR, A NEW FISHERY RESOURCE

Prior to the completion of the Ubolratana Dam, the Department of Fisheries sent a study team to investigate the fishery status in the proposed inundated area. However, due to staff and budget limitations, only information on ichtyofauna was collected during the study (Sidthimunka et al., 1968). As mentioned already above, they recorded 76 species of freshwater fishes from the area (Appendix A).

4.1 Physico-chemical properties of impounded water

Surface water temperature is closely related to atmospheric temperature fluctuations. The water temperature exhibits three typical profiles which characterize the cold season, the transition, and the hot season. During the cold season, water temperature profile is usually uniform with slight variations in the top layer during the day and night. In the transition period from the cold to hot season, the water temperature in the top layer increases and a thermocline forms (Srisuwantaj, 1970; Jindarojana et al., 1979); this is followed by a through mixing during the hot and rainy seasons.

Dissolved oxygen (DO) in the reservoir water is mainly supplied by photosynthesis and agitation. Photosynthesis is predominant when the water is clear, while the agitation is more important during windy and stormy weather when water turns turbid which reduces the photosynthesis. The depletion of DO is caused by the decomposition of organic matter in the water and in the sediment. The average annual sediment inflow into the Ubolratana reservoir is estimated 2 million tons (Jindarojana et al., 1979). Almost all sediment is retained in the reservoir. Large particles are deposited near the point of the inflow, small particles (0.2 mm) are found in the middle portion, and very fine particles are found in the lower portion of the reservoir near the dam.

Concentrations of N,P and K are low. These elements are both dissolved and bound with sediments.

The quality of water in different areas of the reservoir slightly varies in terms of organic constituents. The water in the upstream part usually contains higher concentration of suspended materials than the middle and lower parts of the reservoir. The mean electric conductivity of the reservoir water is around 80 microhos/cm during floods and 150 micromhos/cm during the dry season. The pH of impounded water is slightly above 7. However, it may rise above 8 during the dry season. The impounded water usually contains high concentrations of coliform bacteria which enter the reservoir from the fishing villages scattered along the shoreline.

The tailwater quality is similar to that of the reservoir in front of the penstock intake, and since the water is usually drawn deep below water surface, with the intake at 162 m MSL, the dissolved oxygen in the discharged water is usually low or depleted. Along the flow path downstream, DO is continuously increased by stream reaeration. At the Nong Wai diversion dam the water is aerated vigorously and becomes saturated with dissolved oxygen. Do in the water downstream of the diversion dam is usually more than 6 mg/1 throughout the year.

The pH of the Nam Pong downstream of the dam is around 7. Water turbidity, low at the dam tailwater, gradually increases as it receives sediments from scouring and during the rains the mud from river banks. The water is usually poor in plant nutrients. Potassium is the only plant nutrient available in relative abundance. The water has a low concentration of organic substances. The BOD of the water is low throughout the year, even through the COD is high. While the numbers of coliforms and total bacteria in the water below the dam are usually low, they increase gradually with distance due to the faecal pollution from the river banks.

4.2 Plankton

The primary production of the Ubolratana reservoir fluctuates seasonally, being moderately high in summer, relatively low in rainy season and increasing again after that. Jaiyen et al., (1980) identified 26 species of plankton, i.e. algae which are dominated by Melosira, Microcystis, Pediastrum, and Ceratium. Their standing crop is generally higher in the central area of the reservoir than at the inflow areas, and it is the highest in May.

Copepods are the most abundant zooplankton, followed by cladocerans, rotifers and protozoans. The highest standing crop of zooplankton is found in the inflow areas in April. The blue-green algae were the commonest nanoplankton. They have a similar pattern of occurrence as that of the other phytoplankton. Filamentous blue-green algae, bryozoans and protozoans are the most common periphyton found on the submerged trees from the water surface down to 3 m depth.

4.3 Aquatic macrophytes

Eighteen species of aquatic macrophytes were found in the Ubolratana reservoir in 1980 (Varikul et al., 1980) as compared to 35 species recorded during 1981–82 (Watanadilokgul and Sribanjaem, 1982), (Table 1). Almost all were in the littoral, at a depth of one meter or less, except Potamogeton. The witchgrass (Panicum) was the most abundant species, followed by the Florida elodea (Hydrilla verticillata) and pond weed (Potamogeton). Panicum and Potamogeton dominated during the dry period (November to May), and disappeared in July, as water level reached its peak. The Florida elodea increased during the low water level period, and then disappeared in the early rainy season (May to June) due to a high turbidity (Varikul et al., 1980). The aquatic macrophyte invertebrate fauna is represented predominantly by insects. The mean number and mean weight per m² of invertebrates associated with aquatic macrophytes were 3,034 and 1.48 gm respectively.

4.4 Benthic fauna

Annelids, chironomids, chaoborids, oligochaetes and molluscs dominated the benthos which mostly concentrated down to 6 m depth. The others recorded were ceratopogonids, ostracods, Caenis and some other insect larvae. Their abundance varied from area to area, but was generally higher in open-water than in the inlet areas. The richest area was 2 m depth, but the 0.5 m to 3.5 m depths were generally productive.

4.5 Fish species composition

Changes of fish species composition were observed within one year of the impoundment. Only 52 species were collected by the rotenone treatment as, compared to 76 species prior to impoundment. Of these, 44 species were the same as in the river, and 8 species were new records. The samples were dominated by carnivorous species of murrels (Channa) which comprised 34.8% by weight compared to 24.1% for carps, 1.19 for catfish, and 29.2% of miscellaneous species (Bhukaswan and Pholprasith, 1977).

Further investigations with rotenone sampling showed fluctuations in fish species composition: 76 species in 1965, 52 in 1966, 62 in 1967, 73 in 1969, 58 in 1970, 67 in 1971, 68 in 1973 (Bhukaswan and Pholprasith, 1977), and only 37 species in 1981 and 1982 (Nookour and Pawapootanon, 1982) as shown in Appendix A. The following species eventually disappeared from the impoundment: Rasbora heteromorpha; Barilius quttatus, Labeo bicolor, Crossocheilus reba, Mekongina erythrospila, Botia beauforti, Pteropangasius cultratus, Bagarius bagarius, and Trichogaster microlepis. Several species became dominant such as Pristolepis fasciatus, Cyclocheilichthys apogon, Trichogaster trichopterus, Osteochilus hasselti, Notopterus notopterus, Hampala dispar, Puntius leiacanthus and Channa striata. Some species were found only in post impoundment samples such as Mastacembelus circumcinctus, Rasbora borapetensis, Puntius viehoeveri, Osteochilus duostigma, Labiobarbus lineatus, Clarias macrocephalus, Mystus atrifasciatus and Chanda siamensis. The differences were presumed due either to insufficiency of the sampling method (rotenone) and sample collecting and/or due to accidental infiltration from other areas.

* Reported by Varikul et al., (1980)

4.6 Fish standing crop

The estimation of standing crop of the Ubolratana reservoir was based on data collected from rotenone sampling, which was the only source of information available. Although this method gives only a rough estimate of the fish yield, it is still a useful tool for assessing the annual changes in fish stock. As known for other reservoirs, the fish standing crop of the Ubolratana also rapidly increased during the first two years of impoundment. Thereafter, it started decreasing to reach a minimum in 1970. Afterwards, there has been an increase with the maximum standing crop recorded in 1983 (Table 2).

The commercial catches per unit surface area have shown year to year fluctuations, but no substantial long-term changes have taken place. The maximum was recorded in 1976 which was approximately 3 times greater than that of the second year after impoundment (Table 2).

5. FISHERY DEVELOPMENT IN THE UBOLRATANA RESERVOIR

5.1 The fishermen

Fisheries in Ubolratana reservoir started shortly after the establishment of the impoundment in 1965, when farmers living in villages nearby found fishing the reservoir a rewarding activity. The first fishermen were those farmers who lost their land by inundation and squatted around on whatever land was left, sometimes with relatives, instead of moving elsewhere. The unusual abundance of fish during the first few years together with the relatively low number of fishermen resulted in an exceptionally good catch per person.

These people were soon followed by others, mostly rice farmers, who became attracted by the high income from fishing. The nearby farmers were beginning to move into the reservoir for fishing on a permanent basis. This process was made easy by the fact that migration has been part of the northeast culture and most of the farmers have had experience in fishing with one kind of fishing gear or more. Due to no restriction on entry to the reservoir margin where land is publicly owned, new opportunity provided by fishing was soon exploited to the utmost.

The number of fishermen operating in this reservoir have continuously increased from 268 in 1966 (Sidthimunka et al., 1972), to 3,556 in 1975 (Bhukaswan and Pholprasith, 1977), and to 5,628 in 1978 (Suetrong et al., 1979).

5.2 Fishing gears

Fishing in the Ubolratana reservoir is permitted 24 hours a day throughout the year. The commercial catches were recorded since the beginning of commercial landings in the second half of 1966. Records of fish landings were collected at six landing centres. They are at Tha Rua Ubolratana, Ban Poh-Tak, Ban Nong Tum, Ban Wang Hin Sa, in Khon Kaen province and at Ban Non Sang, Udon Thani province (Fig. 4). Landing statistics were recorded on daily basis at Tha Rua Ubolratana and at Ban Poh-Tak, the others were collected from random sampling done every two weeks. Total weight of fresh and processed fish (smoked, salted and fermented fish) were recorded. Those of processed fish were converted into weight of fresh fish by multiplying with a specific constant. The ratios used for converting weight of processed fish to weight of fresh fish are 1:3, 1:2 and 1:0.8 for smoked fish, salted fish, and fermented fish respectively. The fish were landed as follows: 60% at Tha Rua Ubolratana, 20% at Ban Wang Hin Sa, 10% at Ban Poh-Tak, 5% at Ban Nong Tum, 3% at Ban Non Sang, and 2% at Ban Fah-Liam (Ubolratana Reservoir Fisheries Research Station, 1984).

* Only 6 months commercial catch data available

The commercial catches have fluctuated from year to year. High fish catches were recorded in 1969, 1971, 1974, 1976, 1977 and 1983, while low catches were recorded in 1975, 1979, 1980 and 1982 (Table 3). Records of monthly catches show seasonal fluctuations. Catches usually increase during the low water-level period (November to April).

Cyprinids have dominated the catch, contributing 69.41% (15 year average) to annual fish landings since 1969 (Table 2). The major fish species in the commercial catches were Cirrhinus jullieni, Puntius spp. (mainly Puntius lieacanthus), Corica goniognathus, Puntioplites proctozysron, Osteochilus hasselti, and Morulius chrysophekadion respectively. These contributed 88.21% to the annual catch in 1976. Over the last 15 years these six major species formed 79.65% of the total catch (Table 4).

5.4 Fish stocking

Fish stocking programme has been practised in the Ubolratana reservoir since the filling period. The purpose of stocking is to provide more food fish by utilizing food resources not used by the local fish species, and to control aquatic vegetation in the impoundment. For this, the grass carp (Ctenopharyngodon idella), Thai silver carp (Puntius gonionotus), and the sepat-siam (Trichogaster pectoralis) were introduced immediately after the dam was closed. Plankton feeders such as the bighead carp (Aristichthys nobilis), and silver carp (Cirrhinus molitorella) were also stocked. Pangasius sutchi and Probarbus jullieni were introduced to feed on benthic organisms and molluscs. Later, several other species were added, and so far 19 species have been stocked, totalling 5.8 million fingerlings (Table 5).

It is difficult to evaluate the success or failure of stocking programme due to insufficient data on recapture. Several species of stocked fish were indigenous species which were found living in the inundated areas prior to the impoundment, thus it is impossible to identify which one is native or additionally stocked. The introduced sepat-siam (Trichogaster pectoralis) dominated the yield particularly during 1969–1972, but the other introduced and stocked species have not yet been found in significant numbers.

However, some introduced species have shown a very good growth rate. For example, the grass carp reached 12.40 kg in 2 years; silver carp 5.8 kg in one year; rohu (Labeo rohita), Cyclocheilichthys enoplos, and Datnoides microlepis reached 5.40 kg, 2.60 kg, and 2.6 kg respectively in 3 years, and Probarbus jullieni a weight of 10.70 kg in 4 years (Bhukaswan and Pholprasith, 1977).

5.5 Aquaculture development

Fish raising programme was launched in Khon Kaen province in 1954 when a fisheries station was established in this province. Fish are raised in ponds for household consumption, and the excess of fish produced is sold to neighbours. Most of these fish ponds are small. Rice-cum fish is also practiced in the irrigated areas. Favourable fish species being raised are Oreochromis niloticus, Cyprinus carpio, and Puntius gonionotus. Others include Labeo rohita, Channa striata, Clarias batrachus and Pangasius sutchi. Statistics in 1982 showed 4,336 fish ponds with a total surface area of 665 ha, and 437 ha of paddy fields to be used for fish culture in Khon Kaen province (Table 6).

* Total for six months only

* Numbers in parentheses represent the total annual catch

Besides raising fish in ponds and paddy fields, fish are also being stocked in various water bodies throughout the basin in order to provide a better fishery resources to the rural inhabitants. In 1983, a total of 6,443,800 fish fingerlings were stocked in 370 water bodies covering a surface area of 46,690 ha (291,815 rai). Stocked fish were Oreochromis niloticus, Cyprinus carpio, Puntius gonionotus, Labeo rohita, Aristichthys nobilis, Cirrhinus molitorella and Ctenopharyngodon idella.

With the development of Nong Wai irrigation project, the Fisheries Department has introduced fish raising and fish stocking programmes into Nong Wai irrigated area since 1978. These programmes are well established, with 183 fish ponds (31 ha) and 96 paddy fields (65 ha) being used for fish culture, and 16 impoundments (230 ha) stocked with 604,300 fish fingerling (5–7.5 cm long) in 1983.

The fish yield derived from aquaculture in Khon Kaen province has been increasing since 1975. It was 280 metric tons in 1975, 551 metric tons in 1978 and 1,134 metric tons in 1982 (Table 6). The average annual fish yield in the impoundments following the stocking programme was improved from around 90 kg/ha to 300 kg/ha.