Lake Songkhla
Location:	7°10'-7°50'N, l00°05'-100°40'E; on the east coast of Peninsular Thailand, extending 0-90 km north of the town of Songkhla, Songkhla and Phatthalung Provinces.
Area:	104,000 ha.
Altitude:	Sea level.
Biogeographical Province:	4.7.1.
Wetland type:	01, 07, 08, 14, 18, 19 & 21.
Description of site:	A huge, shallow, coastal lagoon of fresh to brackish water, which opens to the sea by way of a short, narrow channel at the town of Songkhla on the southern shore. The lake is fed by about 100 streams and drains a total basin area of about 8,000 sq.km. The lake system is thought to be no more than 2,000 years old, having become isolated from the sea by the development of beach ridges. A great many small villages containing approximately 80,000 persons are scattered around the lake shore, most of these on the eastern side. The lake is usually divided into four distinct regions: from south to north, these are Thale Sap Songkhla, Thale Sap, Thale Luang and Thale Noi. Thale Noi lies to the north of the main lake and while it is best regarded as merely one part of the entire Songkhla Lake system, it has a number of special features which merit treatment as a separate site (site 37). Songkhla Lake is influenced by run-off from the steep, mainly forested mountains to the west and by the introgression of salt water from the sea. Water quality varies greatly throughout the different parts of the lake; there is much seasonal and spatial variation in salinity and turbidity. In Thale Sap, the salinity declines from a maximum of 5.3 p.p.t. in November to only 0.7 p.p.t. in January, following input of heavy rainfall. The turbidity is highest near the shoreline and increases to a maximum of 95-100 FTU in January. During the drier months, March to August, it is around 30-50 FTU. The average depth of the lake is about 1.0-1 .5m over most areas, and the maximum depth, 2.5m. There are, however, considerable fluctuations in water level. At the Thale Sap Non-Hunting Area, the average depth in December, at the height of the monsoon, is l.46m. This declines to about 0.5m by August. The average tidal range at the mouth of the overflow channel is approximately 0.5m, the maximum, 1 .3m. Detailed information on the water regime of the entire lake basin is available in Sinclair et al.(1985).
Climatic conditions:	Tropical monsoonal climate with an average annual rainfall of 2,094 mm. There is, however, is a great deal of variation in the annual rainfall; in 1983, only 983 mm were recorded. Some 60% of the rain falls during the northeast monsoon, from October to December. The wettest month is usually December, while the driest months are from January to April. The mean relative humidity is 79%, with a minimum of 76% in March and a maximum of 84% in November. The mean daily temperature is 27.6°C (maximum 28.7°C in April, minimum 26.6°C in December). Prevailing winds are easterly during November to April and southwesterly during June to October.
Principal vegetation:	A total of 19 species of aquatic plants has been collected from the Kukut area of Thale Sap. The chief emergents and lake shore plants include Scirpus litoralis, Paspalum vaginatum, Eleocharis dulcis, Fimbristylis ferruginea, Cyperus distans and C. stoloniferus. In addition, there are small areas which are dominated by a mangrove-type community, the component species being Sonneratia caeseolaris, Rhizophora apiculata, Nypa fruticans and Acanthus ebracteatus. At Songkhla, this community occupies waters with a much lower salinity than is typical. Some other lake shore plants, such as Melaleuca leucadendra, Hibiscus tiliatus and Olax scandens, are more typical of sandy, coastal conditions. The chief submerged and floating aquatic species are Chara sp, Ceratophyllum demersum, Hydrilla verticillata, Lemna purpusilla, Najas spp, Pistia stratiotes and Potamogeton malayanus. The principal vegetation in surrounding areas is rice paddy and Borassus palms with some areas of Melaleuca scrub.
Land tenure:	The lake is in public ownership; surrounding areas are privately owned small-holdings.
Conservation measures taken:	Thale Sap Non-Hunting Area covers 31,500 ha, 48% of which is terrestrial. Thale Noi Non-Hunting Area (45,000 ha), at the north end of the lake, is described separately as site 37. The endangered River Terrapin Batagur baska is bred at the Coastal Aquaculture Institute in the town of Songkhla. The shrimp Macrobrachium rosenbergii is also bred in captivity and released into the lake.
Conservation measures proposed:	The proposed establishment of an information centre, together with the imposition of visitors' entrance fees and various improvements in infrastructure, are all aimed at directing benefits to local people who live in and around the sanctuary (Marshall, 1984). If the area were better protected, the reintroduction of Batagur baska might be considered.
Land use:	Chiefly fishing for molluscs, crustaceans and fish, together with some aquaculture. A variety of traps and nets are used. Aquaculture is beginning to be developed, with small areas of ponds for the culture of Machrobrachium rosenbergii and for sea-bass. (Anon, 1984). There is some cattle grazing around the lake. Local people utilize various aquatic plants such as Eichhornia and Ceratophyllum for animal fodder and others such as Eleocharis and Scirpus for weaving mats etc. Surrounding areas are extensively farmed. Over most of the lake basin (1,648 sq.km) there is one crop of rainfed, wet-season rice per year. Field preparation takes place from August, with most planting in October and the crop being harvested in March. Some 808 sq.km are given over to irrigated rice cultivation. The palm Borassus flabellifer is cultivated as a source of sugar and for its fruits. Some caves in limestone islands and other outcrops are important as sources of birds' nests and bat guano. These are leased from the government by a private company and therefore do not directly benefit the local people. There is also a small amount of tin mining in the basin.
Possible changes in land use:	There is a proposal to construct a salinity barrier in the northern part of the lake, dividing Thale Luang from Thale Sap. This would enable fresh water to be stored in Thale Luang during the wet season in order to extend irrigation schemes, thereby enabling farmers to grow a second crop of rice. (Sinclair et al., 1985). The consequences of such a scheme are potentially very serious. The lower part of the lake, Thale Sap, would change from being brackish to being permanently saline and this would greatly change the species composition and abundance of aquatic plants and animals. The water level in Thale Luang would be raised for long periods and this would increase flooding of areas around the lake. The movements of economically important species such as Macrobrachium rosenbergii, which spawns in brackish water and grows to maturity in fresh water, together with clupeid and other fishes, would be disrupted. The industrialization and development of the basin will certainly lead to a rapid increase in the demands for water. In the water catchment area, Sinclair et al. (1985) list seventeen discrete ongoing or committed development projects in the fields of agriculture, aquaculture and construction, which will have direct impact upon the lake basin. Deep water access to the town of Songkhla is to be improved in order to facilitate its development as a port. A new bridge has recently been constructed across the mouth of Lake Songkhla and a new highway is to be constructed across the basin.
Disturbances and threats:	Apart from the above, the level of human use is such that larger wildlife has been hunted out, while many smaller species are subject to continual disturbance. The eggs of some waterbirds, together with many frogs, some reptiles and perhaps small mammals, are taken for food. Over-harvesting of the eggs of the River Terrapin Batagur baska, combined with the slaughter of great numbers of adults, has already destroyed a natural resource of great economic value. Repeated burning or cutting of emergent lake shore vegetation may be the reason for the scarcity of Phragmites and other suitable nesting habitat for large water-birds. Fish yields are said to be lower per unit effort than formerly, although no data have been collected to test this. The decline in fish yields may be due either to over-fishing or to deleterious environmental change. A pumping station at Ranot, near the northern end of the lake, was constructed in order to draw off fresh water for irrigation projects. This led to increased salt water introgression and the practice has since been discontinued.
Economic and social values:	The resources of the lake basin have tremendous impact upon the economy of the region. Approximately 80,000 people (5% of the population of the entire basin) live around the shores of the lake and directly exploit its resources, while as many as 500,000 people benefit in some way from these resources. The annual yield of fish, obtained from both aquaculture and wild capture, is estimated as 7,000 tonnes per year (Sinclair et al., 1985). Net annual income per person is estimated at Bht.7,000 (US$270) per year, an equivalent amount being earned from rice cultivation. The annual yield of rice from the lake basin is 518,000 tonnes (Sinclair et al., 1985). There are approximately 40 edible species of fish in the lake. In addition, many molluscs, crustaceans, insects, amphibians, reptiles, birds and mammals are either eaten by man or used for feeding to domestic stock. The aquatic vegetation is an important source of food for cattle. A total of 29 aquatic plant species and 48 plant species which grow wild in surrounding areas are utilized in some way by villagers. Because of its proximity to Hat Yai, the largest city in southern Thailand, the lake has important recreational and educational values. It also has important research potential and is already receiving study under a project administered jointly by the Prince of Songkla University in Hat Yai and the Institute of South-East Asian Biology, University of Aberdeen.
Fauna:	There are thought to be several hundred species of fish in the lake, of which 100 species are abundant. Of 66 species collected in the vicinity of the Thale Sap Non-Hunting Area, 26 were freshwater species, 28 brackish to brackish/marine and 12 fresh/brackish or fresh/brackish/marine (Marshall, 1984). Approximately 140 species of birds have been recorded from the Thale Sap Non-Hunting Area. Most larger species, such as egrets, are present only as winter visitors. The most abundant breeding or apparently resident species are Tachybaptus ruficollis, Ixobrychus sinensis, I. cinnamomeus, Dendrocygna javanica, Nettapus coromandelianus, Gallinula chioropus and Porphyrio porphyrio. The lake is important as the only known breeding site for Himantopus himantopus in the Malay Peninsula. Wintering concentrations of over 2,000 each of Dendrocygna javanica and Nettapus coromandelianus have been recorded, together with a few hundred Anas querquedula. At least 19 species of Odonata have been recorded among seven aquatic insect orders in total. The macrobenthic fauna is dominated by Nereidae, Gammaridae and Chironomidae. The overall species diversity of Crustacea is very high. A few River Terrapins Batagur baska may still be present. The species formerly nested in large numbers at Khao Chaison, on the western shore of Thale Sap. Otters, probably Lutra perspicillata, are reportedly present on the lake.
Special floral values:	None known.
Research and facilities:	Accommodation is available at the headquarters of the Thale Sap Non-Hunting Area at Kukut, and boats can be rented. A project on the biological resource potential of the Kukut area is being conducted jointly by the Botany Department, Prince of Songkla University, and the Institute of Southeast Asian Biology, University of Aberdeen, U.K.
References:	Anon (1981); Marshall (1984); Sinclair et al. (1985).
Criteria for inclusion:	1b, 1e, 2b, 2c, 3b.
Source:	Jira Jintanugool and Philip D. Round.