Gulf of Thailand
Location:
l3°l0'-l3°33'N, 99°57'-l0l°02'E; the inner Gulf of Thailand in the vicinity of Bangkok. The site extends from Ban Pak Thale, Phetchaburi Province, in the west, north and east past the mouths of the Mae Klong, Tachin, Chao Phraya and Bang Pakong Rivers, to the town of Chonburi, Chonburi Province, in the southeast.
Area:
Length of coastline approximately 150 km; in some areas, the mudflats exposed at low tide extend up to two km from the shore.
Altitude:
Sea level.
Biogeographical Province:
4.5.1.
Wetland type:
01, 02, 06, 07, 09 & 10.
Description of site:
A large area of intertidal mudflats around the shores of a huge, shallow sea bay forming the estuary of four major rivers, the Mae Klong, Tachin, Chao Phraya and Bang Pakong. The area formerly supported extensive mangroves. While the largest areas have now been cleared for aquaculture and salt pans, much secondary mangrove still remains and is usually found as a narrow (10-l00m) fringe along the seaward margins. Extensive areas of low scrub are found in the brackish marshes along the landward edge. In places, the open shrimp ponds and salt pans extend two to three km inland and, together with the offshore mudflats, provide an important feeding and roosting area for many thousands of shorebirds. The human population density is extremely high, and there is an increasing amount of heavy industry, especially extending eastwards from Bangkok along the lower reaches of the Chao Phraya River. The water regime is extremely complex, with great variations in turbidity and salinity influenced by seasonal variation in the amount of freshwater entering via the rivers and by direct run-off from the land. The bay is very shallow, the sea-bed sloping gently to a depth of six metres 10-20 km offshore. The tidal amplitude varies from l.4m at neap tides to 3.8m at spring tides. There are usually two high tides and two low tides per day, but these are often asymmetrical. Throughout the months December-January, the mudflats are covered throughout the daylight hours.
Climatic conditions:
Tropical monsoonal climate with an average annual rainfall of 1,418 mm, 85.8% of which falls during the southwest monsoon (May to October). The mean annual temperature is 28.1°C (range 9.9-39.9°C).
Principal vegetation:
Mangroves in which species of Rhizophora are usually dominant. Nypa fruticans is frequent in the understorey. Extensive degraded areas are dominated by the fern Acrostichum aureum. Large areas of "back mangrove" are dominated by scrub formations grading into Typha marsh in freshwater areas. Other areas inland are mainly cultivated (orange groves, coconut groves and rice paddies) or urbanized.
Land tenure:
The wetlands are mainly state owned. Areas of shrimp ponds and salt pans are occupied both legally and illegally by the operators. Some areas are owned by the Military. Surrounding areas are privately owned farmland and households.
Conservation measures taken:
No protected areas have been established. The Association for the Conservation of Wildlife formerly maintained a few bird observation hides at Bang Pu, four km east of the Chao Phraya river mouth, but these have fallen into disrepair. Some small patches of mangrove derive a measure of protection from the proximity of Buddhist temples, and some reseeding of mangrove has been undertaken.
Conservation measures proposed:
Parts of the area, including selected mangrove, shrimp pond and intertidal habitats, should be set aside as Non-Hunting Areas. The most suitable areas, both in terms of their mangrove resources and in terms of the numbers of roosting and feeding shorebirds which they support, lie between the mouths of the Tachin and Mae Klong rivers and in the major mangrove inlet which lies between the towns of Phetchaburi and Samut Songkhram. Existing legislation should be enforced in order to prevent further encroachment into mangroves and also to protect shorebirds against hunting. Educational and recreational facilities, such as bird observation hides, a nature centre and wooden walkway nature trails through the mangrove, should be established.
Land use:
Fishing from boats, with trawl nets and gill nets; aquaculture for penaeid prawns; salt production. The area is also a rich source of crabs and shellfish. There is an important fishery of the Green Mussel Perna viridis at the mouth of the Bang Pakong River, while cockle culture is practised in Phetburi Province, at the western extremity of the site. Some cockles are also harvested when young and then shipped to southern Thailand for rearing in shellfish beds at Bandon Bay and other localities. Fruits of the Nypa palm are harvested for food. Mangroves are cut for polewood (used in construction and fencing) and for charcoal production. Land use in adjacent areas includes cultivation (wet-season rice, with small areas of second crop rice, coconuts, orange groves and vegetables), housing and industry.

Prawn farming is at present undergoing a transition. The old-style, shallow, naturally-seeded ponds are being replaced by deep, intensively managed ponds which are seeded with purchased larvae. Land prices are escalating rapidly.
Possible changes in land use:
There is an increasing amount of industrialization and urban development throughout the area. There has been a recent proposal for a project to establish an "integrated fishing and industrial community" in the Tachin River estuary. Some 2,400 ha on both banks of the estuary would be affected by reclamation and dredging for the development of a huge marine port and industrial estate with support industries (e.g. fish processing and canning plants). The proposal was made by the Department of Fisheries and has been approved by a joint public/private coordinating sub-committee, which is to forward it to the Policy and Planning Committee in the Ministry of Agriculture.

There is increased industrialization and urban development in the water catchment area. The construction of two large hydro-electric dams on the Khwae River system is believed to have resulted in reduced freshwater inflow from the Mae Klong River. A third such dam has been proposed (the Nam Choan Dam), but this project has recently been shelved.
Disturbances and threats: If the project to establish a fishing and industrial community in the Tachin River estuary is carried out, it will almost certainly have a major destructive impact upon the most important areas for migrant and wintering shorebirds. An important staging area for Limnodromus semipalmatus appears to lie in the heart of the area proposed for reclamation. The project would also damage the local aquaculture and fishery interests. The site is under great human pressure through continued cutting of mangroves and the reclamation of marshy areas for building land. Feeding and roosting areas for shorebirds are being lost as shallow prawn ponds are replaced by deeper, steep-sided and intensively managed ponds. There is a considerable amount of pollution from both industrial waste and raw sewage, and this may be linked to the occasional occurrence of "red tides", caused by sudden blooms of dinoflagellates. In addition, there is widespread hunting of shorebirds and herons for food; birds are both shot and netted. Cultivated areas are suffering as a result of the encroachment of salt water which may be a direct result of the major hydro-electric schemes in the water catchment area.
Economic and social values: The site makes an immense contribution to the living standards of the local inhabitants and people of Bangkok, as a source of seafood and raw materials. The towns of Samut Sakhon and Samut Songkhram are important fishing ports at the mouths of the Tachin and Mae Klong Rivers respectively. The main rivers and interconnecting canals which ramify through the area are important for communications. The site also has immense potential for both research and recreation, due to its proximity to Bangkok.
Fauna: The area is of international importance as a staging and wintering area for shorebirds. There have been no complete counts at times of peak passage, but there is good reason to believe that the site regularly supports concentrations of 10,000-20,000 shorebirds of up to 36 species. An aerial survey in October 1984 revealed 11,310 shorebirds (Parish & Wells 1985). The numbers of birds present in winter may be smaller; the predominant species at this time are Pluvialis dominica, Charadnius alexandninus, C. mongolus, Tninga tolanus, T. stagnalilis. T. glaneola and Calidris ferruginea. Concentrations of over 2,000 of each of these species are regular. The site annually supports more than 300 Tninga erythropus from December to March. Concentrations of up to 130 Ardea cinerea and 36 Mycteria leucocephala have been recorded, together with the occasional Pelecanus philippensis. A spectacular concentration of Asian Dowitchers Limnodromus semipalmatus occurs each spring, when over 500 birds have been recorded on mudflats to the west of the Tachin River during the first week of April. Passage is spread from about mid-March until early May, and so the total number of birds using the site is probably much higher. Several hundred Limosa limosa and L. japponica are also present at the same time. Some 5,000-10,000 gulls and terns (chiefly Larus brunnicephalus and Chlidonias hybrida) are present in late autumn and winter.
The site is also important for breeding birds. There are several colonies of Egretta garzetta and E. alba in the mangroves, and Butorides striatus and Haliastur indus are common and widespread. Both Himantopus himantopus and Sterna albifrons breed in shrimp pond habitats. The mangroves are also important for a number of small land-birds, such as Treron vernans and Pachycephala cinerea, and a great variety of warblers and fiycatchers occur on passage or in winter. The site is a regular wintering area for small numbers of birds of prey such as Pandion haliaetus and Falco peregrinus.
Special floral values: None known.
Research and facilities: Bird count data for the site are held on file at the Centre for Wildlife Research, Mahidol University, in Bangkok and at the Asian Wetland Bureau in Kuala Lumpur. The site continues to be visited regularly by bird-watchers.
References: Lekagul et al. (1985); Parish & Wells (1985).
Criteria for inclusion: 123.
Source:
Jira Jintanugool and Philip D. Round.