Rajang Delta
Location:
1°58'-2°51N, 111°10'-111°51'E; the delta area of the Batang Rajang downstream from Sibu and west of the Batang Igan, Third and Sixth Divisions, Sarawak.
Area:
445,000 ha.
Altitude:
Mostly near sea level, with hillocks rising to 90m.
Biogeographical Province:
4.25.12.
Wetland type:
01, 02, 06, 07, 11 & 21.
Description of site:
An extensive delta system at the mouth of the Batang Rajang. The Rajang is the largest river in Malaysia and is probably amongst the thirty largest rivers in the world. It has a total catchment area of 5,105,300 ha and a mean discharge of 4,033 cubic metres per second. The central delta area is a complex mangrove and nipa system, with further accreting mangroves and extensive mudflats at the northern end of Pulau Bruit. The northeastern section of the site is bounded by Batang Igan, the area consisting of peat swamp forest with an inland riverine mangrove system on the Batang Lassa. A substantial part of the Rajang mangroves are clear-felled in rotation for wood-chips. Maximum peat depths are 4.Om in Daro Protected Forest and 4.7m in Loba Kabang Protected Forest. The peat overlies a clay subsoil. The most highly developed peat swamps run in an arc through Daro Protected Forest, Lassa Protected Forest, the area south of Sungei Kut and Oya-Muka Protected Forest. The domed peat swamps have radial surface drainage, the water table lying close to the surface. The tidal range at Daro is 4.85m. The three most important parts of the delta, namely the Matu-Daro and Sibu Swamp Forests, Pulau Bruit and the Rajang Mangrove Forest, are described separately below (sites 3la, 3lb and 31c).
Climatic conditions:
Humid tropical climate with an annual rainfall of 3,000-3,500 mm. The region is not directly exposed to the northeast monsoon. The peak monthly rainfall occurs in December and January; the difference between the maximum and minimum monthly rainfall increases towards the southwest.
Principal vegetation:
A rich variety of mangrove forest types.
Land tenure:
Partly state owned and partly privately owned.
Conservation measures taken:
Much of the area has been designated as Protected Forest or Forest Reserve.
Conservation measures proposed:
A Wildlife Sanctuary encompassing the northern and northwestern parts of Pulau Bruit is in the process of being gazetted.
Land use:
Traditional fishing activities (as described by Pang, 1985), large-scale clear-felling of mangroves for wood-chips, production of charcoal under licence, boat transportation, shifting cultivation and permanent agriculture, mainly the cultivation of rice, bananas and coconuts.
Possible Changes in Land use:
The Department of Drainage and Irrigation has proposed a reclamation scheme near Tanjung Sink on Pulau Bruit which would involve the conversion of 1,840 ha of mangrove forest into rice paddies (Skim Pengaliran Tanjung Sink, Blocks A and C).
Disturbances and threats:
Extensive logging in the mangroves and peat swamp is resulting in over-exploitation of the forest resources. Hatchlings of the Estuarine Crocodile Crocodylus porosus continue to be harvested for sale to commercial rearing pens in Sarikei and Sibu. There are unconfirmed reports of an illegal trade in crocodiles to Singapore. The considerable river traffic and intensive fishing activities cause disturbance to the crocodiles.
Economic and social values:
The delta supports a rich fishery; the economic values of the traditional fishing activities have been described by Pang (1985). Under proper management, the mangrove and peat swamp forests could have considerable value for timber extraction on a sustainable basis. Locally, the peat swamps act as sponges during periods of heavy rainfall and thereby restrict flooding. In the southern part of the delta, some agriculture is feasible, but most of the area has no agricultural potential (Department of Agriculture, 1982b).
Fauna:
The Rajang Delta is particularly important for herons and egrets, migratory shorebirds and terns; over 500 herons and egrets of twelve species, 20,000 shorebirds of at least 25 species and 14,000 terns of seven species utilize the area at certain times. Most of the waterfowl are concentrated around the northern end of Pulau Bruit, but the sand bars off Kuala Rajang are important for roosting terns and to a lesser extent shorebirds. The most abundant shorebirds are Tringa totanus, Xenus cinereus and Charadrius leschenaultii. Several uncommon species such as Egretta eulophotes, Limnodromus semipalmatus and Numenius madagascariensis have been reported at Pulau Bruit.
At least 43 secies of fishes have been recorded (Pang, 1985). Reptiles include the River Monitor Varanus salvator and Estuarine Crocodile Crocodylus porosus. The latter breeds in the delta, but despite the abundance of suitable habitat, is now rare, presumably because of the harvesting of live hatchlings. Mammals include the endangered Proboscis Monkey Nasalis larvatus as well as Presbytis cristata, Lutra sumatrana, Felis bengalensis and Sus barbatus.
At least five species of prawns and the crabs Scylla serrata and Portunus pelagicus are harvested in the area.
Special floral values:
The delta contains the most extensive mangrove forests in Sarawak, with a great diversity of forest types.
Research and facilities:
Forest inventories were carried out in 1951-54 and 1967 (Yong, 1967c) and a soil survey has been conducted by the Department of Agriculture. The Forest Department has established research plots in the Rajang Delta, in the Matu-Daro Protected Forest and on Pulau Bruit. Coastal areas were surveyed in 1985 and 1986 (Edwards et al., 1986 & in prep; Howes & NPWO, 1986), and studies have been made on the mangrove forest ecosystem (Chai, 1974 & 1975), Estuarine Crocodiles (Cox & Gombek, 1985) and Proboscis Monkeys (Salter & MacKenzie, 1981).
References:
Abu Bakar Jaafar (1986); Bennett (1986); Chai (1974 & 1975); Chai & Lai (1980); Cox & Gombek (1985); Department of Agriculture (1982b); DID Sarawak (1979/80); Edwards et al. (1986 & in prep); Howes & NPWO (1986b); Salter & MacKenzie (1981); Sarawak Marine Fisheries Department (undated-c); Yong (1967c).
Criteria for Inclusion:
123.
Source:
John R. Howes, Albert Chuan Gambang and National Parks and Wildlife Office (Sarawak Forest Department).