Brunei Bay

Brunei Bay "(Malay: Teluk Brunei)" is the gateway to Brunei and Borneo. It is located 4°45'-5°02'N, 114°58'-115°10'E; east of Bandar Seri Begawan. The Brunei portion of the bay is in two sections separated by a finger of Sarawak (Limbang) about 6km wide at the coast. It is a deeply indented bay with an area of about 250,000 ha (c.50,ooo ha in Brunei territory), shared between Brunei Darussalam and the East Malaysian States of Sarawak and Sabah. A chain of islands including the large Malaysian island of Labuan forms the boundary between the bay and the South China Sea. Most of the east and south shores of the bay are covered in extensive mangrove forests with associated mudflats and sandflats at the mouths of the major estuaries. The mangrove forests form a continuous, intact forest within Bruneian territory, but those within the adjacent Sarawak territory have been largely clear-felled to supply the wood-chip industry. Freshwater flows into the bay via a labyrinth of interconnecting channels and waterways.

The major rivers entering the Brunei Estuary in the southwest are the Brunei, Limbang, Temburong, Bangar and Trusan. The Limbang and Temburong drain catchments which are predominantly primary rainforest, and carry high silt loads. The smaller Brunei River receives the drainage from the city of Bandar Seri Begawan and its environment, and is therefore subject to considerable urban pollution. Several smaller rivers drain the extensive peat swamp forests of Temburong District. These carry very small silt loads, but are rich in peat and woody debris.The outer bay varies in depth from about 20 to 40 metres; the inner bay is generally less than 5m deep. The massive inflow of freshwater reduces the salinity to only 2.6 p.p.t. in places, compared with a mean offshore salinity of 31.5 p.p.t. The retention time for water in the bay has been estimated at 2-4 weeks. The tides are diurnal for two or three days in each month and substantially diurnal for the remainder of the month. There is a secondary tide, however, which gradually increases and decreases in magnitude so that for a few days in each month there are semi-diurnal tides of similar amplitude. The tidal amplitude at Muara ranges from about 2.0m at spring tides to 0.9m at neap tides.

Principal vegetation

Mangrove swamps dominated by species of Rhizophora, notably R. apiculata, with mature forest up to 30m in height. Howes and Sahat (in prep) recognized six distinct vegetation zones within their survey area in Brunei Estuary:

1. Avicennia/Sonneratia forest on the seaward edge, dominated by A. marina and S. alba, with some immature Rhizophora apiculata and Lumnitzera coccinea;

2. Rhizophora forest dominated by R. apiculata, with other species such as Bruguiera gymnorhiza, Sonneratia acida and Aegiceras corniculatum in the less frequently inundated zone.

3. A belt of the nipa palm (Nypa fruticans) between the major rivers in the lower reaches of the estuary and along the upper reaches of the rivers.

4. Heritiera/Excoecaria forest dominated by H. littoralis and E. agallocha, forming a landward extension of the Nypa belt.

5. Peat swamp forest with species such as Dyera spp. mixed with a variety of mangrove associates along the riverbanks in the upper reaches of the tidal influence.

6. Sandy areas on exposed coasts and offshore islands with Casuarina equisetifolia and some Melastoma malabaricum and Barringtonia asialica.

The vegetation to the landward of the mangrove in Temburong District is dominated by peat swamp forest, with mangrove extending along the major rivers.

Land tenure

The wetland is state owned (Government of Brunei); some of the surrounding land is privately owned.

Conservation measures taken

Some 483 ha. of mangrove forest and peat swamp forest in north Temburong District are included within the Labu-Selirong Wildlife Sanctuary, established in 1948 (2,499 ha) and 1954 (8,984 ha). In addition, there are small protected areas of mangrove forest along the Sungai Brunei. Wildlife enjoys some protection under the Brunei Wildlife Protection Enactment of 1978.

Conservation measures proposed

There is a proposal to include all uninhabited islands within a conservation management zone. It has been recommended that a large proportion of the mangroves and intertidal mudflats within Brunei Bay be protected in an International Coastal Resource Conservation Zone (Howes & Sahat, in prep). This would involve liaison between Brunei Darussalam and the Malaysian States of Sarawak and Sabah, to form a continuous zone of protected land in sectors of the bay where mangroves and intertidal flats predominate. Caldecott (1987) has proposed that a Joint Management Commission for Brunei Bay be established, with the participation of the national governments of Brunei Darussalam and Malaysia, and the state governments of Sarawak and Sabah. The Commission would be formally responsible for the permanent management of the bay's natural resources on a rational and sustained basis.

Land use

Fishing for fin-fish and prawns, some rearing of Green Mussels (Perna viridis) for local markets, and some harvesting of mangroves and mangrove products for local use. The mangroves were formerly used for firewood and for the production of charcoal and tannin, but in recent years the main use has been for piling material which resists waterlogged soils. The fronds of Nypa fruticans are used for roofing material and weaving, while the sap is used to make a sweet drink and the fruits are eaten. The waterways are still very important for inter-urban transport between coastal towns and the detached portion of Brunei (Temburong). A commercial port, a naval base and various recreation facilities are located in the northwest of the area. Over 40 super-tankers are laid up at moorings within the bay.

Possible changes in land use

Proposals have been made to clear areas of mangrove for rackishwater aquaculture schemes, particularly in Temburong District. It seems likely, however, that the high sulphide content of the soil would render such areas highly unsuitable for aquaculture (Howes & Sahat, in prep).

Disturbances and threats

The Sungai Brunei receives the untreated domestic sewage from a 'water village' of 36,000 inhabitants near Bandar Seri Begawan, as well as the sewage effluent and urban runoff from the city itself. As a result, there is now a significant amount of pollution in the inner bay, and this is increasing. The most immediate threat to Brunei Bay as a whole, however, is destruction of mangrove forest. In Brunei, the cutting of wood for poles and for making charcoal has been carried out at such a low intensity that there appears to have been no serious damage to the mangrove's role in fishery maintenance. However, in recent years the mangroves within Malaysian territory have been seriously over-exploited, and this may now be affecting the fishery resources throughout the bay. Extensive logging activities and clear-felling in the water catchment areas of the rivers also pose a threat to the bay by affecting the water regime. Some mangrove is being cleared for urban and industrial development along the Sungai Brunei, and this could increase in the future.

Economic and social values

The mangrove forests and mudflats are of great importance to the economy of most human communities located around the bay, since they support abundant populations of finfish, prawns and other aquatic animals which are routinely harvested for subsistence consumption or sale. It has been estimated that the mangrove swamps initiate a food chain by depositing sufficient plant material to allow each hectare to support up to 90 kg of prawns each year. In 1985, the full-time registered fishermen in the Brunei portion of the bay landed 2,330 metric tonnes of finfish and prawns. The total number of full-time and part-time inshore fishermen active in the bay as a whole almost certainly exceeds 10,000 individuals (Caldecott, 1987). The waterways are very important for transportation, and the area has considerable potential for outdoor recreation, conservation education and scientific research.

Fauna

Howes and Sahat (in prep) collected 79 species of fishes belonging to at least 34 families in mangrove areas within Brunei Estuary. About half of these species were of some importance in the Brunei markets. The most commonly encountered species, using a variety of sampling techniques, were catfish (Aniidae), Caranx spp., Sardinella spp., Drepane punctata, Coilia dussumieri, Liza vaigiensis, Mugil sp, Plotosus anguillaris, Scatophagus argus. Scomberomorus guttatus and Siganus spp. The intertidal mudflats and sandflats provide foraging areas for a number of migratory shorebirds. Censuses at seven sites in October and November 1986 produced a total of 633 shorebirds of 17 species (Howes & Sahat, in prep). The commonest species were Pluvialis dominica, Charadrius mongolus, Numenius phaeopus, Tringa lotanus, Xenus cinereus, Actitis hypoleucos and Heteroscelus brevipes. Species typical of muddy substrates, such as Limnodromus semipalmatus, Calidris tenuirostris and C. ruficollis, were very scarce. Other waterfowl recorded during the survey included 39 Egretta sacra, small numbers of Butorides striatus, Egretta garzetta, E. alba, Ardea sumatrana and Leptoptilos javanicus, and over 360 terns of seven species, mainly Chlidonias hybrida, C. leucoptera, Sterna dougallii and S. albifrons. The rare and possibly endangered Chinese Egret (Egretta eulophotes) appears to be a regular winter visitor to Brunei Bay in small numbers. Howes and Sahat observed 12 during their survey of the Brunei Estuary in October/November 1986, and reported a maximum of 13 in the nearby Sarawak portion of the bay in May 1986.

The mangrove forests support significant populations of the Proboscis Monkey (Nasalis larvatus) and leaf monkeys (Presbytis sp), as well as large colonies of flying foxes (Pieropus vampyrus). Eleven species of prawns have been recorded in the bay. Three of these, Penaeus merguiensis, P. indicus and Metapenaeus brevicornis, are of high commercial importance, and two others are of minor commercial importance.

Preliminary studies suggest that the intertidal flats support a rather poor zoo-benthos compared with that at many other sites in Southeast Asia. In a recent study, five major taxonomic groups were found from eight sampling sites. Crustacea (Natantia) were the most abundant group, followed by Polychaeta, Bivalvia, Pisces and Gastropoda. Natantia (prawns) were more abundant in the outer estuary, whilst Polychaeta dominated in the mangrove channels near Bandar Seri Begawan sewage outflow (Sahat, 1987; Howes & Sahat, in prep). The poor zoo-benthos may be attributable to the high acidity of the water draining into the bay from the peat swamp forests behind the mangroves.

pecial floral values

Brunei Bay contains one of the largest tracts of relatively undisturbed mangrove forest in eastern Asia.

Research and facilities

A considerable amount of research has been carried out on the finfish and prawn fisheries of Brunei Bay. The Natural History Department of Brunei Museum and the Asian Wetland Bureau (Interwader Programme) conducted a joint study of the littoral ecosystem in Brunei Estuary in 1986.

References & Source

* Caldecott (1987); Currie (l979a, l979b, 1980 & 1982); Farmer (1986); Farmer et al. (1986); Howes & Sahat (in prep); Karpowicz (1985); Lindley (1982); Sahat (1987); Teng (1970 & 1971); UGL Consultants Ltd (1983).
* John R. Howes, Mohammad Jaya bin Haji Sahat and Euan G. Ross.