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Location Malaysia, Sarawak
Central coordinates 115o 9.00' East  4o 54.00' North
IBA criteria A1, A4i
Area 19,500 ha
Altitude 0 - 50m
Year of IBA assessment 2004

Malaysian Nature Society

Summary Its location is complicated as it ranges between 2 different countries and furthermore separated between 2 different states. Rivers and bays makes up most of this area and there are 3 main estuaries which are very significant for birds.

Site description Administratively, Brunei Bay comes under two countries (Malaysia and Brunei). The Malaysian parts of its shoreline are also divided between two States: Sarawak and Sabah. The situation is further complicated by the fact that Brunei constitutes two separate territories (Brunei and Temburong districts) which are separated, along this bay, by Sarawak (Limbang district). The eastern curve of the bay is formed by the estuaries of the Klias, Padas and Menumbok rivers, flowing out of the Klias peninsula in Beaufort district, Sabah (MYSB09).There are three separate areas within this bay which are significance for birds: Limbang estuary, Trusan-Sundar and Menumbok estuary. These are treated separately below.(I) Physical CharacteristicsLimbang Estuary: The Limbang estuary is orientated in a north-south direction, about 20 km in length, bordered to the north and south by the two states of Brunei Darussalam. The area is protected from the north-east monsoon by several Bruneian islands; Pulau Muara Besar (composed of successive sandridges with scrubby vegetation) and Pulau Baru-Baru and Pulau Berbunot (both predominantly rocky with a narrow mangrove strip). The estuary is the emergence point of three main rivers; the Sungai Manunggul, Sungai Limbang and Sungai Pandaruan, each having a high silt load. Intertidal mudflats, consisting of fine-grained pure muds, cover the rivermouth and are replaced by sand-mud ridges to the seaward. The mudflats can extend to over 1 km offshore at low tide in areas like Tanjung Api-Api and Tanjung Tubu-Tubu. The situation is reversed at the rivermouths of smaller rivers such as Sungai Sentabok and Sungai Sapukang (Howes and NPWO, 1986).Trusan-Sundar: The Trusan-Sundar mangroves are orientated in a west-east direction, about 20 km in length, and stretches from Kuala Trusan to Tanjung Perepat. Localised erosion is evident east of the mangrove headland i.e. north-west of Kampung Awat-Awat. Accreting mangrove fringe accompanied by extensive intertidal mudflats occur prominently at the mouth of Sungai Trusan (the area's main river), Kuala Bangau, Kuala Kenaljam and Tanjung Perepat. At Kuala Trusan, the flats extend up to 3 km offshore at low tide and consist of a complicated series of deep water channels with areas of exposed sediment forming 'islands'. The deposits at the rivermouth consist of pure, fine-grained muds and gradually replaced by course sand particles as it extend seaward. Some of the most seaward deposts consist primarily of pure course grained sands. The estuary is sheltered by Pulau Labuan and peninsular to the north-east (Howes and NPWO, 1986).Menumbok Estuary: a wide mangrove estuary with exposed inter-tidal mudflats, formed by the Menumbok and Padas rivers. The part of Brunei bay is sheltered by the exposed, northeast-southwest aligned, Klias ridge. The estuary is continuous with the smaller Sg. Klias estuary further south, also forming a mangrove delta. The Menumbok Forest Reserve is contiguous with the Padas Damit FR.(II) Climatic Conditions Average annual rainfall is 3,500 mm. Small variation in monthly rainfall. Rainfall during monsoon season (September-January) is about 400 mm/month (DWNP, 1987).

Key Biodiversity Brunei Bay is one of the most important wintering sites for migratory waterbirds along Borneo's northern coastline. Its large expanses of mudflats and numerous small islands and exposed sand/mud banks, located within a large, deep bay, provide a sheltered, food-rich environment with numerous high-tide roosts. The Sundar and Lawas areas increase habitat diversity with stretches of sandy beaches and rocky shores.Limbang Estuary: The large expanse mudflats and sandflats of the Limbang estuary is an important wintering and staging area for migratory shorebirds and egrets, attracted to its rich feeding ground. Two globally threatened species have been recorded, the resident Lesser Adjutant Leptoptilos javanicus and migratory Chinese Egret Egretta eulophotes. Other Near Threatened waterbirds recorded in the area include Oriental Darter Anhinga melanogaster, Grey-headed Fish Eagle Ichthyophaga ichthyaetus, Asian Dowitcher Limnodromus semipalmatus, Malaysian Plover Charadrius peronii and Far Eastern Curlew Numenius madagascariensis (DWNP, 1987; Sebastian, 1995; Smythies, 1999).Trusan-Sundar: The Trusan-Sundar mudflats and sandflats are important wintering and staging sites for globally threatened waterbirds especially shorebirds and egrets especially at Kuala Trusan and Kampung Awat-Tanjung Perepat stretch. The Malaysian Plover Charadrius peronii resides along some beach stretches in the estuary (Howes and NPWO, 1986). Four pairs in breeding plumage were seen in November 1995 on the sandy beaches at the mouth of Sg. Kabab (Sebastian, 1995). Grey-headed Fish Eagle Ichthyophaga ichthyaetus was recorded from Sg. Trusan-Sundar and Sg. Kabab (Sebastian, 1995).Three Great-billed Heron Ardea sumatrana were observed in Nov 1995 along Sg. Trusan-Sundar and Sg. Kabab (Sebastian, 1995), the only record of this species for Sarawak. Smythies (1999) attributes a record from Brunei Bay by Mohd. Jaya in 1987.Menumbok Estuary: One Chinese Egret seen on mudflats and five Storm's Stork Ciconia stormi seen upstream of Menumbok (lower part of Padas Damit FR) in December 1997 (Sebastian, 1998).

Non-bird biodiversity: (I) Globally threatened mammals (IUCN, 2002): ENDANGERED: Proboscis Monkey Nasalis larvatus; VULNERABLE: Dugong Dugong dugon; NEAR THREATENED: Silvered Leaf Monkey Trachypithecus cristatus; Long-tailed Macaque Macaca fascicularis; DATA DEFICIENT: Irrawaddy Dolphin Orcaella brevirostris(II) Globally threatened reptiles (IUCN, 2002): CRITICALLY ENDANGERED: Painted Terrapin Callagur borneoensis along Sg. Siang Siang (Sebastian, 1995). A small population of Estuarine Crocodile Crocodylus porosus survives in parts of the bay.(III)Plants: Nepenthes reinwardtiana recorded along Sg. Lawas, a very rare species in Sarawak (Howes and NPWO, 1986).

Populations of IBA trigger species

Species Season Period Population estimate Quality of estimate IBA Criteria IUCN Category
Bornean Peacock-pheasant Polyplectron schleiermacheri resident  2004  present  A1  Endangered 
Lesser Adjutant Leptoptilos javanicus resident  2004  present  A1  Vulnerable 
Storm's Stork Ciconia stormi resident  2004  present  A1  Endangered 
Chinese Egret Egretta eulophotes non-breeding  2004  present  A1  Vulnerable 
Greater Sandplover Charadrius leschenaultii winter  2004  present  A4i  Least Concern 
Spotted Greenshank Tringa guttifer winter  2004  present  A1  Endangered 


IUCN habitat Habitat detail Extent (% of site)
Wetlands (inland)   -

Protection status Limbang Estuary: The Limbang estuary is currently not protected as most of it is untitled state land. However, its adjacent areas in Brunei Darussalam, Pulau Siarau, Pulau Berambang and Sungai Brunei are conservation areas.Howes and NPWO (1986) proposed the conservation of the mangroves and intertidal mudflats to link with adjacent areas in Brunei and to establish an International Coastal Resource Conservation Area within Brunei Bay. Forestry management proposals and restrictions on illegal logging were also recommended. Salter and MacKenzie (1981) also proposed that the Sungai Limbang mangroves be designated as a Wildlife Sanctuary for the protection of the Proboscis Monkey (Nasalis larvatus). Protection of the Limbang mangroves was also echoed by Bennett and Gombek (1986) based on the following reasons;Limbang is Sarawak's only major contribution to Brunei Bay fishery.Limbang links two protected sections of Brunei's mangroves. Destruction of Limbang will result in faunal degradation and reduced protection of Brunei areas.Brunei Bay's Proboscis Monkey (N. larvatus) population is the only significant one between Sandakan and Rajang Delta.Brunei Bay has a population of the Silvered Leaf-Monkey, an endangered primate in Sarawak.Trusan-Sundar: The majority of the Trusan-Sundar mangroves are contained within the Kenalian, Bumbun and Terentang Forest Reserves, where logging has been extremely intensive. Areas up to 1 ha or more have been virtually clear-felled. Only the area between Sungai Sepatai and Sungai Awat-Awat is relatively untouched with a more or less intact canopy. Howes and NPWO (1986) proposed the creation of a Wildlife Sanctuary and management of the mangrove production forest. Under the proposal, the site forms a link with areas in Brunei Darussalam as an International Coastal Resource Conservation Area. Salter and MacKenzie (1981) proposed the undisturbed mangroves between Kuala Bangau and Kuala Trusan to be made a Wildlife Sanctuary for the protection of Proboscis Monkeys (Nasalis larvatus).Menumbok: Menumbok Forest Reserve cover 5,710ha, under the category of Class I FR. The inter-tidal mudflats are not included within the forest reserve.

References DWNP. 1987. Malaysian Wetland Directory. Peninsular Malaysia: Department of Wildlife and National Parks.Howes, J.R. and NPWO. 1986. Evaluation of Sarawak wetlands and their importance to waterbirds. Report 4: Limbang/Lawas Districts of Brunei Bay. INTERWADER Publication No. 14. Kuala Lumpur: Asian Wetland Bureau.IUCN. 2002. 2002 IUCN Red List of Threatened Species. (23 June 2003).Sebastian, A. 1999. 1997-1998 Records of Globally Threatened Species from Peat Swamp Forest in Malaysia. Suara Enggang 1: 17-18.Sebastian, A.C. 1998. Preliminary Ecological Assessment of the Klias Peninsula, Beaufort District, Sabah, Malaysia. Aonyx Environmental Services. (Internal Report)Sebastian, A.C. (1995) Environmental Impact Assessment - Proposed Oil Palm Plantation at Trusan, Lawas. (Ecological section). Tradewinds Plantations.Smythies, B.E. 1999. The Birds of Borneo (4th Edition). Revised by Davison, G.W.H.. Kota Kinabalu: Natural History Publications (Borneo) Sdn. Bhd.

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Recommended citation  BirdLife International (2016) Important Bird and Biodiversity Area factsheet: Brunei Bay (Malaysia). Downloaded from on 25/10/2016

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