- Follows the Gulf of Carpentaria coast in the Northern Territory.
- Gently undulating plains with meandering rivers and coastal swamps.
- Monsoonal climate with distinct wet and dry seasons.
- Most of the land is pastoral leasehold, although over quarter of the bioregion is Aboriginal land.
- Pastoral use is extensive, with low input of labour and capital and marginal profitability.
- Tourism is a growing industry, with fishing being an important attraction.
The Gulf Coastal bioregion includes about 26,900 sq. kms of land that follows the Gulf of Carpentaria coast. The majority of the bioregion lies within Northern Territory (99%) with a small area extending into Queensland. The bioregion is characterised by gently undulating plains with meandering rivers and coastal swamps. The Sir Edward Pellew Islands are part of the bioregion. The bioregion follows the coast from near Numbulwar in Arnhem Land to just east of the Queensland/Northern Territory border. The town of Borroloola (pop. 551) lies on the border with the Gulf Falls and Uplands bioregion. The bioregion has a monsoonal climate with summer rainfall.
The bioregion experiences hot humid summers and mild dry winters. The monsoonal activity is variable and cyclones are common. Rainfall decreases with away from the coast. At Borroloola the mean annual rainfall is 790mm, on the Sir Edward Pellew Islands the mean annual rainfall is about 1038mm. Most of the annual rainfall occurs in the four months from December to March.
The mean summer temperature at Borroloola ranges from 24.3? C to 37.5? C, whereas on the coast the temperature ranges from 26.1? C to 34.4? C. The mean winter temperature at Borroloola range from 11.8? C to 29.6? C and at the coast the temperature ranges from 16? C to 25? C (Kerle, 1996).
Climate averages are available for Centre Island of the Sir Edward Pellew Islands and Borroloola:
Temperature and rainfall graphs are available for Borroloola:
Current seasonal conditions and their historical context can be provided by satellite imagery. The Normalised Difference Vegetation Index (NDVI) is a measure of the vegetation ‘greenness’. The NDVI for the Gulf Coast bioregion for this year and previous years can be found at: http://www.environment.gov.au/erin/ndvi/ttrace/guc.html
The Gulf Coastal bioregion is characterised by Tertiary (less than 65 million years ago) sands, soil, alluvial and coastal deposits. Underlying these sediments are Proterozoic (545-2500 million years ago) shallow-marine and continental sediments and volcanics of the McArthur Basin.
For more detailed geological information and map refer to the Australian Geological Survey Organisation website: www.agso.gov.au/map/ and the Northern Territory Geological Survey website:
The bioregion is characterised by scattered low steep hills, ranges and undulating coastal plains. Several rivers flow through the bioregion into the Gulf of Carpentaria, including the McArthur, Roper and Limmen Bight and Robinson Rivers. The coastal plain consists of low relief country and a coastal strip of beaches and large expanses of saline flats, mud flats and estuaries. The bioregion contains swamps and wetland systems, these include:
Borroloola Bluebush Swamps are a series of small roughly circular swamps near the town of Borroloola. The swamps are floristically diverse wetland supporting a good mix of waterbird species. The combination of vegetation types within the swamps is not seen elsewhere in the Northern Territory"s subhumid tropics.
Limmen Bight (Port Roper) Tidal Wetlands System includes tidal wetland at/near Limmen Bight, in the far southwest of the Gulf of Carpentaria. The system of tidal wetlands (intertidal mud flats, saline coastal flats and estuaries and adjoining permanent shallow marine waters less than 6 m deep at low tide), has a high volume of freshwater inflow; typical of the Gulf of Carpentaria coast. The Limmen Bight Tidal Wetlands are the second-largest area of saline coastal flats in the N.T.
Port McArthur Tidal Wetlands System comprises tidal wetland at and around Port McArthur and the Sir Edward Pellew Islands. The wetland system includes saline coastal flats, tidal channels and intertidal mudflats, which extend along the Gulf of Carpentaria coast. It is a typical tidal wetland including areas of mangrove swamps and the widest and largest area of intertidal mudflats, in the southwest of the Gulf.
For more information on the Borroloola Bluebush Swamp, Limmen Bight (Port Roper) and the Port McArthur Tidal Wetlands Systems refer to Connors, et. al., (1996).
The soils are loose siliceous sands, earthy sands with shallow gravels to sandy soil on the hills and ranges (Kerle, 1996). The coastal plains comprise major alluvial deposits of clay and sand.
For more soils information refer to the Digital Atlas of Australian Soils.
930 plant species have been recorded in the bioregion of which 24 are listed as rare and threatened species (Connors, et. al., 1996). For a list of rare and threatened species refer to Connors, et. al., (1996) at: www.nt.gov.au/paw/fauna/bau/intro.htm
The undulating coastal plains are dominated by stringy bark (Eucalyptus tetrodonta) woodland with rusty bloodwood (Corymbia ferruginea), ironwood (Erythrophleum chlorostachys) and the Darwin woolly butt (Eucalyptus miniata) over curly spinifex (Plectrachne pungens) (Kerle, 1996). Some of the open woodland communities from the Gulf Fall bioregion extend into the Gulf Coast region, including the bloodwoods (Corymbia spp.) Darwin box (Eucalyptus tectifica) and the snappy gum (E. leucophloia) with white grass (Sehima nervosum) and golden beard grass (Chryopogon fallax) grassland. Coolibah (Eucalyptus microtheca) woodland with grassy understorey and paperbark swamps are found along creeks and wetlands (Connors, et. al., 1996).
The saline tidal flats support samphire (Halosarcia indica) shrubland and tall grasslands of tall tamil grass (Vetiveria elongata) occur along adjacent saline flats. Mangrove forests grow along the coast and river mouths.
The vegetation on the Sir Edward Pellew Islands varies from island to island. Variable-barked bloodwoods (Corymbia spp.) are common to all islands. The islands probably contain relic species of vine thickets along the coast (Morton, et. al., 1995).
385 vertebrate species have been recorded in the bioregion, including 18 rare and threatened species (Connors et. al., 1996). Several threatened vertebrate species occur in the bioregion, most notably the critically endangered carpentarian rock-rat (Zyzomys palatalis), which is largely restricted to a small area of this bioregion and the adjoining Gulf Falls and Uplands bioregion. For a list of rare and threatened species refer to Connors, et, al., (1996) at: www.nt.gov.au/paw/fauna/bau/intro.htm
The mammal species are typical of those found in the eucalypt woodland, such as the agile wallaby (Macropus agilis), antilopine wallaroo (Macropus antilopinus) and the northern nail-tailed wallaby (Onychogalea urguifera) (Kerle, 1996). There are a number of mammal species on the Sir Edward Pellew Islands, which have become extinct on the mainland portion of the bioregion. These include the brush-tailed phascogale (Phascogale tapoatafa), northern quoll (Dasyurus hallucatus), brush-tailed rabbit-rat (Conilurus penicillatus) and the canefield rat (Rattus sordidus) (Woinarski, et. al., in prep.).
Species endemic to the region include the undescribed skink (Ctenotus sp.) from the Sir Edward Pellew Islands. Significant population of pale field-rats (Rattus tunneyi) and the fat tailed antechinus (Pseudantechinus mimulus) occur on the Sir Edward Pellew Islands (Morton, et. al., 1995).
The permanent fresh water streams and pools are inhabited by a variety of frog species. The reptile species are diverse including tropical species such as the frill-necked lizard, arid species like the central netted dragon and endemic species including the gehyra borroloola. The rivers support both fresh water and saltwater crocodiles and at least 2 species of freshwater turtles (Emydura victoriae & Ehelodina regosa) (Kerle, 1996).
A total of 23 species were recorded at the Borroloola Bluebush Swamps, includes 3 darters and cormorants, 8 herons and allies, 6 ducks and allies. It is a regionally significant breeding area for magpie geese (Anseranas semipalmate), pacific heron (Ardea pacifica), wandering whistling duck (Dendrocygna arcuata), plumed whistling duck (Dendrocygna eytoni), pacific black duck (Anas superciliosa) and green pygmy goose (Nettapus pulchellus) (Connors, et. al., 1996).
The wetland systems are important coastal sites for migration stop-over area for shorebirds such as the brolga (Grus rubicundus) and the straw-necked ibis (Threskiornis spinicollis) and an important seabird (tern) breeding area. The wetlands are important for seabird colonies, shorebird feeding and roosting sites, and high significance for breeding sites of marine turtles and waterbird rookeries. The seagrass beds are a major breeding area for prawns and an important feeding area for Dugong (Dugong dugon) (Connors, et. al., 1996).
Land Tenure & Use
The Northern Territory component of the bioregion comprises 65% pastoral leasehold and Aboriginal Land comprises about 27% of the land. There are small areas of freehold or crown land and a nature reserve (0.5%). The nature reserve is the Barranyi National Park on North Island of the Sir Edward Pellew Islands. Aboriginal owners lease the land to the Parks and Wildlife Commission NT for use as a national park. The whole Sir Edward Pellew Islands are listed on the register of the National Estate.
The Sir Edward Pellew Islands are considered an important a refuge for endemic and rare plants and animals. The sub-tropical islands are characterised by remnant vine thickets and surrounding mangroves and seagrass beds (Morton, et. al., 1995).
The main land use is cattle grazing, mining, commercial and recreational fishing and tourism (Morton, et. al., 1995). There is a significant port at Bing Bong primarily used for transport the ore from the McArthur mine south of Borroloola. Tourism is becoming a major industry with fishing being the important attraction.
Pastoralism on marginal land is leading to vegetation changes and some erosion (Woinarski, et. al., in prep.). Degradation of wetland vegetation is occurring due to feral animals especially goats. A range of factors, such as high frequency of intense fire, feral herbivores and weeds are leading to some damage to monsoon rainforest patches (Connors, et. al., 1996).
Dugong populations are threatened by the commercial barramundi fishery through incidental deaths in nets (Connors, et. al., 1996).
Feral goats have a substantial impact where present. Cane toads have localised impacts on quoll, goanna, snake and turtle species. Feral cats are common across the bioregion (Woinarski, et. al., in prep.). Pigs are damaging large areas of flood plains. Horses and buffalos are reported along the coastal regions.
14 weed species have been recorded in the bioregion. For a list of the weed species refer to Connors, et. al., (1996).
Weeds considered a problem throughout the region include the noogoora burr (Xanthium pungens) and hyptis (Hyptis sauveolens). Mexican poppy (Argemone ochroleuca) occurs in some river catchments including the McArthur and the Calvert Rivers. Khaki weed (Alternanthera pungens) and star burr (Acanthospermum hispidum) are two nuisance plants that occur in settled areas throughout the Gulf region (www.savanna.ntu.edu.au/information/savannaexplorer.html).
Social & Economic Aspects
The Gulf Coastal bioregion is sparsely populated and the resident population would be well outnumbered by the visitors to the region. The main regional centre is Borroloola, which lies on bioregion’s border. The regional economy has been boosted by the recent development of the large MacArthur River mine.
The Gulf Coastal bioregion is currently dominated by pastoralism. The style of pastoral operations in the Territory are still very traditional–very few fences, low input of labour and capital and fairly marginal profitability.
The near-coastal waters and estuaries support a major commercial barramundi and salmon fishery; major harvest of crabs occurs at Port Roper and aquaculture is established near Roper River (www.savanna.ntu.edu.au/information/savannaexplorer.html).
Aboriginal Land within the bioregion includes Maria, Wada Wadalla, Wurralibi, and part of Arnhem Land, Garawa and Narwinbi (Hema Maps, 1997). The bioregion is within the ATSIC region of Katherine and is managed by the Garrak Jarru regional council (McLennan, 1997). For more information on the Aboriginal people of this region refer to Horton, (1994) and the relevant websites in the reference list.
Resources, References & Contacts
- Connors G., Oliver B., & Woinarski, J. 1996, Bioregions in the Northern Territory: Conservation Values, Reservations Status and Information Gaps. Final report to ANCA National Reserves System Cooperative Program (Project N607), Parks and Wildlife Commission of the Northern Territory, Palmerston, Northern Territory. (www.nt.gov.au/paw/fauna/bau/intro.htm.)
- Hema Maps 1997, Australia Touring Atlas, Fergies Colour Printers, Brisbane, Queensland.
- Horton, D. R. 1994, The Encyclopaedia of Aboriginal Australia, Aboriginal Studies Press for the Australian Institute of Aboriginal and Torres Strait Islander Studies, Canberra, ACT.
- Kerle, J.A. 1996, Bioregions of the Northern Territory. Draft report Conservation Commission of Northern Territory, Palmerston, Northern Territory.
- McLennan. W. 1997, 1994 National Aboriginal and Torres Strait Islander Survey: Social Atlas, Australian Bureau of Statistics, Canberra, ACT.
- Morton, S.R., Short, J., & Barker, R.D. with an Appendix by Griffin, G.F., & Pearce, G. 1995, Refugia for Biological Diversity in Arid and Semi-arid Australia, Department of the Environment, Sport and Territories, Canberra, ACT.
- Thackway, R. & Cresswell I.D. 1995, An Interim Biogeographical Regionalisation for Australia: a Framework for Setting Priorities in the National Reserves System Cooperative Program, Australian Nature Conservation Agency, Canberra.
- Woinarski J., Fensham, R., Whitehead, P. & Fisher, A., with map production by Verhagen, C. in prep., Biodiversity in the Australian Rangelands: a Review of Changes in Status and Threatening Processes. Draft report prepared as a resource document for Project 3: Developing an Adaptive Framework for Monitoring Biodiversity in Australia’s Rangelands, of the National Land and Water Resources Audit, Theme 4 (Rangelands monitoring) by the Tropical Savannas Cooperative Research Centre, Darwin, Northern Territory.
Aboriginal languages of Australia
Aboriginal Studies WWW Virtual Library
Australian Geological Survey Organisation, Geology of Australia
Bureau of Meteorology, Climate averages
Bureau of Meteorology, Temperature and Rainfall graphs
Bureau of Rural Sciences, Digital Atlas of Australian Soils
Charles Sturt University: Guide to Australia — NT
Connors G., Oliver B., & Woinarski, J. 1996, Bioregions in the Northern Territory: Conservation Values, Reservations Status and Information Gaps. Final report to ANCA National Reserves System Cooperative Program (Project N607), Parks and Wildlife Commission of the Northern Territory, Palmerston, Northern Territory. (www.nt.gov.au/paw/fauna/bau/intro.htm.)
Department of Primary Industries and Fisheries, Rangelands of the Northern Territory
Department of Environment and Heritage, Normalized Difference Vegetation Index information including bioregional information
Kimberley Development Commission
Northern Lands Council
Northern Territory Department of Lands, Planning and Environment
Northern Territory Geological Survey
Northern Territory Government Tourism www.nt.gov.au/ntg_internet/profile/regions_alice_springs.shtml
Tropical Savanna Co-operative Research Centre
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