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In this section you will find detailed information, including national overviews and state and regional level assessments, from the 2000-2002 National Land and Water Resources Audit theme assessments.
Biodiversity Assessment - Gulf Coastal
Gulf Coastal
Introduction
The Gulf Coastal bioregion comprises gently undulating coastal plains with scattered rugged areas of Proterozoic sandstones and Tertiary sediments. Soils are predominantly sandy red earths and shallow gravelly sands.
The bioregion includes two subregions, with one of these comprising the Sir Edward Pellew Island group.
Summary of overall condition and trend
Much of the bioregion is in reasonably good condition, although this is being destabilised by increasing impacts of weeds, feral animals, changed fire regimes and grazing. There are also more localised impacts from mining and exploration. Condition is generally better on the islands than on the mainland, except that Vanderlin Island is exposed to threats from an increasing population of semi-feral goats. Both subregions are continental landcape stress class 5 as assessed by the Landscape Health report (1 is most stressed, 6 is least stressed).
Summary of conservation priorities
The NRM priorities for this bioregion include a mix of additional reservation (particularly in the Wollogorang-Wentworth area, and also including possible Indigeonous Protected Areas or other collaborative agreements on islands of the Pellew group additional to North Island), and enhanced broad-scale management of key threatening processes (feral animals, weeds and changed fire regimes). Management of these threats requires additional resources, support for capacity-building among land-holders, and better integration of actions across tenures and jurisdictions.
Natural values
The Pellew islands are an important refuge area, containing populations of many species which have declined or become regionally extinct from the adjacent mainland. Most are relatively undisturbed and in unusually good condition. The islands, and some coastal areas in the mainland subregion, are also nationally significant as nesting sites for marine turtles and colonial seabirds, and as feeding sites for migratory shorebirds.
Click here to link to a table of natural values within each subregion
Wetlands
Three nationally significant wetlands are recognised from this bioregion: Borroloola bluebush swamps (NT006: wetland types B14 and B13), Limmen Bight (Port Roper) tidal wetlands system (NT007: wetland types A7, A8, A9, A6 and A2), and Port McArthur tidal wetlands system (NT008: wetland types A1, A7, A8, A6, A2, A9 and B5). These are generally in good condition, but are affected by feral animals, and have occasional or potential threats from commercial fishing and/or pollution associated with mining.
A range of permanent rivers and some swamps are of significance on the mainland subregion, and the large freshwater lake, Lake Eames, on Vanderlin Island, is significant in the Pellews subregion.
Nationally important wetlands
Map: IBRA map showing DIWA locations, towns, subregions, major roads and reserves and most common threatening processes.
Click here to link to a table of Australia's Important Wetlands (Directory of Important Wetlands of Australia): their type, condition, trend and threatening processes within each subregion.
Regionally important wetlands
Click here to link to a table of provisional identification of wetlands of regional significance: their type and special values within each subregion. The reliability of the overall subregional assessment is indicated.
Click here to link to a table of provisional identification of wetlands of regional significance: their condition, trend and threatening processes within each subregion.
Riparian Zones
The mainland part of this bioregion includes the lower reaches of several main watercourses, notably including the Roper, McArthur, Calvert, Robinson, Limmen Bight, Wearyan, Foelsche and Towns Rivers. Riparian areas are generally in reasonably good condition, but are suffering some degradation from uncontrolled livestock and feral animals. There are also more localised or less serious extensive problems from weed infestations, pollution associated with mining, and altered fire regimes.
Map: Riparian threatening processes.
Click here to link to a table of riparian zones: their average condition, trend and threatening processes for each subregion. The reliability of this overall assessment is indicated.
Ecosystems at risk
No ecosystems are formally recognised as threatened, however rainforest patches, riparian areas and some wetlands have been subject to degradation, and these threatening processes remain uncontrolled.
Map: IBRA map showing frequency of threatening processes for ecosystems.
Click here to link to a table of provisional list of threatened ecosystems in Australia: their broad vegetation type (National Vegetation Information System - Major Vegetation Subgroup), recommended status, current legislative protection as a threatened ecosystem, trend and bioregional distribution. These ecosystems are arranged in the bioregion of their principal occurrence. The reliability of the recommended status is indicated.
Click here to link to a table of provisional list of threatened ecosystems in each subregion: their threatening processes.
Click here to link to a table of provisional list of threatened ecosystems in each subregion: their recommended recovery actions
Species at risk
This bioregion includes 16 species listed as threatened at Commonwealth or Territory level. This includes a set of 6 marine turtles, of which at least 4 have significant populations and/or nesting sites within this bioregion. Two of the listed threatened mammal species (carpentarian antechinus and canefield rat) occur in the Northern Territory only in this bioregion (both only on the Pellew Islands).
There is also some substantial evidence that there is broad scale decline affecting at least some groups of mammals and birds in this bioregion, in addition to those species currently listed as threatened. Several mammal species occur on the Pellew Islands but not in comparable habitats on the nearby mainland.
Number of taxa in the Gulf Coastal bioregion listed as threatened at national and/or NT level (nb this table includes only species definitely recorded from the bioregion (rather than putative occurrences based on modelling) and presumed to be still extant in the bioregion).
| Taxa | Commonwealth | Northern Territory | ||
|---|---|---|---|---|
| Endangered | Vulnerable | Endangered | Vulnerable | |
| Plants | 0 | 0 | 0 | 0 |
| Reptiles | 2 | 4 | 0 | 1 |
| Birds | 1 | 2 | 1 | 2 |
| Mammals | 1 | 3 | 1 | 3 |
Map: IBRA map showing frequency of threatening processes for species.
Click here to link to a table of species at risk in each subregion: their status, trend and subregional distribution. The reliability of the assessment of trend is indicated and whether recovery plans have been prepared.
Click here to link to a table of species at risk in each subregion: their threatening processes.
Click here to link to a table of species at risk in each subregion: their status recommended recovery actions.
Eucalypts and Acacias
Endemism
The subregions of this bioregion contain no known endemic acacia or eucalypt species.
Richness
The mainland subregion has moderate richness for eucalypts (25 species) and acacias (41 species); the Pellew Island subregion has low richness (9 and 16 species respectively).
Birds
Although a mere dozen surveys were available for analysis, trends are remarkably consistent with nearby bioregions. Overall the composition of the bioregion is similar to the other tropical savanna bioregions with a moderate proportion of the restricted range Purple-crowned Fairy-wren along the rivers, a few records of the Vulnerable Painted Snipe and none of introduced species.
Status: Tropical woodland avifauna.
Rare and threatened: No major populations.
Increasers: None indicative of landscape health.
Indicators: Emu, Australian Bustard, Flock Bronzewing, Varied Lorikeet, Black-tailed Treecreeper, Purple-crowned Fairy-wren, Jacky Winter.
Trend: None detected.
Scenario: The change in fire regime to large scale fires may gradually reduce the abundance of some species.
Actions: Ensure representative areas have an appropriate fire regime to maintain diversity.
Click hereto download a summary report including the physical characteristics of the bioregion, a species list, and summary statistics [Excel file]. The file may open on your screen. To save it to your system 'Save as' under the File menu.
Mammals
Number of species and status
There are 48 mammal species within this bioregion. (The maximum number of species recorded in a bioregion is 86 and the minimum is 25).
Click here to link to a table of number of species in each status class for this bioregion.
Click here to link to a list of mammal species and their status for this bioregion.
Critical weight range
The critical weight range (35 - 5500 g) of mammals is the size range of Australian mammals that have been most affected by environmental changes following European settlement. In this bioregion, the proportion of mammal fauna within the critical weight range is .563. (The maximum proportion of fauna within the critical weight range recorded in a bioregion is 0.632 and the minimum is 0.222).
Faunal Attrition Index
Faunal attrition is a measure of contraction or loss of species richness with a region. A high index value means many species have declined or are extinct in the bioregion. The index can be used to compare the status of mammal fauna to regional attributes such as changes since European settlement and average annual rainfall. The Faunal Attrition Index for mammals in this bioregion is .17. (The maximum faunal attrition index value recorded in a bioregion is 0.66 and the minimum is 0).
Click here to link to a table of Faunal Attrition Index for groups of mammals shows the contributions of each group to overall patterns of faunal decline.
Faunal Contraction Index
A range contraction index is a measure of the extent to which the range inhabited by a particular species has contracted. A high index value means that many of the species comprising the region's original mammal fauna have contracted from a high proportion of the regions they originally occurred in. The faunal contraction index for the mammal fauna in this bioregion is .14. (The maximum faunal contraction index value recorded in a bioregion is 0.51 and the minimum is 0.07).
Faunal Endemism Index
Endemic species are those restricted to certain regions. Regions containing endemic species are considered to have high biodiversity conservation values because opportunities to conserve those species do not exist elsewhere. A high index value means that the species comprising the original mammal fauna typically occurred in few bioregions. The faunal endemism index value for the mammal fauna in this bioregion is .65. (The maximum faunal endemism index value recorded in a bioregion is 0.79 and the minimum is 0.52).
New Endemism Index
Extant (still surviving) species that have undergone major range contractions can be considered 'new endemics'. Bioregions that contain new endemic species are often important refugia for threatened species. The new endemism index for the mammal fauna in this bioregion is .75. (The maximum new endemism index value recorded in a bioregion is 0.93 and the minimum is 0.5).
Table: Translocated Species
There is no data available for this table within the bioregion.
Exotic Mammals
The number of introduced exotic mammal species that occur within this bioregion is 8. (The maximum number of introduced exotic mammal species in a bioregion is 16 and the minimum is 5).
Click here to link to a list of introduced exotic mammal species for this bioregion.
Extinct mammal species
The number of extinct mammal species that previously occurred within this bioregion is 3. (The maximum number of extinct mammal species in a bioregion is 29 and the minimum is 0).
Table: Extinct Species
There is no data available for this table within the bioregion.
Management responses
Reserve consolidation
This bioregion includes two large reserves - Barranyi (North Pellew Island) and the recently declared Limmen Gate National Park. Together, these provide reasonably good representation of the bioregion's environmental variation. However, many localised conservation attributes (significant seabird breeding colonies, occurrences of the highly localised endangered carpentarian rock-rat) are unreserved, and warrant some formal protection. The carpentarian rock-rat distribution falls entirely within one pastoral holding (Wollogorang-Wentworth), which also contains the highest density and diversity of monsoon rainforest patches in the bioregion.
Click here to link to a table of comprehensiveness, adequacy and representativeness (CAR) of the National Reserve System in terms of ecosystems and area sampled and a ranking of reserve management. The bioregional priority for consolidating the National Reserve System is based on this CAR analysis and threat.
Click here to link to a table of bioregional and subregional priorities and ecosystem priorities to consolidate the National Reserve System and associated ecosystem constraints.
Off-park conservation for species and ecosystem recovery
The main priority for species management in the bioregion involves the protection of significant breeding sites for colonial seabirds and marine turtles. Mostly, these are not facing immediate or major threats, but there is potential for damage from increased spread of feral animals (especially pigs), uncontrolled visitor access, and overexploitation of eggs.
This bioregion contains one successful example of off-reserve conservation activity, with exclosure fencing of a significant stand of cycads on Manangoora pastoral leasehold.
Integrated NRM
As with most other bioregions in northern Australia, the major NRM priorities concern broad-scale control of threatening processes, especially feral animals, weeds and altered fire regimes. To deliver this control, there needs to be increased resourcing, better coordination across landholders and tenures, and some capacity building.
Map: IBRA map showing frequency of recovery actions (species).
Map: IBRA map showing frequency of recovery actions (ecosystems).
Map: IBRA map showing existing projects part of NRM.
Click here to link to a table of contribution of integrated Natural Resource Management to the protection of biodiversity in each subregion: existing measures and effectiveness.
Click here to link to a table of contribution of integrated Natural Resource Management to the protection of biodiversity in each subregion: feasible opportunities and comments.
Further Information & Gaps
Data gaps and research priorities
The biodiversity of the Gulf Coastal bioregion is moderately well known through a series of surveys, but these haven't been integrated, most were conducted 10-30 years ago, and some large portions of the bioregion were not represented in these samples.
Management would also benefit from more detailed environmental mapping, in particular vegetation mapping at the scale of 1:250,000 or better.
Currently in this bioregion, there is no substantial monitoring program which includes as a major goal the assessment of trends in biodiversity conservation. Such a program should be a management priority.
References
Environment Australia 2000. Revision of the Interim Biogeographic Regionalisation of Australia (IBRA) and the Development of Version 5.1. - Summary Report. Department of Environment and Heritage, Canberra.
A complete list of references is available by clicking here.
Further information
View the Landscape Health in Australia report.
View the Terrestrial Biodiversity Assessment 2002 report.
Download the Terrestrial Biodiversity Assessment 2002 Database - Biodiversity Audit Data Entry System (BADES), and specifications
Click here to link to a table of some major data gaps in each subregion in terms of protecting biodiversity.
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