Gulf coastal
Bioregional Description
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.
Special 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.
- 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 scored as continental stress class 5. - Summary of priority management/conservation priorities
The NRM priorities for this bioregion include a mix of additional reservation (particularly in the Wollogorang-Wentworth area, and also including possible IPAs 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. - Wetlands
- Nationally important 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.
- Other wetlands of subregional significance
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
- 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. - 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. - Species at risk
This bioregion includes 16 species listed as threatened at national of 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).
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 | National | 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 |
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.
- Other flora values for 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).
- Endemism
- Birds
This bioregion was not surveyed sufficiently often to detect changes over the period between the two Bird Atlases. However, longer-term changes are evident: for example, the partridge pigeon and red goshawk appear to have become regionally extinct over the last century. - Mammals
The Gulf Coastal bioregion has suffered moderate loss of its mammal fauna. Of 48 species recorded, 3 have become regionally extinct, 2 have suffered severe decline, 7 have declined, and 36 are static.
Management Responses
- Reserve consolidation
This bioregion includes two large reserves - Barranyi (North Pellew Island) and the recently declared Limmen Gate NP. Together, these provide reasonably good representation of the bioregions 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. - 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.
Further Information and Gaps
- Major data gaps and research priorities for bioregion
The biodiversity of the Gulf Coastal bioregion is moderately well known through a series of surveys, but these havent 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. - Other information