The Gulf Plains IBA encompasses an extensive mosaic of saline mudflats, coastal grasslands, wetlands and woodlands in an area stretching from west of Burketown to north of the mouth of the Mitchell River, in the south-eastern Gulf of Carpentaria. The whole length of the coast is included within a single IBA as the whole area is used by significant numbers of birds, although the distribution of some species varies between years depending on the extent of flooding. This low-lying area is at the interface of the shallow Gulf of Carpentaria and the outflow of numerous river systems including the Mitchell, Gilbert, Norman, Flinders, Leichhardt and Nicholson Rivers. In the summer (December to March) wet season much of the area can be inundated as rivers overflow their banks, occasionally submerging all but the highest sand ridges. Rivers are fringed with woodlands dominated by Melaleuca spp., frequently with some rainforest elements including Nauclea orientalis, Ficus spp. and Cathormium umbellatum. Many of these riparian areas are dominated by the invasive, introduced species rubber vine Cryptostegis grandiflora that is altering the structure of the woody strata. Levees are generally dominated by Corymbia spp. (bloodwood) woodlands. Extensive floodplain vegetation includes grassy eucalypt woodlands and open-woodlands, generally dominated by Eucalyptus microtheca, and freshwater grasslands dominated by Dichanthium spp.. Depressions on the floodplains contain Oryza spp. (rice) grasslands that are of great importance to birds. These floodplains and levees are also an important resource for grazing cattle, the dominant industry in the region. In some parts, overgrazing has seen a change in the ground layer from being dominated by perennial grasses to annuals which has implications for granivorous bird species. Numerous freshwater wetlands are present, both permanent and ephemeral, and these have great importance for waterbird populations as breeding areas and feeding grounds. Marine wetlands are both subtidal and intertidal, comprising open water over unconsolidated muddy to sandy bottoms (Blackman et al. 1999). Along coastal margins, tidal inlets are fringed with mangrove low open-forests, while extensive salt flats support Halosarcia spp. (samphire) low shrublands and patchy grasslands of Sporobolus virginicus and Xerochhloa imberbis. The Gulf of Carpentaria region is an important fishery, with permanent fishing camps situtated on each major estuary. In general terms, apart from shorebirds, the fauna of the IBA is poorly documented, and the IBA may be globally important for other waterbirds. In particular, with better data, the IBA could be extended north and east of Normanton through Glenore, Miranda Downs and Dunbar to include breeding habitat for Sarus Crane. Although most of the area is cattle-grazing leasehold (with an area of freehold at Kowanyama), some areas are designated or proposed as 'Wild Rivers', which commits the Queensland government to conserving the ecological integrity of these catchments.
Individual locations are important breeding sites for congregatory waterbirds. A 1992 survey at Macaroni Swamp included Magpie Goose (c. 3500), Pacific Black Duck and Grey Teal (c. 2000), Sarus Crane (c. 100) and Australian Pelican (c. 500). The great concentration of wetlands in the Smithburne-Gilbert Fan Aggregation north of Karumba is important for many species. In 1992 a breeding colony of herons and cormorants estimated at 10-12,000 birds was noted along the Smithburne River and included egrets and Little Black Cormorant (Blackman et al. 1999). In 1982, heronries of several thousand Great, Intermediate and Little Egrets, Pied Heron, Rufous Night-Heron, Royal Spoonbill, Australian White Ibis, Australian Darter, Little Black and Little Pied Cormorant (Garnett 1985). Smaller colonies at the mouth of the Bynoe and Flinders Rivers in 1983 contained, in addition, a nest of Great-billed Heron. Mangrove Grey Fantail, White-breasted Whistler, nationally significant numbers of many other non-breeding waders, some of which show declines perhaps related to seasonal fluctuation or count timing, including Bar-tailed Godwit (1443-2087); Greater Sand Plover (1732-2504); Red-capped Plover (324-679 from 5000 in 1993); Pacific Golden Plover (48-70 from 2000); Common Greenshank (2751-6331), Marsh Sandpiper (2943-4661), Terek Sandpiper (289-4315), Curlew Sandpiper (8500 recorded 1993 and 371-537 recorded 1999); Whimbrel (1031-3441), Masked Lapwing (1514-2520), Grey Plover (577-1279) (Garnett 1989, Watkins, 1993; Driscoll 2001). Listed as endangered in Queensland, Little Tern is recorded breeding in the area, and sightings of Grey Falcon, Bush Stone-curlew, White-browed Robin and Masked Finch are recorded in the Atlas of Australian Birds database.
Non-bird biodiversity: The Southeast Gulf of Carpentaria contains important populations of Saltwater Crocodile (Vulnerable) and the more common Freshwater Crocodile. Loggerhead Turtle, Green Turtle, Hawksbill Turtle, Olive Ridley and Flatback Turtle have been recorded from the adjacent ocean and are likely to utilise the beaches of the IBA. Rare plants include Aponogeton queenslandicus and Sesbania erubescens, both found in wetlands of the area. In general, the flora and fauna of the area is poorly documented.
Pressure/threats to key biodiversity
Manage invasion of invasive alien weeds including Cryptostegia grandiflora and Parkinsoniana aculeata on floodplains and riparian areas, and Cenchrus ciliaris and Ziziphus mauritianus on dunes and abandoned levees. Monitor grazing of wetlands by cattle, feral horses and feral pigs.
Conservation responses/actions for key biodiversity
The Queensland Herbarium, Environmental Protection Agency is currently mapping regional ecosystems of the area to a scale of 1:100,000 with the program scheduled for completion in 2006-2007.
The IBA contains one protected area (Finucane Island National Park) and overlaps with four protected areas (Mutton Hole Wetlands Conservation Park, Morning Inlet-Bynoe River Fish Habitat Area A, Nassau River Fish Habitat Area A and Staaten-Gilbert Fish Habitat Area A).
Lease-hold stations; Crown Land below high water mark.
Site access / Land-owner requests
The majority of the IBA is Crown Land under grazing lease. Access is restricted to people with permission from individual leasees.