Sessional Committee on Environment and Sustainable Development Written Submissions Received Volume 2 Issues associated with the progressive entry into the Northern Territory of Cane Toads October 2003
Tabled Paper 1123
Tabled Papers for 9th Assembly 2001 - 2005; Tabled Papers; ParliamentNT
Tabled by Delia Lawrie
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ERISS Kakadu Report 2002 Written Submissions Cane Toad Inquiry Report Volume 2 40 Identification of the problem Since their introduction to Australia in 1935 to control sugar cane pests in Queensland, cane toads have spread naturally and with human assistance throughout much of Queensland, northern NSW and the Top End of the NT. The cane toad's preference for certain disturbed areas means that areas of degraded natural habitat have probably helped their spread. They eat a wide variety of prey, breed opportunistically, have a far greater fecundity than native anurans, and develop rapidly particularly in warmer waters. They tolerate a broad range of environmental and climatic conditions, can occupy many different habitats and compete for resources with many native species. Most significantly, they possess highly toxic chemical predator defences, with many experimental and anecdotal reports of deaths of native predators that have attempted to consume cane toads. It is accepted that the cane toad will establish and spread rapidly in Kakadu National Park - a World Heritage area with Ramsar listed wetlands, well known for its spectacular wilderness, nature conservation values, rich diversity of habitats, flora and fauna, and cultural significance. There is serious concern that the World Heritage status of Kakadu National Park could be diminished if any of these attributes were adversely affected by cane toads. The potential extent of cane toads in Kakadu National Park Cane toads are likely to colonise almost every habitat type within Kakadu National Park. The saline regions of the coastal plains and deltaic estuarine floodplains will most likely support some cane toads at various times, although they are not likely to use these habitats on a permanent basis. Other less suitable areas include deep open water and/or flowing channel habitats and tidal regions of larger rivers (excluding riparian zones) which extend 70 to 80 km inland during the Dry season. The steady range expansion over the last ten years indicates that most wetland habitats are probably suitable as breeding habitat and also as Dry season refuges. Patterns of dispersal within Kakadu will probably rely on the transport corridors and the major rivers and creeks. Dispersal rates within a catchment could be up to 100 km y-i. The current location of cane toads would indicate an initial progression down the South Alligator River catchment via its sub-catchments (e.g. Jim Jim Creek, Deaf Adder Creek). Invasion of other areas of the Park will likely depend on which waterways' headwaters are colonised first (e.g. Mary River, East Alligator River). Maximum population densities of various cane toad life stages for limited areas of suitable habitat in Kakadu could be expected to be in the order of. 4000 to 36 000 eggs per metre of shoreline; ~15 to 60m- for tadpoles; 2.5m- for metamorphlings; and 2000 ha-1 for adults, depending on temporal and spatial factors. The Dry season will see a gradual retreat of many cane toads from seasonally inundated wetlands. The vegetation and cracks in the black soils on the floodplains should offer sheltered, moist habitat during the mid Dry season. In the late Dry season, adult cane toads will congregate near permanent water with adequate shelter. Few cane toads would be present in the drier areas of the tall, open eucalypt forest and woodland habitats of the lowland plains. The first rains of the Wet season will stimulate dispersal and increased breeding activity. With the progression of the Wet season, cane toads will disperse into terrestrial habitats, namely the open forests and woodlands. When large areas of the floodplains are inundated, cane toads will be concentrated on the remaining dry ground, which may make them highly visible to Park visitors.