Invasion and establishment of the Cane Toad Bufo marinus was listed as a KEY THREATENING PROCESS on Schedule 3 of the Threatened Species Conservation Act 1995 [21 April 2006].
The Cane Toad is a highly invasive species of amphibian which was originally introduced into Queensland in 1935. It has since spread west into the Northern Territory and south into NSW, where they exist in a patchy distribution extending from the Queensland border south to Broadwater and west to Lismore and the headwaters of the Richmond River Valley. Small disjunct populations occur at Yamba and Port Macquarie.
The current spread in NSW is approximately 3-4km per year, which may be punctuated by brief spreads of relatively rapid movement often assisted inadvertently by human movement e.g. by “hitch-hiking” with produce or landscaping materials.
Cane toads are capable of exploiting a wide variety of habitats from moist forest to beach dunes and are often found in gardens and along roads. Dense vegetation tends to act as a barrier to movement (DEH 2005). Breeding occurs in both permanent and temporary water bodies, including brackish ponds and slow-flowing streams and intensifies after rain. Females lay clutches of 8,000 to 35,000 eggs up to twice per year (Barker et al 1995, Anstis 2002, DEH 2005). Adults mature in 6-18 months and live for about five years (DEH 2005).
The impacts of cane toads on native biodiversity occurs through predation and lethal ingestion of cane toad toxin. In addition, cane toads are likely to cause declines in faunal biodiversity by competing with other carnivores for food resources.
Threatened species potentially at risk include the Spotted-tailed Quoll (Dasyurus maculatus), Pale-headed Snake (Hoplocehalus bitorquatus) and Stephens Banded Snake (Hoplocephalus stephensi) which are likely to suffer population declines as individuals are poisoned while preying upon young toads. Predation by adult cane toads on threatened frog species and by cane toad tadpoles on the tadpoles of these species including the Green and Golden Bell Frog (Litoria aurea), Wallum Froglet (Crinia tinnula), Green-thighed Frog (Litoria brevipalmata) and Olongburra Frog (Litoria olongburensis) is expected to reduce population viability of these species and potentially contribute to extinction. Severe disruption to the biodiversity of Lord Howe Island is anticipated if the cane toad becomes established in this ecosystem.
There is no current efficient method for significantly reducing established populations of cane toads. Trapping has some potential to eradicate small, isolated populations or create a barrier to expansion, but is labour-intensive.
A National Cane Toad Taskforce, established by the Australian Government, recently reviewed potential options for control including cane toad-specific pathogens, production of sterile males, a cane toad-specific toxin and genetically modified organisms that could interfere with toad development (Vertebrate Pests Committee, 2005). However, these measures require detailed research over a considerable period and the Taskforce has recommended that modelling be undertaken to determine the control measures with the highest probability of success. When this work has been completed it is understood that governments will be approached to support a coordinated, national research program.