Invasion and establishment of the cane toad (Bufo marinus) - key threatening process listing

The Scientific Committee, established by the Threatened Species Conservation Act, has made a Final Determination to list the Invasion and establishment of the Cane Toad Bufo marinus as a KEY THREATENING PROCESS in Schedule 3 of the Act. Listing of key threatening processes is provided for by Part 2 of the Act.

NSW Scientific Committee - final determination

The Scientific Committee has found that:

1. The Cane Toad Bufo marinus L. is a large, squat member of the 'true toad' family, Bufonidae. Adult size is variable, averaging about 120 mm in length yet reaching 250 mm. A bony ridge runs along the top of each eye to the snout, creating a square-headed profile. The hind feet are partially webbed; the front toes are free. The upper body colour ranges from grey to brown and the granulated skin of the belly is cream or yellow. The dorsal skin is very warty, with a greatly enlarged pair of parotoid glands behind the eardrum (Barker  et al. 1995). When the toad is handled or bitten, these glands exude a milky fluid that contains numerous types of toxins, which primarily affect the heart (Queensland Museum 2000). Tadpoles, which are black and up to 27 mm in total length, are also poisonous to predators. Upon metamorphosis, young toads are about 10 mm long (Anstis 2002).

2. Cane Toads are terrestrial, nocturnal and active during warmer months. They survive cold or dry periods by sheltering in shallow excavations under ground litter, often near water (Queensland Museum 2000). 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).

3. Breeding occurs in both permanent and temporary water bodies, including brackish ponds and slow-flowing streams, and intensifies after rain. Females lay long, double-rowed strings of black eggs in continuous jelly, with each producing clutches of 8000 to 35,000 eggs up to twice per year (Barker et al. 1995, Anstis 2002, DEH 2005). Tadpoles congregate and can dominate a water body. Cane Toads mature in 6-18 months and live for about five years (DEH 2005).

4. Cane Toads have a catholic diet, with almost any vertebrate or invertebrate that can be swallowed being vulnerable to predation. Terrestrial arthropods provide the bulk of the diet. The tadpoles of this species sometimes feed on smaller tadpoles of their own and other species (Crossland 1998, Williamson 1999).

5. Cane Toads are native to Central and South America, but have been intentionally and accidentally translocated across the world. In 1935, the species was introduced to cane fields in Queensland in the hope that it would control insect pests. Further translocations and natural dispersal saw the Cane Toad spread rapidly throughout coastal Queensland (Queensland Museum 2000). Subsequently the species has moved west into drier portions of Queenland, north west into Cape York and the Northern Territory, and south into NSW (Freeland 1986).

6. In NSW Cane Toads currently exist in a patchy distribution extending from the Queensland border south to Broadwater and west to Lismore and the headwaters of Richmond River Valley. Isolated populations occur at Yamba and Port Macquarie. The species has been found in many National Parks (NP) and Nature Reserves in north east NSW, including Nightcap NP, Mebbin NP, Border Ranges NP, Yuraygir NP and Lake Innes Nature Reserve. There are no known records of Cane Toads on Lord Howe Island although accidental introduction for example via supply boats from Yamba is a potential risk (DEC 2005 in lit.).

7. The predicted range over which Cane Toads might readily expand is dependent on assumptions about the species environmental tolerances. Under current bioclimatic models, the distribution in NSW is expected to readily expand south to Port Macquarie, occupying reserves such as Hat Head NP and the southern end of Yuraygir NP. Similarly, the distribution may extend from the upper catchment of the Tweed River into headwaters of the Clarence River (DEC 2005 in lit.). The current rate of spread in NSW is approximately 3-4 km per year, but may be punctuated by brief periods of relatively rapid movement in some years (DEC 2005  in lit.).

8. Modelling of the potential distribution of Cane Toads in NSW predicts range extensions into north-western slopes of the Great Dividing Range and throughout coastal areas, with potential expansion into Victoria (Seabrook 1991, Sutherst et al. 1996). However, the recent discovery of thirteen Cane Toads at 1000 m elevation in the Border Ranges NP (D. Newell pers. comm.) may demonstrate a greater adaptability than was previously assumed for this species. Anticipated climate change due to greenhouse effects may also facilitate a broader distribution inland by 2030 (Sutherst  et al. 1995, Taylor and Edward 2005).

9. Native Australian predators do not commonly kill or eat Cane Toads with impunity due to the toxicity of both toads and tadpoles (with the possible exception of a few snakes, Phillips et al. 2003). Cane Toad populations can reach very high densities (e.g. 2000 individuals per hectare), and there is currently no efficient method for significantly reducing established populations (DEH 2005). Trapping has some potential to eradicate small populations or create a barrier to expansion, but is labour-intensive. The potential for biological control has been investigated, but is not promising due to the lack of specificity among control agents available (DEH 2005).

10. 'The biological effects, including lethal toxic ingestion, caused by Cane Toads (Bufo marinus)' has been listed as a Key Threatening Process  under the Commonwealth  Environment Protection Biodiversity Conservation Act 1999, citing, amongst other biodiversity impacts, a rapid and potentially permanent decline of Northern Quoll ( Dasyurus hallucatus) populations as Cane Toads expanded into the Northern Territory (Oakwood 2004). In NSW the same effect is anticipated as toads expand further into the range of the Spotted-tailed Quoll ( Dasyurus maculatus), which is listed as Vulnerable in NSW. In addition, two other threatened predators of amphibians - the Pale-Headed Snake ( Hoplocephalus bitorquatus, Vulnerable) and Stephens' Banded Snake ( Hoplocephalus stephensii, Vulnerable) - 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 - is expected to reduce population viability of the following species and potentially contribute their extinction.

11. In addition, Cane Toads are likely to cause declines in faunal biodiversity by competing for food with other carnivores, by preying upon small vertebrates (such as skinks) and by causing intoxication among larger predators such as goannas (Varanus spp.) and raptors (Burnett 1997, Catling  et al. 1999, Woinarski  et al. 2001).

12. Severe disruption to the biodiversity of Lord Howe Island is anticipated if Cane Toads become established in this ecosystem (DEC 2005 in lit.), including predation by toads on the Lord Howe Island Wood-eating Cockroach  Panesthia lata and  Lord Howe Placostylus  Placostylus bivaricosus, both of which are Endangered.

13. Invasion and establishment of the Cane Toad Bufo marinus is eligible to be listed as a key threatening process as, in the opinion of the Scientific Committee it adversely affects threatened species, populations or ecological communities, or could cause species, populations or ecological communities that are not threatened to become threatened.

Associate Professor Lesley Hughes
Chairperson
Scientific Committee

Proposed Gazettal date: 21/04/06
Exhibition period: 21/04/06 - 16/06/06

References: 

Anstis, M (2002) 'Tadpoles of south-eastern Australia.' (Reed New Holland: Sydney)

Barker J, Grigg GC, Tyler MJ (1995) A field guide to Australian frogs. (Surrey Beatty: Chipping Norton, NSW)

Burnett S (1997) Colonising cane toads cause population declines in native predators: reliable anecdotal information and management implications. Pacific Conservation Biology 3, 65-72.

Catling PC, Hertog A, Burt RJ, Wombey JC, Forrester RI (1999) The short-term effect of cane toads (Bufo marinus) on native fauna in the Gulf Country of the Northern Territory.  Wildlife Research 26,161-185.

Crossland MR (1998) A comparison of cane toad and native tadpoles as predators of native anuran eggs, hatchlings and larvae. Wildlife Research 25, 373-381.

DEH (2005) 'The biological effects, including lethal toxic ingestion, caused by Cane Toads (Bufo marinus).' Final determination as a Key Threatening Process under the Commonwealth  Environment Protection Biodiversity Conservation Act 1999. Department of Environment and Heritage, Canberra.

Freeland WJ (1986) Populations of cane toad, Bufo marinus, in relation to time since colonization.  Australian Wildlife Research 13, 321-329.

Oakwood M (2004) 'The effect of cane toads on a marsupial carnivore, the northern quoll, Dasyurus hallucatus.' Department of Environment and Heritage, Darwin.

Phillips BL, Brown GP, Shine R (2003). Assessing the potential impact of cane toads on Australian snakes. Conservation Biology 17, 1738-1747.

Queensland Museum (2000) Cane toads. Retrieved 20 June, 2005.

Seabrook W (1991) Range expansion of the introduced cane toad Bufo marinus in New South Wales.  Australian Zoologist 27, 58-62.

Sutherst RW, Floyd RB, Maywald GF (1996) The potential distribution of the cane toad, Bufo marinus L. in Australia.  Conservation Biology 10, 294-299.

Taylor R, Edwards G (2005) (Eds) 'A review of the impact and control of cane toads in Australia with recommendations for future research and management approaches.' Retrieved 12 July, 2005.

Williamson I (1999) Competition between the larvae of the introduced cane toad Bufo marinus (Anura: Bufonidae) and native anurans from the Darling Downs area of southern Queensland.  Australian Journal of Ecology 24, 636-643.

Woinarski JCZ, Milne DJ, Wanganeen G (2001) Changes in mammal populations in relatively intact landscapes of Kakadu National Park, Northern Territory, Australia. Austral Ecology 26, 360-370.