Assessing the impact of the Cane Toad,
Bufo marinus, on the terrestrial fauna of the
East Kimberley using best-practice terrestrial fauna surveys
Graham G Thompson and Philip C Withers
School of Animal Biology, University of Western Australia
Cane toads (Bufo marinus) will invade the east Kimberley of Western Australia in the next few years and will have a devastating negative impact on the fauna and the ecosystems of region. Species identified as being at serious risk include: the Northern Quoll , Sand Goanna, Yellow Spotted Goanna, Spotted Tree Goanna and the Water Monitor. Many other species have been identified as ‘probably’ at risk, but we are unsure of their status because of a lack of information.
A plethora of investigations have assessed the impact of cane toads on single species or taxa but only two have assessed the impact on broad scale terrestrial ecosystem function. Both of these studies have serious limitations due to small sample sizes and an inability to accommodate normal temporal variations. We therefore have little understanding of the impact that cane toads have on ecosystem function, and on all but a few significant species. Our study will address this issue and will be the first study in Australia that comprehensively sets out to measure the impact of cane toads on ecosystem function on a regional scale. We also intend to investigate, and if feasible, implement a program that relocates goannas onto islands in Lake Argyle , to preserve aspects of the Kimberley biodiversity considered to be most at risk as a consequence of the cane toad invasion.
We propose a comprehensive four year survey program that will:
- establish quality baseline data on small vertebrate assemblages in the east Kimberley , to assess the long-term impact that cane toads have on these assemblages;
- validate and refine our Degradation Index to quantitatively measure the impact that cane toads have on the functional ecosystems of the Kimberley ;
- provide an improved strategy of assessing the small vertebrate terrestrial fauna in the wet-dry tropics of WA (essential for the purpose of preparing EIA statements);
- establish monitoring protocols for key vertebrate species thought to be at risk; and
- explore, and if feasible, develop a relocation and breeding program for a number of goanna species on islands in Lake Argyle .
We will employ two basic survey strategies to collect the necessary data; a) a comprehensive trapping program over three years in three of the major habitat types typical of the east Kimberley, and b) a series of transects that target key species (e.g. goannas, birds of prey, frogs, mammals in riparian habitats and fish).
These basic survey data are absolutely essential if management plans are to be developed to minimise the impact that cane toads will have on the Kimberley . It will also have two other important benefits; namely providing quality base line data on the faunal assemblages of the east Kimberley, and providing a tool that measures changes in ecosystem function as a consequence of disturbance (e.g. agriculture, cane toads, mining).