Conservation of the endangered Green and Golden Bell Frog: what contribution has ecological research made since 1996?

The status and conservation requirements of the Green and Golden Bell Frog Litoria aurea were the focus of immense scrutiny 12 years ago. In this paper I review what progress has occurred since then in understanding the ecology of this species because ecological research is of fundamental importance to the recovery of threatened species. Field surveys and collation of unpublished information have led to a very detailed understanding of the distribution of this species, including recognition that some populations have become extinct since 1996. Population studies involving the permanent tagging of individuals have revealed substantial variation in the size of populations but further research is needed to relate population size to viability. Two major threatening processes (habitat loss and predation by exotic fish) were implicated in 1996 in the decline of the Green and Golden Bell Frog, though others were acknowledged. Provision of breeding habitat has been a key element of bell frog management since then but despite some success, there have been few general insights gained concerning its effectiveness to allow existing populations to expand. Attempts to translocate bell frogs to suitable breeding habitat have failed to establish self-sustaining populations but insights have been gained concerning husbandry, infection control and optimal field conditions for tadpole development. Studies conducted since 1996 have confirmed the negative impact of predation by the exotic Plague Minnow Gambusia holbrooki on bell frog breeding success. Although fish predation is a prominent consideration when devising management plans for breeding habitat, our understanding of the role of this threat in regulating frog populations is still limited. The amphibian chytrid fungus Batrachochytrium dendrobatidis has now been recognized as an additional key threat to bell frog populations but research on this is in its infancy. My attempt at a general synthesis to understand the dramatic decline of the Green and Golden Bell Frog suggests that habitat loss and fragmentation were the ultimate cause because they predisposed the species to the impacts of fish predation and disease. The species has persisted where multiple waterbodies, including those that are fish-free, occur within 1-2 km of each other. This provides a clue to conserving populations - it is likely that local population size and viability will be correlated with the number of available waterbodies. Progress to enhance the viability of key populations in each region has been slow. If this does not occur more quickly then extinction will prevail.