Green and Golden Bell Frog - Conservation Status

Conservation Status

The numbers of Green and Golden Bell Frogs are estimated to have declined by more than 30% in the past ten years. It is listed as globally and nationally vulnerable, and as endangered under the New South Wales Threatened Species Conservation Act, 1995. Although it is only classified as vulnerable at national level, the National Frog Action Plan classifies the Green and Golden Bell Frog as endangered. In contrast to Australia, the frogs are abundant in New Zealand and classified as feral and unprotected.

There are many factors thought to be responsible for the dramatic decline of this species in Australia: these include habitat fragmentation, erosion and sedimentation of soil, insecticides and fertilisers contaminating water systems, the introduction of predatory fish and alteration of drainage regimes. Population declines are closely related to the introduction of the Eastern Mosquitofish (Gambusia holbrooki), a species native to North America that was introduced in order to control mosquito larvae. Laboratory studies have demonstrated that the eggs and tadpoles of the Green and Golden Bell Frog are extremely susceptible to predation by this fish, and in 77 of the 93 sites in New South Wales where the Green and Golden Bell Frog was known to have disappeared before 1990, Eastern Mosquitofish was found to be present. The frogs have been known to inhabit waters containing the fish, but breeding is rarely successful there, pointing to the fish's voracious eating of eggs and tadpoles. The fish are not yet present in eastern Victoria, where Green and Golden Bell Frog numbers have remained solid, but it is anticipated that the fish will spread to rivers there, possibly inflicting heavy losses on the frogs.

Other factors thought to affect this species include predation by introduced mammals such as cats and foxes, changes to water quality at breeding sites, herbicide use, and loss of habitat through the destruction of wetlands. The amphibian chytrid fungus appears to have led to at least some of the decline in numbers, but the relative importance of the various factors is unclear. It is also speculated that the frogs have become more susceptible to chytrid rather than the fungus being more common. The genetic pool of the frogs has been found to be relatively small, something attributed to habitat destruction, which has confined the smaller groups of frogs to isolated pockets and increased the incidence of in-breeding. This has led to proposals for frog populations to be mixed by human intervention in an attempt to reduce negative genetic effects and boost survival rates.

There has also been speculation that the cannibalism of the frog has caused its decline in some areas, because the smaller tadpoles that it eats can be toxic. Other postulated causes of the decline include increased ultra-violet radiation due to the hole in the ozone layer, global warming and increased drought. The first theory was tested and the results were inconclusive. Global warming is not thought to be a credible cause as the extremities of the frog's range has not changed, while declines in population have occurred in both dry and wetter areas.

The Green and Golden Bell Frog has been the subject of much research and monitoring, important to improving its conservation. Research focuses on the development of management measures to keep the introduced mosquitofish under control. These include poisoning the fish, but the waterways are large and trials have given mixed results. Predators of the mosquitofish have also been tried. Other strategies may allow for the development and improvement of suitable habitat, and to increase the reproductive success of the species. Parallel to these measures, community awareness programmes have also been proposed. One difficulty in protecting the frog is that only 20% of the known populations in New South Wales since 1990 occur in conservation parks. Of the eight populations that occur in conservation parks, only five are wholly located within them and one of these is non-breeding. There have been calls for legislation to be introduced to stop habitat degradation on private land to prevent detrimental effects to the frogs. Many proposed developments have been subjected to legal action to protect the habitat, and some communities have started "Friends of the Green and Golden Bell Frog" action groups. As public awareness has increased, documentary and news segments on the deteriorating situation have become more frequent and references to the frog in environmental logos and artworks have increased. The effort to increase public consciousness of the Green and Golden Bell Frog has also been aided by the fact that its colours are the same as the national colours. Restrictions on logging close to areas inhabited by the frogs have been put in place. As Green and Golden Bell Frogs are mostly observed in environments disturbed by humans, targeted environmental interference is seen as a possible means of enhancing habitats.

In 1998 a captive breeding program was set up by the herpetofauna staff at Taronga Zoo in Sydney, sponsored by the ASX Frog Focus. The purpose of the program was to help preserve declining populations of Green and Golden Bell Frogs in the Sydney region. It involved the captive breeding of wild frogs and releasing large numbers of tadpoles back into the wild, habitat restoration and post-release monitoring. The program was initially titled Frog Focus Botany as Botany was the original focus site. Thousands of tadpoles were released into a site in Sir Joseph Banks Reserve and post-release monitoring was done by the local community. It was also the first time that school students had been involved with endangered species monitoring. The program has since branched off into several other areas. Between 1998 and 2004, tadpoles were released into specially designed ponds and dams on Long Reef Golf Course at Collaroy in northern Sydney, with little success. Although Green and Golden Bell Frogs had previously been located in the area, the population had since been lost. Mature male Bell Frogs are occasionally found there; however, a permanent breeding population is yet to be established. An attempted reintroduction at Marrickville in inner-Sydney has failed due to chytrid.