Gambusia control through the manipulation of water levels in Narawang Wetland, Sydney Olympic Park 2003-2005

Narawang Wetland, a precinct of Sydney Olympic Park, was constructed to provide habitat for the Green and Golden Bell Frog Litoria aurea. The Plague Minnow Gambusia holbrooki invaded Narawang following flooding soon after the wetland's completion in 2000. Narawang contains 22 habitat ponds, each attached to a water reticulation system. Predation by Gambusia has been identified as a key threatening process for the Green and Golden Bell Frog and may be a major contributor to the disappearance of many frog species in Australia. Its presence in Narawang Wetland offered a unique opportunity for investigation into its management and control. Three groups of ponds in Narawang Wetland were alternately drained in August/October each year between 2003 and 2005. Each year one pond-group was drained and left to dry for four weeks to reduce the population of Gambusia before the onset of breeding by bell frogs. Control of water levels in ponds reduced the Gambusia population. Bell frog tadpoles and metamorphs were observed only in ponds that had been drained and re-filled, however, adult frogs were distributed throughout drained and non-drained ponds. Ongoing monitoring of breeding in Narawang Wetland has shown an increase in breeding activity by bell frogs since the introduction of this program.