Long-term monitoring of Watson’s Tree Frog Litoria watsoni and other lotic species of amphibian in the Shoalhaven Local Government Area, New South Wales

Abstract

ABSTRACT Replicated systematic nocturnal searches were conducted along creeks for the endangered Watson’s Tree Frog Litoria watsoni located in heath and woodland at or above 90m AHD on the south coast of New South Wales. Thirteen sites were surveyed in spring from 2001-2023. Breeding activity, including the occurrence of calling males, tadpoles, spawn and amplecting pairs was detected at 12 of the 13 surveyed sites. Within the duration of the surveys the south coast region experienced two major droughts, two wildfires and one year of exceptionally high rainfall. The number of frogs detected per year ranged from 23 to 109, with the lowest number found in 2020, some eight months after a wildfire burnt all sites. Comparisons of the mean number of frogs detected among years revealed the population took 13 years to recover from a wildfire in 2002 and was significantly impacted again by wildfire in 2020. There is evidence that drought that preceded the fires in the summer of 2019-2020 reduced the number of frogs observed prior to the commencement of the fires in late spring 2019. Fire and below average rainfall are implicated in a significant decline in L. watsoni. The number of L. watsoni and several other common species of frog observed differed among and within sites over time and illustrate the value of multi-year monitoring to understand the dynamics of population distribution and abundance with long-term variations in climatic conditions, and the effects of extreme events such as wildfire and flood. The non-endemic yabbie Cherax destructor expanded its distribution since it was initially detected at one site in 2006 and now occurs in the upper laterals of two catchments, having moved above waterfalls.