The southern bell frog (Ranoidea raniformis) is a federally listed Vulnerable species that has experienced substantial declines across much of its distribution since the early 1970s. Declines have been particularly severe in the Murray-Darling Basin, with only four populations of the subspecies R. r. raniformis known to persist in New South Wales. Historically recorded from the Greater Cumbung region in the floodplain of the lower Lachlan River, southern bell frog records declined markedly following extensive habitat drying in the late 1990s and early 2000s. Following major flooding events during 2021 and 2022, the species has again been detected by NSW DCCEEW. As a highly mobile and opportunistic species, southern bell frogs move and breed among permanent and ephemeral wetlands in response to favourable hydrological conditions. Given the increased connectivity between the Greater Cumbung region and Lowbidgee floodplain during flooding events, it is plausible that the newly detected frogs have recolonised from the adjacent Lowbidgee population, are representatives of remnant lower Lachlan populations, or both.
This study aimed to determine the origin of southern bell frogs in the Greater Cumbung region. Tissue samples from frogs in the Cumbung and Lowbidgee were collected and analysed, investigating for any genetic structuring corresponding to the Lachlan and Murrumbidgee rivers. Preliminary analyses revealed no detectable genetic differentiation between the two groups, suggesting that frogs occupying the lower Lachlan and Lowbidgee floodplains form a single, dynamic population. Field surveys also documented widespread breeding and recruitment, with approximately two-thirds of sampled individuals identified as juveniles or subadults. Together, these findings indicate population recovery across the Lachlan floodplain, likely due to both dispersal and low-density persistence of individuals in the lower Lachlan. Continued monitoring will improve understanding of dispersal, floodplain connectivity and habitat use, providing valuable information for future conservation management efforts.