Considerable investment in managing water for the environment in the Murray Darling Basin relies on systematic monitoring at relevant spatial and temporal scale to assess the outcomes of environmental flows for wetland-dependent fauna, including frogs. Here we report on results of frog monitoring in the Northern Basin where we assess the ecological relevance of two key environmental water considerations: flow timing and flow magnitude.
We undertook systematic surveys during natural floods and during periods of low flows, when small environmental flows were delivered, in two large semi-arid floodplain wetland systems in northern MDB (the Macquarie Marshes and the Gwydir Wetlands). Both systems have wetlands that are Ramsar-listed and therefore considered wetlands of international significance. Survey sites were spatially stratified by vegetation type and flooding frequency. We identified all species, breeding behaviour, recorded habitat variables and local weather conditions. Inundation extent across the floodplain and individual wetland sites was calculated from Landsat imagery and matched with survey dates to determine flooding metrics.
We identified three ecohydrological groups based on adult frog activity during floods, which broadly reflected morphological and physiological characteristics: flow-responsive, flow-ambivalent and flow-oblivious. Flow-responsive species were observed calling in all survey months, but calling intensity was higher at the start of flow event. The density of individuals (individuals ha-1) remained relatively constant with flow event magnitude. Increases in calling activity and density of species in the other two groups corresponded primarily with changes in local rainfall. Managed flow events that commence in spring appeared to provide optimal breeding conditions for flow-responsive frogs in the northern MDB, with larger floods contributing to higher overall abundance and breeding activity necessary for population persistence. These findings demonstrate how long-term monitoring is critical for understanding responses of flow-dependent fauna in large variable systems and informing the planning and management of environmental water.