Water for the environment is delivered to inundate wetland habitats in the Gwydir Wetland system to support vegetation and wetland-dependent fauna including waterbirds, fish and frogs. Frog surveys were undertaken in the Gwydir Wetlands each spring from 2015 to 2019 to document frog responses to managed and natural flows. This information was used to support environmental water management by government agencies in consultation with environmental water advisory groups.
Visual encounter surveys were completed in 16 sites to assess frog species richness, relative abundance and breeding activity. We used Random Forest Analysis to examine 19 explanatory variables and their influence on flow-responsive frog calling activity and breeding success. This included: inundation extent and duration, local rainfall, water depth, habitat structure and cumulative river discharge prior to the surveys.
Our analysis highlighted that multiple variables influenced breeding attempts (calling activity) and breeding success (number of juvenile frogs) in flow-dependent frog species in the Gwydir Wetlands. The most important metrics related to wetland inundation and cumulative river flows. The extent of inundation in each survey site was the most important variable for predicting high numbers of calling male frogs, followed by inundation timing and the proportion of short emergent aquatic vegetation. Whereas cumulative river flows prior to the surveys (120, 60 and 30 days) had the greatest influence on frog breeding success.
Our results hold important implications for environmental water management, highlighting flows that inundate floodplain wetlands over spring and summer can support the breeding requirements of flow-dependent frog species. While widespread inundation can maximise frog breeding activity, successful breeding outcomes rely on adequate water depths being maintained for tadpoles to complete metamorphosis into juvenile frogs (i.e. more than three months).