Fish on the run: facilitating fish passage from drying floodplains

In the Murray-Darling Basin, river managers are implementing site-scale managed floodplain inundations for vegetation outcomes but there is a risk of native fish stranding during floodplain recession due to the absence of natural cues. In 2014, at the 5,000 ha Gunbower floodplain, central Murray River, we devised a fish exit strategy which included: (i) a fish ‘exit hydrograph’, a designed recession to cue fish to leave the floodplain, (ii) evaluation of a new fishlock to facilitate fish passage from the floodplain to the permanent Gunbower Creek. During our evaluation of the exit strategy we collected 113,099 fish exiting the fishlock at up to 20,000 fish/hr, with juvenile non-native carp, native Australian smelt and native carp gudgeons dominating the catch. Fish were 15-500 mm long. Native fish exited the floodplain during the initial drop where carp exited during the later half of the recession. In addition, 30 golden perch were acoustic tagged to identify their floodplain exit pathways. The implications of our results are discussed in the context of maximizing safe exit of fish from other temporary floodplain habitats