Non Technical Summary

Many of the commercially important fish and prawns in southeastern Australia spawn in the ocean but use estuaries as nurseries. In the estuaries of northern and central New South Wales, floodgates often form barriers that prevent these juvenile fish and prawns from reaching preferred nursery areas. Many of these barriers can be modified and managed to maximize the passage of juvenile fish and prawns during specified periods, but fish passage is only one of many competing considerations when assessing schedules for opening floodgates. It is therefore important to determine if there are seasons when the influx of juvenile fish is particularly high, so that this consideration can be incorporated into floodgate management policies. Information about juvenile fish from a recent study of the impacts of floodgates on fish and prawns in the Clarence River was analysed and compared with other sources of information about juvenile fish in southeastern Australia. It was found that winter and spring are particularly important seasons for juvenile fish and prawns in northern New South Wales and these seasonal influxes are related to rainfall patterns. Patterns in the seasonal influx of juvenile fish must be considered when developing floodgate management policies in this region.