River flows affect the growth of a tropical finfish in the wet-dry rivers of northern Australia, with implications for water resource development

Freshwater is a critical input to estuaries but is under increasing demand to support upstream human activities. In this study, otolith biochronology was used to quantify the relationship between river discharge and juvenile growth rates of barramundi ( Lates calcarifer ) in three regions of the Gulf of Carpentaria in northern Australia. In all regions, river discharge had a strong positive effect on juvenile growth rates. Models were also developed which incorporated the Southern Oscillation Index (SOI) and the Madden–Julian Oscillation (MJO). SOI values corresponding to La Niña events had strong positive consequences for juvenile barramundi growth rates in all regions, and the intensity of positive wet season MJO pulses had a strong positive effect on growth rates in the perennially flowing river, but not the intermittently flowing rivers. The consequences of three hypothetical water development scenarios were estimated for the perennial river. The model predicted a 12%, 8% and 1% reduction in annual barramundi growth rates under proposed scenarios for 18%, 8%, and 3% reduction in river discharge, respectively. Fish growth is a robust, quantitative metric that can be monitored pre and post water resource development to identify the least impactful development scenario and monitor its compliance and success through time.