Effects of density-dependent and environmental processes on long-term recruitment dynamics of barramundi (Lates calcarifer) in a tropical wetland

Context Understanding the biological and environmental processes that regulate populations is a central goal of ecology and is fundamental to fisheries management. Aims This study aims to quantify the environmental and biological factors influencing barramundi (Lates calcarifer) recruitment dynamics in Corroboree Billabong, a seasonally isolated reach of the Mary River, located in the wet–dry tropics of northern Australia. Methods Depletion sampling was conducted annually by using gillnets, and the age of sampled individuals was estimated, providing age-specific abundance estimates across a 20-year period. To explore the biotic (e.g. density dependence) and abiotic (e.g. rainfall) drivers of recruitment and size-at-age, a Piecewise Structural Equation Model was developed. Key results Young-of-year recruitment was negatively correlated with 1-year-old abundance, and size-at-age was negatively correlated with cohort strength, suggesting that cannibalism and intraspecific competition are important determinants of recruitment and juvenile growth rates respectively. Wetter years were associated with stronger recruitment, and higher rates of emigration by 1-year olds. Conclusions Our results provided new insights into river–floodplain fish recruitment dynamics showing that both density-dependent and abiotic drivers can affect recruitment dynamics. Implications Incorporating both abiotic and biotic drivers may improve the predictive capacity of population and stock assessment models to underpin sustainable management of this valuable and iconic species.