Post-release monitoring of site and group fidelity in acoustically tagged stocked fish

Abstract Understanding post-release dynamics of stocked fish is essential to successful stock enhancement. This study aimed to match existing life history knowledge to optimise productivity of releases of mulloway, Argyrosomus japonicus (Temminck & Schlegel) into an urban estuary. Passive acoustic telemetry was used to monitor the movement of juvenile mulloway in the Georges River, New South Wales, Australia, and assess the effect of release site and abiotic factors on broad-scale movements of individuals for 26 weeks. This study found that release site primarily determines the location within the estuary where individuals reside. Water temperature, atmospheric pressure and rainfall did not correlate with fish distribution, although a flood drove fish stocked from upper and mid-river sites down the estuary in February 2008. Fish gradually returned to these sites over the following 9 weeks. Emigration rates showed an initial downstream migration and an overall egression of ~50% of fish from the release site over 26 weeks. Fish released in this study showed a degree of site- and group-fidelity, with fish distributing according to release site. It is recommended that future releases of mulloway are undertaken directly into nursery habitat in upper estuarine regions to minimise emigration and maximise efficiency of stocking programmes.