Estuarine movements in a sparid hybrid complex

Abstract

Context Movements of purebred and hybrid complexes of species show the interactions that facilitate hybridisation and genetic introgression. Aims This study combines genetic analysis of Acanthopagrus spp. and acoustic tracking to understand the spatial ecology of this species complex. Methods Acanthopagrus australis (yellowfin bream) and the Acanthopagrus hybrid complex of A. australis and Acanthopagrus butcheri (black bream) were tracked using acoustic telemetry within a south-eastern Australian estuary. Key results Movements between A. australis and Acanthopagrus hybrids showed similarities, fish displayed high levels of residency and site fidelity, with peak distributions occurring 15 and 32 km upstream of the river entrance. Offshore movements were recorded for 43% of A. australis and 38% of Acanthopagrus spp. hybrids where fish did not return to the study estuary. Estuarine movement patterns in A. australis and A. spp. hybrids were significantly related to conductivity, freshwater flow, temperature, genetic classification, and capture location. Repetitive spawning migrations were not observed for either A. australis or A. spp. hybrids. Overlap in distributions throughout the spawning period did occur. Conclusions This study highlighted the complexity of estuarine movement patterns in A. australis and Acanthopagrus hybrids because they appear to be dependent on freshwater flow, temperature, and ancestry. Implications A. australis and A. spp. hybrids may be capable of spawning within estuaries, and adult offshore movements may play a role in the genetic mixing of populations.