Migratory dynamics and recruitment of snapper (Pagrus auratus) in Victorian Waters
Over the past decade there has been a major decline in the commercial and receational snapper fishery in Port Phillip Bay, the commercial catch declining from 200 t to 40 t. At present, the status of the Port Phillip Bay snapper fishery is in doubt because the relationship between the Port Phillip fishery and the western stock as a whole is unknown. Whether catch declines in Port Phillip Bay are a result of local factors such as overfishing or local recruitment variability, or whether they are the result of change in the migratory dynamics of snapper between Port Phillip and offshore waters, will not be known without new research that is novel in its approach. At present we cannot be certain whether the apparent decline snapper in Port Phillip Bay mirrors a decline in the entire western stock. Imposing management controls is difficult in the face of such uncertainty, and therefore the snapper fishery in Port Phillip is under threat. This project, endorsed by the recent workshop on snapper research in Victoria, aims to clarify some aspects of the relationship between snapper in Port Phillip Bay and the rest of the western stock. Otolith microchemistry is a novel technique that may prove very powerful in answering questions about the origin and migration patterns of snapper in the Port Phillip. In addition, pre-recruit sampling across the Victorian coast will indicate whether high recruitment variability observed in Port Phillip is reflected by the entire stock.
1. Determine whether high annual variability in the abundance of pre-recruit snapper in Port Phillip Bay is reflected by the entire western stock
2. Determine the importance of spawning of snapper within Port Phillip Bay to the western stock as a whole.
3. Determine the movement patterns of snapper between Port Phillip Bay and offshore waters and whether they are changing over time
4. To determine the proportion of the snapper population on the open coast that originates from Port Phiilip Bay and how this changes with age.
5. To determine the proportion of the snapper population in Port Philip Bay that originates from areas outside the bay and how this changes with age.
Principal Investigator: Paul A. Hamer and Gregory P. Jenkins