Closing the life history loop on a fish species with embayment, coastal and oceanic life phases

The King George whiting, Sillaginodes punctatus, is a key fishery species in southern Australia that has a long larval duration and potentially extensive larval dispersal from coastal spawning grounds to juvenile nursery areas... [ view full abstract ]

The King George whiting, Sillaginodes punctatus, is a key fishery species in southern Australia that has a long larval duration and potentially extensive larval dispersal from coastal spawning grounds to juvenile nursery areas in embayments with seagrass. Currently the connectivity between populations in different States in south-eastern Australia (Victoria, South Australia, Tasmania) is poorly understood, creating difficulties with cross-jurisdictional management. To date the only confirmed spawning area is in Investigator Strait, South Australia. We are using otolith chemistry and microstructure to examine whether post-larvae collected from nursery areas in Victoria and South Australia come from the same or different spawning areas, whether juveniles remain in the embayment they settled in for their early life or move between embayments, and whether sub-adults leaving Victorian embayments migrate back to the known spawning area in South Australia. Results from larval otolith chemistry and daily increment widths provide support for the hypothesis that different spawning sources may contribute to post-larval recruitment in South Australia and Victoria. Differences in otolith chemistry between States and sampling years were mainly driven by Magnesium, and the differences were reflected in early larval growth rates determined from otolith microstructure, indicating that chemical differences were physiologically based. We have also found differences in chemistry at the edge of otoliths from post-larvae and 3 year old sub-adults from nursery embayments that are consistent with ambient water chemistry effects. Evidence to date suggests that sub-adults in Victorian embayments do not migrate to the Investigator Strait spawning area in South Australia. Finally, we now have evidence for a second spawning area in north-western Tasmania that is consistent with earlier modelling studies suggesting that is could be a potential spawning area for post-larvae settling in Victorian embayments. This project is nearing completion and the presentation will give an overview of the project outcomes to date.