The apparent biomass of snapper in northern Gulf St Vincent (GSV) has increased considerably over the last three years above historic levels. This observation has coincided with a marked decline in catches by GSV Prawn and Blue Crab fishers to the extent that it has required a considerable reduction in fishing effort to promote stock recovery. As snapper are known to predate upon blue crabs and prawns, there is concern and uncertainty among fishers and managers that the downturn in these crustacean fisheries has occurred in part due to predatory ‘top-down’ regulation by snapper within GSV. The potential interaction between these three high value fisheries and their respective management has consequently generated a need to better understand the trophic interactions that underpin production of these fisheries in GSV, how exploitation rates within each fishery may impact on production in the others and what balanced exploitation scenarios would optimise production and value across fisheries, while minimising ecosystem impacts.
A GSV Ecosystem model is needed to assess the linkages between increased snapper abundance and reduced production in crustacean fisheries. Sensitivity analyses and scenario testing will identify the ecological factors important to production across the three fisheries, assessing the ecological and production implications of greater selectivity of fishing methods in king prawn fisheries and mutli-species optimisation scenarios. It will provide a decision support tool as a basis for multi-species fisheries management in GSV, and a step toward fully integrated (EBFM) whole of system management.