A Numerical Modelling Study for the Proposed Increase in Barramundi Production, Cone Bay, Western Australia

Cone Bay is located in the Kimberly region of Western Australia. It is an area of fast flushing rates and dynamic circulatory patterns due to a 9 to 11 m tide, the second largest tide in the world after the Bay of Fundy in Canada. Marine Produce Australia (MPA) currently operates at a maximum production of 150 tonnes of arramundi per year within Cone Bay and was seeking a licence to increase the production into a commercialised venture of 1,000 tonnes per year. As part of the environmental assessment proposal, a staged desktop modelling study was carried out to examine the potential changes in circulation following the presence of sea cages and the potential for deposition and accumulation of fish waste and fish food. A side-by-side comparison of the circulation patterns indicated that for the existing environment currents within the operational area would be reduced to by the inclusion of the sea cages, but no changes in current directions were indicated. A numerical dye-study showed that Hushing times for the modified setting took approximately one day longer, due to retardation of the tidal flows. The fate of fish waste and food pellets was simulated at various sites of the existing operational area, and there was a tendency for the waste material to settle close to the release sites and along the east-west tidal axis. Based on these results, MPA had decided to position the sea cages a set distance from the boundaries to ensure that the potential effects are contained and that the environmental integrity of the area is maintained.