The current assessment of the Northern tiger prawn fishery is based upon a separate analysis of the fishery for each of the two species (Wang & Die, 1996). An alternative stock modelling approach, which considered both species together (Haddon, 1997, 1998), supports the results of the first method but is somewhat more pessimistic. This alternative model provides an independent view of the status of the tiger prawn stocks and the uncertainties affecting the analysis are also different. That both approaches produce a similar conclusion (that the stocks appear to be vulnerable and fishing mortality is currently too high to be sustainable in the long term), increases confidence in the conclusion that there are serious problems with the fishery.
A weakness of the alternative model is that it is based upon commercial catch-effort data summarized over the statistical reporting areas and for each year. It is likely that this aggregation of catch and effort data is obscuring or biasing details of the stock dynamics. If the seasonal fishing behaviour of the trawl fleet, in terms of its use of the fishing grounds, has altered either in a steady manner or over shorter periods, this could have large implications for the real status of the tiger prawn stock which may have been obscured by the aggregation of the commercial catch-effort data. This may lead to the stock appearing to be more stressed than it is in reality. To test whether the alternative model is overly pessimistic, and to refine the analysis of stock dynamics, it would be necessary, using the same approaches as in the earlier model, to investigate stock and fleet dynamics at finer spatial and temporal scales.
The proposed modelling should reduce uncertainty over the present status of the tiger prawn stocks.