Stock-recruitment relationships for the tiger prawn (Penaeus esculentus) stocks in Western Australia

The tiger prawn (Penaeus esculentus) catch in the multispecies fishery of Shark Bay, Western Australia, has undergone a 50% decrease during the 1980s compared with the previous decade. To assess the cause of this decrease, the stock-recruitment relationship (SRR) has been evaluated. The effect of fishing effort on survival of the spawning stock has been assessed and a relationship between recruitment and subsequent spawning stock determined. This assessment indicates that recruitment overfishing has occurred and that a decrease in fishing effort is required if the stock is to recover. A similar conclusion was reached for the adjacent Exmouth Gulf tiger prawn fishery and the effort was subsequently reduced. However, in contrast to the Exmouth Gulf fishery, there has not yet been any major management initiative to reduce effort and improve the spawning-stock level in Shark Bay. These different management strategies for the two fisheries can be regarded as an example of the actively adaptive policies for replicated systems advocated by C. J. Walters. An update of the SRR from the Exmouth Gulf fishery shows that a marked improvement in the abundance of spawning stock has increased the level of recruitment, while the Shark Bay stock and recruitment levels continue to remain low. This contrast in the response of the two stocks to the different management measures provides supporting evidence that recruitment overfishing has occurred in these two fisheries.