Prawns, climate change, rising costs and falling prices : managing NSW#146;s prawn stocks in a world of uncertainties : a quantitative analysis of prawn harvesting strategies

摘要

The monitoring and assessment of prawn populations in New South Wales (NSW), Australia, has been identified as a continuing research priority by both the fishing industry and the fisheries managers. This dissertation presents a series of dynamic population models developed to evaluate the status of the eastern king prawn (Melicertus plebejus) and eastern school prawn (Metapenaeus macleayi) populations within NSW and to analyse the relative performance of a number of alternative management strategies involving the three fisheries that target these species. Monthly commercial prawn catch and effort data from 1984 to 2006 were used to calibrate the stock assessment models. Where possible, the results of previous research were used to develop the structure of the model and to provide estimates of biological parameters. A process of increasing model complexity, including the addition of physical processes, such as river discharge events and economic considerations, was undertaken in an attempt to develop the most appropriate model for the analysis of management strategies.The first model presented was used to undertake a single-species assessment of the eastern king prawn stock and was based on a delay-difference population model with four different representations of recruitment. This model was calibrated to observations using the Bayesian sampling/importance re-sampling method and used to test the effect of significant changes in the future catch on the stock. The second model presented is a size-based metapopulation model which incorporated the dynamics of school prawns over three habitats, being harvested by three different fishing methods. This model was used to test the effect of alternative climate variability scenarios on the stock. The third model presented is a multi-species, multi-fishery bio-economic model. This model was used to examine the impact of nine alternative economic scenarios, incorporating various combinations of input costs and product prices. The results from the use of these models indicated that neither of the prawn population appeared to be over-exploited. The analyses also indicated that none of the alternative management strategies were found to stand-out enough to justify a move away from the current management strategy of input controls and spatio-temporal closures, even under a range of future scenarios including climate change and large movements in input costs and product prices.