Prawn fisheries throughout Australia are intensively fished and some have shown signs of overfishing. In some cases, the current stocks of prawns are now lower than those which would produce maximum yields. The enhancement of Australian penaeid prawn fisheries has the potential to be a useful management tool to increase fishery yields, rebuild over-exploited stocks, and reduce fluctuations in catch due to variable recruitment. Stock enhancement also has the ability to improve the management of fisheries by collecting more precise information about the biological characteristics of the stock (e.g. survival and growth, production in nursery grounds, migration pathways and factors affecting fluctuation in populations).
Prawn stocks can vary greatly from year to year because of environmental fluctuations and this leads to highly variable catches. Fishery managers must therefore adopt conservative harvest strategies to prevent fishers from reducing stocks to dangerous levels in years when recruitment is low. However, the harvesting and processing sector tend to be on average, over-capitalised, in order to cope with years of high recruitment. Enhancement of prawn stocks through releasing juvenile prawns has the potential to reduce fluctuations in stocks. It provides a possible way of adjusting the catching and processing capacity to more stable levels of prawn stocks, which would reduce the need for over-capitalisation.
For stock enhancement to be successful, the biology and ecology of the target animal must be thoroughly understood (including the production of the postlarvae/juveniles, environmental requirements, carrying capacity, and all factors that contribute to mortality), and methods must be available to monitor and assess the success of the releases. Much ecological information for stock enhancement is now available for many commercially important species of penaeid prawn in Australia, and novel approaches to tagging prawns (e.g. stable isotopes, rare alleles and reporter genes), release strategies, and assessment of carrying capacity are being developed. However, the utility of stock enhancement as a management tool for Australian fisheries, particularly prawns, has not been assessed.
The feasibility study of Exmouth Gulf has shown that it is an ideal fishery in which to evaluate the effectiveness of stock enhancement for Australian prawn fisheries. It also found that the enhancement of tiger prawns in Exmouth Gulf is potentially viable and that the risks of introducing disease and affecting the genetic composition of the wild population are likely to be low and manageable. Before proceeding to commercial scale releases, it is important to establish techniques for such releases on a smaller scale. Prawn fisheries throughout Australia are intensively fished and some have shown signs of overfishing. In some cases, the current stocks of prawns are now lower than those which would produce maximum yields. The enhancement of Australian penaeid prawn fisheries has the potential to be a useful management tool to increase fishery yields, rebuild over-exploited stocks, and reduce fluctuations in catch due to variable recruitment. Stock enhancement also has the ability to improve the management of fisheries by collecting more precise information about the biological characteristics of the stock (e.g. survival and growth, production in nursery grounds, migration pathways and factors affecting fluctuation in populations).
The farm production of prawns in arid environments, where evapouration rates are high and freshwater is scarce, has not been attempted in Australia. However, there are proposals for this to take place in the Exmouth Gulf region (Cape Sea Farm). The results from our proposed research in Exmouth Gulf will provide new information on the production of juvenile prawns at much higher densities than previously attempted in Australia. We anticipate the development of successful techniques that would be suitable for a broad range of environments, apart from the arid conditions at Exmouth Gulf.
The M.G. Kailis Group of companies has demonstrated it’s commitment to this project by advancing funds ($23, 000) to commence work on the project before July 1999. The beneficiaries of stock enhancement would be expected to contribute to the costs of research and monitoring, and ultimately pay for the enhancement at commercial scales. Therefore, stock enhancement must be cost-effective and a cost-benefit analysis using a bioeconomic model, is an essential part of any enhancement project. The bioeconomic model developed during the feasibility study (FRDC 98/222) will be revised as the results of the current proposal become available. It will then be used to assess the commercial viability of large scale enhancement and optimise the design of the experimental enhancement (Stage 3). The results of the feasibility study suggest that it would be possible to enhance the tiger prawn fishery in Exmouth Gulf by about 100 t with releases of about 7 to 10 million juveniles.
